Dear Participant,magnonics2019.poliba.it/wordpress/Book of Abstract.pdf · collinear spin textures,...

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Dear Participant,

It is our great pleasure to welcome you to the Magnonics 2019 Conference, organized at Riva Marina Resort in Carovigno (Puglia, Italy) by the Politecnico di Bari and the Institute of Materials (IOM) of the National Research Council, in collaboration with the IEEE Magnetics Society, the Italian association of Magnetism, Petaspin Association, Fondazione Puglia and several other Italian Universities and Institutions.

Magnonics 2019 is the 6th in a series of biennial conferences aimed at presenting and discussing recent achievements in both fundamental and applied aspects magnon and spin wave dynamics and nanomagnetism, putting together researchers from Universities, public Institutions and companies working in the field of Magnonics and Spintronics. Magnonics as a relatively new research field which is currently gaining momentum, attracting more and more researchers from various sub-fields of magnetism, materials science, microwave engineering, and beyond.

We hope that Magnonics 2019 will pave the way to the cross-fertilization between the magnonics community and those of photonics, spin-orbitronics, spintronics and straintronics thus being useful in establishing new collaborations and providing a forum for scientific discussions within existing ones.

Magnonics 2019 follows the series of previous Conferences that started in Dresden (Germany) in 2009 and then continued in Recife (Brasil) in 2011, Varberg (Sweden) in 2013, Seeon (Germany) in 2015 and in Oxford (UK) in 2017.

The Magnonics 2019 conference brings together scientists and engineers interested in recent developments in studies ranging from fundamental magnonic properties to their application in the information technologies. The scientific topics at the Magnonics2019 include:

• Magnetization dynamics, damping and ultrafast switching • Spin waves, magnonics and magnonic applications, Opto-magnonics • Spin-wave logic, artificial crystals and quasi-crystals for spin waves • Spin waves on curved surfaces and 3D heterostructures • Excitations in magnetic ‘textures’ such as Skyrmion lattices • Hybrid magnonic heterostructures (metal-insulator, metal-ferroelectric, metal-heavy

metal, metal-antiferromagnet) • Domain wall dynamics and devices • Spin torque switching and spin torque nano-oscillators • Static and dynamic spin Hall and spin-orbital torques • Spin injection and spin-dependent tunneling • Spintronic, Antiferromagnetic spintronic and spin-caloritronics

The structure of the conference follows the tradition of being held in a single session style. It consists of 3 tutorial lectures, 27 invited and 37 contributed oral presentations given by world leading experts.

There will be extensive poster sessions where scientists and students present their work related to the Magnonics research field. All posters presented by students will be eligible for nomination for the Best Poster Award supported by the Italian Association on Magnetism.

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There will be three poster awards and the winners will be announced during the social dinner.

Finally, we want to thank all people who contributed to the organization of this conference.

On behalf of the Management Committee of Magnonics 2019, we wish all participants a fruitful conference time and an enjoyable stay in Puglia.

The Conference Chairs:

Mario Carpentieri (Politecnico di Bari, Italy) Gianluca Gubbiotti (IOM-CNR Perugia, Italy)

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POLITECNICO DI BARI IEEE MAGNETICS SOCIETY

ISTITUTO OFFICINA DEI MATERIALI DEL CNR FONDAZIONE PUGLIA

ASSOCIAZIONE ITALIANA DI MAGNETISMO UNIVERSITA’ DI PERUGIA

UNIVERSITÀ DI MESSINA POLITECNICO DI MILANO

DIPARTIMENTO DI MATEMATICA E FISICA, UNIVERSITÀ DI LECCE PROGETTO CORDIS “SWING”

QUANTUM DESIGN PETASPIN

Tutorial session Sunday, July 28

T.1 6

Novel magnonic device concepts for information processing

Burkard Hillebrands

Fachbereich Physik and Landesforschungszentrum OPTIMAS,

Technische Universität Kaiserslautern, 67663 Kaiserslautern, Germany

In the field of magnonics, wave-based logic devices are constructed and studied based on the utilization of

spin waves and their quanta - magnons. The field is developing rapidly due to its potential to implement

innovative ways of data processing as a CMOS complementary technology. Basic building blocks of

magnonics have already been realized. Examples are linear and nonlinear spin-wave waveguide structures,

magnonic logic, as well as magnonic amplifiers such as the magnon transistor and parametric amplification.

In this tutorial talk, I will give an overview over the fundamentals and the current trends in magnonics.

One topic is the realization of new functionalities and devices by using novel concepts borrowed from

integrated optics and combining them with the specific advantages found in magnetic systems. Examples are

directional couplers and quantum-classical analogy devices, such as a magnonic Stimulated Raman Adiabatic

Passage (STIRAP) device.

Another important direction is to use fundamentally new macroscopic quantum phenomena such as a Bose-

Einstein condensate (BEC) at room temperature as a novel approach in the field of information processing

technology. Very promising is the use of magnon supercurrents driven by a phase gradient in the magnon BEC.

I will demonstrate evidence of the formation of a magnon supercurrent along with second magnonic sound,

and its spatiotemporal behaviour, which is revealed by means of time- and wavevector- resolved Brillouin

light scattering (BLS) spectroscopy. I will conclude with an outlook.


T.2 7

Launching magnons and switching magnetization with light pulses

Andrei Kirilyuk

FELIX Laboratory, Radboud University, 6525 ED Nijmegen, The Netherlands

The interaction of laser pulses with magnetically ordered materials has developed into a fascinating

research topic in modern magnetism. From the discovery of ultrafast demagnetization over two decades ago

to the demonstration of magnetization reversal by single femtosecond laser pulses, the manipulation of

magnetic order by ultrashort laser pulses has become a fundamentally challenging topic with a potentially high

impact for future spintronics, data storage and processing. [1].

Thus, laser pulses were shown to launch both homogeneous magnetic precession and propagating spin

waves, modify magnetic anisotropy and exchange interaction, and ultimately lead to an all-optical reversal of

magnetization direction. Various mechanisms, from thermal to purely polarization-dependent, were shown to

be efficient stimuli.

As one of the highlights, it has been demonstrated that the magnetization of ferrimagnetic RE-TM alloys

and multilayers can be reversed by the purely heating effect of single fs laser pulses, without any applied

magnetic field [2]. This switching is found to follow a very peculiar pathway, that crucially depends on the

dynamic balance of net angular momentum, set by the two sublattices.

On the other hand, a purely non-thermal all-optical switching was demonstrated in transparent films of

magnetic dielectrics [3]. A linearly polarized fs laser pulse resonantly pumps specific d-d transitions, creating

strong transient magneto-crystalline anisotropy. Selecting the polarization of the pulse changes the direction

of magnetic precession. This mechanism outperforms existing alternatives in terms of the speed (less than 20

ps) and the unprecedentedly low heat load.

In this talk various mechanisms for excitation of coherent precessional motion and full magnetization

reversal will be considered and compared, with the goal to provide a clear picture of the processes

accompanying the reversal at these ultrafast time scales.

[1] A. Kirilyuk, A.V. Kimel, and Th. Rasing, Rev. Mod. Phys. 82, 2731 (2010).

[2] C.D. Stanciu et al, Phys. Rev. Lett. 99, 047601 (2007).

[3] A. Stupakiewicz et al., Nature 542, 71 (2017); Nature Comm. 10, 612 (2019)


T.3 8

On-chip emission and detection of short-wave magnons: from conversion to spin

textures and grating couplers

Dirk Grundler

Laboratory of Nanoscale Magnetic Materials and Magnonics (LMGN), Institute of Materials (IMX) and

Institute of Microengineering (IMT), School of Engineering (STI), Ecole Polytechnique Fédérale de

Lausanne (EPFL), Switzerland

Magnetic nanomaterials play an important role in current technologies ranging from sensing to data storage

and processing [1]. To develop novel applications beyond todays information technology [2] the exploration

of magnons at 10 GHz and beyond becomes of key importance. At such frequencies they exhibit wavelengths

λ of 100 nm and below. To perform experimental studies routinely in the laboratory in this regime relevant

instrumentation is still under development. Traditional techniques based on e.g. neutron diffraction, spin-

polarized electron loss spectroscopy and light scattering do not allow for studying the tiny volumes foreseen

for technological applications, do not provide sufficient frequency resolution and require overcoming the

diffraction limit at about 250 nm, respectively. New approaches are needed to obtain experimental data on

short-wave magnons and thereby explore both fundamental aspects and possible novel functionalities.

We review approaches realized recently to emit and detect magnons with λ of a few 10 nm on a chip. The

approaches include wavelength converters, anisotropic spin textures and grating couplers which incorporate

periodic nanomagnet lattices. They are complementary in that they allow for emission in one- and two-

dimensional configurations [3,4] as well as emission of multi-directional plane-wave magnons [5,6]. We also

discuss our recent experiments performed on aperiodic grating couplers and coplanar waveguides

incorporating a ferromagnetic layer which serve as efficient wavelength converters.

Experimental work by K. An, K. Baumgaertl, V. Bhat, P. Che, J. Chen, C. Dubs, M.-C. Giordano, A.

Mucchietto, and S. Watanabe is gratefully acknowledged. We thank for financial support by the Swiss National

Science Foundation (SNSF) via sinergia project NanoSkyrmionics CRSII5 171003, grants No. 163016 and

IZRPZ0 177550, as well as by the EPFL COFUND Grant No. 665667 (EU Framework Programme for

Research and Innovation (2014-2020)).

[1] S. Bhatti et al., Materials Today, Volume 20, Number 9, November 2017.

[2] A.V. Chumak et al., Nature Physics 11, 453–461 (2015).

[3] V. Demidov et al., Applied Physics Letters 99, 082507 (2011).

[4] V. Sluka et al., Nature Nanotechnology 14, 328 (2019).

[5] H. Yu et al., Nature Communications 4, 2702 (2013).

[6] H. Yu et al., Nature Communications 7, 11255 (2016).

Session IA Monday, July 29

IA.1 10

Magnon Transport in Spin Textures

Helmut Schultheiss

Institute for Ion Beam Physics and Materials Research

Helmholtz-Zentrum Dresden-Rossendorf, Dresden, Germany

One of the grand challenges in cutting edge quantum and condensed matter physics is to harness the spin

degree of electrons for information technologies. While spintronics, based on charge transport by spin

polarized electrons, made its leap in data storage by providing extremely sensitive detectors in magnetic hard-

drives, it turned out to be challenging to transport spin information without great losses. With magnonics a

visionary concept inspired researchers worldwide: Utilize magnons - the collective excitation quanta of the

spin system in magnetically ordered materials - as carriers for information. Magnons are waves of the

electrons’ spin precessional motion. They propagate without charge transport and its associated Ohmic losses,

paving the way for a substantial reduction of energy consumption in computers.

While macroscopic prototypes of magnonic logic gates have been demonstrated, the full potential of

magnonics lies in the combination of magnons with nano-sized spin textures. Both magnons and spin textures

share a common ground set by the interplay of dipolar, spin-orbit and exchange energies rendering them perfect

interaction partners. Magnons are fast, sensitive to the spins’ directions and easily driven far from equilibrium.

Spin textures are robust, non-volatile and still reprogrammable on ultrashort timescales. The vast possibilities

offered by combining this toolset of magnetic phenomena, add value to both magnonics and the fundamental

understanding of complex spin textures.

I will give an introduction about magnon propagation and manipulation in microstructures with non-

collinear spin textures, in particular magnons propagating in nano channels formed by magnetic domain walls.

Furthermore, I will address how magnons can be excited in domain wall channels by pure spin currents

originating from the spin Hall effect and the nonlinear generation of whispering gallery magnons in a magnetic

vortex [3].

[1] K. Wagner, et al. Nature Nanotech 11, 432 (2016).

[2] K. Vogt, et al., Nat Comms 5, 3727 (2014).

[3] K. Vogt, et al., PRL accepted, arXiv:1806.03910

https://arxiv.org/abs/1806.03910


IA.2 11

Control of spin-wave transmission by a programmable domain wall

Sampo J. Hämäläinena, Marco Madamib, Huajun Qina, Gianluca Gubbiottic, Sebastiaan van Dijkena

a NanoSpin, Department of Applied Physics, Aalto University School of Science, FI-00076 Aalto, Finland b Dipartimento di Fisica e Geologia, Università di Perugia, 06123 Perugia, Italy

c Istituto Officina dei Materiali del CNR (CNR-IOM), Sede Secondaria di Perugia, c/o Dipartimento di Fisica e

Geologia, Università di Perugia, 06123 Perugia, Italy

Wave-like computing based on active spin-wave manipulation has generated interest as a potential low-

power and parallel computing alternative for conventional CMOS technologies [1]. Here, we demonstrate

programmable spin-wave filtering by resetting the spin structure of pinned 90° magnetic domain walls [2]. We

experimentally realize strong pinning of straight magnetic domain walls by growing CoFeB films onto

ferroelastic BaTiO3 substrates with ferroelastic stripe domains. Via interface strain transfer and inverse

magnetostriction, this results in regular 90° rotations of uniaxial magnetic anisotropy in the CoFeB film and

strong domain wall pinning onto ferroelectric boundaries [3,4]. Because of pinning, a magnetic field can switch

the internal structure of the magnetic domain walls between two non-volatile states; narrow 90° head-to-tail

and wide 90° head-to-head (or tail-to-tail) walls. Moreover, the pinned domain walls do not move under the

action of spin waves. Using micro-focused Brillouin light scattering (BLS) we show that broad domain walls

are transparent for spin waves over a broad frequency range. In contrast, narrow domain walls strongly reflect

spin waves. Micromagnetic simulations reveal that a domain-wall resonance mode, which is characterized by

two oscillatory out-of-plane antinodes, reduces the transmission of spin waves through narrow domain walls.

Based on these results, we propose a new structure for active spin-wave manipulation. Our device concept

consists of three stripe domains with uniaxial magnetic anisotropy and two pinned domain walls. In this

configuration, magnetization reversal in the central domain switches the domain-wall state from two broad

walls to two narrow walls or vice versa. Toggling between these two states changes the transmission of spin

waves from nearly 100% to 0% at the resonance frequency.

[1] A.V. Chumak et al., Nat. Phys. 11, 453 (2015).

[2] S.J. Hämäläinen et al., Nat. Commun. 9, 4853 (2018).

[3] T.H.E. Lahtinen, J.O. Tuomi and S. van Dijken, Adv. Mater. 23, 3187 (2011).

[4] T.H.E. Lahtinen, K.J.A. Franke and S. van Dijken, Sci. Rep. 2, 258 (2012).

Figure 1: (a,b) Magneto-optical Kerr microscopy images of broad head-to-head/tail-to-tail and

narrow head-to-tail domain walls in a CoFeB/BaTiO3 bilayer. Reversible switching between

the two configurations is attained by the application of a magnetic field. (c) BLS intensity

recorded from the antenna edge across a pinned domain wall demonstrating efficient

transmission of spin waves through a broad head-to-head domain wall and nearly complete

spin-wave reflection at a narrow head-to-tail domain wall.


IA.3 12

Artificial writing of magnonic waveguides by focused ion beam

Lukáš Flajšmana, Kai Wagnerb, Jonáš Glossc, Marek Vaňatkaa, Helmut Schultheißb and Michal

Urbáneka, d

a CEITEC BUT, Brno University of Technology, Brno, Czech Republic b Institute of Ion Beam Physics and Materials Research, HZDR, Dresden, Germany

c Institute of Applied Physics, TU Wien, Vienna, Austria d Institute of Physical Engineering, Brno University of Technology, Brno, Czech Republic

Direct writing of magnetic patterns by focused ion beam (FIB) irradiation presents a favorable alternative

to the conventional lithography approaches. It allows for a rapid prototyping of a large variety of

nanostructured samples. Unfortunately, the FIB processed materials usually show high damping and thus the

spin-wave propagation is not possible on the distances of even few micrometers. In our approach we use

metastable paramagnetic fcc Fe78Ni22 films grown on Cu(100) substrate. This system can be locally

transformed by focused ion beam (FIB) to ferromagnetic bcc phase [1]. The transformed areas still retain

ordered crystalline structure, where the properties can be controlled by the FIB irradiation procedure [2]. Using

a directional scanning of the FIB it is possible to grow/transform different crystallographic orientations of the

bcc structure with different directions of uniaxial anisotropy. This allows us to spatially control the direction

of the uniaxial magnetic anisotropy while keeping the saturation magnetization constant.

In this work we study spin wave propagation in FIB written magnonic waveguides and we show, that spin-

wave propagation is comparable to propagation in epitaxial iron thin films. Additionally, we also show that

we are able to achieve propagation of spin waves in Daemon-Eshbach geometry in zero external field, as the

writing process allows us to tune the magnetocrystalline anisotropy of the resulting structures to point

perpendicularly to the waveguide long axis. We employ phase resolved micro-Brillouin light scattering to

access the dispersion of the structures both in applied and in zero external magnetic fields.

[1] J. Gloss, et al., Appl. Phys. Lett. 103, 262405 (2013)

[2] M. Urbánek, et al., Apl. Mater. 6, 060701 (2018)


IA.4 13

Nanomagnonics with engineered spin-textures

Edoardo Albisettia,b, Daniela Pettia, Silvia Tacchic, Raffaele Silvanic,d, Giacomo Salaa, Giuseppe

Scaramuzzia, Simone Finizioe, Sebastian Wintze, Jörg Raabee, Giovanni Carlottic, Elisa Riedob,f,

Riccardo Bertaccoa

a Dipartimento di Fisica, Politecnico di Milano, 20133 Milano, Italy. bAdvanced Science Research Center, New York, NY 10031, USA.

cIstituto Officina dei Materiali del CNR (CNR-IOM), Unità di Perugia, c/o Dipartimento di Fisica e

Geologia, Perugia, Italy. dDipartimento di Fisica e Geologia, Università di Perugia, Via A. Pascoli, Perugia, I-06123, Italy

ePaul Scherrer Institute, 5232 Villigen PSI, Switzerland fTandon School of Engineering, New York University, New York NY 11201, USA

The control of spin-waves holds the promise to enable energy-efficient computing. However, controlling spin-

waves at the nanoscale, which is crucial for the realization of magnonic nanodevices, is extremely challenging

due to the difficulty in controlling the nanoscopic magnetic properties via conventional nanofabrication

techniques. We recently demonstrated a new technique for creating reconfigurable magnonic structures by

performing a highly localized field cooling with the hot tip of a scanning probe microscope, in an exchange

bias bilayer. In such structures, the spin-wave excitation and propagation can be spatially controlled with no

need for external fields. [1,2]

By controlling the patterning geometry and external magnetic field direction, we demonstrate a strategy for

stabilizing complex multidimensional spin-textures ranging from 2D domains with tailored spin-configuration,

to straight and curved 1D magnetic domain walls,[3] to 0D tailored topological solitons such as vortices and

Bloch lines with deterministically controlled chirality, position and vorticity.[4] We show that such engineered

spin-textures can be used effectively as waveguides and controlled sources of propagating spin-waves.

In particular we demonstrate the channeling and steering of propagating spin-waves in arbitrarily shaped

nanomagnonic waveguides based on straight and curved domain walls, and a prototypic nanomagnonic circuit

based on two converging waveguides, allowing for the tunable spatial superposition and interference of

confined spin-waves modes. [5] Finally, we present an optically-inspired platform realized by patterning

tailored nanoscale spin-textures in an exchange biased synthethic antiferromagnet (SAF), where we show the

nanoscale spatial shaping of propagating wavefronts, and the generation of robust multibeam interference

patterns with short-wavelength spin-waves. [6]

The ability to control magnons via nanoscale-designed spin-textures opens-up a plethora of exciting

possibilities for the realization of energy-efficient digital and analog computing platforms.

[1] E. Albisetti et al., Nat. Nanotechnol. 11 (6), 545–551 (2016).

[2] E. Albisetti et al., AIP Advances, 7(5), 55601 (2017).

[3] E. Albisetti and D. Petti, J. Mag. Magn. Mater. 400, 230–235 (2016).

[4] E. Albisetti et al., App. Phys. Lett. 113, 162401 (2018).

[5] E. Albisetti et al., Commun. Phys. 1, 56 (2018).

[6] E. Albisetti et al., in preparation


IA.5 14

Caustic-beam-based two-dimensional microscale magnonic devices

A.A. Sergaa, F. Heussnera, G. Talmellib, M. Geilena, B. Heinza,c, K. Yamamotod, T. Brächera,

C. Adelmannb, F. Ciubotarub, B. Hillebrandsa, P. Pirroa

a Fachbereich Physik and Landesforschungszentrum OPTIMAS, Technische Universität Kaiserslautern,

Kaiserslautern, Germany b imec, Leuven, Belgium

c Graduate School Materials Science in Mainz, Mainz, Germany d Advanced Science Research Center, Japan Atomic Energy Agency, Tokai, Japan

Investigation of an anisotropic spin wave (SW) transport is of special interest for the creation of two-

dimensional information processing circuits and spatially extended magnonic logic networks, where SWs are

used to transport information and to perform logic operations. In magnetic films with externally induced

anisotropy (created by an in-plane external magnetic field), a wave source of sufficiently small size can excite

SW beams with stable sub-wavelength transverse aperture [1]. Generally, the effect appears if the orientation

of the group velocity vectors of the excited plane waves becomes independent of their wavevectors and wave

energy is concentrated along specific directions forming strong energy beams called SW caustics [1, 2]. The

direction of these beams can be controlled by rotating the bias magnetic field Hext. Such an excitation scheme

represents a practically ideal data splitter or combiner, which can be utilized in SW logic devices.

Here, we present the micromagnetic modelling [3, 4] and experimental realization of energy splitting and

frequency-division multiplexing in caustic-based magnonic networks at the micrometer scale. By means of

Brillouin light scattering microscopy, we investigate the frequency dependency of the propagation direction

of caustic SW beams. For the first time, we use the results to design and experimental demonstration a

demultiplexing device which separates SW signals of different frequencies into different SW waveguides (see

Fig. 1).

Financial support by DFG within project SFB/TRR 173 Spin+X and by H2020 FET Open program

CHIRON funded by the European Union is acknowledged.

[1] T. Schneider et al., Phys. Rev. Lett. 104 (2010), 197203.

[2] V. E. Demidov et al., Phys. Rev. B 80 (2009), 014429.

[3] F. Heussner et al., Appl. Phys. Lett. 111 (2017), 122401.

[4] F. Heussner et al., Phys. Stat. Sol. RRL 12 (2018), 1800409.

Figure 1: Micromagnetic modelling (left) and Brillouin light scattering measurement (right)

of the frequency demultiplexing function in a microscale magnonic network: depending on

their frequency, the spin waves are channelled from the common input waveguide into

different output waveguides.


IA.6 15

Magnonic networks based on YIG microwaveguide

Y. Khivintsev1, A. Kozhevnikov1, G. Dudko1, V. Sakharov1, Y. Filimonov1, A. Khitun2

1Kotelnikov IRE of RAS, Saratov Branch, 410019, Saratov, Russia

2University of California - Riverside, CA 92521, Riverside, USA

Spin waves (SW) propagation and interference in tangentially magnetized magnonic network based on 2x2

grid of the orthogonal YIG microwaveguides were studied both numerically and experimentally. Eight-

ports structure was fabricated from d≈1 μm thick epitaxial YIG film by means of the conventional

photolithography and ion etching. Each waveguide had the length of L≈100μm and width of w≈10 μm. The

distance from the ends of waveguides and nearest cross-junction was lC1≈35 μm. Parallel waveguides in the

network were spaced by lC2≈30 μm apart. The π-shaped copper microstripe antennas with length ≈ 14μm

and width ≈ 6 μm were made at the ends of waveguides by lift-off lithography and magnetron sputtering,

see numbers 1-8 on Figure (a). SW transmission characteristics Sj1 (j=2,8) for bias filed H≈550 Oe parallel

to the input transducer 1 are shown of Figure (b). The frequency interval ΔF≈700 MHz, where signal

amplitude at the output antennas 2-8 exceeds level of the -60 dB coincided with overlapping frequency

intervals of the magnetostatic surface (MSSW) and backward volume (BVMSW) waves in separate

waveguides, see Figure (c) and corresponds to estimation ΔF by appropriate formula from [1,2]. SW

interference at output transducer 4 was studied as a function of phase shift Δφ≈0-2π between SW excited

by antennas 1 and 8, see Figures (d) and (e). The constructive and distractive interference were observed,

see insert to Figure (e).

This work was supported by the Russian Science Foundation (grant No. 17-19-01673).

[1] M. Balynsky, A. Kozhevnikov, Y. Khivintsev, et al. Journal of Applied Physics 121, 024504 (2017);

doi:10.1063/1.4973115

[2] G.M.Dudko, et al. Journal of Communication Technologies and Electronics.


IA.7 16

How good are spin waves for information processing?

Gyorgy Csaba

Faculty for Information Technology and Bionics

Pazmany University, Budapest Hungary

The talk will address an important question for magnonics, i.e. the possibility of efficiently use spin- waves

for information processing. Computing by spin waves is an emerging beyond-Moore computing concept. A

number of device constructions have been proposed, among them logic gates [1], microwave signal processing

hardware [2] and non-Boolean computing schemes [3]. Recent developments in low- damping magnetic

materials may enable scalable, practically useful computing devices. A killer application, however where a

spin wave device significantly outperforms semiconductor-based circuits, have not been demonstrated yet.

This is largely due to the high overhead introduced by magneto-electrical interconversions. Input/output

interfaces to semiconductor circuitry accounts for vast majority of energy consumption and significantly

increases circuit complexity; by consequence small-scale, simple processing devices have low net energy

efficiency.

Conceptual sketch of a spin-wave-based spectrum analyzer [1] and circuit schematics of an on-chip

amplifier for spin wave detection [3].

The presentation will review recent developments on various spin-wave based information processing

devices. I will compare the information transmitting capabilities of spin-waveguides with electrical

transmission lines and other microwave passive structures and I will attempt to benchmark spin-wave based

devices against their electrical counterparts. High-speed (microwave) signal processors and special purpose

hardware (such as image processing co-processors) are envisaged as attractive application areas. Spin waves

may also provide dense, low-power physical interconnections for neuromorphic computing concepts, which is

a largely unexplored research area.

[1] Chumak, A. V., V. I. Vasyuchka, A. A. Serga, and Burkard Hillebrands. "Magnon spintronics." Nature

Physics 11, no. 6 (2015): 453.

[2] Papp, A,Porod W., Csurgay A. I., Csaba, G. "Nanoscale spectrum analyzer based on spin-wave

interference." Scientific Reports 7, no. 1 (2017): 9245.

[3] Csaba, Gyorgy, Adam Papp, and Wolfgang Porod. "Perspectives of using spin waves for computing and

signal processing." Physics Letters A 381, no. 17 (2017): 1471-1476.

Session IB Monday, July 29

IB.1 17

Magnon straintronics as an alternative controllable way of spin-wave

computation

Alexandr V. Sadovnikova, Andrew A. Gracheva, Svetlana E. Sheshukovaa,

Evgeny N. Beginina, Sergey A. Nikitova,b

a Saratov State University, Nonlinear Physics, Saratov, Russia b Kotel’nikov Institute of Radio Engineering and Electronics, RAS, Moscow, Russia

In recent years much research has been directed towards the use of spin waves for signal processing at

microwave and subterahertz frequencies due to the possibility to carry the information signal without the

transmission of a charge current [1,2]. Recent theoretical and experimental studies suggest that strain can be

used to engineer energy-efficient complicated 2D and 3D piezoelectric material and heterostructures [3,4]. The

main topic of the proposed talk will be devoted to the the experimental observations of the strain-mediated

spin-wave coupling phenomena in different magnonic structures based on the asymmetric adjacent magnonic

crystals, adjacent magnetic yttrium iron garnet stripes and array of magnetic stripes, which demonstrates the

collective spin-wave phenomena. The voltage-controlled spin-wave transport along bilateral magnonic stripes

was demonstrated. The model describing the spin-wave transmission response and predicting its value is

proposed based on the self-consistent equations [4]. It was shown that the strain-mediated spin-wave channels

can be used to route the magnonic information signal and thus the composite magnon-straintronic structure

could provide to fabricating magnonic platforms for energy-efficient signal processing. The three-channel

isolator-based directional coupler (Fig.1) distinguishes itself as an ideal platform for magnonics in three key

aspects: first, dual tunability with both the magnetic and electric field; second, it supports large spin-wave

propagation distances, which is appropriate for spin-wave interference in magnonic logic applications; and

third, its versatile magnonic component with the voltage-controlled frequency-selective characteristics.

This work was supported partly by the grant of Russian Science Foundation (#18-79-00198). S.E.S.

acknowledges support from the Scholarship and Grant of the President of the RF (No. SP-2819.2018.5, No.

MK-3650.2018.9).

[1] V. V. Kruglyak, S. O. Demokritov, and D. Grundler, J. Phys. D 43, 264001 (2010).

[2] A. V. Chumak, et.al. Nat. Phys. 11, 453 (2015).

[3] Y. K. Fetisov and G. Srinivasan, Appl. Phys. Lett. 88, 143503 (2006).

[4] A. V. Sadovnikov, Phys. Rev. Lett. 120, 257203 (2018)

[5] A. V. Sadovnikov, et. al., Phys. Rev. B 99, 054424. 2019.

This work was supported by Russian Science Foundation, Grant No 19-19-00607.

Figure 1: The distribution of stress tensor component Sxx showing a local deformation of

the PZT layer (a) and induced stress on the surface of YIG stripes (b).


IB.2 18

Magnetization dynamics driven by strain waves

M. Foerster1, B. Casals2, J.M. Hernandez3, F. Macia2,3, L. Aballe1

1 ALBA Synchrotron Light Facility, Carrer de la llum 2-26, 08290 Cerdanyola del Valles, Spain

2 Institut de Ciencia de Materials de Barcelona (ICMAB-CSIC), Campus UAB, 08193 Bellatera, Spain

3 Department of Condensed Matter Physics, University of Barcelona, 08028 Barcelona, Spain

We report measurements of dynamic magnetization processes in Ni driven by surface acoustic waves

(SAW, 125-500 MHz) excited in underlying LiNbO3 substrates. Using a stroboscopic technique based on

synchrotron PhotoEmission Electron Microscopy with X-ray Circular Magnetic Dichroism contrast (XMCD-

PEEM), the SAW and the magnetic domain configuration can be imaged with 100 nm lateral spatial resolution

and 80 ps time resolution. The magnetic response of Ni is mediated by magnetoelasticity (inverse

magnetostriction) and results from the dynamic strain of the SAW.

In patterned Ni microstructures we observe fast magnetic domain wall motion (order of 100 m/s) and coherent

magnetization rotation, depending on the relative alignment of the structures and the SAW. Notably, we

measure different time delays between strain wave and magnetic response of about 270 ps and 90 ps

respectively, which are understood considering the acting magnetic torques, and reproduced by micromagnetic

simulations [1].

In continuous Ni thin films, we discovered large angle amplitude (more than 20 degrees) magnetic oscillations

propagating over long distances (cm scale) [2], which we call strain spin waves (SSW) (Figure 1). Their

oscillation amplitude can be tuned by an applied external magnetic field. Using interfering SAW, also standing

SSW can be generated.

Figure 1. Left: schematic of the PhotoEmission Electron Microscope (PEEM) experiment detecting strain spin waves.

The magnetic oscillation is driven by elastic deformation waves (surface acoustic waves, SAW) which are synchronized

to the pulsed illumination of the ALBA synchrotron. The sample is imaged using photoemitted electrons. Right: XMCD-

PEEM image taken at the Ni L3 absorption edge showing strain spin waves with 8 um periodicity.

[1] M. Foerster et al., Nat. Comm. 8, 407 (2017)

[2] B. Casals et al., in preparation (2019)

LiNbO3

Nickel


IB.3 19

Mode conversion of magneto-elastic waves

Tomosato Hiokia, Yusuke Hashimotob, Eiji Saitohb-e

a Institute for Materials Research, Tohoku Univ., Sendai, Japan b Advanced Institute for Materials Research, Tohoku Univ., Sendai, Japan

c Dept. of Applied Physics, University of Tokyo, Tokyo, Japan dCenter for Spintronics Network, Tohoku Univ., Sendai, Japan

eAdvanced Science Research Center, Japan Atomic Energy Agency, Tokai 319-1195, Japan

In magnetic media, spin waves and elastic waves form hybridized state, so-called magneto-elastic waves

(MEWs), by magneto-elastic coupling. We here report the mode conversion of magneto-elastic waves by their

reflection at a sample edge observed by time-resolve magneto-optical imaging. Systematic measurements in

terms of the incident angle revealed that the conversion ratio is explained by the model considering the mode

conversion of elastic waves and magneto-elastic coupling.

Spin waves and elastic waves interact through spin-orbit coupling and form hybridized wave, so-called

magneto-elastic wave (MEWs) [1]. MEWs have characteristics of both elastic and spin waves, and thus can

play a role in the manipulation of the propagation of spin waves through elastic wave. Elastic waves have one

longitudinal acoustic (LA) mode and two transverse acoustic (TA) modes. These modes are no longer the

eigenstate at the edge of the sample, where the translational symmetry is broken. Consequently, when elastic

waves reflect, the mode is converted from longitudinal to transverse or vice versa. In the case of MEWs, edge

reflection is expected to change the wavevector of both spin and elastic waves.

In this study, we observed the mode conversion of magneto-elastic waves due to the mode conversion of

elastic waves. The propagation dynamics of magneto-elastic wave in a Bi-doped Lutetium iron garnet

(Bi1Lu2Fe3.6Ga1.4O12) was observed by using the time-resolved magneto-optical imaging, based on the pump-

and probe technique and the magneto-optical imaging method [2]. This method is sensitive to the spin-wave

component of MEWs. We found that the incident spin waves split into two waves with different propagation

orientations and wavelengths. The reflection and the conversion ratio of spin waves were explained by the

model taking the mode conversion of elastic wave and magneto-elastic coupling into account. This result

suggests that the magneto-elastic coupling can be used to control the wavevector of spin waves on the future

spin-wave based devices.

[1] C. Kittel, Phys. Rev. 110, 836 (1958).

[2] Y. Hashimoto, et al., Nature Communications 8, 15859 (2017).

Fig.1 (a): Real-space magneto-optical image of magneto-elastic waves at the time delay(t) between

pump and probe beam, (b): Wavenumber space spectrum of before and after the edge reflection


IB.4 20

Spin current generation using surface acoustic wave in metals

Yukio Nozakia,d, Yuki Kurimunea, Tsubasa Sasakia, Mamoru Matsuob,

Sadamichi Maekawac

a Department of Physics, Keio University, Yokohama, Japan b Kavli Institute for Theoretical Sciences, University of Chinese Academy of Sciences, Beijing, China

c RIKEN Center for Emergent Matter Science (CEMS), Wako, Japan d Center for Spintronics Research Network, Keio University, Yokohama 223-8522, Japan

According to the conservation low of angular momentum, spin angular momentum can be converted from

a mechanical rotation even for free electrons in non-magnetic metals with a weak spin orbital coupling [1,2].

We demonstrated a conversion of alternating spin current (SC) from a macroscopic rotation in a surface

acoustic wave (SAW) which propagates in a bilayer consisting of NiFe / NM bilayers (NM = Cu, Pt, and Ti).

A resonant excitation of spinwave which is attributable to a spin transfer torque of the alternating spin current

generated via SAW was successfully observed in NiFe [3]. The spinwave excitation was strongly suppressed

when the Cu was removed or an insulating SiO2 was inserted between NiFe and Cu. This is clear evidence that

the SC is generated in Cu layer via spin-vorticity coupling [1,2]. Figure 1 shows the frequency dependence of

the amplitude of spinwave excitation which is occurred when the SAW is injected to Cu / NiFe, Pt / NiFe and

Ta /NiFe bilayers. As shown in Fig. 1, a larger spin transfer torque can be generated when a nonmagnetic metal

with a larger electrical conductivity is deposited on NiFe. From a power law analysis for frequency dependence

of SC amplitude, it was also confirmed that the spin-transfer torque from the SC in Cu was much stronger than

a magnetic torque owing to a direct Barnet effect and/or a magnetostriction effect in NiFe. The result will open

the way to generate the SC without using ferromagnets and/or nonmagnetic materials with large spin-orbital

coupling.

[1] M. Matsuo et al., Phys. Rev. B, 87, 180402 (2013).

[2] M. Matsuo et al., Phys. Rev. B, 96, 020401(R) (2017).

[3] D. Kobayashi, Y. Nozaki, et al., Phys. Rev. Lett., 119, 077202 (2017).

Figure 1: Frequency dependence of spinwave amplitude excited by injecting surface

acoustic wave in NiFe / Cu, NiFe / Pt, and NiFe / Ti bilayers. For comparison, similar

experiment was conducted for NiFe monolayer.

Session IC Monday, July 29

IC.1 21

Coherent propagation of spin excitations along skyrmion strings

Shinichiro Sekia

a Department of Applied Physics, University of Tokyo, Tokyo, Japan b RIKEN Center for Emergent Matter Science (CEMS), Wako, Japan

Magnetic skyrmion, a topological soliton characterized by swirling spin texture appearing in two-

dimensional system, has recently attracted attention as a stable particle-like object. In the three-dimensional

system, skyrmion forms a string structure in analogy with the vortex-line in superconductors / superfluids and

cosmic string in the universe, whose unique topology and symmetry may also host nontrivial response

functions. In this talk, we discuss the propagation character of spin excitations on skyrmion strings. We find

that this propagation is directionally non-reciprocal, and the degree of non-reciprocity, as well as the associated

group velocity and decay length, are strongly dependent on the character of the excitation modes. Our

theoretical calculation establishes the corresponding dispersion relationship, which well reproduces the

experimentally observed features. Notably, these spin excitations can propagate over a distance exceeding 103

times the skyrmion diameter, demonstrating the excellent long-range nature of the excitation propagation on

the skyrmion strings. The present results offer a comprehensive picture of the propagation dynamics of

skyrmion string excitations, and suggest the possibility of unidirectional information transfer along such

topologically-protected strings.

Figure 1. Schematic illustration of spin excitation propagating along skyrmion strings.


IC.2 22

Reservoir computing with the frequency, phase and amplitude of spin-torque

nano-oscillators

D. Markovića, N. Lerouxa, M. Rioua, F. Abreu Araujob, J. Torrejona, D. Querliozc, A.

Fukushimad, S.Yuasad, J. Trastoya, P. Bortolottia, J. Grolliera

a Unité Mixte de Physique CNRS/Thales, Palaiseau, France b Institute of Condensed Matter and Nanosciences, UCLouvain, Louvain-la-Neuve, Belgium

c Centre de Nanosciences et de Nanotechnologies, Palaiseau, France d National Institute of Advanced Industrial Science and Technology, Tsukuba, Japan

Magnetic tunnel junctions can emulate neurons at nanoscale. Amplitude of voltage oscillations across the

junction was used to classify different waveforms through current-induced dynamics, distinguishing sines from

squares, and even spoken digits [1]. Other dynamical variables are interesting to leverage for computing, such

as the frequency or phase of the oscillators. Unfortunately, the frequency and phase of spin-torque nano-

oscillators are noisy, which is detrimental for pattern classification. Indeed, their dynamics takes place in

nanoscale magnetic volumes, which makes them sensitive to thermal fluctuations. In this work, we show that

synchronizing the oscillator to the input waveform that it has to process considerably reduces magnetization

fluctuations and enables pattern recognition [2]. We use a sinusoidal input waveform that carries information

encoded in its modulated frequency, chosen close to the oscillator frequency. With this method we classify

sine and square waveforms with an accuracy above 99% when decoding the output from the oscillator

amplitude, phase or frequency. We show that the recognition rates are directly related to the noise and non-

linearity of each variable. These results prove that the rich dynamical features of magnetic tunnel junctions

offer a compelling platform to implement and compare different neuromorphic computing approaches.

Figure 1: Success rates obtained when decoding from (a) frequency, (b) phase and (c) amplitude of the

oscillator, as a function of the center of the frequency range chosen for encoding the input data.

[1] J. Torrejon, Nature 547, 7664 (2017).

[2] D. Marković, App. Phys. Lett. 114, 012409 (2019).


IC.3 23

A magneto-optical study of spin-orbit torque acting on a nano-ellipse with in-

plane magnetization

Paul S. Keatleya, Takashi Managoa,b, Goran Mihajlovićc, Lei Wanc, Young-suk Choic, Jordan A.

Katinec, and Robert J. Hickena

a Department of Physics and Astronomy, University of Exeter, Exeter EX4 4QL, UK b Department of Applied Physics, Fukuoka University, Fukuoka, Japan

c San Jose Research Center, HGST, a Western Digital Company, San Jose, California 95135, USA

In-plane magnetized elements activated by spin-orbit torque (SOT) combine simplicity of design with

energy efficient switching for future magnetic memory applications. SOT switching of in-plane magnetized

CoFeB(2 nm) nanoscale ellipses fabricated at the centre of Pt Hall crosses has previously been investigated

using a differential planar Hall effect technique [1]. These planar devices allow complementary optical

techniques to directly probe the magnetization dynamics within the ellipse. Time-resolved (TR) scanning Kerr

microscopy of a 400 nm×1000 nm ellipse has previously revealed the action of SOT on GHz frequency

magnetization precession [2]. The SOT generated by a sub-nanosecond current pulse passing through the

device leads to differences in relaxation that depend on field history, and a transient out-of-plane deflection

[3]. However, the presence of an associated sub-ns Oersted magnetic field pulse (Oe-field) prevents full

characterisation of the SOT.

In this work, scanning Kerr microscopy has been used in a quasi-static (QS) and spin torque ferromagnetic

resonance (ST-FMR) configuration with the aim of disentangling the response of an 800 nm×2000 nm ellipse

to SOT and the Oe-field. The polar Kerr effect was used to detect the change of the out-of-plane component

of the magnetization in response to (i) a modulated DC current (QS mode), and (ii) a combination of microwave

(RF) and DC current (ST-FMR mode). For both measurement modes the current was passed through a Pt(6

nm) Hall cross parallel to the ellipse minor (hard) axis. The associated Oe-field, and the polarization of spins

traversing the Pt/CoFeB interface due to the spin Hall effect, were then parallel to the ellipse major (easy) axis.

In QS mode, the Kerr signal reveals an out-of-plane deflection of the magnetization that is maximum when

the applied field is perpendicular to the spin polarization and Oe-field, but vanishes when they are parallel.

When the magnitude of the applied field is smaller than the anisotropy field, significant peaks in the out-of-

plane deflection are observed at the ellipse switching field. In ST-FMR mode, field swept spectra reveal a

variation of resonance field as a function of magnetic field angle, but little change in the spectral shape when

the DC current is zero, suggesting that the Oe-field dominates the excitation. When a DC current of 10 mA

was applied, marked differences in the amplitude and linewidth emerged and may be ascribed to an

enhancement or compensation of the magnetic damping by the SOT. At the same time a detectable shift in

resonance field, of opposite sign to either side of the hard axis, is ascribed to the DC Oe-field. Detailed

analysis, and modelling is in progress to disentangle the Oe-field and SOT contribution to the out-of-plane

deflection and the FMR spectra.

[1] G. Mihajlović, Appl. Phys. Lett., 109, 192404 (2016).

[2] P. S. Keatley, ‘Picosecond reorientation of in-plane magnetization within a nano element by spin orbit

torque’ FB-14, 2019 Joint MMM-Intermag, Washington DC.

[3] X. Fan Nat. Comms. 5, 3042 (2014).


IC.4 24

Phase shift keying using spin-torque oscillators

A. Litvinenkoa, P. Sethia, C. Murapakaa, A. Jenkinsb, L. Vilaa, V. Crosc, P. Bortolottid, R. Ferreirab,

B. Dienya and U. Ebelsa

aUniv. Grenoble Alpes, CEA, CNRS, Grenoble INP*, IRIG-Spintec,

38000 Grenoble, France. * Institute of Engineering Univ. Grenoble Alpes b International Iberian Nanotechnology Laboratory (INL), Braga, Portugal

c Unité Mixte de Physique CNRS, Thales, Univ. Paris-Sud, Univ. Paris-Saclay, Paris, France

d THALES TRT, Palaiseau, France

Spin torque oscillators (STO) are promising for wireless communication schemes due to their nano-scale

size and frequency tunability via either a dc current or an applied field. However, their relatively large

linewidth and high phase noise figure can limit the data transmission rate in frequency and amplitude shift

keying schemes [1,2]. One possibility to reduce the STO phase noise and hence the linewidth is to couple

several oscillators or to injection lock the STO to an external rf current source [3]. Such synchronization opens

the possibility of implementing the third concept of data transmission which is phase shift keying (PSK) as

will be demonstrated here. A specific feature of the synchronization phenomenon is that the phase of the locked

oscillator is shifted with respect to the source [4]. This phase shift is determined by the detuning which is

the frequency difference of the free running oscillator and the rf source. For STOs, due to their non-isochronous

properties the frequency of the free running state and thus the detuning can be easily changed through the DC

current or field. In this presentation we validate this concept of PSK for magnetic tunnel junction (MTJ) based

vortex STOs whose free running parameters are f=300MHz, f=100kHz and P=1µW. They are characterized

by perfect locking to external sources at 2f and f/2 for which the phase noise is strongly reduced [3]. The vortex

devices studied here show a phase noise reduction of -50dBc/Hz at 10kHz offset frequency in the synchronized

state. The frequency detuning of the STO is induced by injecting (in addition to the DC current) a low

frequency digitally modulated current. This will lead to shifts of the phase difference with values up to π/2

and π for synchronization at 2f and f/2 respectively. For vortex MTJs we obtained a maximum PSK data

transmission rate of 4Mb/s for the synchronization at 2f. This rate is of the order of the amplitude relaxation

frequency [3]. We also demonstrate advanced PSK techniques such as quadrature phase shift keying, direct

read-out of the phase shift as well as data transmission and demodulation over a distance of 10m. This concept

can be applied also to uniform magnetized STO devices oscillating at higher frequencies and providing

consequently higher data rates [2]. This gives prospect for novel, robust wireless communication schemes

based on STOs, at high signal to noise ratio.

Financial support is acknowledged from the EC programme ERC MAGICAL 669204, from the French

space agency CNES and the Enhanced EUROTALENT programme.

[1] H. S. Choi et al., Sci. Rep. 4, 5486 (2014)

[2] A. Ruiz-Calaforra et al, Applied Physics Letters 111, 082401 (2017)

[3] R. Lebrun et al. Phys. Rev. Lett. 115, 017201 (2015)

[4] A. Pikovsky, M. Rosenblum, and J. Kurths, “Synchronization: a universal concept in nonlinear sciences”.

Cambridge University Press, Cambridge, 2001


IC.5 25

Magnon fluxonics

O. V. Dobrovolskiya,b , R. Sachsera, T. Brächerc, T. Böttcherc,d, V. V. Kruglyake, R. V. Vovkb,

V. A. Shklovskijb, M. Hutha, B. Hillebrandsc and A. V. Chumakc

a Physikalisches Institut, Goethe-Universität Frankfurt am Main, Germany b Physics Department, V. Karazin National University, Kharkiv, Ukraine

c FB Physik and LFZ OPTIMAS, Technische Universität Kaiserslautern, Germany d Materials Science in Mainz, Johannes Gutenberg University Mainz, Mainz, Germany.

e School of Physics and Astronomy, University of Exeter, Exeter, United Kingdom

Ferromagnetism and superconductivity are most fundamental phenomena in condensed matter

physics. Entailing opposite spin orders, they share an important conceptual similarity: Disturbances

in magnetic ordering in magnetic materials can propagate in the form of spin waves (magnons) [1]

while magnetic fields penetrate superconductors as a lattice of magnetic flux quanta (fluxons) [2].

Recently, the interaction of spin waves with a flux lattice in ferromagnet/ superconductor Py/Nb

bilayers has been observed experimentally [3]. In particular, we have demonstrated that, in this

system, the magnon frequency spectrum exhibits a Bloch-like band structure with forbidden-

frequency gaps which can be finely tuned by the biasing magnetic field. Furthermore, Doppler shifts

have been observed in the frequency spectra of spin waves scattered on a flux lattice moving under

the action of a transport current in the superconductor, see Fig. 1, suggesting tunable spin-wave

devices and the electrical detection of the vortex motion with high precision.

In all, our obsevations [3] set the stage for magnon-fluxonics as a new research domain at the

interface between superconductivity and magnetism.

Fig. 1. Normalized spin-wave

transmission as a function of the

absolute value of the current in the Nb

layer at T = 8 K. The dashed lines are

fits for the location of for-bidden-

freqeuncy gaps with account for the

Doppler effect. The current-voltage

curve of the Nb film is shown by the

blue spheres. In this, regions (I), (II)

and (III) correspond to the pin-ned,

trancient, and free flux-flow regimes

in the vortex motion.

[1] Gurevich, A. & Melkov, G. Magnetization Oscillations and Waves (CRC Press, NY, 1996).

[2] Abrikosov, A. A. Nobel lecture: Type II superconductors and the vortex lattice. Rev. Mod. Phys. 76, 975

(2004).

[3] Dobrovolskiy, O. V et. al. Magnon–fluxon interaction in a ferromagnet/superconductor hetero-structure.

Nat. Phys. (2019), DOI: 10.1038/s41567-019-0428-5.


IC.6 26

Analysis of switching times statistical distributions for perpendicular spin-

torque magnetic memories

Massimiliano d’Aquinoa, Valentino Scalerab, Claudio Serpicob

aEngineering Department, University of Naples “Parthenope”, I-80143 Napoli, ITALY

bDepartment of Electrical Engineering and ICT, University of Naples Federico II, I-80125 Napoli, ITALY

Magnetization switching in nanomagnets is the fundamental issue to deal with in order to obtain high

speed and energy-efficient recording devices[1].

To realize fast magnetization switching with greater efficiency, strategies as microwave-assisted

switching[2] and precessional switching[3] have been proposed. In particular, the latter occurs by applying a

field transverse to the initial magnetization and yields much smaller switching times than conventional

switching. However, extremely precise design of the field pulse is required for successful switching. Then, the

equilibrium magnetization is reached after quasi-random relaxation from a high-to low-energy state. This

mechanism is probabilistic even when thermal fluctuations are neglected, but the stochasticity is much more

pronounced when the latter are considered[3]. On the other hand, magnetic recording devices must fulfill strict

reliability requirements in terms of very low write-error rates, which can be realized at expense of the write

process speed.

In this paper, we theoretically analyze the magnetization switching for a single magnetic bit cell subject to

applied field/spin-polarized current pulses and room temperature thermal fluctuations. By using analytical

techniques, we derive expressions for the switching times distribution functions in terms of material,

geometrical and external current/field properties[4]. Numerical simulations (macrospin and full

micromagnetic) are performed to validate the analytical predictions. Fig. 1 reports an example of comparison

between analytical approach, numerical macrospin and full micromagnetic simulations in the case of a

perpendicular spin-torque magnetic random access memory cell.

Figure 1: Switching times probability and cumulative distributions as function of applied current pulse amplitude

computed by analytical theory, macrospin and micromagnetic simulations.

[1] J.-P. Wang, Nature Mater. 4, 191, (2005)

[2] C. Thirion et al., Nature Mater. 2, 524, (2003)

[3] S. Kaka et al., Appl. Phys. Lett. 80, 2958, (2002)

[4] M. d’Aquino et al., J. Magn. Magnet. Mater. 475, 652 (2019)


IC.7 27

Voltage controlled mutual synchronization of spin Hall nano-oscillators

M. Zahedinejada, S. Fukamib, S. Kanaib, H. Ohnob, J. Åkermana

a Physics Department, University of Gothenburg, Gothenburg, Sweden b Laboratory for Nanoelectronics and Spintronics, Tohoku University, Sendai, Japan

Mutual synchronized spin transfer torque nano-oscillators (STNOs) is one of the promising platforms for bioinspired

computing and microwave signal generation [1,2]. Using STNOs one can achieve 90% recognition rate in spoken

vowels [3]. However, in order to do more complex tasks, larger scale synchronized oscillators with individual control

are needed, something that is not easily done with STNOs demonstrated so far. In addition, all STNO platforms use

external memory in order to tune the coupling and frequency of individual oscillators, something that has to be

addressed with actual internal memory hardware as well.

In this work, we present W/CoFeB/MgO based spin Hall nano-oscillators (SHNOs) with an embedded memristor

(CoFeB/MgO/AlOx/SiNx/Ti/Cu) having both a high-resistance state (HRS) and a tunable low-resistance state (LRS),

which we successfully use to tune the SHNO frequency. Fig.1A shows the SHNO frequency versus drive current

(ISHNO) of four free running oscillators in a chain without any applied voltage to the memristor. At their threshold

current, the oscillators start out in a mutually synchronized state, but then break away for ISHNO > 600 µA. We then

set ISHNO = 712 µA and study the output signal of the chain vs. memristor voltage. When the memristor operates in

its HRS (Fig.1B) it acts as an insulating gate applying a strong electric field to the MgO/CoFeB interface. The electric

field modifies the perpendicular magnetic anisotropy (PMA), which directly translates into a change auto-oscillation

(AO) frequency of the two SHNOs affected. At a memristor voltage of about 2.5 V, the SHNO chain mutually

synchronizes. As the voltage is further increased, the memristor switches to its LRS (VG = Vset), and a certain amount

of additional current Im is then injected into the SHNO underneath. As a consequence, the AO frequency experiences

a drastic change, now based on current dependent tuning. The oscillators remain synchronized when the voltage is

swept back until the memristor switches to LRS (Fig.1C).

Figure 1. (A) Frequency vs. SHNO current profile. The inset shows were to top electrodes are located. (B) Voltage

sweep applied to G2 pushing the upper-frequency branch down making entire chain synchronized. Once memristor

switches to LRS, the chain stays synchronized. (C) The chain remains synchronized while the voltage is swept back

until the memristor switches back to HRS.

We have hence demonstrated both instantaneous and non-volatile tuning of SHNO synchronization, which can be

used for on-chip learning at the oscillator level. Our demonstration can be extended to larger 1D and 2D SHNO

arrays where the individual oscillators frequencies can be tuned to push the entire ensemble to synchronization at a

frequency corresponding to a memorized template to be recognized by the network. Embedding the memristors helps

to recall the previous coupling value (weight) between oscillators.

[1] M. Zahedinejad , et al. arXiv preprint arXiv:1812.09630 (2018).

[2] A. A. Awad, et al. Nature Physics 13.3 (2017): 292.

[3] M. Romera, et al. Nature 563.7730 (2018): 230.


IC.8 28

Damping Modulation in Perpendicular Magnetic Thin Films

S. Sahaa,b, A. Hrabeca,b, Z. Luoa,b, C. Abertc, D. Suessc and L. J. Heydermana,b

aLaboratory for Mesoscopic Systems, Department of Materials, ETH Zurich, 8093 Zurich, Switzerland

bPaul Scherrer Institut, 5232 Villigen, Switzerland

cChristian Doppler Laboratory of Advanced Magnetic Sensingand Materials, Faculty of Physics,University

of Vienna, Austria

Understanding and controlling the damping in ferromagnetic thin films is very important for emerging

technologies including magnonics and spintronics. One of the possible ways to manipulate magnetic damping

is injection of spin current generated due to spin Hall effect [1] which is an emerging phenomenon where the

properties of electrical charge current can be transferred to the electron’s intrinsic angular momentum (spin

current), and vice versa. This enables a mutual data transfer between spin and charge, and the generated spin

currents can be used to manipulate magnetic moments as well as the intrinsic damping of the ferromagnetic

material. These phenomena have a high potential for the development of future low-power electronics based

on the spin-orbit interaction. To measure the modulation of damping, we use a time-resolved magneto-optical

Kerr effect microscope (TR-MOKE), which has the best spatial and temporal resolution to measure the

damping of the ferromagnetic film. In this project, we have demonstrated that the damping of Pt/Co/Ta film

with high perpendicular anisotropy varies linearly with the electrical current density. The observations will

have a strong impact on the development of spintronics devices, such as spin transfer torque nano-oscillators

or domain wall racetrack memories.

Acknowledgement:

We acknowledge ETH Zurich Post Doctoral fellowship and Marie Curie actions for People COFUND program

and Mr. T. P. Dao and Prof. Pietro Gambardella valuable discussions.

References:

[1] L. Liu et. Al., Science, 336, 555-558 (2012)

Session IIA Tuesday, July 30

IIA.1 29

Excitation and amplification of spin waves by spin-orbit torque

V. E. Demidov

University of Münster, Münster, Germany

Downscaling poses a number of new challenges for the implementation of magnonic devices utilizing spin

waves as nano-scale information carrier. In particular, the traditional inductive method for spin wave excitation

becomes inefficient at nanoscale. An alternative approach to the excitation of spin waves can utilize the spin-

transfer torque generated due to the spin-orbit interaction – the spin-orbit torque (SOT). Important advantages

of SOT are the possibility to utilize low-damping insulating magnetic materials and to compensate the spin-

wave damping over extended areas.

In the recent years, it has been experimentally demonstrated that SOT allows one to significantly enhance

propagation length of spin waves and to achieve excitation of localized coherent magnetic auto-oscillations.

However, for a long time, it was not possible to achieve SOT-induced generation of coherent propagating spin

waves, which is a prerequisite for development of efficient magnonic devices making use of all the advantages

provided by SOT.

In this talk, I review our recent experimental studies on the excitation and the amplification of propagating

coherent spin waves by SOT in magnonic nanostructures based on conductive and insulating magnetic

materials using micro-focus Brillouin light scattering (BLS) spectroscopy, which allows the direct

visualization of spin-wave propagation with the submicrometer spatial resolution. I demonstrate two novel

approaches that enable an efficient emission of coherent spin waves by SOT-driven devices. First, the emission

can be achieved by utilizing the new concept of nano-notch SOT oscillators directly incorporated into 200 nm

wide magnonic nano-waveguides. In these devices, the demagnetization effects allow one to match the

frequency of spatially localized SOT-induced auto-oscillations with the frequencies of propagating spin waves

in the nano-waveguide resulting in a uni-directional emission of spin waves, which can be controlled by the

direction of the static magnetic field. Second, the generation of propagating spin waves can be achieved by

suppressing the nonlinear self-localization phenomena by utilizing effects of perpendicular magnetic

anisotropy (PMA) in Bi-doped nanometer-thick films of magnetic insulator - Yttrium Iron Garnet (YIG). I

show that, by tuning the PMA strength, one can supress the nonlinear frequency shift of the auto-oscillations

and achieve emission of short-wavelength spin waves even in extended magnetic films. In both these systems,

the same SOT mechanisms can be used to generate spin waves and simultaneously compensate their

propagation losses over a spatially extended region providing a route for the implementation of highly efficient

magnonic devices.

[1] V. E. Demidov, et al., Nat. Commun. 7, 10446 (2016).

[2] M. Evelt, et al., Appl. Phys. Lett. 108, 172406 (2016).

[3] V. E. Demidov, et al., Phys. Rep. 673, 1 (2017).

[4] B. Divinskiy, et al., Adv. Mater. 30, 1802837 (2018).

[5] M. Evelt, et al., Phys. Rev. Appl. 10, 041002 (2018).


IIA.2 30

Parametric resonance in a nanowire spin Hall device

Rodrigo E. Ariasa, Liu Yangb, Alejandro A. Jarac, Ilya N. Krivorotovc

a Universidad de Chile, Santiago, Chile b Amazon, USA

c University of California, Irvine, USA

Parametric resonance is a versatile tool for excitation of spin waves in nano-magnonic devices. Here we

present a joint theoretical and experimental study of parametric resonance of magnetization in nanowires made

from bilayers of Pt and Permalloy (Py). In this system, damping of spin waves in Py can be tuned via

antidamping spin Hall torque arising from electric current in the Pt layer. We report parametric excitation of

spin waves driven by microwave current applied to the nanowire, and tuning of the resonance propertied by

direct current. Under magnetic field applied perpendicular to the wire axis, we observe parameter excitation

of two types of spin wave eigenmodes: bulk and edge modes. Comparison of our theoretical description of

parametric resonance of these modes to the experimental data reveals important role played by the Oersted

field produced by ac and dc currents for the excitation process. Theoretical analysis of the data allows us to

extract information on the spin Hall efficiency in the Pt/Py device as well as on damping parameters of the

excited spin wave modes.

[1] Z. Duan et al, Nature Comm. 5:5616 (2014).

[2] Z. Duan et al, Phys. Rev. B 90, 024427 (2014).

[3] Z. Duan, I.N. Krivorotov, R.E. Arias, N. Reckers, S. Stienen, J. Lindner, Phys. Rev. B 92, 104424

(2015).

Fig: Nanowire spin Hall device: transversely magnetized Pt/Py nanowires, traversed

by dc-ac electric currents.


IIA.3 31

Identification, enhancement and time-resolved study of YIG spin wave modes in

a MW cavity in strong coupling regime

Angelo Leoa, Silvia Rizzatob, L. Martina a, Anna Grazia Monteduroa,b, Giuseppe Maruccioa,b

a Mathematics and Physics Department “E. De Giorgi”, University of Salento, Lecce, Italy b CNR Nanotec – Institute of Nanontecnology, Lecce, Italy

Recently, the hybridization of microwave-frequency cavity modes with collective spin excitations attracted

large interest for the implementation of quantum computation protocols, which exploit the transfer of

information among these two physical systems [1, 2]. In this frame, magnons exhibited strong stability in

coupling with photons, when they are excited in ferro/ferri-magnetic (FM) materials, especially if Yttrium Iron

Garnet (YIG) single crystals are used. In contrast with paramagnetic spin ensembles [1, 2], which at room

temperature (RT) are weakly coupled to the photons, the YIG presents at least a three orders greater net spin

density, which permits to achieve strong coupling [3, 4]. Interaction with the uniform Kittel mode was initially

the focus of literature and later, among the key advances, it is worth mentioning the demonstration of magnon-

based memories at room temperature [5], the implementation of hybrid systems among ferrimagnetic magnons

and superconducting qubits [6], and the description of coherent photon-phonon interactions within a magnonic

resonator working as an information trasductor device [7]. Even non-uniform magnetostatic modes (MSMs)

can be sustained by the material, depending on its shape and they can be also coupled to cavity modes [8, 9].

Here, we report the strong coupling of a small YIG sphere to the MW photons resonating in a 3D aluminum

cavity at RT. In our experiments, we recorded the cavity response in stationary regime such as to observe clear

Rabi splittings, which are fingerprints of the hybridization between magnons in the FM crystal and photons in

the cavity (see fig 1); the time-resolved studies show evidence of Rabi oscillations, demonstrating coherent

exchange of energy among photons and magnonic modes. Moreover, we proposed a new procedure based on

the introduction of a novel functional variable, in order to facilitate the identification of MSMs whose signature

was found to be enhanced by coupling to adjacent metal layers. The ability to access and identify further MSMs

makes the hybrid magnon-photon system an even more versatile tool.

Figure 1: Left: Transmission spectrum of 3D cavity loaded with YIG sphere as a function of bias magnetic

field, near fundamental mode. Right: Rabi oscillations of the signal from cavity strongly coupled with two

MSMs of the YIG sphere.

1. P. Bushev, Physical Review B. 2011. p. 060501.

2. S. Saito, Physical review letters, 2013. 111(10): p. 107008.

3. Y. Tabuchi, Physical review letters, 2014. 113(8): p. 083603.

4. X. Zhang, Physical review letters, 2014. 113(15): p. 156401.

5. X. Zhang, Nature communications, 2015. 6.

6. D. Lachance-Quirion, Science advances, 2017. 3(7): p. e1603150.

7. X. Zhang, , Science advances, 2016. 2(3): p. e1501286.

8. X. Zhang, Journal of Applied Physics, 2016. 119(2): p. 023905.

9. R. Morris, Scientific Reports, 2017. 7.


IIA.4 32

Spin current generation, detection, and transport with antiferromagnets

Axel Hoffmannc

Materials Science Division, Argonne National Laboratory, Argonne, IL 60439, USA b

Harnessing spin currents is a promising pathway towards low-power electronics [1]. Towards this end, it

recently has been recognized that antiferromagnetic materials can play a more active role beyond their

traditional use for providing a reference magnetization direction via exchange bias. Namely, antiferromagnets

may be conduits for spin currents, as well as, actively enable spin current generation and detection [2]. With

respect to the later, we demonstrated spin current generation both via spin Hall effects in conducting

antiferromagnets and spin Seebeck effects in insulating antiferromagnets. Using CuAu-I-type metallic

antiferromagnets (PtMn, IrMn, PdMn, and FeMn) we showed by using spin pumping that these alloys have

significant spin Hall effects, which in the case of PtMn become comparable to the ubiquitously used Pt [3].

The spin Hall angles increase for the alloys with heavier element; a behavior that is well reproduced by first-

principle calculations of the spin Hall conductivities based on intrinsic spin Hall effects. Furthermore, the

calculations suggest pronounced anisotropies of the spin Hall conductivities, which we tested using spin

transfer torque ferromagnetic resonance measurements using epitaxially grown antiferromagnetic films [4].

We observe that indeed the spin Hall conductivity is maximized for different growth orientations (a-axis for

PtMn and PdMn, and c-axis for IrMn) in accordance with the first principle calculations. Interestingly, despite

this striking anisotropy the influence of the exact microscopic antiferromagnetic spin structures appears to

have a negligible influence on the spin orbit torques [5]. In addition, using spin pumping measurements with

permalloy/FeMn/W trilayers, we observe that there are two distinct mechanism for transporting a spin current

in the metallic antiferromagnet, which we associate with electronic and magnonic spin transport, respectively

[6].

This work was supported by the U.S. DOE, Office of Science, Materials Sciences and Engineering

Division, French Projet d’Investissement d’Avenir project “Lorraine Université d’Excellence,” Project No.

ANR-15-IDEX-04-LUE, and DFG.

[1] A. Hoffmann and S. D. Bader, Phys. Rev. Appl. 4, 047001 (2015).

[2] J. Železný, P. Wadley, K. Olejník, A. Hoffmann, and H. Ohno, Nature Phys. 14, 220 (2018).

[3] W. Zhang, M. B. Jungfleisch, W. Jiang, J. E. Pearson, A. Hoffmann, F. Freimuth, and Y. Mokrousov,

Phys. Rev. Lett. 113, 196602 (2014).

[4] W. Zhang, M. B. Jungfleisch, F. Freimuth, W. Jiang, J. Sklenar, J. E. Pearson, J. B. Ketterson,

Y. Mokrousov, and A. Hoffmann, Phys. Rev. B 92, 144405 (2015).

[5] H. Saglam, J. C. Rojas-Sanchez, S. Petit, M. Hehn, W. Zhang, J. E. Pearson, S. Mangin, and

A. Hoffmann, Phys. Rev. B 98, 094407 (2018).

[6] H. Saglam, W. Zhang, M. B. Jungfleisch, J. Sklenar, W. Jiang, J. E. Pearson, J. B. Ketterson, and

A. Hoffmann, Phys. Rev. B 94, 140412(R) (2016).


IIA.5 33

Spin wave magnonic cavity fabricated using a femto second laser

Lekha P. Na, Manobalashankar Ma, Prachi Ca, G Venkatb, M Malathia, A Prabhakara

a EE dept., Indian Institute of Technology, Chennai, India

b Physics. Dept., Loughborough University, UK

Magnons, the quanta of spin waves (SW), recently find extensive attention as information carriers. SWs,

whose frequency ranges from GHz to THz and capable of operating in wavelengths of nm, show promises of

miniaturization of devices without Joule heating. SW majority logic gate [1] has been experimentally

demonstrated and magnonic crystals have been utilized to process analog and digital information [2]. A SW

magnonic cavity is designed with two sets of magnonic grating having a period of 10, on either side of a plane

film. In this work, we fabricate a 1D SW magnonic grating and simulate it’s expected action using

micromagnetic simulation OOMMF.

Gratings were fabricated in BLIG ((LuBi)3Fe5O12) film, of 8 μm thick using a Ti : S, 800 nm, 6 W, and 35

fs, femto second laser. The incident laser power was optimized after a roughness study to produce uniform

gratings as shown in the surface profiler image in Fig 1(a). The period of the gratings is 15 μm, width 8 μm

and depth 6 μm. In simulations, BLIG film of scaled dimensions of 90 × 8 × 1 nm3 with 3 grooves as shown

in Fig.1(b) was used. Initially, the magnetization (M) of the film is saturated with HDC of 1.3 × 105 A/m along

x direction. An excitation broadband in time and space was applied to excite BVSWs as in Fig. 1b. The

simulations were run for 4 ns, sampled at 1ps.

We probed the temporal evolution of the dynamic component of magnetization at the right of the grating

as in Fig. 1(b) and obtained its Fourier transform. We applied a Hanning window and fft on it as in [3] which

gave us the modes transmitted through the grating. We compared the spectra of the grating film and a plane

film in Fig. 1c and observe that the mode at 14 GHz is allowed in the grating. We shall extend the same for a

grating with 10 grooves and to a 1D spin wave resonator.

Figure 1. (a): Surface profiler characterization of magnonic grating (b): Simulation set up along the side of the

grating in Fig. 1a (c): Resonant modes transmitted in plane film and grooved film

[1] T. Fischer et al., Appl. Phys. Lett. 110, (2017), 152401-1 – 152401-4. [2] A V Chumak et al., J. Phy. D: App. Phy. 50 (2017), 244001-1 – 244001-20. [3] G Venkat et al., IEEE Trans. On Mag., 49, (2013), 524 – 529.


IIA.6 34

Twisted magnon beams carrying orbital angular momentum

Chenglong Jiaa, Decheng Maa, Alexander F. Schäfferb, Jamal Berakdarb

a Key Laboratory for Magnetism and Magnetic Materials of the Ministry

of Education & Institute of Theoretical Physics, Lanzhou University, China b Institut für Physik, Martin-Luther-Universität Halle-Wittenberg, Halle (Saale), Germany

Low-energy eigenmode excitations of magnetically ordered systems are spin waves that can

be quantified by quasiparticles termed magnons. Magnons can be thermally and non-thermally excited,

confined, spectrally shaped, and guided by material design [1]. Magnonic currents are routinely generated at

low energy cost and do not suffer from Ohmic losses, which make them an attractive medium for

communication, and processing of information. Here we present propagating spin waves that carry a definite

and electrically tunable orbital angular momentum (OAM) constituting a ”twisted magnon beam”. Starting

from fundamental equations for spin dynamics we present how OAM beams emerge in magnonic waveguides

and how to topologically quantify and steer them. A key finding is that the topological charge associated with

OAM of a particular beam is tunable externally and protected against damping. Coupling to an external electric

field via the Aharanov-Casher effect allows for electrical tuning of the topological charge. This renders

possible OAM-based robust, low-energy consuming multiplex magnonic computing, analogously to using

photonic OAM in optical communications [2], and high OAM-based entanglement studies [3], but here at

shorter wavelength and lower energy consumption, and ready integration in magnonic circuits utilizing the

versatile toolbox for material and spin waves engineering.

[1] Chumak, A. V. et al., Nature Physics 11, 453 (2015).

[2] Willner, A. E. et al., Adv. Opt. Photon. 7, 66 (2015).

[3] Mair A. et al., Nature 412, 313–316 (2001).

Fig.1: Spin wave propagating along a cylindrical microtube of the

insulting magnet yttrium iron garnet. a) Snapshot of the magnon beams

after 2 ns for the x component of the triggered magnetization. b) Vortex

configuration of the excitation modes along the tube. c) The z resolved

amplitude and the orbital angular momentum of spin waves. In a), b),

and c) the spin waves are excited locally at z = 0 interface by a twisted

rf magnetic field having the amplitude Bmax = 10 mT and frequency B

= 5 GHz.


IIA.7 35

Nutation spectroscopy of the precessing magnetization in a nanomagnet in the

strong nonlinear regime

Yi Lia, Vladimir Naletova,b, Olivier Kleinc, José Luis Prietod, Manuel Muñoze, Vincent Crosf, Paolo

Bortolottif, Madjid Ananef, Claudio Serpicog, Grégoire de Loubensa

a Service de Physique de l’Etat Condensé, CEA, CNRS, Université Paris-Saclay, Gif-sur-Yvette, France b Institute of Physics, Kazan Federal University, Kazan, Russia

c Univ. Grenoble Alpes, CEA, CNRS, Grenoble INP, INAC-Spintec, Grenoble, France d Instituto de Sistemas Optoelectronicos y Microtecnologia (UPM), Madrid, Spain

e Instituto de Microelectronica de Madrid (CNM-CSIC), Madrid, Spain f Unité Mixte de Physique CNRS, Thales, Univ. Paris-Sud, Université Paris-Saclay, Palaiseau, France

g Dipartimento di Ingegneria Elettrica e Tecnologie dell’Informazione, Università Federico II, Napoli, Italy

The Landau-Lifshitz equation which governs the motion of magnetization in ferromagnetic bodies is highly

nonlinear, yielding a series of interesting phenomena. It is well-known that in ferromagnetic resonance

experiments, spin-wave instabilities quickly develop as the excitation power is increased, preventing to achieve

large angles of coherent precession [1]. This limitation can be overcome in nanostructures, where high

amplitude magnetization dynamics can be driven by spin transfer torque. In this work we show that the

magnetization of a nanomagnet can be driven to unprecedented large steady state motion by a time-harmonic

magnetic field, as in conventional FMR. For this, we probe the magnetization dynamics of an ultra-low

damping YIG nano-disc [2] using a magnetic resonance force microscope. Ultra-large amplitude precession

with a characteristic foldover shape of the resonance curve and a nearly complete suppression of the

longitudinal component of magnetization is achieved by pumping the sample with a strong uniform microwave

field. Strikingly, signatures of nonlinear energy dissipation towards non-uniform quantized spin-wave modes

are observed, but only far beyond the threshold for foldover instability. In addition, we move to the rotating

frame by applying a second weaker microwave field to spectroscopically probe the excitations on top of this

dynamical state, which allows us to study the stability of the coherent precession of magnetization in the strong

nonlinear regime. The lowest energy mode corresponds to the uniform nutation of the magnetization about its

stable precession trajectory, and higher order modes are identified as nutation modes with spatial gradients.

Our experimental findings are well accounted for by an analytical model derived for systems with uniaxial

symmetry [3], which confirms that magnetization dynamics in nanomagnets is a realistic test bed to study

highly nonlinear dynamical systems. They also suggest interesting opportunities in the context of

neuromorphic applications.

[1] H. Suhl, J. Phys. Chem. Solids 1, 209 (1957)

[2] C. Hahn, et al., Appl. Phys. Lett. 104, 152410 (2014)

[3] G. Bertotti, I. D. Mayergoyz and C. Serpico, Phys. Rev. Lett. 87, 217203 (2001)

Session IIB Tuesday, July 30

IIB.1 36

Strong interlayer magnon-magnon coupling in magnetic hybrid nanostructures

J. Chena, C. Liua, T. Liub, Y. Xiaoc, K. Xiad, G.E.W. Bauere,f, M. Wub and H. Yua

a Fert Beijing Institute, BDBC, School of Microelectronics, Beihang University, Beijing, China b Department of Physics, Colorado State University, Fort Collins, Colorado, USA

c Department of Applied Physics, Nanjing University of Aeronautics and Astronautics, Nanjing, China d Department of Physics, Beijing Normal University, Beijing, China

e Institute for Materials Research, WPI-AIMR and CSNR, Tohoku University, Sendai, Japan f Zernike Institute for Advanced Materials, University of Groningen, Groningen, The Netherlands

The strong couplings between a cavity photon and spin wave excitations (magnons) have been recently

investigated [1-4], known as cavity photon-magnon polaritons. We studied experimentally strong couplings

between in-plane standing spin waves in 20 nm-thick YIG film and ferromagnetic resonance (FMR) of metallic

nanowires [5]. Such observations are considered as magnonic cavities in view of its analog to the cavity

photon-magnon polaritons. Large anticrossing gaps up to 1.58 GHz are observed experimentally (Fig. 1).

Control experiments and simulations reveal that the interface exchange coupling is the dominating mechanism.

The coupling strength is tunable over a large interval by switching between different magnetic states. The

coherent control of spin waves by surface induced strong coupling is of interest for magnonic devices.

[1] H. Huebl, C.W. Zollitsch, J. Lotze, F. Hocke, M. Greifenstein, A. Marx, R. Gross and S.T.B.

Goennenwein, Phys. Rev. Lett. 111, 127003 (2013).

[2] X. Zhang, C.-L. Zou, L. Jiang and H.X. Tang, Phys. Rev. Lett. 113, 156401 (2014).

[3] Y. Cao, P. Yan, H. Huebl, S.T.B. Goennenwein and G.E.W. Bauer, Phys. Rev. B 91, 094423 (2015).

[4] L. Bai, M. Harder, Y.P. Chen, X. Fan, J.Q. Xiao and C.M. Hu, Phys. Rev. Lett. 114, 227201 (2015).

[5] J. Chen, C. Liu, T. Liu, Y. Xiao, K. Xia, G.E.W. Bauer, M. Wu and H. Yu, Phys. Rev. Lett. 120, 217202

(2018).

Fig. 1 Anticrossings between the YIG in-plane standing spin wave mode and the Co nanowire

FMR mode at anitiparallel state of Co/YIG hybrid structures.

Figure 1: Top row: hysteresis loops of samples with different thickness. Bottom row: corresponding

MFM images at remanence.


IIB.2 37

Low-loss YIG-based magnonic crystals with large tunable bandgaps

Huajun Qina, Gert-Jan Botha, Sampo J. Hämäläinena, Sebastiaan van Dijkena

a NanoSpin, Department of Applied Physics, Aalto University School of Science, 00076 Aalto, Finland

Magnonic crystals made of yttrium iron garnet (YIG) with ultralow damping offer promising prospects for

spin-wave manipulation [1]. However, the frequency bandgap attained in YIG-based magnonic crystals has

thus far been limited to a few tens of MHz. The realization of large tunable bandgaps in YIG-based magnonic

crystals is essential for low-power magnonics.

Here, we report on one-dimensional magnonic crystals comprising 2 to 4 discrete nanometer-thick YIG

stripes and experimentally demonstrate robust bandgaps up to 200 MHz for Damon-Eshbach-type spin waves

[2]. Using broadband spin-wave spectroscopy and micromagnetic simulations, we show that the bandgaps are

formed by strong Bragg reflection of spin waves with k = n/a, as depicted in Figs. 1(a) and 1(b). Spin wave

transmission within the bandgap is almost completely suppressed. By changing external magnetic field, lattice

constant, or stripe width, we establish strong tuning of the bandgap size from 50 MHz up to 200 MHz, as

shown in Fig. 1(c). Next, we compare results on discrete YIG stripes separated by airgaps and gaps filled by

CoFeB. After the insertion of CoFeB, the transmission of spin waves in the allowed minibands is enhanced

substantially while the size of the bandgap is reduced only slightly. We attribute low-loss spin-wave

propagation in YIG/CoFeB magnonic crystals to enhanced dynamic dipolar coupling between the YIG stripes.

This result illustrates that strong ferromagnets can act as mediator of magnetic interactions in YIG-based

magnonic crystals. We also show that Bragg scattering on two airgaps or CoFeB stripes i.e., only 1 YIG stripe

separated from a continuous YIG film, already produces clear frequency gaps in spin-wave transmission

spectra. The integration of strong ferromagnets in nanometer-thick YIG-based magnonic crystals provides

effective spin-wave manipulation and low-loss propagation, a vital parameter combination for magnonic

technologies.

[1] A.V. Chumak et al., Nat. Phys. 11 (2015), 453-461.

[2] H.J. Qin et al., Nat. Commun. 9 (2018), 5445.

Figure 1: (a) Contour plot of spin-wave transmission spectra (amplitude of S12) for a YIG/CoFeB

magnonic crystal as a function of magnetic bias field. (b) Micromagnetic simulations of the spatial

distribution of spin-wave intensity for a YIG/CoFeB crystal. The right panel compares simulated

(orange line) and measured (blue line) spin-wave spectra with bandgaps at k = n/a for a magnetic

bias field of 5 mT. In (a) and (b), a = 30 m, w_CoFeB = 2.5 m. (c) Measured (solid circles) and

simulated (empty circles) size of the first bandgap as a function of lattice constant.


IIB.3 38

Spin waves in thin films and magnonic crystals with Dzyaloshinskii-Moriya

interactions

Rodolfo Gallardoa,b, David Cortés-Ortuñoc, Roberto Troncosod, Pedro Landerosa,b

a Departamento de Física, Universidad Técnica Federico Santa María, Valparaíso, Chile b Center for the Development of Nanoscience and Nanotechnology (CEDENNA), Santiago, Chile

c Faculty of Engineering and Physical Sciences, University of Southampton, Southampton, United Kingdom d Center for Quantum Spintronics, Department of Physics, Norwegian University of Science and

Technology, Trondheim, Norway

The influence of the Dzyaloshinskii-Moriya interaction (DMI) on the behavior of spin waves in ultra-thin

ferromagnetic films and chiral magnonic crystals is reviewed [1]. During the last decade, it has been shown,

both theoretically and experimentally, that this anisotropic exchange interaction produces non-reciprocal

features on the spin-wave spectrum of a magnetic system, a phenomenon that occurs both for bulk [2-3] and

interfacial Dzyaloshinskii-Moriya coupling [4-6]. More recently, the concept of a chiral magnonic crystal has

been introduced [7], where the interfacial Dzyaloshinskii-Moriya interaction is periodic. The effect of this

periodicity includes additional features such as flat bands, indirect gaps, and an unusual spin-wave evolution,

with standing waves showing finite phase velocities in the zones where the DMI is nonzero. These results have

been obtained with micromagnetic simulations and using a theoretical approach based on the plane-wave

method. These chiral magnonic crystals with periodic DMI, which may be attained for instance by covering a

thin ferromagnetic film with an array of heavy-metal wires [7], host interesting physical properties,

encouraging future experimental studies to prove and evidence these phenomena.

[1] R. A. Gallardo, D. Cortés-Ortuño, R. E. Troncoso, and P. Landeros, To be published on: Three-

dimensional Magnonics: Layered, micro- and nano-structures, Ed. by G. Gubbiotti, arXiv:1903.04288

(2019).

[2] Y. Iguchi, S. Uemura, K. Ueno, and Y. Onose, Phys. Rev. B 92 (2015), 184419.

[3] S. Seki, Y. Okamura, K. Kondou, K. Shibata, M. Kubota, R. Takagi, F. Kagawa, M. Kawasaki, G. Tatara,

Y. Otani, and Y. Tokura, Phys. Rev. B 93 (2016), 235131.

[4] K. Di, V. L. Zhang, H. S. Lim, S. C. Ng, M. H. Kuok, J. Yu, J. Yoon, X. Qiu, and H. Yang, Phys. Rev.

Lett. 114 (2015), 047201.

[5] J. Cho, N.-H. Kim, S. Lee, J.-S. Kim, R. Lavrijsen, A. Solignac, Y. Yin, D.-S. Han, N. J. J. van Hoof, H.

J. M. Swagten, B. Koopmans, and C.-Y. You, Nat. Commun. 6 (2015), 7635.

[6] M. Belmeguenai, J.-P. Adam, Y. Roussigné, S. Eimer, T. Devolder, J.-V. Kim, S. M. Cherif, A.

Stashkevich, and A. Thiaville, Phys. Rev. B 91 (2015), 180405.

[7] R. A. Gallardo, D. Cortés-Ortuño, T. Schneider, A. Roldán-Molina, F. Ma, R. E. Troncoso, K. Lenz, H.

Fangohr, J. Lindner, and P. Landeros, Phys. Rev. Lett. 122 (2019), 067204.


IIB.4 39

Spin wave power flow and caustics in thin films with Dzyaloshinskii-Moriya

interaction

Joo-Von Kim

Centre for Nanoscience and Nanotechnology, Université Paris-Saclay, France

Ultrathin ferromagnetic films in contact with strong spin-orbit coupling (SOC) materials can

exhibit interesting chiral phenomena, such as skyrmions and chiral domain walls. These are made

possible by the lack of structural inversion symmetry and a Dzyaloshinskii-Moriya interaction (DMI)

induced by the SOC. We will discuss another important consequence, namely the nonreciprocal

propagation of spin waves in the film plane that result from the DMI [1]. In particular, we will

describe how spin wave power flow is influenced by the DMI, with particular attention to caustics

and focusing effects. Caustics represent particular directions along which wave energy flows from a

point source and is a well-known phenomenon in anisotropic elastic systems [2]. We find that the

combination of dipolar interactions, which leads to anisotropic flow, and the DMI, which favors

unidirectional flow, can give rise to focused beams along one direction in the film plane. By using

micromagnetics simulations and analytical models, we determined the radiation patterns due to point

source excitations in extended films. We find a variety of different focusing effects and interference

patterns, which are asymmetric. Because the DMI results in an intrinsic Doppler shift in the spin wave

flow, similar effects appear when spin-polarized currents are applied in the film plane, since adiabatic

spin torques also cause a Doppler shift [4]. This suggests that spin currents, combined with DMI, will

open up new possibilities for controlling spin wave power flow for magnonics applications.

This work was partially supported by the Agence Nationale de la Recherche (France) under grant agreement

No. ANR-16-CE24-0027 (Swangate) and No. ANR-17-CE24-0025 (Topsky).

[1] L. Udvardi and L. Szunyogh, Phys. Rev. Lett. 102, 207204 (2009).

[2] B. Taylor, H. J. Maris, and C. Elbaum, Phys. Rev. Lett. 23, 416 (1969).

[3] J.-V. Kim, R. L. Stamps, and R. E. Camley, Phys. Rev. Lett. 117, 197204 (2016).

[4] V. Vlaminck and M. Bailleul, Science 322, 410 (2008).

Session IIIA Wednesday, July 31

IIIA.1 40

Terahertz magnonics in antiferromagnets

Rostislav Mikhaylovskiya

a Lancaster University, Lancaster, United Kingdom

The antiferromagnetic materials appeal to spintronics and magnonics because of their very high (terahertz)

frequencies of spin dynamics and unique functionalities in comparison to conventional ferromagnets. Recently

the freely propagating terahertz electromagnetic radiation has been suggested as the most direct interface to

the antiferromagnets, able to detect and control spin motion in them. Here we show that due to the strong

coupling of the propagating THz electromagnetic fields with magnons, the hybrid magnon-polariton modes

start to play a significant role. For instance, by measuring the terahertz emission and transmission of an

archetypical antiferromagnet TmFeO3 we found a clear beating between the frequencies just below and above

the frequency of antiferromagnetic resonance in this crystal [1]. Our theoretical analysis indicates that the

beating arises due to the energy exchange between the higher and lower polariton branches formed in vicinity

of the antiferromagnetic magnon frequency.

Polaritonic nature of spin modes in antiferromagnets has important implications for THz-driven spin control

[2]. In DyFeO3 orthoferrite the lattice-mediated coupling of the electric fields produced by otherwise

orthogonal magnon modes leads to internal resonance, when the frequencies of the modes are close to each

other. This resonance results in a dramatic enhancement of spin oscillations excited by THz magnetic field.

Finally, we couple spins in TmFeO3 with the locally enhanced THz electric fields of custom-tailored antennas.

The strong near fields drive the magnons into distinctly nonlinear regime characterized by a phase slip in the

time domain and a magnon band splitting in the frequency domain. We interprete this behaviour as a fingeprint

of ballistic switching of antiferromagnetic order parameter.

[1] K. Grishunin, R. V. Mikhaylovskiy, et al. ACS Photonics 5 (2018), 1375-1380.

[2] S. Baierl, R. V. Mikhaylovskiy, et al. Nature Photonics 10 (2016), 715-718.


IIIA.2 41

Exchange-enhanced ultrastrong magnon-magnon coupling in a compensated

ferrimagnet

Lukas Liensbergera,b, Akashdeep Kamrac, Hannes Maier-Flaiga,b, Stephan Geprägsa, Andreas Erba,

Sebastian T. B. Goennenweind, Rudolf Grossa,b,e,f, Wolfgang Belzigg, Hans Huebla,b,e,f, Mathias

Weilera,b

a Walther-Meißner-Institut, Bayerische Akademie der Wissenschaften, Garching, Germany b Physik-Department, Technische Universität München, Garching, Germany

c Center for Quantum Spintronics, Department of Physics, Norwegian University of Science and

Technology, Trondheim, Norway d Institut für Festkörper- und Materialphysik, Technische Universität Dresden, Dresden, Germany

e Nanosystems Initiative Munich, Munich, Germany f Munich Center for Quantum Science and Technology (MCQST), Munich, Germany

g Department of Physics, University of Konstanz, Konstanz, Germany

The ultrastrong coupling of (quasi-)particles has gained considerable attention due to its application

potential and richness of the underlying physics. Coupling phenomena arising due to electromagnetic

interactions are well explored. In magnetically ordered systems, the quantum-mechanical exchange-interaction

should furthermore enable a fundamentally different coupling mechanism.

Here, we report the observation of ultrastrong intralayer exchange-enhanced magnon-magnon coupling in

a compensated ferrimagnet [1]. We experimentally study the spin dynamics in a gadolinium iron garnet (GdIG)

single crystal using broadband ferromagnetic resonance. Close to the ferrimagnetic compensation temperature,

we observe ultrastrong coupling of clockwise and anticlockwise magnon modes. The magnon-magnon

coupling strength reaches more than 30% of the mode frequency and can be tuned by varying the direction of

the external magnetic field. We theoretically explain the observed phenomenon in terms of an exchange-

enhanced mode-coupling mediated by a weak cubic anisotropy.

Figure 1: (a) Schematic broadband ferromagnetic resonance setup. (b),(c) Resonance frequencies of the

spin-up and spin-down mode vs. magnetic field applied along the (b) magnetic easy axis and along the (c) hard

axis. In the easy axis case (b) we observe weak coupling and in the hard axis case (c) ultrastrong coupling

between the magnon modes is observed.

[1] L. Liensberger et al. arXiv:1903.04330 (2019)


IIIA.3 42

Backward volume vs Damon-Eschbach: A travelling Spin wave spectroscopy

comparison

U.K. Bhaskar,a G. Talmelli,b,c F. Ciubotaru,b C. Adelmann,b and T. Devoldera

aCentre de Nanosciences et de Nanotechnologies, CNRS, Université Paris-Sud, Université Paris-Saclay,

91405 Orsay Cedex, France bImec, 3001 Leuven, Belgium

cDepartement Materiaalkunde, KU Leuven, 3001 Leuven, Belgium

Pertubations to the magnetic state can propogate through space in the form of spinwaves (SWs). In contrast to

Damon-Eschbach SWs (DESWs) and forward volume SWs (FVSWs), the negative dispersion of backward

volume SWs (BVSWs) implies that finite wavevectors correspond to frequencies below the Ferromagnetic

resonance (FMR) [1],[2]. In addition to this inherent uniqueness, BVSWs possesses certain attributes which

point towards a favourable role in future logic devices for example: 1) The collinearity between wave-vector

and magnetic field orientation of BVSWs allows excitation of spinwaves in the magnetic state favoured by the

shape anisotropy, potentially circumventing the need for an external magnetic field; 2) RF excitation with

microstrip antennas results in reciprocal amplitude for both directions of BVSW propogation – a key

requirement for reconfigurable logic circuits. Despite these advantages, BVSWs, when compared to DESWs,

remains relatively less explored for nano-scale logic applications [3], owing to limitations of group velocity

and excitation efficiency using standard microstrip techniques. In this work, leveraging recent optimizations

of the CoFeB stack (Fig 1(a)) and dimensional scaling of U-shaped antennas (Fig 1(b)), we are able to excite

and compare both DESW (Fig 1(c)) and BVSW (Fig 1(d)) propogation in the same device. The reciprocal

nature, and smaller amplitude of BVSW excitation becomes evident while comparing Fig 1(c) and Fig 1(d).

The group velocity of BVSWs/DESWs increases/decreases with applied field, resulting in a

broadening/narrowing of transmitted wavevector bands.

Figure 1(a) Complete ferromagnetic stack along with the metal antenna, isolation and buffer layers; (b)

In-line design of spin-wave bus with multiple tap-outs using four U-shaped microwave antennas; Frequency-

field map of (c) DESWs and (d) BVSWs, respectively.

[1] A. V Chumak, A. A. Serga, B. Hillebrands, A. V Chumak, and T. Neumann, “YIG magnonics,” J.

Phys. D Appl. Phys., vol. 43, p. 264002, 2010.

[2] V. Vlaminck and M. Bailleul, “Spin-wave transduction at the submicrometer scale : Experiment and

modeling,” Phys. Rev. B - Condens. Matter Mater. Phys., vol. 81, no. 014425, 2010.

[3] N. Sato, N. Ishida, T. Kawakami, K. Sekiguchi, N. Sato, N. Ishida, T. Kawakami, and K. Sekiguchi,

“Propagating spectroscopy of backward volume spin waves in a metallic FeNi film,” Appl. Phys.

Lett., vol. 104, no. November 2018, p. 032411, 2017.


IIIA.4 43

Spin precessional dynamics in metallic ferrimagnets revisited

Shigemi Mizukami a,b,c

a WPI Advanced Institute for Materials Research, Tohoku University, Sendai, Japan b Center for Spintronics Research Network, Tohoku University, Sendai, Japan

c Center for Science and Innovation in Spintronics, Tohoku University, Sendai, Japan

In recent years magnetization dynamics for ferrimagnets and antiferromagnets have attracted much

attention. Recent domain wall study suggested that the magnetization dynamics for GdFeCo amorphous

metallic ferrimagnets at the angular momentum compensation temperature TA is analogous to that for

antiferromagnets [1]. The past all-optical experiments succeeded to observe the ferromagnetic resonance and

exchange resonance modes for the GdFeCo films at the temperature near TA [2,3], whereas the physics of the

modes in terms of antiferromagnetic dynamics is not clear yet.

In this study we revisit the spin precessional dynamics for the GdFeCo films to gain further insight into

the physics of spin dynamics at the temperature about TA. The experiments were performed with the all-optical

pump-probe measurements for the GdFeCo films having TA just above the room temperature. The sample

temperature was then effectively changed with changing the pump laser fluence. For a higher pump pulse

fluence, the frequency of the observed magnetization precession increased when the applied field was

increased. On the other hand, for a low pump pulse fluence, the frequency for the observed magnetization

precession tended to decrease when the applied magnetic field was increased. These different responses to the

magnetic field application were well consistent with the left-handed and right-handed precession modes of the

antiferromagnetic-like resonance exited by the pulse laser at the temperature near TA. Meanwhile, the

experimental data were in agreement with the result of the theoretical simulation [4]. The physics of the left-

and right- handed spin precessional dynamics will be discussed in detail.

The work was partially supported by KAKENHI (16H03846, 26103004) and the Center for Spintronics

Research Network (CSRN).

[1] K.-J. Kim et al., Nat. Mater. 16, 1187 (2017).

[2] C.D. Stanciu et al., Phys. Rev. B 73, 1 (2006).

[3] A. Mekonnen et al., Phys. Rev. Lett. 107, 117202 (2011).

[4] S. Mizukami et al., arXiv:1808.0570.


IIIA.5 44

Direct imaging of higher order modes in magnonic waveguides

Nick Trägera, Paweł Gruszeckib, Filip Lisieckic, Johannes Förstera, Felix Großa, Markus Weiganda,

Piotr Kuświkc, Janusz Dubowikc, Gisela Schütza,

Maciej Krawczykb, Joachim Gräfea

a Max Planck Institute for Intelligent Systems, Stuttgart, Germany

b Faculty of Physics, Adam Mickiewicz University, Poznan, Poland c Institute of Molecular Physics, Polish Academy of Sciences, Poznan, Poland

Nowadays, miniaturization of CMOS technologies is limited by physical restrictions of the manufacturing

process. These limits may be overcome by data processing with magnons within magnonic waveguides. Thus,

guiding a path towards smaller elements and miniaturization of various devices at technologically relevant

radio frequencies [1, 2].

Here, we use scanning transmission x-ray microscopy (STXM) with magnetic contrast and spatial and

temporal resolution of 18 nm and 35 ps respectively to investigate the fundamental dynamics of spin-wave

propagation in magnonic Py and Co/Fe waveguides.

Via a global continuous wave or burst RF excitation, short wavelength spin-waves can be excited from the

edges forming a standing spin-wave pattern. Due to the physical constriction of the width of the waveguide,

standing spin-waves also exist in lateral dimension. Therefore, the dispersion relation exhibits higher order

modes in backward volume (BV) configuration (cf. Fig 1(a)) [3].

We directly observe corresponding mode profiles of higher order modes at one single excitation frequency

revealing characteristic nodes with a phase shift of standing spin-waves for Py exemplarily shown in Fig 1(b)

and (c). Additionally, excitation frequencies up to 18 GHz show similar behaviour within Co/Fe waveguides

paving the way for high frequency spin-wave excitation beyond the fundamental BV mode.

[1] Chumak, A.V. et al., Nat. Phys. 11(6) (2015), 453-461.

[2] Kruglyak, V.V. et al., J. Phys. D 43(26) (2010), 264001.

[3] Brächer, T. et al., Phys. Rep. 699 (2017), 1-34.

Figure 1: (a) Dispersion relation in BV geometry. Higher order modes (n=1,2,…) are

depicted which intersect the excitation frequency. (b) Corresponding mode profiles reveal

node behaviour with a phase shift in the upper mode profile (n=2). The lower one shows

the mode profile of the fundamental and the first higher order. (c) Exemplary STXM mode

profile of a third order mode (n=3) with two nodes across the Py waveguide.


IIIA.6 45

Broadband spin wave and elastic magnetization wave emission by magnetic

domain walls

Rasmus B. Holländera, Cai Müllera, Julius Schmalzb, Martina Gerkenb, Jeffrey McCorda

a Institute of Materials Science, Kiel University, Kiel, 24143, Germany b Institute of Electrical and Information Engineering, Kiel University, Kiel, 24143, Germany

Time-resolved wide-field Kerr microscopy allows for the selection of individual dynamic magnetization

components [1] and for the direct observation of coherent magnetization waves in dynamic equilibrium [2].

Here, the dynamic magnetization response of various micromagnetic configurations in soft-magnetic CoFeB

stripe elements is investigated by exciting with a homogeneous Oersted-field and detecting by stroboscopic

magneto-optical imaging in the regime of linear response.

Distinct modes of magnetization wave emission by the magnetic domain walls are directly observed and

can be tuned by their dispersion relation in a broad range of excitation frequencies [3]. Figure 1 displays the

dynamic component-selective magnetization response of a stripe element at 1.9 GHz. Domain wall emitted

elastic waves are observed in the magnetization components Δmy and Δmz. Elastic waves and magnetostatic

surface spin waves are distinguished by their dependence on the magnetic domain structure. The emitted

magnetization waves are inherently coherent and directional. Micromagnetic modeling and mechanical finite-

element calculations support the emission of magnetostatic surface spin waves and elastic magnetization

waves.

The emission of magnetization waves from excited micromagnetic objects is a general physical

phenomenon relevant for magnetization dynamics in patterned magnetic thin films. Our results enable new

and reconfigurable schemes for the excitation of spin waves and elastic waves.

We acknowledge funding from the DFG (Mc9/9-2, Mc9/10-2).

[1] R.B. Holländer et al. JMMM 432, 283–290 (2017)

[2] M. Lohman et al. JMMM 450, 7 (2018).

[3] R.B. Holländer et al. Sci. Rep. 8, 13871 (2018)

Figure 1: Component-selective differential magnetization response of a stripe element

excited at 1.9 GHz. Three different points in time are shown for each component. Figure

adapted from [3].

Figure 1: Top row: hysteresis loops of samples with different thickness. Bottom row:

corresponding MFM images at remanence.


IIIA.7 46

Spintronic operations with antiferromagnets

Takahiro Moriyama

Institute for Chemical Research, Kyoto University, Uji, Kyoto, 611-0011

E-mail: [email protected]

Various spintronic operations with antiferromagnets (AFMs), including static and dynamic controls

of the magnetic moments, are a key for emerging antiferromagnetic spintronics [1]. This presentation will be

based on our recent investigations on spin torque control of and magnetization dynamics with

antiferromagnetic materials. I will show the demonstrations of sequential antiferromagnetic memory

operations with a spin-orbit-torque write, by the spin Hall effect, and a resistive read in various

antiferromagnets [2,3]. I will also speak about the magnetic damping modification of a ferromagnet (FM)

reflecting the Neel order in the AFM in exchange coupled FM/AFM bilayers. A wide range control of magnetic

damping is shown to be possible by utilizing antiferromagnets, which is quite beneficial for spintronic

applications [4,5].

[1] V. Baltz, A. Manchon, M. Tsoi, T. Moriyama, T. Ono, and Y. Tserkovnyak, Rev. Mod. Phys. 90, 015005 (2018);

T. Jungwirth, X. Marti, P. Wadley, and J. Wunderlich, Nat. Nanotechnol. 11, 231 (2016).

[2] T. Moriyama, K. Oda, T. Ohkochi, M. Kimata, and T. Ono, Sci. Rep. 8, 14167 (2018).

[3] T. Moriyama, W. Zhou, T. Seki, K. Takanashi, and T. Ono, accepted in Phys. Rev. Lett. [4] T. Moriyama, M. Kamiya, K. Oda, K. Tanaka, K.-J. Kim, and T. Ono, Phys. Rev. Lett. 119, 267204 (2017).

[5] T. Moriyama, K. Oda, and T. Ono, submitted.

Session IIIB Wednesday, July 31

IIIB.1 47

Probing magnon-phonon and magnon-electron interactions via

thermoelectric measurements

B. Flebus

Department of Physics and Astronomy, University of California, Los Angeles, California 90095, USA

In this talk, I will address how the interplay between magnetization dynamics and other degrees of freedom,

such as electrons and phonons, can affect spin and electric transport properties. Specifically, I will show that:

i) we have unveiled a new contribution, stemming from an adiabatic Berry-phase force, to the magnon-drag

thermopower in ferromagnetic metals [1]; ii) we have derived a transport theory for hybridized magnon-

phonon modes in magnetic insulators, which explains the anomalous features recently observed in the

magnetic-field dependence of the Spin Seebeck effect [2,3].

[1] B. Flebus, R. A. Duine, and Y. Tserkovnyak, EPL 115, 57004 (2016).

[2] T. Kikkawa, K. Shen, B. Flebus, R. A. Duine, K. Uchida, Z. Qiu, G. E. W. Bauer, and E. Saitoh, Phys.

Rev. Lett. 117, 207203 (2016).

[3] B. Flebus, K. Shen, T. Kikkawa, K. Uchida, Z. Qiu, E. Saitoh, R. A. Duine, and G. E.

W. Bauer, Phys. Rev. B 95, 144420 (2017).


IIIB.2 48

Interactions between magnetic solitons and magnons: from weak to strong

Fusheng Ma

School of Physics and Technology, Nanjing Normal University, Nanjing, China

Magnetic solitons, such as domain-walls, vortex, and skyrmions, play an important role in the field of low

dimensional magnets [1]. The dynamics of these solitons have attracted much reserching attention due to their

fundamental properties and promising technological applications. Magnons, the quanta of collective spin

excitations in magnetically ordered systems, has attracted growing interest in the recent years. Motivated by

the aim of reducing energy dissipation in trditional electronic devices, magnons are considered as an alternative

information carrier in the emerging field of magnonics or magnon-spintronics [2].

Although magnetic solitons show especially interesting for applications in magnonic devices due to their

non-volatile and reprogrammable characters, their interaction with magnons is also of fundamental physical

interest. The dynamical motion and excitation of these solitons are resulting from the angular momentum

transfer. In the first part, we will present the weak interactions between magnetic solitons and magnons.

Specifically, it has been demonstrated that domain-walls can serve as reflectors, phase shifter, reconfigurable

nanochannels, as well as polarizer of magnons [3]. On the other hand, domain-walls can be driven to motion

by magnons [4]. The interaction between magnons and the gyrotropic motion of the vortex core can be used

to explain the excitation mode splitting [5]. Recently, it is observed that magnetic skyrmions can be driven to

motion by magnons [6]. At the meantime, magnons can be scatterred and refracted from skyrmion arrays [7,8].

In the second part, we will present the strong interactions, i.e. the strong coupling, between magnetic solitons

and magnons. Particularly interesting is the case of magnetic skyrmions with topologically nontrivial textures,

whose excitation modes have been studied theoretically [9] and experimentally [9-12]. The strong coupling

character between magnons and skyrmions was indicated by the presence of anticrossing behavior in the

frequency-field dispersion relations.

[1] A. M. Kosevich, B. A. Ivanov, and A. S. Kovalev, Phys. Rep. 194, 117 (1990).

[2] A. V. Chumak, V. I. Vasyuchka, A. A. Serga, and B. Hillebrands, Nat. Phys. 11, 453 (2015).

[3] R. Hertel, W. Wulfhekel, and J. Kirschner, Phys. Rev. Lett. 93, 257202 (2004).

[4] P. Yan, X. S. Wang, and X. R. Wang, Phys. Rev. Lett. 107, 177207 (2011).

[5] J. P. Park and P. A. Crowell, Phys. Rev. Lett. 95, 167201 (2005).

[6] X. Zhang, J. Müller, J. Xia, M. Garst, X. Liu, and Y. Zhou, New J. Phys. 19, 065001 (2017).

[7] C. Schütte and M. Garst, Phys. Rev. B 90, 094423 (2014).

[8] K.-W. Moon, B. S. Chun, W. Kim, and C. Hwang, Phys. Rev. Appl. 6, 064027 (2016).

[9] M. Mochizuki, Phys. Rev. Lett. 108, 017601 (2012).

[10] Y. Onose, Y. Okamura, S. Seki, S. Ishiwata, and Y. Tokura, Phys. Rev. Lett. 109, 037603 (2012)

[11] Y. Okamura, F. Kagawa, M. Mochizuki, M. Kubota, S. Seki, S. Ishiwata, M. Kawasaki, Y. Onose, and

Y. Tokura, Nat. Commun. 4, 2391 (2013)

[12] T. Schwarze, J. Waizner, M. Garst, A. Bauer, I. Stasinopoulos, H. Berger, C. Pfleiderer, and D.

Grundler, Nat. Mater. 14, 478 (2015).


IIIB.3 49

Control and stimulation of three-magnon scattering in a magnetic vortex

Lukas Körbera,b, Katrin Schultheissa, Tobias Hulaa,c, Roman Verbad, Toni Hachea,c and Helmut

Schultheissa,b

a Helmholtz-Zentrum Dresden - Rossendorf, Institute of Ion Beam Physics and Materials Research, Bautzner

Landstraße 400, 01328 Dresden, Germany b Technische Universität Dresden, 01062 Dresden, Germany

c Technische Universität Chemnitz, 09111 Chemnitz, Germany d Institute of Magnetism, National Academy of Sciences of Ukraine, Kyiv 03680, Ukraine

When applying a large enough RF field amplitude, spin waves in a magnetic vortex disk can decay into

two other spin waves via three-magnon scattering. In order to reach the threshold of this process, the energy

flux from the decay of the directly excited mode must overcome the internal losses of the secondary modes.

The resulting scattering processes obey certain selection rules which result in the two output frequencies to be

distinct from one another. Moreover, three-magnon scattering of the directly excited mode into multiple pairs

of secondary modes is possible. However, typically one of these scattering channels has a lower threshold than

the others which leads to this channel being activated first and limiting the energy flux in the other possible

“silent” channels. Here, we show that three-magnon scattering in such a system can be stimulated below the

usual instability threshold by additionaly pumping one of the secondary modes. This is achieved by coupling

the magnetic vortex to an adjacent magnonic wave guide. The response to the stimulation is instantaneous and

can be used to activate the silent three-magnon channels, as well.

The authors acknowledge financial support from the Deutsche Forschungsgemeinschaft within programme

SCHU 2922/1-1.


IIIB.4 50

Pure Spin Current Driven by a Thermally Induced Magnon Chemical Potential

X. Li

University of Texas-Austin, USA

In magnetic insulators (MIs), spin current is carried by quantized spin excitations known as magnons.

Applying a temperature gradient to a MI offers a simple and ubiquitous method for generating spin

current. However, a thermally induced magnon chemical potential, key for describing the spin current

in such nonequilibrium systems, has never been measured. Here, we report the first direct

measurements of a magnon chemical potential generated by a thermal gradient, in the MI yttrium iron

garnet (YIG): Y3Fe5O12. Subsequently, two components of the spin current, driven by temperature

and chemical potential gradients respectively, are quantified. In addition, the wavevector and energy

distributions of the nonequilibrium magnons are identified. These measurements directly evaluate the

intrinsic capability of a MI in generating spin current and provide valuable guidance to developing

future spin caloritronic devices.

Session IIIC Wednesday, July 31

IIIC.1 51

Spin caloritronic nano-oscillator

Christopher Safranskia, Igor Barsukova, Han Kyu Leea, Alejandro Jaraa, Andrew Smitha, Tobias

Schneiderb, Kilian Lenzb, Juergen Lindnerb, Houchen Changc, Mingzhong Wuc, Yaroslav

Tserkovnyakd, Ilya Krivorotova

a University of California, Irvine, USA b HZDR, Dresden, Germany

c Colorado State University, Fort Collins, USA d University of California, Los Angeles, USA

Energy loss due to ohmic heating is a major bottleneck limiting down-scaling and speed of nano-electronic

devices, and harvesting ohmic heat for signal processing is a major challenge in modern electronics. In this

talk, I will demonstrate that thermal gradients arising from ohmic heating can be utilized for excitation of

coherent auto-oscillations of magnetization and for generation of tunable microwave signals [1]. We observe

the heat-driven dynamics in Y3Fe5O12/Pt bilayer nanowires schematically shown in the left panel of Figure 1,

where ohmic heating of the Pt layer results in injection of pure spin Seebeck current into the Y3Fe5O12 (YIG)

layer. This leads to excitation of auto-oscillations of the YIG magnetization and generation of coherent

microwave radiation by the device (see right panel of Figure 1). This heat-driven auto-oscillatory spin wave

dynamics can be understood as bosonic condensation of non-equilibrium incoherent magnons into a coherent

low-frequency spin wave mode [2]. Our work demonstrates that phase-coherent magneto-dynamic states can

spontaneously emerge from thermal magnon currents.

[1] C. Safranski, I. Barsukov, H. K. Lee, T. Schneider, A. Jara, A. Smith, H. Chang, K. Lenz, J. Lindner,

Y. Tserkovnyak, M. Wu, I. N. Krivorotov, Nat. Commun. 8 (2017), 117.

[2] S. A. Bender, Y. Tserkovnyak, Phys. Rev. B 93 (2016), 064418.

Figure 1: Left panel: Sketch of the YIG/Pt nanowire spin Seebeck oscillator. Right panel:

Microwave power generated by the nanowire at 3.2 GHz as a function of magnetic field and

direct current bias.


IIIC.2 52

Electric-field-induced switching in antiferromagnets using voltage-controlled

magnetic anisotropy

Victor Lopez-Dominguez, Jiacheng Shi, Hamid Almasi, Pedram Khalili Amiri

Department of Electrical and Computer Engineering, Northwestern University, Evanston, Illinois, USA

Magnetoresistive random access memory (MRAM) based on spin transfer torque (STT) is entering volume

production in the semiconductor industry. While STT-MRAM offers nonvolatile embedded memory operation

with high endurance, its ultimate energy efficiency, speed and scalability are limited by its current-controlled

write mechanism. In this talk we discuss device concepts and materials which may enable > 10× improvements

in speed and energy efficiency in magnetic switching compared to STT. Building on the success of STT-

MRAM, these emerging device candidates may not only address a broader cross-section of the memory

hierarchy, but also enable new computing architectures with simultaneously ultralow-power and high-

performance attributes, which are important for machine intelligence on both edge and cloud platforms.

We first briefly review the recent progress of voltage-controlled ferromagnetic memory devices, which

use interfacial magnetoelectric effects arising from spin-orbit interaction, to switch the magnetization in

memory bits. We discuss progress in the development of magnetic tunnel junctions using voltage-controlled

magnetic anisotropy (VCMA) for switching, which exhibit the lowest-energy MRAM cells to date [1-2]. The

device and materials-level challenges and opportunities are discussed, including biasing, VCMA coefficients,

and write error rates.

As a strategy to further reduce switching time, and improve energy efficiency of VCMA-based MRAM

towards picosecond and atto-Joules respectively, we then examine the VCMA effect in new free layer

structures consisting of antiferromagnetic materials. We propose a method for switching the Néel vector of an

antiferromagnetic thin film, by the application of an ultrashort electric field pulse [3]. The electric field induces

a reorientation of the antiferromagnetic order parameter, due to the voltage-induced modification of the

magnetic anisotropy. When the electric field pulse is timed to half the oscillation period of the Terahertz

antiferromagnetic dynamics, it induces a picosecond time-scale reversal of the Néel vector. Importantly, the

electric field required to induce this reversal is as small as ~ 100 mV/nm, comparable to fields used for

switching of ferromagnetic tunnel junctions in earlier works. This electric field is determined by the anisotropy

of the antiferromagnet, while the much larger exchange field determines the frequency of the resulting

dynamics (and hence the switching time). Our simulation results indicate the possibility to switch a 50 nm

circular antiferromagnetic element with an energy dissipation of 250 aJ, in less than 30 ps, and in the absence

of any current-induced torque. The electric-field-induced switching of the Néel vector opens a new route

towards energy-efficient and ultrafast magnetic memories and computing devices based on antiferromagnets.

[1] P. Khalili Amiri et al., IEEE Trans. Magnetics, 51, 3401507, (2015)

[2] C. Grezes et al., Appl. Phys. Lett., 108, 012403 (2016)

[3] V. Lopez-Dominguez, H. Almasi, P. Khalili Amiri, Phys. Rev. Applied 11, 024019 (2019)


IIIC.3 53

Voltage control of Rashba effects in GeTe

S. Varottoa, L. Nessia, M. Cantonia, S. Cecchib, R. Calarcob, M. Cantonia, C. Rinaldia,c, R.

Bertaccoa,c

a Dipartimento di Fisica, Politecnico di Milano, via G. Colombo 81, 20133 Milano, Italia b Paul-Drude-Institut für Festkörperelektronik, Hausvogteiplatz 5-7, 10117 Berlino, Germania

c Istituto di Fotonica e Nanotecnologie (IFN-CNR), c/o Politecnico di Milano, 20133 Milano, Italia

The Rashba semiconductor GeTe [1] stands out as material for the non-volatile modulation of both charge and

spin transport. Its ferroelectricity provides a state variable able to generate and drive a giant bulk Rashba-type

spin-splitting of the electronic bands, offering the intriguing possibility for controlling the spin degree of

freedom through the electrical inversion of the Rashba spin texture. Moreover, the switchable polarization

charge at the surfaces of GeTe(111) thin films can be exploited to control the band profile at the interfaces,

paving the way to electro-resistive applications.

We have already demonstrated the ferroelectric control of the Rashba spin texture [2]. Here we provide the

first evidence of the ferroelectric switching of GeTe through gate electrodes, achievable despite the

semiconducting nature of the material. While the relatively high conductivity impedes the use of

characterization techniques employed for standard ferroelectric oxides (like PUND), we demonstrated the

switching by measuring the resistance variation of metal/GeTe heterojunctions induced by the application of

short voltage pulses. Piezoresponse Force Microscopy was used to correlate the microscopic distribution of

ferroelectric domains underneath the gate with the resistivity of the junction, whose change is ascribed to the

different local band bending in the semiconductor due to the screening of the polarization charge.

The ferroelectric switching of GeTe offers a resistance modulation up to 300%. The switching is robust,

with an endurance up to 104 cycles. Ferroelectric minor loops permit to obtain the quasi-continuous resistance

variation typical of memristors [3].

The result paves the way to the implementation of fully reconfigurable computing devices based on

both charge and spin transport in a semiconductor compatible with the Si-based technology. Applications to

the non-volatile voltage control of magnetic layers in contact with GeTe, with potential for reconfigurable

magnonics, are also foreseen.

[1] D. Di Sante et al., Adv. Mater. 25, 509 (2013)

[2] C. Rinaldi et al., Nano Letters 18, 2751 (2018).

[3] A. Chanthbouala et al., Nature Materials 11, 860 (2012)


IIIC.4 54

Magnon valve effect based on YIG/NiO/YIG magnon junction

Xiufeng Han

Institute of Physics, University of Chinese Academy of Sciences, Chinese Academy of Sciences, Beijing

100190, China

Data processing and transmission in sophisticated microelectronics rely strongly on electric current, which

inevitably wastes a large amount of energy due to Joule heating. However, Magnons which possess angular

momenta and can also transfer the momenta, can be regarded as a new information carrier free from Joule

heating due to electric neutrality. Recently, magnon valves and magnon junctions with perpendicular

heterostructures of ferromagnetic insulator (MI)/space layer (S)/ferromagnetic insulator (MI) [MI/S/MI,

MI=Y3Fe5O12 (YIG); S=Au, Pt, NiO and CoO etc.] were experimentally fabricated and used for regulating

magnon transport. Magnon current can be modulated high and low by the parallel and antiparallel magnetic

configurations of the magnetic YIG layers [1, 2]. Especially, for pure magnon valves with typical

heterostructure using YIG/NiO/YIG sandwiches. Such a MI/AFI/MI heterostructure (AFI=antiferromagnetic

insulator) is named as an insulating magnon junction (MJ). Fully electric-insulating and merely magnon-

conductive magnon valves have been demonstrated by the YIG/NiO/YIG MJs in which output spin current in

a Pt detector can be tuned with a high on-off ratio between parallel (P) and antiparallel (AP) states of the two

YIG layers near room temperature. When temperature gradient is applied through an MJ, magnon current

would flow from one MI to the other MI through the AFI spacer. So, the net magnon current in the second MI

are easily influenced by the first MI layer. Then setting a heavy metal Pt on the top MI layer, one could detect

the magnon current via inverse spin Hall effect, similar to the TMR effect observed in a magnetic tunnel

junction (MTJ). Furthermore, the magnon valve ratio (MVR) or on-off ratio of the so-called MJs can be as

high as 100%. Hence, these typical MJ devices are likely to play a core role in the future magnon devices of

integrated magnon circuits for information transmission, logic computing and magnetic field sensing.

Fig.1: Microstructure of GGG/YIG(100)/NiO(15)/

YIG(60 nm) MJ. (a) The cross-sectional TEM image

of the sample. HRTEM images of (b) the

GGG/YIG(100 nm) and (c) YIG(100)/NiO(15)/

YIG(60 nm) interfaces. Fourier transformation of

HRTEM for (d) the bottom YIG and (e) the top YIG

only. (f) Schematic diagram of spin Seebeck effect

and its measurement setup for an IMJ. During

measurement, a field in the x-axis is applied.

Fig.2: (a) The dependence of switching

fields of all the MJs and the control

samples on temperatures. (b) VAP/VP

ratios for the MJs. Inset shows the field

dependence of VSSE for the MJ with 6

nm NiO spacer and ultrahigh on-off ratio

at 260 K. (c) Thickness dependence of lnδ

at medium temperatures. Insets show

derived magnon decay length λNiO.

[1] H. Wu, and X. F. Han* et al., Phys. Rev. Lett. 120(9) (2018), 097205-6.

[2] C. Y. Guo, C. H. Wan, and X. F. Han* et al., Phys. Rev. B 98 (2018), 134426-8.


IIIC.5 55

Broadband emission and detection of magnons from hybrid magnetic

waveguides down to 100 nm wavelength

Ping Chea, Korbinian Baumgärtla, Anna Kúkol'ováa,b, Carsten Dubsc, Dirk Grundlera,d

a Laboratory of Nanoscale Magnetic Materials and Magnonics, Institute of Materials (IMX), School of

Engineering, École Polytechnique Fédérale de Lausanne (EPFL), 1015 Lausanne, Switzerland b Laboratory of Semiconductor Materials, Institute of Materials (IMX), School of Engineering, École

Polytechnique Fédérale de Lausanne (EPFL), 1015 Lausanne, Switzerland c INNOVENT e.V. Technologieentwicklung, Prüssingstraße 27B, D-07745 Jena, Germany

d Institute of Microengineering (IMT), School of Engineering, École Polytechnique Fédérale de Lausanne

(EPFL), 1015 Lausanne, Switzerland

Exchange-dominated magnons are essential for magnonics due to the miniaturization requirements and the

need for higher information transfer rate of prospective magnon-based logic and memory devices. The

excitation of short-wavelength magnons in thin films has so far been achieved via e.g. nanopillars and nano-

magnonic grating couplers which all require challenging nano-fabrication. We demonstrate the emission and

detection of magnons down to a 100 nm wavelength, using conventional coplanar waveguides (CPWs) with

micrometer-sized lateral dimensions prepared by photo-lithography. To emit the short-wavelength magnons

we incorporated an additional ferromagnetic layer to create hybrid magnetic CPWs (mCPWs) consisting of a

multilayer of Fe|Ti|Au.

Broadband magnon emission was observed in yttrium iron garnet thin films quasi-continuously covering

a frequency band of 4 to 7 GHz in an applied field of 90 mT. The large frequency band is different from grating

couplers. The minimum detected wavelength λ amounted to 101 nm ± 2 nm extracted from transmitted magnon

spectra according to the Kalinikos and Slavin formalism [1]. λ was smaller by a conversion factor of 79

compared to the principal wavelength λ1 = 2π/ k1 supported by the inhomogeneous microwave field of the

CPW. The large conversion was achieved by the modification of the effective field in YIG close to the mCPWs

due to the stray field of Fe.

The simulation of Mumax3 shows a field enhancement in between leads of the mCPW, which is consistent

with the observed resonance frequencies. The results pave the way for on-chip design of magnon-based devices

with simplified structure and fabrication requirements while at the same time for higher efficiency in reducing

the wavelength and obtaining exchange magnons.

We acknowledge the financial supports from SNSF via Sinergia Network NanoSkyrmionics CRSII5

171003 and Grant No. 163016, and from the Deutsche Forschungsgemeinschaft via the Grant No. DU 1427/2-

1.

[1] Kalinikos, B. A. & Slavin, A. N. J. Phys. C: Solid State Phys. 19, 7013–7033 (1986).


IIIC.6 56

Inelastic scattering of spin wave beam at the edge localized spin waves and

second harmonic generation of spin waves

Pawel Gruszeckia, Konstantin Guslienkob, Igor Lyubchanskiic, and Maciej Krawczyka

a Faculty of Physics, Adam Mickiewicz University in Poznan, Poznan, Poland b Depto. Física de Materiales Universidad del País Vasco UPV/EHU, San Sebastian, Spain; IKERBASQUE,

The Basque Foundation for Science, Bilbao, Spain. c Donetsk Institute for Physics and Engineering of the National Academy of Sciences of Ukraine; Faculty of

Physics, V. N. Karazin Kharkiv National University, Kharkiv, Ukraine.

Spin waves at certain conditions can be confined in particular regions of the sample, exemplary in a

potential well created by the demagnetizing field near the film’s edge. Typical frequencies of the edge-

localized spin waves lay below the bottom of the spin wave spectrum. Here, we study theoretically dynamics

of spin waves localized at the edge of thin permalloy film and their influence on the reflection of spin wave

beams incident at the edge.

Firstly, we analyze the behavior of the edge spin waves in dependence on their amplitude. We show that

for high amplitudes the additional mode with doubled frequency (2) is present in the spectrum (see Figure 1).

This additional mode is related to the second harmonic of the edge spin waves, and it propagates obliquely

with respect to the interface with the plane wavefronts. Interestingly, our findings show that this phenomenon

can be used to excite spin waves propagating in the film plane of the wavelengths shorter even than 100 nm.

Secondly, we analyze the interaction of an obliquely incident spin wave beam (at frequency f) with the

edge spin waves. We find that due to the inelastic scattering the secondary spin wave beams with shifted

frequency (f-, f+) can be excited (see Figure 1). This phenomenon is a purely magnonic counterpart of the

Brillouin scattering. Moreover, we observe angular shifts between the primary incident and the beams with

shifted frequencies. Also, different lateral shifts along the interface for all the reflected beams are present.

These can be related to the Goos-Hänchen angular and lateral shifts [1] between the incident and reflected

waves.

Acknowledgments. This work was supported by grant: EU’s Horizon2020 MSCA RISE programme

GA No. 644348(MagIC).

[1] P Gruszecki et al., Appl. Phys. Lett. 105 (2014), 242406.

Figure 1: Spin wave spectrum. The most pronounced peaks for ν = 12 and f = 50 GHz

correspond to the edge-localized spin waves and the incident spin wave beam,

respectively. Peak at the frequency 2ν is related to the spin waves excited in the second

harmonic generation process, whereas the peaks at f ± ν are related to the inelastically

scatered beam on the edge spin wave.

Session IIID Wednesday, July 31

IIID.1 57

Ultrafast Spin Dynamics in Ferromagnetic Thin Films and Heterostructures

Anjan Barman

Department of Condensed Matter Physics and Material Sciences, S. N. Bose National Centre for Basic

Sciences, Salt Lake, Kolkata 700106, India

Ferromagnetic/nonmagnetic (FM/NM) thin film heterostructures show a range of important properties

such as perpendicular magnetic anisotropy, spin pumping, spin transfer torque, spin Hall effect, Rashba effect

and interfacial Dzyaloshinskii-Moriya interaction. The above properties are generally controlled by the

interface and they have huge potential applications in new generation spintronic and magnonic devices.

Here, we present the investigation of time- and wave-vector-resolved ultrafast spin dynamics in

ferromagnetic (FM) thin films and ferromagnet/nonmagnet (FM/NM) heterostructures induced by optical,

thermal and spin-orbit-torque excitation using time-resolved magneto-optical Kerr microscope and Brillouin

light scattering spectroscopy [1]. We present a unified approach towards investigation and control of spin

dynamics occurring between femtosecond and nanosecond timescales in NiFe thin film and Co/Pd multilayers

[2-3]. We demonstrate an energy efficient spin-wave propagation and magnonic bandgap formation by

controlling domains in Co/Pd multilayers [4]. Further we introduce a new method to investigate spin Hall angle

(SHA) and spin pumping in FM/NM bilayers [5] and show a giant SHA in β-W [6]. Finally we investigate the

interfacial Dzyaloshinskii-Moriya interaction (IDMI) using Brillouin light scattering and show pure IDMI in

NM(W, Ta, graphene)/FM(CoFeB, NiFe)/SiO2, TaOx) heterostructures [7-9]. The effects of variation of

thicknesses of FM and NM layers are also discussed.

The author gratefully acknowledges financial assistance from Department of Science and Technology,

Department of Information Technology and S. N. Bose National Centre for Basic Sciences.

[1] A. Barman and A. Haldar, Solid State Physics 65, 1-108 (2014)

[2] S. Mondal and A. Barman, Phys. Rev. Applied 10, 054037 (2018).

[3] S. Pan, O. Hellwig and A. Barman, Phys. Rev. B 98, 214436 (2018).

[4] C. Banerjee et al., Phys. Rev. B 96, 024421 (2017)

[5] A. Ganguly et al., Appl. Phys. Lett. 105, 112409 (2014).

[6] S. Mondal at al., Phys. Rev. B 96, 054414 (2017).

[7] A. K. Chaurasiya et al., Sci. Rep. 6, 32592 (2016).

[8] A. K. Chaurasiya et al., Phys. Rev. Applied 9, 014008 (2018).

[9] A. K. Chaurasiya et al., Phys. Rev. B 99, 035402 (2019).


IIID.2 58

Spin wave collimation using flat metasurface

M. Zelent1, M. Mailian2, V. Vashistha1, P. Gruszecki1, O.Yu. Gorobest2,3, Yu.I. Gorobest3, M.K rawczyk1

1Faculty of Physics, Adam Mickiewicz University in Poznan, Umultowska 85, Poznan, 61-614, Poland

2Faculty of Physics and Mathematics, National Technical University of Ukraine “Igor Sikorsky Kyiv Polytechnic

Institute”, 37 Peremogy Avenue, Kyiv, 03056, Ukraine

3Institute of Magnetism, National Academy of Sciences of Ukraine, 36-b Vernadskogo Street, Kyiv, 03142, Ukraine

*E-mail: [email protected]

We show analytically and numerically that the phase shift of the spin waves can be controlled by

metasurface formed by an ultra-narrow non-magnetic spacer separating two thin ferromagnetic films. For this

purpose, we exploit the exchange coupling of RKKY type between the film edges which allows to tune the

phase of the transmitted spin waves in the wide range of angles [-π/2; π/2]. We combine the phase-shift

dependency along the interface with the lens equation to demonstrate the metalens for spin waves in

micromagnetic simulations. With properly designed metasurface the substantial focusing of the spin wave can

be achieved at the arbitrarily selected point on the film. The effectiveness of the focusing depends on the

correct representation of the phase profile along the interface, the type of the exchange coupling and it is

limited by the transmission efficiency through the interface.

Fig. 1. Schematic of the system design with a focusing metasurface. The system involves two ferromagnetic thin

films of Co with a nonmagnetic metallic material (Cu) of varying width along the interface (metasurface).

The project is financed by the European Union Horizon 2020 Research and Innovation Program under

Marie Sklodowska- Curie grant agreement No. 644348.


IIID.3 59

Coherent excitation of heterosymmetric spin waves

with short wavelengths

G. Dieterle a, J. Förster a, H. Stoll a, A. S. Semisalova b, S. Finizio c, A. Gangwar d,

M. Weigand a, M. Noske a, M. Fähnle a, I. Bykova a, J. Gräfe a, D. A. Bozhko e,

H. Y. Musiienko-Shmarova e, V. Tiberkevich f, A. Slavin f, C. Back d, J. Raabe b,

G. Schütz a, and S. Wintz b,c

a Max-Planck-Institut für Intelligente Systeme, Stuttgart, Germany

b Helmholtz-Zentrum Dresden-Rossendorf, Dresden, Germany

c Paul Scherrer Institut, Villigen PSI, Switzerland d Universität Regensburg, Regensburg, Germany

e Technische Universität Kaiserslautern, Kaiserslautern, Germany

f Oakland University, Rochester MI, USA

The investigation of spin-wave phenomena, also referred to as magnonics, plays an important role in

magnetism research [1]. In particular, spin waves are envisioned as signal carriers for future information and

communication technology devices, with a high potential for device miniaturization and reduced power

consumption. Yet a successful implementation of magnonic technology will require the use of spin waves with

nanoscale wavelengths. In line with this, promising spin-wave excitation mechanisms were found recently,

overcoming the minimum excitable wavelength limit conventionally imposed by the smallest patterning size

of the antenna. One of those methods utilizes the driven gyration of layered spin vortex cores to locally generate

short wavelength propagating spin waves in a controlled way [2].

Here we will show that the vortex core based excitation mechanism can be generalized to plain magnetic

film systems, in our case a Ni81Fe19 layer with 80 nm thickness [3]. The resulting spin waves were directly

imaged by means of time-resolved x-ray microscopy, where a 7.4 GHz excitation led to the emission of

concentric spiraling spin waves of ~140 nm wavelength. Furthermore, the emitted waves are efficiently tunable

in wavelength by the excitation frequency between 5 GHz and 10 GHz, resulting in ultrashort wavelengths of

~80 nm at 10 GHz. At such frequencies, remarkably, the spin waves observed exhibit much shorter

wavelengths than those expected for the common Damon-Eshbach mode having a quasi-uniform precession

amplitude over the film thickness. Analytic calculations identified the emitted spin waves to belong to the first

higher order mode of the Damon-Eshbach geometry, which is known to be antisymmetric in amplitude over

the film thickness (bearing a precessional node in both dynamic components) for the ferromagnetic resonance

case of infinite wavelengths. Our calculations, however, show that for the short wavelengths observed in our

experiment, multi-mode hybridisation leads to a heterosymmetric spin-wave thickness profile with a node only

in one of the dynamic magnetization components. This peculiar profile coincides with a cross-sectional line of

pure linear magnetic oscillation as well as of regions with reversed (anti-Larmor) magnetization precession

sense.

Figure: Spin waves. (a) Vortex. (b) Absolute and (c) normalized x-ray imaging at 7.4 GHz

[1] A. V. Chumak et al., Nat. Phys. 11 453 (2015).

[2] S. Wintz et al., Nat. Nanotech. 11 948 (2016).

[3] G. Dieterle et al., Phys. Rev. Lett. (in print) (2019).


IIID.4 60

Database search and special type data processing with spin wave devices

Alexander Khitun

Department of Electrical and Computer Engineering, University of California -Riverside, Riverside,

California, USA 92521

The size of databases is growing exponentially due to the rapid development of Big Data techniques,

Internet of Things (IoT), and Bioinformatics. Data centers based on magnetic storage technology have proved

to be the core platforms for cloud computing and Big Data storage. There is a great need for a novel technology

for parallel magnetic bit read-out and processing. In our preceding works [1, 2], we have developed magnonic

holographic memory (MHM) devices aimed at exploiting spin waves for parallel read-in and read-out. The

operation of MHM is similar to optical holographic devices which use coherent optical beams for information

retrieval. In this talk, we will present experimental data on the parallel database search and prime factorization

using spin waves [3, 4]. The use of classical wave interference may results in a significant speedup over the

conventional digital logic circuits in special task data processing (e.g. √n in database search). Potentially,

magnonic holographic devices can be implemented as complementary logic units to digital processors.

Physical limitations and technological constrains of the spin wave approach are also discussed.

[1] A. Khitun, "Magnonic holographic devices for special type data processing," JOURNAL OF APPLIED

PHYSICS, vol. 113, Apr 28 2013. DOI: 164503 10.1063/1.4802656

[2] F. Gertz, A. Kozhevnikov, Filimonov Y., D. E. Nikonov, and A. Khitun, "Magnonic Holographic

Memory: From Proposal to Device," IEEE Journal on Exploratory Solid-State Computational Devices

and Circuits, vol. 1, pp. 67-75, 2015

[3] A. Khitun, "Parallel database search and prime factorization with magnonic holographic memory

devices," Journal of Applied Physics, vol. 118, Dec 2015. DOI: 10.1063/1.4938739

[4] Y. Khivintsev, M. Ranjbar, D. Gutierrez, H. Chiang, A. Kozhevnikov, Y. Filimonov, and A. Khitun,

"Prime factorization using magnonic holographic devices," Journal of Applied Physics, vol. 120, Sep

2016. DOI: 10.1063/1.4962740

D)

Figure 1. (A) Schematics of the 8-terminal MHM prototype made of YIG with

four micro-magnets placed on the top of the cross junctions. The core of the

structure is a magnetic matrix comprising a 2×2 grid of magnetic waveguides with

magnets placed on top of the waveguide junctions. B) Photo of the prototype

device packaged. (C) Connection schematics. The antennas are connected to a

Vector Network Analyzer (VNA) via a number of splitters [S], attenuators [A],

and phase shifters [P]. The operational frequency is 5.4GHz. All experiments are

done at room temperature. (D) Experimental data demonstrating parallel database

search using spin wave superposition. The maximum output of 16 possible

magnetic bit configurations is evaluated in one measurement.


IIID.5 61

Large nonreciprocal frequency shift of propagating spin waves in synthetic

antiferromagnets

Mio Ishibashi, Yoichi Shiota, Tian Li, Shinsaku Funada, Takahiro Moriyama, Teruo Ono

Institute for Chemical Research, Kyoto University, Uji, Kyoto 611-0011, Japan

Nonreciprocal spin wave propagation is of great interest for the realization of spin-wave-based logic circuits.

It is known that spin wave packets excited by antennas exhibit different amplitudes depending on the relative

direction between magnetization and microwave field [1]. In addition, asymmetric spin wave dispersion due

to Dzyaloshinsky-Moriya interaction leads to nonreciprocal frequency shifts of propagating spin waves [2]. In

this study, we observed large nonreciprocal frequency shifts of propagating spin waves in interlayer exchange-coupled synthetic antiferromagnets.

Ta (3 nm)/Ru (3 nm)/FeCoB (15 nm)/Ru (0.6 nm) /FeCoB (15 nm)/Ru (3 nm) were deposited on a thermally

oxidized Si substrate by dc magnetron sputtering. From a magnetic hysteresis loop at 300 K, the canted

magnetization configuration of two layers was confirmed in the low magnetic field region below the saturation

field of approximately 1 kOe. The films were patterned into 50 µm×100 µm wires by EB lithography and Ar

ion milling. Subsequently, 80-nm-thick SiO2 insulating layer was deposited by rf magnetron sputtering. Then,

two coplanar waveguides consisting of Cr (5 nm)/Au (100 nm) were fabricated at the distance of 10 µm by EB

lithography and evaporator. The propagating spin waves were measured using vector network analyzer at room

temperature. Figure 1(a) shows the propagating spin wave spectroscopy (PSWS) under the bias magnetic field

H = 200 Oe, when the bias magnetic field is applied to the perpendicular direction of the microwave field,

namely transverse pumping configuration as shown in the inset of Fig. 1(a). The different amplitudes

depending on the propagation direction were observed due to nonreciprocal coupling between microwave

fields and spin waves [1]. Figure 1(b) shows PSWS under H = 200 Oe, when the bias magnetic field is applied

along the microwave field, namely longitudinal pumping configuration as shown in the inset of Fig. 1(b).

Unlike the results in the case of transverse pumping configuration, a large nonreciprocal frequency shift

depending on the propagating direction was observed in the case of longitudinal pumping configuration. This

nonreciprocal frequency shift is attributed to the asymmetric spin wave dispersion due to dipolar contribution

[3]. In the presentation, we will discuss the microscopic origin of the asymmetric spin wave dispersion in

synthetic antiferromagnets.

[1] V. E. Demidov et al., Appl. Phys. Lett. 95, 112509 (2009).

[2] J.-H. Moon et al., Phys. Rev. B 88, 184404 (2013).

[3] F.C. Nortemann et al., Phys. Rev. B 47, 11910 (1993).

Figure 1: (a): Re[S21] and Re[S12] spectrum measured with transverse pumping

configuration under 200 Oe. (b): Re[S21] and Re[S12] spectrum measured with longitudinal

pumping configuration under 200 Oe.

(a) (b)

Session IVA Thursday, August 1

IVA.1 62

Nano-scaled magnonic half-adder: Simulations and progress towards its

experimental realization

Andrii Chumaka

aFachbereich Physik and Landesforschungszentrum OPTIMAS, Technische Universität Kaiserslautern,

Kaiserslautern, Germany

Spin waves and their quanta, magnons, open up a promising branch of high-speed and low-power

information processing. Several separate magnonic data processing devices were realized recently. In

particular, the realization of the magnon transistor [1] opened up a way towards all-magnon data processing.

Nevertheless, the realization of an integrated magnonic circuit consisting of at least two logic gates suitable

for further integration is still a challenge.

In my talk I will demonstrate such an integrated circuit at the example of a magnonic half-adder [2]. Its

key element is a nonlinear magnonic data processing element serving as an AND logic gate which is combined

with an interference-based XOR logic gate using a nano-scale directional coupler [3] – Fig. 1A. The

functionality of this nano-sized magnonic circuit is investigated and tested by means of numerical simulations.

The progress towards the experimental realization of such a device will be presented in the second part of

the talk. Spin wave conduits made of Yttrium Iron Garnet (YIG) of widths down to 40 nm were fabricated (see

Fig. 1B) and characterized by means of Brillouin Light Scattering (BLS) spectroscopy [4]. The measurements

of standing and propagating spin waves show that the spin wave lifetime is essentially preserved during the

YIG nano-structuring. Moreover, a critical minimal width of the waveguides is found, below which the

exchange interaction suppresses the dipolar pinning phenomenon [4]. This changes the quantization criterion

for the spin wave eigenmodes and results in a pronounced modification of the spin wave mode profiles and

dispersion relations.

The results clearly prove the suitability of magnonic devices for miniaturization, which is one of the main

advantages of the field of magnonics, and provide guidelines for the utilization of magnons to process data at

the nano-scale.

[1] A.V. Chumak, et al., Nat. Commun. 5, 4700, (2014)

[2] Q. Wang, et al., arXiv: 1902.02855 (2019)

[3] Q. Wang, et al., Sci. Adv. 4, e1701517 (2018)

[4] Q. Wang, et al., arXiv: 1807.01358 (2018)

Figure 1: A: Magnonic half adder design and operational principle for the “1”-”1” logic

input combination. The colour encodes the spin wave amplitudeі. B: SEM picture of a YIG

spin wave waveguide of width 40 nm and a microstrip antenna for spin wave excitation.


IVA.2 63

Magnons in a Quasicrystal: Propagation, Extinction and Localization of Spin

Waves in Fibonacci Structures

Filip Lisiecki1, Justyna Rychły2, Piotr Kuświk1,3, Hubert Głowiński1, Jarosław W. Kłos2, 4,

Felix Groß5, Nick Träger5, Iuliia Bykova5, Markus Weigand5, Mateusz Zelent2, Eberhard J.

Goering5, Gisela Schütz5, Gianluca Gubbiotti6, Maciej Krawczyk2, Feliks Stobiecki1, Janusz

Dubowik1, Joachim Gräfe5

1Institute of Molecular Physics, Polish Academy of Sciences, Poznań, Poland 2Faculty of Physics, Adam Mickiewicz University, Poznań, Poland

3Centre for Advanced Technologies, Adam Mickiewicz University, Poznań, Poland 4Institute of Physics, University of Greifswald, Greifswald, Germany

5Max Planck Institute for Intelligent Systems, Stuttgart, Germany 6Istituto Officina dei Materiali del Consiglio Nazionale delle Ricerche, Perugia, Italy

Magnonic quasicrystals exceed the possibilities of spin wave (SW) manipulation offered by regular

magnonic crystals, because of their more complex SW spectra with fractal characteristics. Here, we report a

combined X-ray microscopic and Brillouin Light Scattering observation of propagating SWs in a magnonic

quasicrystal, consisting of dipolar coupled permalloy nanowires arranged in a one-dimensional Fibonacci

sequence. SWs from the first and second band as well as evanescent waves from the band gap between them

are imaged (cf. Figure). Moreover, additional mini-band gaps in the spectrum are demonstrated, directly

indicating an influence of the quasiperiodicity of the system. Finally, the localization of SW modes within the

Fibonacci crystal is shown. The experimental results are interpreted using numerical calculations and we

deduce a simple model to estimate the frequency position of the magnonic gaps in quasiperiodic structures.

The demonstrated features of SW spectra in one-dimensional magnonic quasicrystals allows utilizing this class

of metamaterials for magnonics and makes them an ideal basis for future applications. We confirm the

existence of collective spin waves propagating through the structure as well as dispersionless modes; the

reprogammability of the resonance frequencies, dependent on the magnetization order; and dynamic spin wave

interactions. With the fundamental understanding of these properties, we lay a foundation for the scalable and

advanced design of spin wave band structures for spintronic, microwave and magnonic applications.

Figure: (a) SW amplitude and phase for different excitation frequencies at 5 mT. The transparent gray

rectangles mark the position of the CPW and the dashed white lines mark the gaps between the stripes. (b)

Color code for SW amplitude (brightness) and phase (color). (c) Static image of the Fibonacci structure (light

gray) with the signal line (dark gray) near the center of the image, and the ground lines at the top and bottom

edges of the image (dark gray).


IVA.3 64

A strategy to design magnonic crystals on atomic length scales

Kh. Zakeria, H J. Qina,b, S. Tsurkana, A. Ernstc,d a Heisenberg Spin-dynamics Group, Physikalisches Institut, Karlsruhe Institute of Technology, Karlsruhe,

Germany b NanoSpin, Department of Applied Physics, Aalto University School of Science, FI-00076 Aalto, Finland

c Institute for Theoretical Physics, Johannes Kepler University, Altenberger Str. 69, 4040 Linz, Austria d Max-Planck Institute of Microstructure Physics, Weinberg 2, D-06120 Halle, Germany

In single-element bulk ferromagnets, one expects to observe a single exchange-dominated magnon band

within the terahertz frequency regime. However, in atomically engineered ultrathin ferromagnetic films and

multilayers the quantum confinement permits the existence of multiple magnon modes [1]. We present our

recent experimental results regarding observation of terahertz confined magnon modes in various

ferromagnetic layered structures. The experiments are performed by means of spin-polarized high-resolution

electron energy-loss spectroscopy. We discuss how one may tune the properties of these confined magnon

modes and achieve entirely different in-plane magnon dispersions, characterized by positive and negative

group velocities.

Comparing the results to the ones of first-principles calculations we comment on the spin-dependent many-

body correlation effects in ferromagnetic films and their role in the determination of the magnon energies.

Moreover, we will discuss the possibilities to design multi-magnon band systems exhibiting magnonics

bandgaps.

[1] Y.-J. Chen, Kh. Zakeri, A. Ernst, H. J. Qin, Y. Meng and J. Kirschner, Phys. Rev. Lett. 119, 267201

(2017).


IVA.4 65

YIG-film based Quantum Magnonics

Mikhail Kostyleva

a The University of Western Australia, Crawley WA, Australia

Recently, a huge progress in Quantum Information and Quantum Computing has been achieved. Yttrium

iron garnet (YIG) based devices hold great potential in the field due to the strong matter-field coupling for

YIG. In addition, it was found that the strong non-linearity of magnetostatic waves and oscillations in YIG

may also be very useful for those applications. So far, most of the activities have focused on YIG spheres. In

this talk, very important advantages of travelling magnons in YIG films with respect to standing-wave

magnons in YIG spheres will be discussed. It will be shown that the travelling magnons can be used for

efficient conversion of the microwave-frequency output of superconductor-based based quantum gates into the

optical domain for long-distance transmission [1]. Furthermore, three- and four-magnon processes in the YIG

films can be used to generate squeezed magnon quantum states for applications in Continuous Variable

Quantum Computing [2].

[1] M. Kostylev and A. Stashkevich, arXiv:1712.04304 (2017).

[2] M. Kostylev, A. B. Ustinov, A. V. Drozdovskii, B. A. Kalinikos, and E. Ivanov, arXiv:1811.02104

(2018).


IVA.5 66

Stimulated k-vector selective magnon excitation in NiFe films using femtosecond

laser pulse trains

Shreyas Muralidhara, Ademir Alemana, Ahmad Awada, Roman Khymyna, Mykola Dvornika, Dag

Hanstorpa, Johan Åkermana,b.

a Department of Physics, University of Gothenburg, Kemivägen 9, 41296, Göteborg, Sweden. b KTH Royal Institute of Technology, Electrum 229, 164 40 Kista,Sweden.

Spin waves (magnons) provide an immense potential to replace the existing Si-based technology with

faster, smaller and energy-efficient devices due to its low power operation and easy tunability. Spin waves

(SWs) could be excited electrically using microwave sources or direct current and more directly by focused

optical pulses [1] in a thin magnetic film. It has been observed that the optical excitation happens a few orders

of magnitude faster than electrical excitation [2]. However, due to fast decay time of the SWs, the optical

emission of SWs is not continuous. To obtain sustainable spin waves, we have to use repetitive pulses with a

very short time period between pulses. There are still very few works addressing such an option [3]. So far,

optical pump-probe measurements have primarily been based on Magneto-Optical Kerr Effect (MOKE)

microscopy using low repetition rate. Here, we instead attempt to investigate the optically excited spin

dynamics using a µ-focused Brillouin light scattering (BLS) technique with much higher sensitivity to coherent

and incoherent SWs.

We show a stimulated emission of SWs at multiple harmonics of a 1 GHz repetition rate of the pulsed laser

[Fig 1(a)]. The high sensitivity of detection scheme, using scanning micro-Brillouin Light Scattering (BLS),

shows both localized and propagating spin wave emission. in the spatial profile measurements [Fig 1(b)].

Tuning the strength and direction of the applied magnetic field, we can further choose which wave vector to

coherently amplify and control the spin wave emission direction and pattern [4]. Our results clearly indicate

that it is possible to create and control SWs of high amplitude using a high-repetition-rate pulsed laser emitting

femtosecond pulses.

[1] M. van Kampen et. al., Phys. Rev. Lett. 88, 22 (2002).

[2] B. Koopmans et. al., Nat. Mats. volume 9, pages 259–265 (2010).

[3] M. Jäckl et. al. Phys. Rev. X, 7, 021009 (2017).

[4] V. Veerakumar and R. E. Camley Phys. Rev. B 74, 214401 (2006).

Figure 1: (a) BLS signal as a function of frequency and the applied field on Py thin film

sample. (b) Spatial profile of spin waves in Py thin film at H = 600 mT oblique field.


IVA.6 67

Spin currents in systems with magnetic dipole interaction

Sergej Demokritova

a University of Münster, Germany

The concept of spin current, introduced analogously to charge current, has gained a great importance in

spintronic and magnonic systems. Basically, there are exist two different types of spin current. The first one is

associated with transport of spin-polarized electrons from one part of the system to another with the following

relaxation of the transferred spin due to the exchange interaction between the conducting and localized

electrons. The second one is due to transfer of spin between localized spins due to their mutual interaction. A

pictorial consideration of the latter is transfer of spin by propagating spin waves.

While the expression for the spin current for the spin current associated with transport of spin-polarized

electrons can be written analogously to charge current using the spin-polarization of the electrons, their density

and the drift velocity, the situation with the spin current transferred by spin waves is more complex. For the

simplified model system with the only exchange interaction between the localized spins this expression can be

written as

𝑗𝑠 ∝ 𝑚2 𝑑𝜑

𝑑𝑥 (1)

where m is dynamic magnetization of the spin wave and (x) its phase varying along x, the direction of the

spin-wave propagation. Correspondingly the continuity equation 𝑑𝑀

𝑑𝑡+ 𝑑𝑖𝑣𝑗𝑠 = 0 (2)

directly results from the Landau-Lifshitz equation with included exchange terms. However, if any relativistic

interactions, including the magnetic dipole interaction, are concerned, the validity of Eq. (1) is questionable.

Moreover, since the Hamiltonians of the relativistic interactions such as the magnetic dipole interaction or

magnetic anisotropy do not commute with the operator of spin [1], the entire concept of spin current breaks

down, if those interactions are relevant. In fact, since the total spin of the magnetic subsystem of a sample is

not conserved, one cannot write the continuity Eq. (2). Instead, the flow of spin from the lattice caused by

relativistic magnetic interactions should be taken into account [2].

An important example for consideration from the point of view of spin current is Bose-Einstein condensation

(BEC) of magnons in YIG [3], where one creates a quasi-equilibrium magnon gas using parametric pumping.

A possible spin superfluidity associated with BEC should be considered in terms of dissipationless spin current.

Not discussing here the issue of dissipationless properties of non-equilibrium thermodynamic systems, let us

emphasize that the entire concept of spin current in magnon condensate in YIG is questionable. It is known

that for this system BEC takes place at a non-zero wavevector k, at the point of magnon spectrum,

corresponding to the minimum of the magnon frequency. For those magnon the magnetic dipole interaction is

as important as the exchange one. Therefore, a description of magnons condensate based on Eq. (1) provides

incorrect results: on one hand, since the minimum of the spectrum, where BEC takes place, corresponds to a

non-zero wavevector 𝜑 = 𝑘𝑥. Correspondingly, Eq. (1) predicts that such spin wave carries out a spin current.

On the other hand, the spin wave corresponding to the minimum is not a propagating wave, therefore it cannot

transfer any spin. This discrepancy is solved if one takes into account the flow of spin from the lattice

associated with the magnetic dipole interaction.

[1] N. Bloembergen et al. Phys. Rev. 114, 445 (1959)

[2] H. Kurebayashi et al., Nature Mat. 10, 660 (2011).

[3] S.O. Demokritov et al., Nature 443, 430 (2006).


IVA.7 68

Magnonic band structure in thin magnetic films with stripe domains

configuration

S. Tacchia, R. Silvanib, I. Camara c, L.C. Garnier c,d, G. Carlottib,

M. Eddrief c, M. Marangoloc

a Istituto Officina dei Materiali del CNR (CNR- IOM), Sede Secondaria di Perugia, Italy.

b Università di Perugia, Dipartimento Fisica e Geologia, Perugia, Italy. c Sorbonne Université – CNRS, Institut des Nanosciences de Paris, UMR 7588 Paris, France.

d Université Versailles St-Quentin, LISV, Versailles, France.

Stripe domains structure, characterized by a periodic modulation of the out-of-plane magnetization component

alternately directed up and down with respect to the sample surface, represents an attractive magnetic

configuration. [1,2] This structure can develop in thin magnetic films with perpendicular magnetic anisotropy,

due to the energy competition between the perpendicular magnetic anisotropy and the easy-plane dipole-dipole

interaction. Interestingly, it has been found that the direction of the stripes domains is always parallel to the

last saturation direction, and it is independent on the crystallographic direction. Here, we present the

investigation of the magnetic excitations in stripe domains configuration in a 78-nm nitrogen-implanted iron

FeN film, performed by broadband ferromagnetic resonance (CPW-FMR) and Brillouin light scattering (BLS).

The experimental results are successfully interpreted on the basis of dynamical micromagnetic simulations

performed using by the open-source, GPU-accelerated software MuMax3. Several surface and volume modes

have been observed and their behavior as a function of the external magnetic field applied along the stripes

direction has been investigated.[3] The dispersion relation of the spin waves modes has been measured by

means of BLS for the in-plane transferred wave vector parallel and perpendicular to the stripes axis, and

compared with the simulated band structure. In particular, propagation perpendicular to the stripes was found

to be an attractive configuration for magnonic applications, because the band structure presents either

forbidden or allowed frequency ranges for SWs propagation.

[1] U. Ebels et al., Phys. Rev. B 63, 174437 (2001)

[2] N. Vukadinovic et al., Phys. Rev. Lett. 85, 2817 (2000)

[3] Camara, I. S. et al., J. Phys.: Condens. Matter 29, 465803 (2017)

Session IVB Thursday, August 1

IVB.1 69

Second sound in magnonic gases

V. Tiberkevich

Oakland university, USA

Vasil Tiberkevich developed a general theory of the second sound in different gases of quasi-particles,

including magnons and phonons. Second sound is a quantum mechanical effect manifesting itself as a wave-

like heat transfer, in a gas of quasi-particles. The developed theory is applied to a room-temperature magnonic

second sound in a quasi-eqilibruim gas of magnons undergoing Bose-Einstein condensation in a ferrite film.


IVB.2 70

New skyrmion resonance modes in a chiral magnetic insulator

A. Aqeela, J. Sahligera, T. Taniguchia, D.Mettusa, A. Bauera, C. Pfleiderera, C.H. Backa

a Physik Department, Technische Universität München, Garching, Germany

Recently, a new independent low-temperature skyrmion (LTS) phase has been discovered [1] in addition

to the previously observed high temperature skyrmion pocket [2] in a chiral magnetic insulator Cu2OSeO3.

Unlike the high temperature skyrmion phase, the LTS phase has a different stabilization mechanism. The

skyrmion lattice is stabilized by the cubic anisotropy contribution [1,3] and not by fluctuations. The key

question here is how a different stabilization mechanism would influence the magnetization dynamics and

modify the magnetic resonant response of skyrmions. Using a broadband spin-wave spectroscopy technique,

we systematically track the magnetic resonance response in different magnetic phases of Cu2OSeO3, focusing

on the LTS phase around 5K. We identify distinct resonances associated with the newly discovered tilted

conical and LTS phases of Cu2OSeO3. We observed a strong dependence of these modes on static magnetic

field history. We identified an increase in the weights of skyrmion resonance modes by cycling magnetic field

within this phase. The magnetic phase boundaries and effect of field cycling on the population of different

phases agrees well with our magnetometery measurements. To understand the observed resonance spectra, we

used a phenomenological model based on previous work [4] with an addition consideration of different cubic

anisotropy contributions. Our theoretical model confirms that the cubic anisotropy contribution is the key

ingredient for the observed resonance spectra. Moreover, theoretical modeling provides evidence that the

hybridization mechanism of different resonance modes is solely provided by the cubic anisotropy.

[1] A. Chacon, et al., Nature Physics 14, 936 (2018).

[2] S. Seki, et al., Science 336, 198 (2012).

[3] M. Halder, et al., Physical Review B 98, 144429 (2018).

[4] T. Schwarze, Nature Materials 14, 478 (2015).

http://www.nature.com/articles/s41567-018-0184-y#auth-10


IVB.3 71

Topological Magnons and Edge States in Antiferromagnetic Skyrmion Crystals

Sebastián A. Díaz, Jelena Klinovaja, Daniel Loss

Department of Physics, University of Basel, Basel, Switzerland

Antiferromagnetic skyrmion crystals are spatially periodic noncollinear magnetic phases predicted to exist

in antiferromagnets with Dzyaloshinskii-Moriya interactions. We show for the first time that their bulk magnon

band structure, characterized by nonzero Chern numbers, is topologically nontrivial and that they support

topologically-protected chiral magnonic edge states. Of particular importance for experimental realizations,

magnonic edge states appear within the first bulk magnon gap, at the lowest possible energies they can exist

and where magnon-magnon interactions are reduced. Thus, antiferromagnetic skyrmion crystals show great

promise as novel platforms for topological magnonics.

[1] S. A. Díaz, J. Klinovaja, and D. Loss, arXiv:1812.11125.

Figure 1: Antiferromagnetic skyrmion crystal, which is predicted to host topological

magnons and chiral magnonic edge states [1].


IVB.4 72

Electronic and magneto-optical signatures of the spectral distribution and

mechanisms of magnon generation by spin current

Sergei Urazhdina, Andrei Zholuda, Ryan Freemana, Vladislav Demidovb, Sergej Demokritovc

a Emory University, Atlanta, USA b University of Münster, Germany

While the nature and the mechanisms of spin current-induced excitation of quasi-uniform magnetization

dynamics and dipolar spinwaves are well-established, little is known about it effects on the rest of the

dynamical magnetic spectrum, typically spanning the frequency range from GHz to dozens of THz. The micro-

focus magneto-optical Brillouin light spectroscopy (BLS) technique is sensitive only to magnons with

wavevectors smaller than the inverse of the size of the probing light spot. To access higher-frequency magnons,

we tailored the thickness and the geometry of the magnetic films to enhance the dispersion of magnon

spectrum. We have also utilized sub-diffraction confinement of light to enhance the accessible spectral range.

These approaches allowed us to determine the spectral distribution of magnons excited by spin current.

Analysis shows that the enhancement of magnon population by the spin current can be well described in terms

of the increased effective chemical potential at a constant effective temperature, providing a tentative

connection between the spin current-induced phenomena and Bose-Einstein condensation.

We also show that the current-dependent resistance R(I) provides direction information about the effects of

spin current on the magnon population, not limited to the long-wavelength magnons. Our observation of

singular piecewise-linear R(I) in nanoscale magnetic spin valves allowed us to uncover the previously

unrecognized non-classical mechanisms of magnon generation by spin current. Furthermore, combined

variable-temperature electronic and BLS measurements in ferromagnet/spin Hall material bilayers demonstrate

that both long-wavelength and THZ magnons can significantly contribute to the spin current-induced

magnetization dynamics. By harnessing the spectral characteristics of spin current-driven magnons, it may

become possible to control the efficiency of excitation and the coherence of the dynamical magnetization

states.

[1] V. E. Demidov et al., Nature Comm. 8, 1579 (2017).

[2] A. Zholud et al., Phys. Rev. Lett., 119, 257201 (2017).

[3] I.V. Borisenko et al., Appl. Phys. Lett. 113, 062403 (2018).

Figure 1: Current dependences of the chemical potential in the frequency units (point-up

triangles) and of the effective temperature (diamonds) of the magnon gas for I<0 (a) and

I>0 (b). Point-down triangles in (b) show the frequency of the lowest magnon state.

Poster session Monday, July 29

73


P01 74

Scattering of Acoustic Waves from 1D Arrays of Magnetic Inclusions

Oliver S. Latchama, Yuliya Gusievab, Andrey V. Shytova, Oksana Y. Gorobetsb, Volodymyr V.

Kruglyaka

a University of Exeter, United Kingdom b Igor Sikorsky Kyiv Polytechnic Institute, Ukraine

The promise of energy savings inherent to non-volatile devices has spurred the rapid growth of research in

magnonics, which exploits spin waves as a signal or data carrier. Yet, the progress is hampered by the magnetic

damping, which is high in ferromagnetic metals while low-damping magnetic insulators are difficult to

structure into nanoscale devices. In contrast, the propagation distance of acoustic waves is typically much

longer than that of spin waves at the same frequencies. The use of the magneto-elastic coupling allows one to

control the waves with a magnetic field [1].

Here, we explore theoretically novel energy-efficient magneto-elastic devices in which the energy is

carried by acoustic waves while the magnetic field controls its propagation via isolated magneto-elastic

inclusions. By tuning the applied field, we can shift the frequency at which the acoustic and magnetic resonance

modes of the inclusions hybridize. Thereby, we control the reflection and transmission coefficients of acoustic

waves due to individual inclusions. From periodic arrays of inclusions form artificial magnon phononic

crystals we find also that the scattering strength is determined and may be enhanced by an interplay between

Fano and Fabry-Perot atop Bragg resonances, but is countered by the magnetic loss in the inclusions (see e.g

fig. 1). Our results were obtained for the case of transverse acoustic waves normally incident on quasi-1D

structures, both acoustic and magneto-elastic constituents of which represented infinite slabs. We discuss

potential issues and benefits associated with application of our theory to more realistic systems, as well as

further routes to enhance the resonance effects for a new class of magnetoelastic devices [2].

The

research leading to these results has received funding from the EPSRC of the UK (Project EP/L019876/1) and

the European Union’s Horizon 2020 research and innovation program under Marie Sklodowska-Curie GA No

644348 (MagIC).

[1] V. V. Kruglyak, S. O. Demokritov, and D. Grundler, “Magnonics”, J. Phys. D: Appl. Phys. 43, 264001

(2010).

[2] A. Kamra, H. Keshtgar, P. Yan, and G. E. W. Bauer, Phys. Rev. B 91, 104409 (2015)

Figure 1: Colour map of the reflection coefficient from an array of magnetic inclusions as a function

of the frequency and the array’s period.


P02 75

Bridging magnonics and spin-orbitronics

B. Divinskiya, V. E. Demidova, S. Urazhdinb, R. Freemanb, S. O. Demokritova

a University of Münster, Münster, Germany b Emory University, Atlanta, GA, USA

The emerging field of nano-magnonics utilizes high-frequency waves of magnetization – spin waves – for

the transmission and processing of information on the nanoscale. The advent of spin-transfer torque has spurred

significant advances in nanomagnonics, by enabling highly efficient local spin wave generation in magnonic

nanodevices. Furthermore, the recent emergence of spin-orbitronics, which utilizes spin-orbit interaction as

the source of spin torque, has provided a unique ability to exert spin torque over spatially extended areas of

magnonic structures, enabling enhanced spin wave transmission.

Here, we experimentally demonstrate that these advances can be efficiently combined. We utilize the same

spin–orbit torque mechanism for the generation of propagating spin waves, and for the long-range

enhancement of their propagation, in a single integrated nano-magnonic device. The demonstrated system

exhibits a controllable directional asymmetry of spin wave emission, which is highly beneficial for applications

in non-reciprocal magnonic logic and neuromorphic computing.

[1] B. Divinskiy et al., Adv. Mater. 30 (2018), 180237.

Figure 1: Left: schematic of the experiment. Right: unidirectional spin wave emission by

the nano-notch oscillator. Dashed lines on the maps show the outlines of the waveguide and

of the nano-notch.


P03 76

Controllable excitation of quasi-linear and bullet modes in a spin-Hall nano-

oscillator

B. Divinskiya, V. E. Demidova, S. Urazhdinb, R. Freemanb, S. O. Demokritova

a University of Münster, Münster, Germany b Emory University, Atlanta, GA, USA

The ability of the spin-Hall effect to generate spin currents in a simple thin-film geometry has facilitated

the development of a variety of spin-Hall nano-oscillator (SHNO) configurations. Two fundamentally different

auto-oscillation modes were observed in SHNOs, depending on the geometry and the experimental conditions.

The quasi-linear mode continuously evolves from the linear eigenmodes of the magnetic system. In contrast,

the self-localized bullet mode does not evolve from the linear spectrum but is instead abruptly spontaneously

formed at the auto-oscillation onset. Only one of these modes is typically dominant in SHNOs demonstrated

so far, even though the other mode may appear under special conditions whose significance is not yet well

understood. Since the two modes exhibit substantially different oscillation characteristics, beneficial for

different specific applications, it is highly desirable to identify the mechanisms controlling the preferential

formation of each of these modes and develop approaches to control them.

Here, we experimentally demonstrate a spin-Hall nano-oscillator that enables controllable excitation of the

quasi-linear and bullet dynamical modes. This is facilitated by the injection of spin current into an extended

region of the active magnetic film, avoiding the conditions that result in the preferential formation of the bullet

mode. Thanks to the ability to excite these fundamentally different modes in the same device, we were able to

directly compare their spatial and temporal characteristics and show that the operation of the SHNOs in the

regime of quasi-linear mode oscillations is favorable for the generation of short microwave pulses, while the

bullet-mode regime is limited in this respect by the significant time required for the formation of this dynamical

state. Our results provide insight into the dynamical mechanisms relevant to the practical applications of

SHNOs as nano-scale microwave sources.

[1] B. Divinskiy et al., Appl. Phys. Lett. 114 (2019), 042403.

Figure 1: Left: schematic of the experiment. Right: spatial profiles of the quasi-linear and

bullet modes. The shadowed area shows the region of the nano-gap.


P04 77

How to generate whispering gallery magnons

K. Schultheiss1, R. Verba2, F. Wehrmann1, K. Wagner1,3, L. Körber1,3, T. Hula1,4,

T. Hache1,5, A. Kákay1, A.A. Awad6, V. Tiberkevich7, A.N. Slavin7, J. Fassbender1,3, H.

Schultheiss1,3

1Institut für Ionenstrahlphysik und Materialforschung, Helmholtz-Zentrum Dresden – Rossendorf, D-01328

Dresden, Germany 2Institute of Magnetism, National Academy of Sciences of Ukraine, Kyiv 03142, Ukraine

3TU Dresden, D-01062 Dresden, Germany 4Westsächsische Hochschule Zwickau, 08056 Zwickau, Germany

5Institut für Physik, Technische Universität Chemnitz, D-09107 Chemnitz 6Department of Physics, University of Gothenburg, 412 96 Gothenburg, Sweden

7Department of Physics, Oakland University, Rochester, MI 48309, USA

One of the most fascinating topics in current quantum physics are hybridized systems, in which resonators

of different quantum systems are strongly coupled. Prominent examples are circular resonators with high

quality factors that allow the coupling of optical whispering gallery modes to microwave cavities or magnon

resonances. However, the coupling to magnons with finite wave vectors has not yet been achieved due to the

lack of efficient excitation schemes.

Here, we present the generation of whispering gallery magnons with unprecedented high azimuthal wave

vectors via nonlinear 3-magnon scattering in a μm-sized NiFe disk exhibiting a vortex state [1]. These modes

show a strong localization at the perimeter of the disk and practically zero amplitude in an extended area

around the vortex core. They originate from the splitting of the fundamental radial magnon modes, which can

be resonantly excited in a vortex state by an out-of-plane microwave field. We will shed light on the basics of

this non-linear scattering mechanism from experimental and theoretical point of view. Using Brillouin light

scattering (BLS) microscopy, we investigated the frequency and power dependence of this nonlinear

mechanism. The spatially resolved mode profiles give evidence for the localization at the boundaries of the

disk and allow for a direct determination of the modes’ wavenumbers. Furthermore, time resolved BLS in

combination with pulsed microwave excitation revealed the temporal evolution of the 3-magnon splitting and

its dependence on the applied microwave power.

Financial support from the Deutsche Forschungsgemeinschaft within programme SCHU 2922/1-1 is

gratefully acknowledged. Samples were prepared at the Nanofabrication Facilities (NanoFaRo) at the Institute

of Ion Beam Physics and Materials Research at the Helmholtz-Center Dresden-Rossendorf (HZDR). K.S.

acknowledges funding within the Helmholtz PostDoc Programme.

[1] K. Schultheiss et al. Phys. Rev. Lett. 122, 097202 (2019)


P05 78

Worm-like nanochannels in artificial ferromagnetic quasicrystals

Sho Watanabea, Vinayak S. Bhata, Korbinian Baumgaertla, Dirk Grundlera, b

a Laboratory of Nanoscale Magnetic Materials and Magnonics, Institute of Materials,

Ecole Polytechnique Fédérale de Lausanne (EPFL), Station 17, 1015 Lausanne, Switzerland b Institute of Microengineering, Ecole Polytechnique Fédérale de Lausanne (EPFL),

Station 17, 1015 Lausanne, Switzerland

Quasicrystals exhibit long-range order but an absence of translational invariance. Therefore, constituents

in quasicrystals possess non-identical local environment. The collective spin excitations of artificial

ferromagnetic quasicrystals (AFQs), a counterpart of photonic quasicrystals in magnetism, have gained recent

interest [1]. Still, experimental studies on AFQs are at their infancy [2].

We performed broadband spin wave (SW) spectroscopy and spatially resolved micro-focus Brillouin light

scattering (BLS) on AFQs. The AFQs consisted of ferromagnetic thin films such as CoFeB with nanoholes in

an arrangement of a Penrose tiling, i.e., a 2D analogue of a 3D quasicrystal. Experiments were based on

different AFQs where we varied the diameters of nanoholes, the type of Penrose tiling and the lateral size.

Depending on the orientation of an in-plane field we detected different sets of SW eigenmodes, which

displayed a ten-fold rotational symmetry on a five-fold rotationally symmetric Penrose lattice. SW resonances

showed similar field dependencies for the different generations of AFQs. Micro-focused BLS and

micromagnetic simulation data indicated SW nanochannels which incorporate peculiar sequences of bends.

Via phase-resolved micro-focused BLS technique, phase fronts of the SWs were found to be irregular in the

low magnetic field regime. Our results suggest that nanohole-based AFQs promise a new class of magnonic

devices such as ultra-compact and dense wavelength division multiplexers. The work was supported by SNSF

via grant number 163016.

[1] J. Rychly et al., J. Magn. Magn. Mater. 450 (2018), 18-23

[2] S. Choudhury, et al., ACS Nano 11 (2017), 8814-8821


P06 79

Vortex dynamics in microscopic magnetic thin film spherical shells

Katie A. Lewisa, Conor McKeevera, Farkhad G. Alievb, J Roy Samblesa ,Alastair P. Hibbinsa,

Feodor Y. Orgin

a Department of Physics and Astronomy, University of Exeter, Exeter EX4 4QL b Departamento Física Materia Condensada, Universidad Autónoma de Madrid, 28049, Madrid, Spain

The ability to create materials with tuneable magnetic responses has generated much interest due to the

potential applications in microwave signal processing, magnetic memory and sensors [1]. This work aims to

experimentally verify the high dynamic susceptibility observed at high frequencies [tens of GHz] that has been

predicted by micromagnetic simulation in thin magnetic shells when vortices are present (Figure 1A) [2].

Nanosphere lithography and sputtering [3] were used to make microscopic shells and their dynamic

properties were experimentally investigated using VNA-FMR spectroscopy.

To obtain the necessary vortex configuration in the structures, the nucleation field of the vortex has been

measured as function of the film thickness (Figure 2B). It was found that for thicknesses above 30nm the

switching field is above 0 Oe and vortex structures can be formed with no bias field. The majority of the shells

exhibit the same magnetic configuration.

We further demonstrate that by tailoring the radius of the spheres (with RIE) we can further improve the

characteristics of the whole array. VNA-FMR is then applied to measure the lattices of semi-shells and examine

the dynamic modes present in vortex configuration. The results are produced for spheres of different

dimensions and compared with the numerical simulations.

[1] Maksymov, I.S. and Kostylev, M., 2015. Physica E: Low-dimensional Systems andNanostructures, 69,

pp.253-293.

[2] McKeever, C., Ogrin, F.Y. and Aziz, M.M (Submitted to PRB)

[3] Weekes, S.M., Ogrin, F.Y., Murray, W.A. and Keatley, P.S., 2007. Langmuir 23(3), pp. 1057-1060.

Figure 1: A) Micromagnetic simulations for dynamic susceptibility in the absence and presence of vortices [2].

B) Magnetic response of a 780 nm monolayer of magnetic spherical shells with Permalloy thickness of 30 nm

with varying applied magnetic field. A nucleation field can be seen around 50 Oe, the switching magnetisation

indicating the presence of a vortex state. Insert shows the increasing nucleation field with increasing Permalloy

thickness.


P07 80

Brillouin light scattering investigation of the spin wave beam focusing effect

under excitation by curved transducer

M. Madami1, Y. Khivintsev2,3, G. Gubbiotti4, G. Dudko2,

A. Kozhevnikov2, V. Sakharov2, A. Stal’makhov3, Y. Filimonov2,3

1University of Perugia, I-06123 Perugia, Italy

2Kotelnikov IRE RAS, 410019, Saratov, Russia

3Saratov State University, 410012, Saratov, Russia

4Istituto Officina dei Materiali del CNR (IOM), Unità di Perugia, Italy

Anisotropy of the spin waves (SW) dispersion in tangentially magnetized ferromagnetic films can

be used for SW beam focusing and propagation control [1,2]. We employed micro-focused Brillouin

light scattering (µ-BLS) technique [3-4] and micromagnetic simulation [5] to study the focusing

effect of SW, excited by a curved coplanar transducer in an yttrium iron garnet (YIG) film, in the

backward volume spin waves (BVSW) geometry. Experimentally we observed a clear nonreciprocity

in the excitation and propagation of SW on both sides of the coplanar transducer with very well-

defined SW beams propagating, and intersecting, on the concave side of the transducer.

Measurements have been performed on a 5 μm thick YIG film, within an applied magnetic field of

H=100 mT and over an area of 400×600 μm2. Micromagnetic simulations have been performed, using

the OOMMF code, over an area of 3×3 mm and with the cell size of 3×3×1 μm. The results of

micromagnetic simulations show a good agreement with the experimental results and successfully

reproduced the nonreciprocity of the SW propagation. An influence of nonlinear effects on focusing

effect of BVSW under excitation by curved and linear transducers were studied as well. We show

that threshold amplitude of input microwave signal hz for focused beam collapse is smaller for curved

transducer then for linear one.

This work was supported by the Russian Science Foundation (grant No. 17-19-01673).

[1] F.A. Pizzarello et al., JAP, 41, 1016 (1970).

[2] A. Vashkovskii et al., Sov. Phys., Journ., 31, 908 (1988).

[3] M. Madami et al., Solid State Physics, Vol. 63, 79, (Academic Press SSP, UK, 2012).

[4] J. Stigloher et al., Phys. Rev. Let., 117, 037204 (2016).

[5] M. J. Donahue and D. G. Porter, OOMMF User's Guide, NISTIR 6376 (1999).


P08 81

3D FDTD-LLG modelling of magnetisation dynamics in thin film ferromagnetic

structures

Feodor Y. Ogrin

School of Physics and Astronomy, University of Exeter, UK

There is a growing need in high frequency tuneable microwave materials for applications in the areas of

microwave electronics, transformation optics, photonics. Due to their intrinsic RF phenomena, such as FMR,

ferromagnetic thin films have always been of great interest and led to a great amount of experimental research

very often supported by numerical simulations. While purely magnetostatic solvers, such as OOMMF or

Mumax, have always been the standard benchmark tools and usually provide a precise description of the

magnetisation processes in thin-film ferromagnetic structures, these systems are however limited in

applications where full electromagnetic solutions are required, especially when the material properties are

extremely non-uniform (e.g. dielectric/metal interfaces). In such cases one needs to consider a modelling

approach where a full solution of Maxwell equations is needed alongside the materialistic equations, such as

e.g. Landau-Lifshits-Gilbert (LLG) providing the relation between the magnetisation and the magnetic field

[1]. Here I propose such a model which uses 3D finite-difference-time-domain (FDTD) approach together with

LLG to find the exact solutions for magnetisation dynamics in thin film ferromagnetic structures. As a

benchmark test, we demonstrate application of such model for different classical phenomena such as Faraday

effect, and then explore the dynamic characteristics of thin films in magnetostatic applications. In particular

we consider propagation of magnetostatic/spin waves in metallised magneto-dielectric and metallic thin films

and demonstrate their dispersion characteristics, including those that cannot be obtained by purely

magnetostatic approach. In one example we demonstrate a formation of fast TE and TM electromagnetic waves

in THz frequency band propagating in geometry of transverse and longitudinally applied magnetic field. In the

second example we consider a model of a ferrite loaded patch antenna. I demonstrate how the FMR

characteristics of the load modify the electromagnetic properties of the radiation. The results are compared

with the experimental work on antennas using YIG.

[1] M. M. Aziz, Progress In Electromagnetics Research B 15, (2009) 1–29.


P09 82

A micron-scale spin-orbit-torque emitter of coherent spin waves for YIG

magnonics M. Evelt1, L. Soumah2, A. B. Rinkevich3, S. O. Demokritov1,3, V. Cros2, Jamal Ben Youssef4, P.

Bortolotti2, V.E. Demidov1, A. Anane2

1Institute for Applied Physics and Center for Nonlinear Science, University of Muenster, 48149 Muenster,

Germany 2Unité Mixte de Physique, CNRS, Thales, Univ. Paris-Sud, Université Paris-Saclay, Palaiseau, France

3Institute of Metal Physics, Ural Division of RAS, Ekaterinburg 620108, Russia 4LABSTICC, UMR 6285 CNRS, Université de Bretagne Occidentale, 29238 Brest, France

Spin-orbit-torque coherent emission of short wavelength spin waves [1] in ultralow damping magnetic

insulators [2] is demonstrated. If magnetic materials combining low losses and large Perpendicular Magnetic

Anisotropy (PMA) were still a missing brick in the magnonic and spintronic fields it is mostly by the due to

difficulty to conciliate strong-spin-orbit-coupling (SOC), necessary to induce PMA with the detrimental effect

that usually has SOC on the magnetic losses. We reporte on the growth of ultrathin Bismuth doped Y3Fe5O12

(BiYIG) films on Gd3Ga5O12 (GGG) and substituted GGG (sGGG) (111) oriented substrates [2]. A fine tuning

of the PMA was possible to achieve using both epitaxial strain and growth induced anisotropies. Both

spontaneously in-plane and out-of-plane magnetized thin films can be elaborated. Ferromagnetic Resonance

(FMR) measurements demonstrate the high dynamic quality of these BiYIG ultrathin films, PMA films with

Gilbert damping values as low as 3 10-4 and FMR linewidth of 0.3 mT at 8 GHz are achieved even for films

that do not exceed 30 nm in thickness. Those films are suitable for magneto-optical technics as micro-Brillouin

light scattering (BLS), their Fraday rotation exceeding that of YIG by a factor of 80. We demonstrate

generation of coherent propagating magnons in those films by spin-orbit torque induced by dc electric current

[1] on a 20 nm thick BiYIG film with PMA. Fine tuning of the PMA allows to exactly cancel the dipolar field

(the effective magnetization M ≈ 0). As a result, the usually observed non-linear shift of the auto-oscillation

frequency is suppressed. Hence, the dominant mechanism for self-localization of the auto-oscillations is

inhibited. We demonstrate simple and versatile spin-orbit torque devices, which can be used as highly efficient

nanoscale sources of coherent propagating magnons for insulator-based spintronic applications.

[1] M. Evelt et al., “Emission of coherent propagating magnons by insulator-based spin-orbit torque

oscillators”.Phys. Rev. Applied 10, 041002 (2018)

[2] L. Soumah et al., Ultra-low damping insulating magnetic thin films get perpendicular. Nat. Commun.

9, 3355 (2018).

Figure 1: left: µ-BLS of the spin wave emission from a Pt/BiYIG emitter, materialized by the discontinuous

lines. Right : FMR characterisation of a 30 nm thick BiYIG film.


P10 83

Magnonic crystals using a nano-patterned ultrathin YIG film

H. Merbouchea, M. Colleta, M. Eveltb, V. E. Demidovb, J. L. Prietoc, M. Muñozd

, J. Ben Youssefe, G. de

Loubensf, O. Kleing, S. Xavierh, L. Soumaha, V. Crosa, P. Bortolottia, S. O. Demokritovb,i, A. Ananea

a Unité Mixte de Physique CNRS, Thales, Univ. Paris-Sud, 91767 Palaiseau, France b Institute for Applied Physics, University of Muenster, 48149 Muenster, Germany cISOM-UPM, Ciudad Universitaria, Madrid 28040, Spain d IMM-Instituto de Microelectrónica de Madrid, E-28760 Tres Cantos, Madrid, Spain e LabSTICC-UMR 6285/ CNRS, Université de Bretagne Occidentale, 29200 Brest, France f Service de Physique de l’État Condensé, CEA, CNRS, 91191 Gif-sur-Yvette, France g INAC-SPINTEC, CEA/CNRS and Univ. Grenoble Alpes, 38000 Grenoble, France h Thales Research and Technology, Thales 91767 Palaiseau, France

i M.N. Miheev Institute of Metal Physics, Yekaterinburg 620041, Russia

Two different types of magnonic crystals (MC) based on ultra-thin YIG films (20 nm thick) have been

characterized. Propagative Spin Wave Spectroscopy (PSWS) and Micro-focused Brillouin Light Scattering

spectroscopy (µ-BLS) techniques have been used. With the support of large scale micro-magnetic simulations,

we provide new insights on spin-waves (SWs) propagation in periodic and confined systems for which the

SWs attenuation length is much larger than the MC periodicity.

The first MC is implemented in a form of a microscopic waveguide (WG), whose width is periodically

varied between 1 and 0.8 µm. We study the propagation characteristics of SWs in this system using µ-BLS.

Experimental data shows a 20MHz gap evidenced by a 5-fold decrease of the attenuation length. Using micro-

magnetic simulations, we are able to reproduce not only the band gap characteristics but also subtler features

such as the spatial beating of the amplitude, signs of multi-mode contributions and a huge coupling asymmetry

with the antenna when the frequency is varied across the gap.

The second MC is obtained by etching 150nm-wide, periodically spaced grooves in an array of 2.5µm-

wide WGs (see inset). The grooves depth is incremented from 0 to 23nm. PSWS is used to characterize SWs

propagation at various magnetic fields. Successful filtering is obtained for grooves greater than 5nm. In Fig1.

A 15MHz transmission gap is observed at 1.4GHz corresponding to a decrease by a factor of 5 of the SW

intensity at 30µm from the excitation antenna when compared to the reference WG. Importantly, the

transmission outside the frequency gap is weakly affected by the presence of the periodic grooves, even when

we fully etch our WGs.

Figure 1: Spectrum of the attenuation of the spin-

waves-induced mutual inductance for a MC with

8nm grooves compared to the reference, showing

a 15MHz gap (shaded area) for an applied field of

115Oe.

Inset: Sketch of the studied system


P11 84

Propagating spin waves induced by spin-orbit torque

Himanshu Fularaa, Mohammad Zahedinejada, Roman Khymyna, Mykola Dvornika,b, Shreyas

Muralidhara, Ahmad. A. Awada,b, and Johan Åkermana,b,c

aDepartment of Physics, University of Gothenburg, 412 96 Gothenburg, Sweden bNanOsc AB, Kista 164 40, Sweden

cDepartment of Applied Physics, School of Engineering Sciences, KTH Royal Institute of Technology,

Electrum 229, SE-16440 Kista, Sweden

Magnonic nanoscale devices require propagating spin waves to operate at higher frequencies for data

transfer and wave-based computation [1]. Recent experimental and theoretical studies have witnessed the

ability of spin-orbit torque (SOT) to compensate magnetic damping over the spatially extended regions of both

conducting and insulating materials [2]. While SOT can induce highly non-linear localized spin wave auto-

oscillations in different device geometries known as spin Hall nano-oscillators (SHNOs) [3], the excitation of

propagating spin waves in a local magneto-dynamical region is still lacking.

Here, we experimentally demonstrate how interface induced perpendicular magnetic anisotropy (PMA)

can overcome the localization phenomenon and enable SOT-driven efficient and controllable excitation of

field- and current-tunable propagating spin waves in nano-constriction based

W(5nm)/CoFeB(1.4nm)/MgO(2nm) SHNO devices. High frequency electrical measurements combined with

micromagnetic simulations reveal that the large positive non-linearity brought about by interface induced

strong PMA of thinner CoFeB layer allows the frequency of the auto-oscillations to move well above the

corresponding FMR spectrum indicating the propagating nature of spin wave auto-oscillations (see Figure 1b-

c).

Thanks to low operational current excitation of propagating spin waves, our devices holds great promise

to directly integrate SHNOs into magnonic circuits for highly energy efficient spin wave-based technology. In

addition, the reduced fabrication complexity of these devices will enable us to make use of these propagating

spin waves in mediating a long-range mutual synchronization of large number of SHNO chains or networks

for neuromorphic computing.

[1] J. Slonczewski, J. Magn. Magn. Mater. 195, 261–268 (1999).

[2] P. Gambardella et al., Philos. Trans. A Math. Phys. Eng. Sci. 369, 3175–3197 (2011).

[2] T. Chen et al., Proc. IEEE 104, 1919–1945 (2016).

Figure 1: (a) Schematic of a SHNO device with nano-constriction width w. (b) Field sweep

(c) Current sweep, spin-wave auto-oscillations, excited on a 150 nm nano-constriction

width SHNO device.


P12 85

Spin wave propagation in ultrathin magnetic insulators with perpendicular

magnetic anisotropy

Jilei Chen1, Chuangtang Wang2,3,4, Chuanpu Liu1, Sa Tu1, Hanchen Wang1, Lei Bi2,3,4, and Haiming Yu1,*

1 Fert Beijing Institute, BDBC, School of Microelectronics, Beihang University, Xueyuan Road 37, Beijing

100191, China 2National Engineering Research Center of Electromagnetic Radiation Control Materials, University of

Electronic Science and Technology of China (UESTC), Chengdu 610054, P.R.China 3 State Key Laboratory of Electronic Thin Films and Integrated Devices, UESTC,Chengdu 610054,

P.R.China 4 Key Laboratory of Multi-spectral Absorbing Materials and Structures of Ministry of Education, UESTC,

Chengdu 610054, P. R. China

The study of spin waves has been drawn much attention recently due to its potential applications in the

information processing and logic devices. Spin waves can carry and transport information without charge

current which is key to the low-energy-consumption computing systems beyond CMOS. A desirable magnetic

material for hosting the spin wave propagation is the yttrium iron garnet (YIG) which offers a low damping

coefficient even as nanometer-thick thin films. Magnetic thin films with perpendicular magnetic anisotropy

(PMA) offer novel opportunities for studying magnetostatic forward volume mode (MSFVM) spin waves with

isotropic propagation. Here, we realize the full reciprocal MSFVM spin wave propagation in a 30-nanometer-

thick manganese doped YIG with PMA only applying an external field of 50 Oe. The external magnetic field

required for investigating the MSFVM spin waves in YIG is reduced by 34 times compared to the in-plane

magnetized one. The spin wave group velocity and decay length are also investigated. Our finding paves the

way to the applications of the isotropic magnonic computing systems and logic devices.

Figure: (a) Schematic of the Mn doped YIG based magnonic device. The external field is applied

perpendicular to the thin film plane. (b) Gray-scale plot of the transmission spectrum S12 measured on the Mn

doped YIG. (c) A single lineplot extracted from (b) at 100 Oe.

*Email: [email protected]


P13 86

Spinwave tunnelling effect at heterojunction

Kenji Tanabea, Satoshi Sumia, Hiroyuki Awanoa

a Toyota Technological Insutitute, Nagoya, Japan

Magnonics, which is a research field toward control of magnons (elementary excitation of spinwaves), has

been attracted much attention as a candiate for next-generation electronics [1]. Although the magnons have

been studied as a propagating wave in single ferromagnetic materials by many rearch groups, reports on

magnonic heterojunctions are very few [2-4]. The heterojunction studies such as a p-n junction, a tunneling

effect, a giant magnetoresistance, and Josephson effect have played a crucial role in several research fields

such as electronics, spintronics and fundamental physics. Here we present spinwave propagation in a

heterojunction having a mechanical gap, which is termed spinwave tunneling effect[2].

Figure 1(a) shows schematic diagram of our experimental setup. The heterojunction consists of Ni10Fe90

(100 nm) and Ni20Fe80 (100 nm) strips on a Si substrate and has a mechanical gap from 2 to 10 m. Two

electrodes for excitation and detection are fabricated on each strips. Spinwaves excited by an electrode pass

thorough the mechanical gap and are detected by another electrode. Figure 1(b) shows the frequency

dependences of absorption and transmission of the spinwaves measured by vector network analyser. We can

see the spinwave propagation at the resonant frequency, which indicates the spinwave tunnelling effect through

the heterojunction. Figure 1(c) shows gap-distance dependence of the S21 phase shift. In spite of the different

gap distance, the phase shifts completely overlap on single curve, which suggests that the velocity of spinwave

transmission in the gap is much faster than that of the spinwave propagation in NiFe alloy. Furthermore, we

will present influence of Gd-doping in transition metal on spinwave tunnelling effect and angular momentum

transport in the poster presentation.

[1] A. A. Serga et al., J. Phys. D: Appl. Phys. 43, 264002 (2010).

[2] T. Schneider et al., Euro. Phys. Lett. 90, 27003 (2010).

[3] K. Tanabe et al., Appl. Phys. Express 7, 053001 (2014).

[4] J. Stigloher et al., Phys. Rev. Lett. 117, 037204 (2016).

Figure 1: (a) Schematic diagram of experimental setup. (b) Absorption and transmission of

spinwaves as afunction of frequency. (c) Gap dependence of S21 phase shift as a function

of frequency.


P14 87

Magnetoelastic excitation in non-uniformly magnetized waveguides

Frederic Vanderveken1,2, Florin Ciubotaru1, Marc Heyns1, Bart Soree1, Iuliana P. Radu1, and

Christoph Adelmann1

a Imec, B-3001 Leuven, Belgium b KU Leuven, Faculty of Engineering, B-3001 Leuven, Belgium

Spin waves in magnetic waveguides have been proposed as data carriers in future information processing

systems [1,2]. In particular, spin wave-based majority gates promise significant power and area reduction per

computing throughput with respect to conventional CMOS [2,3]. To compete with CMOS, spin wave devices

[4,5] need to be miniaturized down to the nanoscale. However, this miniaturization of the magnetic devices

also changes their behaviour. In nanoscale devices, finite size effects together with inhomogeneous static and

dynamic internal field strongly affect the spin wave properties. Furthermore, at the nanoscale, spin wave

excitation via electrical currents becomes inefficient due to the high required current densities. Hence, new

voltage-based transducers are proposed as energy efficient spin wave excitation mechanisms at the nanoscale.

However, the fundamental understanding of these transducers is generally missing.

In this paper, both challenges - miniaturization of the magnetic conduits and voltage-based excitation of

magnons - are investigated using micromagnetic simulations. The system under study is based on a CoFeB

magnetic conduit of 200 nm width and 10 nm thickness, magnetized non-uniformly by an in-plane magnetic

bias field transverse to the conduit. The excitation of spin waves is realized using the magnetoelastic effect

induced by bi-axial or shear in-plane strains [6] applied locally to the magnetic waveguide. To note that the

magnetoelastic excitation field depends on both the strain in the waveguide and its magnetization orientation.

Hence, the non-uniform magnetization state results in a non-uniform excitation field along the width of the

waveguide. The extracted dispersion relations reveal the excitation of quantized width modes with both odd

and even mode numbers, predominantly the first (n1) and second (n2) width modes. When the magnetization

is non-uniformly oriented, the mode profiles change which consequently affects their excitation efficiency. In

specific configurations, this could eventually lead the higher excitation efficiency of the second order width

mode, n2, as compared to the first order width mode, n1. We demonstrate that a spin-wave mode selection can

be achieved by applying proper strain states. Furthermore, we show that the mode selection also can be realized

by tuning the excitation area. This work has been partially funded by the European Union’s Horizon 2020

research and innovation programme within the FET-OPEN project CHIRON under grant agreement No.

801055. This work is supported by FWO (Fonds voor Wetenschappelijk Onderzoek).

[1] A. Khitun and K.L. Wang, J. Appl. Phys. 110, 034306 (2011).

[2] I.P. Radu, et al., Proc. 2015 IEEE Intern. Electron Devices Meet. (IEDM), 32.5 (2015).

[3] O. Zografos, et al., Proc. 2014 IEEE/ACM NANOARCH, 25 (2014).

[4] A. V. Chumak et al., Nat. Commun. 5, 4700 (2014)

[5] T. Fischer, et al., Appl. Phys. Lett. 110, 152401 (2017).

[6] R. Duflou, et al., Appl. Phys. Lett. 111, 192411 (2017).


P15 88

Modeling inductance spectra of non-reciprocal surface spin waves due to

Dzyaloshinskii-Moriya interaction

A. Magni, P. Ansalone, M. Kuepferling, V. Basso

Istituto Nazionale di Ricerca Metrologica (INRIM), 10135 Torino, Italy

Pushed by the search for new materials for spintronics, the study of spin structures with certain

topologically protected arrangements has recently moved into worldwide focus. Such structures, as chiral

domain walls or skyrmions, are emerging as promising information carriers for future spintronic technologies

due to their unusual properties. They are in general unstable, unless a selection of the ground state is caused

by symmetry breaking, which leads to non-collinear or chiral spin interactions. A chiral exchange interaction

was first time defined by Dzyaloshinskii, to account for weak ferromagnetism and generalized by Moriya.

Today the interaction is well known as DMI (Dzyaloshinskii-Moriya-interaction), providing a parameter D,

which quantifies the stabilization of chiral spin structures.

The quest for new materials and systems with stable chiral spin structures requires a precise understanding

and knowledge of the D value. However, validated measurement tools for this parameter do not currently exist.

One of the promising methods is the measurement of the non-reciprocity of spin waves caused by DMI at the

interface between a ferromagnetic (FM) thin film and a heavy metal (HM) thin film [1]. Such non-reciprocity

is experimentally accessible by Brillouin light scattering (BLS) [2], time resolved Kerr effect [3] or all electric

spin wave spectroscopy [4]. The latter could be an easy to handle alternative to optical methods, but is limited

to lower wave vector number (k) values and sensitivity.

The aim of this work is to analyse and model theoretically the inductance spectra of magneto-static spin

waves of Damon-Eshbach type in FM/HM bilayers obtained by coplanar waveguides. In this way it is possible

to understand the applicability of the method to measure the D value and obtain method limitations as

sensitivity at a given signal-to-noise-ratio, minimum k value, D uncertainty, maximum damping factor, etc..

The method used follows the analysis of Vlaminck and Bailleul [5] of a meander shaped ground-signal-

ground (GSG) waveguide deposited directly on the bilayer sample. It employs the surface permeability, as

introduced by Emtage [6], in order to obtain self-and mutual inductance, which contain directly information

about the non-reciprocity and are comparable with the electrical measurement. The model accounts for the

magnetic field discontinuity across the antenna by the difference of surface permeabilities above and below

the antenna. This formulation is extended to include DMI in the permeability tensor which leads to a k

dependent term in the permeability tensor. The model neglects exchange interaction (second derivatives of the

magnetization) and anisotropy, both reasonable assumptions for the experimental conditions. The results show

that the electrical spin wave measurement is a valid alternative to BLS under certain conditions.

[1] M.Kostylev, JAP 115, 233902, 2014, doi:10.1063/1.4883181

[2] K.Di, et al., PRL 114, 047201, 2015, doi:10.1103/PhysRevLett.114.047201

[3] H.S.Koerner, et al., PRB 92, 220413(R) , 2015, doi:10.1103/PhysRevB.92.220413

[4] J.M.Lee, et al., NanoLett. 16, 62, 2016, doi:10.1021/acs.nanolett.5b02732

[5] V.Vlaminck and M.Bailleul, PRB 81, 014425, 2010, doi:10.1103/PhysRevB.81.014425

[6] P.R.Emtage, JAP 49, 4475, 1978, doi:10.1063/1.325452


P16 89

Engineering of Sputter Deposited YIG - A Comprehensive Protocol for Ultra-

low Damping Magnetic Thin Films

Simon Mendischa, Martina Kiechlea, Valentin Ahrensa, Adam Pappa,b, Markus Becherera

a Technical University of Munich, Germany b Pázmány Péter Catholic University, Budapest, Hungary

We present a full fabrication recipe for Yttrium Iron Garnet (YIG) thin films, deposited by RF magnetron

sputtering on Gadolinium Gallium Garnet (GGG) substrates. The experiments result in reproducible Gilbert

damping values down to 1.1∙10-4 and a saturation magnetization as high as 118.2 kA/m (148.6 mT). Various

process parameters such as working pressure, substrate temperature, magnetron distance and power, as well as

the post deposition annealing profiles are altered. The acquired magnetic properties, i.e. saturation

magnetization, damping and frequency independent linewidth broadening, are extracted by in-plane and

perpendicular broadband Ferromagnetic Resonance (FMR). In in-plane configuration, field linewidths >

0.3 mT are obverved for frequencies below 5 GHz. For perpendicular applied bias fields, FWHM linewidths

in the range of 0.5 mT are obtained, respectively. Furthermore, hysteresis measurements are conducted by

means of magneto optical Kerr effect (MOKE). The Q-factor of the reported fabrication process is validated

for YIG film thicknesses down to 20 nm so far. The topographical properties of the respective samples are

inspected by confocal laser scanning microscopy (CLSM) and atomic force microscopy (AFM). Substrate

surface investigations reveal extensive scratches originating from chemical mechanical polishing (CMP)

during fabrication. Unexpectedly, those do not affect the magnetic properties extracted from broadband FMR

measurements of the deposited YIG thin films. Since the dimensions of the CMP scratches are much smaller

than the overall characterized film area, we speculate their effect is imperceptible in the measurement data. As

structuring the YIG area is of large interest for spin wave devices, this could potentially become an issue when

downscaling to the order of the scratch dimensions.

Figure 1: In-plane Ferromagnetic Resonance Measurement data of a 100 nm thick YIG thin film

on GGG. The left plot shows the Kittel fit to the resonance peaks and right plot illustrates the

obtained field linewidths extracted for the respective frequencies.


P17 90

Micromagnetic study of skyrmions in magnetic multilayers

Anna Giordanoa, Riccardo Tomasellob, Stefano Chiappinic, Mario Carpentierid, Bruno Azzerbonia,

G.Finocchioa

a University of Messina, Italy b Foundation for Research and Technology - Hellas Irákleion, Crete, Greece

c Istituto Nazionale di Geofisica e Vulcanologia, Roma, Italy dPolitecnico di Bari, Italy

Magnetic skyrmions are topologically-protected magnetization textures characterized by a non-trivial

topology [1]. Skyrmions are usually obtained in presence of the DMI, arising in systems lacking or breaking

the inversion symmetry [1]. Recently, a growing interest have been devoted to magnetic multilayers [2–4],

where tiny “hybrid skyrmions” can be stabilized at room temperature in absence of DMI. Such “hybrid

skyrmions” are characterized by a thickness-dependent reorientation of their domain wall chirality and the

equilibrium configuration depends on the interplay between dipolar interactions and DMI. In addition,

theoretical studies have pointed out that SHE-driven skyrmion motion in these multilayers is characterized by

a skyrmion Hall angle (SHA) dependent on the value of the DMI and/or on the number of repetitions of the

ferromagnetic layer [3,5]. Therefore, by proper designing the IDMI and/or the number of repetitions, it is

possible to achieve a zero SHA.Here, we micromagnetically investigate a squared 500x500nm2 multilayer

characterized by 20 ferromagnetic repetitions, similarly to experimental studies [6]. At zero DMI, when the

dipolar interactions are the dominant energy term, the hybrid skyrmion has a chirality going from an outward

Néel skyrmion in the top layer to a Bloch skyrmion in the middle layer and to an inward Néel skyrmion in the

bottom layer. On the other hand, when the IDMI is increased, the Bloch skyrmion is shifted towards the upper

layers, until, beyond a threshold IDMI value, a pure Néel skyrmion is obtained along the whole thickness [3,4],

as observed in Figure 1. We have performed also micromagnetic simulations as a function of the number of

ferromagnetic repetitions, finding similar results.

Figure 1: Pure Néel skyrmion. (a) Cross-sectional view of the 20-repeat multilayer. (b) – (d)Spatial distribution

of the magnetization for different layers (top, middle, bottom).

[1] G. Finocchio et al., J. Phys. D. Appl. Phys. 49, 423001 (2016).

[2] S. A. Montoya et al., Phys. Rev. B 95, 024415 (2017).

[3] W. Legrand et al., Sci. Adv. 4, (2018).

[4] W. Li et al., Adv. Mater. 31, 1807683 (2019).

[5] I. Lemesh and G. S. D. Beach, Phys. Rev. B 98, 104402 (2018).

[6] A. Soumyanarayanan et al., Nat. Mater. 16, 898 (2017).


P18 91

Phase-resolved imaging of non-linear spin-wave excitation at low magnetic bias

field

Rouven Dreyera, Lea Apela, Niklas Liebinga, Georg Woltersdorfa

a Martin Luther University Halle-Wittenberg, Institute of Physics, Von-Danckelmann-Platz 3, 06120 Halle

(Saale), Germany

Recently it was shown that the prediction of the non-linear spin-wave excitation in the framework of Suhl

instability processes is not adequate at low magnetic bias fields. In particular, it was shown by spatially

averaged and time-resolved x-ray ferromagnetic resonance spectroscopy that in the low field regime non-linear

spin waves are excited parametrically at 3/2 of the excitation frequency [1].

Here we demonstrate the 3/2 ω non-linear spin-wave (NLSW) excitation in Ni80Fe20 microstructures using

time-resolved table-top magneto-optical microscopy. We have developed a novel variant of scanning magneto-

optical microscopy which we term super-Nyquist sampling microscopy (SNS-MOKE) [2]. This technique

allows for phase-resolved imaging of the sample at arbitrary frequencies. In this way we detect the

parametrically excited NLSWs at 3/2 ω of the excitation frequency in space and time directly. The

corresponding wave vectors obtained from the two-dimensional Fourier transformation of the observed spin-

wave pattern at 3/2 ω and higher harmonics are in agreement with the theoretical predictions from Bauer et al.

[1].

Our results are further supported by micro focus Brillouin light scattering (µBLS) experiments and NV-

center photoluminescence spectroscopy performed in the same samples.

[1] H. G. Bauer et al., Nat. Commun. 6:8274 (2015)

[2] R. Dreyer et al., arXiv:1803.04943 [cond-mat.mes-hall] (2018)


P19 92

Electric field effects on magnetostatic modes in a hollow cylinder

P. Ansalone(a), C. Beatrice(a), S. Dobák(a,b), F. Fiorillo(a) and V. Basso(a)

(a) Istituto Nazionale di Ricerca Metrologica, Strada delle Cacce 91, Torino, Italy (b) Institute of Physics, P.J. Safarik University, Park Angelinum 9, Kosice, Slovakia

There has been recently a renewed interest on the effects of the electric field on spin waves in ferromagnetic

insulators [1]. In particular it is expected that spin waves would acquire a phase when traversing a region with

an electric field perpendicular to both the magnetization direction and the wave packet direction, as it occurs

in the Aharonov-Casher effect for a particle with a magnetic moment [2]. The exploitation of the phase change

would give interesting possibilities to build magnonic devices based on the phase interference effect [3]. The

physics of the phase change is related to the conservation of the total momentum given by the sum of kinetic

and electromagnetic ones, the last one being proportional to the transverse electric field. In the present paper

we study the properties of the dispersion relation for spin waves in the geometry of a hollow cylinder

magnetized along the z axis. We show that the magnetostatic modes along the circumference are localized at

the inner and outer lateral surfaces and have properties similar to the Damon Eshbach-type surface waves [4].

We finally introduce the electric field effects and analyze the conditions for constructive and destructive

interference of the spin waves. The effect of a radial electric field Er on the dispersion relation is a shift along

the wave-number of the quantity LEr/c2, where L is the gyromagnetic ratio and c is the speed of light. The

results will be compared with experiments of ferromagnetic resonance in soft ferrite rings subjected to

radiofrequency excitation on coaxial transmission lines [5].

[1] K. Nakata et al. Phys. Rev. B, 90, 144419 (2014).

[2] Y. Aharonov and A. Casher, Phys. Rev. Lett. 53, 319 (1984).

[3] X. Wang et al, J. Appl. Phys. 124, 073903 (2018).

[4] D. D. Stancil and A. Prabhakar, Spin Waves, Springer, New York (2009).

[5] F. Fiorillo, Measurement and characterization of magnetic materials, Elsevier, (2004).


P20 93

Spin pumping and spin wave damping in low damping Co25Fe75 heterostructures

Luis Flackea,b, Lukas Liensbergera,b, Matthias Althammera,b, Hans Huebla,b,c,d, Stephan Geprägsa,b,

Katrin Schultheisse, Aleksandr Buzdakove, Tobias Hulae, Helmut Schultheisse, Eric Edwardsf, Hans

T. Nembachf, Justin M. Shawf, Rudolf Grossa,b,c,d, Mathias Weilera,b

a Walther-Meißner Institute, Bayerische Akademie der Wissenschaften, Garching, Germany b Physics Department, Technichal University of Munich, Garchin, Germany

c Nanosystems Initiative Munich, Munich, Germany d Munich Center for Quantum Science and Technology (MCQST), Munich, Germany

e Helmholtz-Zentrum Dresden Rossendorf, Dresden, Germany f Quantum Electromagnetics Division, National Institute of Standards and Technology, Boulder, CO, USA

Spin wave propagation plays an important role in magnonics, where quantized magnetic excitations are

used as information carriers. A crucial parameter for the spin wave propagation length is the magnetic Gilbert-

damping constant. Itinerant ferromagnets offer advantages for magnonics and spintronics, but typically suffer

from drastically higher damping than insulating ferrimagnets. Motivated by the work of Schoen et al. [1], we

investigated Co25Fe75-heterostructures and analysed their Gilbert damping using broadband ferromagnetic

resonance spectroscopy.

Using different thicknesses for the ferromagnet and different seed and cap layers (e.g. Pt and Ta), we

systematically investigated the spin pumping contribution to the Gilbert damping. From these measurements,

we extrapolated the intrinsic damping of the magnetic alloy. From our results we find an optimal approach to

obtain low 10-4 Gilbert damping in Co25Fe75. The performance of Co25F75-based magnonic devices is evaluated

by microfocused Brillouin-Light-Scattering, which spatially resolves the magnetization dynamics. In our

nanopatterned devices, we find spin wave propagation lengths in agreement with the Gilbert-damping for

corresponding plain films. Our results confirm that Co25Fe75 thin films are ideal candidates for future magnonic

devices and pave the way for novel functionalities.

Financial support by Deutsche Forschungsgemeinschaft via projects WE5386/4, WE5386/5 and

Germany’s Excellence Strategy EXC-2111-390814868 is gratefully acknowledged.

__________________________

[1] M.A.W. Schoen, Nat. Phys 12, 839 (2016).

Figure 1: a) Spin pumping contribution and intrinsic Gilbert damping vs. 1/t. of investigated

Co25Fe75-heterostructures with different ferromagnet thicknesses t. b) Experimentally

determined spin wave propagation length vs. frequency in a 26 nm thick Co25Fe75 magnonic

wave-guide.


P21 94

Pulsed laser deposition of yttrium iron garnet thin films towards minimum

magnetic damping

J. D. Costaa, S. A. Bunyaevb, F. Amarc, D. Tiernoa, G. Talmellia, M. Dekkersd, G. Kakazeib, T.

Devolderc, F. Ciubotarua, C. Adelmanna

a IMEC, Leuven, Belgium b IFIMUP-IN, Departamento de Física, Universidade do Porto, Porto, Portugal

c CNRS, Centre de Nanosciences et de Nanotechnologies, Paris, France d Solmates B.V., Enschede, Netherlands

Yttrium iron garnet (YIG) is the reference material for magnonic applications due to its very low magnetic

Gilbert damping (α). This allows for spin wave lifetimes of hundreds of ns and propagation lengths of the order

of mm. Furthermore, its insulating nature prevents eddy current losses and parasitic effects and effectively

decouples electrical and magnetic effects. The downscaling of magnonic devices requires high quality thin

films (thicknesses < 100 nm) that preserve their spin wave propagation properties.

Pulsed laser deposition (PLD) is an outstanding technique for the deposition of YIG thin films as it allows

for nm thickness control as well as epitaxial and stoichiometric deposition leading to very low magnetic

damping below 1 × 10−4. It has been observed that the highest quality films require deposition in an O2

atmosphere. Moreover, most reports indicate that post deposition annealing is necessary to achieve well

crystallized films. Yet, the effects of laser energy, deposition pressure, deposition temperature, annealing

temperature, and the interplay between them are not well understood.

To obtain the full picture of YIG PLD growth, we performed a thorough study of the deposition and

annealing parameters on YIG film properties. Such properties include dynamic and static magnetic

characterization, crystal structure, and stoichiometry. In particular, an in-depth ferromagnetic resonance

(FMR) analysis was used to compare YIG films with very low magnetic damping. It was observed that a high

temperature annealing (800 – 900 C) is needed to achieve state-of-the-art YIG films. Nevertheless, during

crystal growth an intermediate deposition temperature (650 °C) optimizes the film quality. In fact, a higher

deposition temperature hampers the optimal growth for magnonic applications. The laser energy, frequency

and deposition pressure also affect the ablation plume and thus the film quality.

This work enables a more complete understanding of the effect pulsed laser deposition parameters on

nanometric YIG films. Such comprehension is a significant step towards scalable magnonic applications.


P22 95

Chiral excitations of magnetic droplet solitons driven by their own inertia

, J. bPirro, P. c, S.A.H. Banouazizic, M. AhlbergcS. Chung, a, M. Saghafia,bMorteza Mohsenia, and Majid Mohsenic,dÅkerman

aFaculty of Physics, Shahid Beheshti University, Evin, Tehran 19839, Iran bFachbereich Physik and Landesforschungszentrum OPTIMAS, Technische Universität Kaiserslautern,

67663 Kaiserslautern, Germany cMaterials and Nano Physics, School of Engineering Sciences, KTH Royal Institute of Technology, Electrum

229, 164 40 Kista, Sweden d Department of Physics, University of Gothenburg, Fysikgränd 3, 412 96 Gothenburg, Sweden

Inertial effects of magnetic solitons play a crucial rule on their dynamics and stability. However,

governing their inertial effects is a challenging task for their use in real devices. Here, we present the

observation of the inertial effects of magnetic droplet solitons and we show how these effects can be controlled.

Magnetic droplets are strongly nonlinear and localized auto-solitons which can form in spin torque nano

oscillators (STNOs) with large prependecular magnetic anisotropies [1]. Droplets can be considered as

dynamical particles with an effective mass [2]. We demonstrate that the dynamical droplet bears a second

excitation under its own inertia. These excitations which comprise a chiral profile and appear as sidebands to

the main droplet frequency, emerge when the droplet resists the force induced by the Oersted field of the

current injected into the nanocontact (NC). We show how to control these chiral modes with the current and

the field.

Fig. 1: A) Schematic of the system under study and the droplet nucleation under the NC; B) STNO

frequency versus the applied current indicating the presence of the sidebands to the droplet frequency; C)

Frequency spectrum of the system when Idc = - 6.5 mA extracted from (B).

[1] S. M. Mohseni et al., Science. 339, (2013) 1295–1298.

[2] L. D Bookman, M.A Hoefer, .Proc. R. Soc. A 471 (2015) 20150042.


P23 96

Nonlinear magnetization dynamics in yttrium iron garnet microstructures

Morteza Mohsenia, Martin Keweniga, Thomas Brächera, Burkard Hillebrandsa, Andrii Chumaka, and Philipp

Pirroa


67663 Kaiserslautern, Germany

The use of spin waves (SWs) and their quanta, the magnons opens many opportunities in wave-based data

processing units [1]. Owing to their low magnetic losses, yttrium iron garnet (YIG) films are known as the

most promising hosts for SWs. However, downscaling YIG films to nanometer sizes is a necessary task for

the realization of the SW based devices [2]. Here, we present linear and nonlinear magnetization dynamics in

microstructured waveguides of YIG with nanoscale thickness. Using microfocused Brillouin light scattering

spectroscopy (µBLS), we characterize the direct excitation of different waveguide modes using a simple stripe-

line antenna. In addition, we investigate experimentally the parallel parametric amplification of thermal spin

waves in such structures [3]. Our results indicate that, the expected low threshold of the parametric instability

in YIG are preserved in microstructures. Our experimental results are compared to micromagnetic simulations

to clarify the role of the excitation source and the potential contribution of high wave vector magnons. Our

study paves the way for the realization of integrated magnonic circuits.

Fig. 1: (a) Frequency spectrum of a microstructured (1 µm wide, 85 nm thick) YIG waveguide under

parametric pumping, red curve indicates the experimental results from µBLS, while the blue curve are the

results from micromagnetic simulations, (b) SWs dispersion of the same system under pumping obtained from

micromagnetic simulations.

[1] A.V. Chumack, et al, Nat. Phy. 11 (2015), 453–461.

[2] A.V. Chumack, et al, J. Phys. D: Appl. Phys. 50 (2017) 244001.

[3] T. Brächer, et al, Physics Reports 699 (2017) 1–34.


P24 97

Relation between unidirectional spin Hall magnetoresistance and spin current-

driven magnon generation

I.V. Borisenko1, 2, V.E. Demidov1, S. Urazhdin3, A.B. Rinkevich4, and S. O. Demokritov1,4

1Institute for Applied Physics and Center for Nanotechnology, University of Muenster, 48149 Muenster,

Germany

2Kotel’nikov Institute of Radio Engineering and Electronics, Russian Academy of Sciences, 125009

Moscow, Russia

3Department of Physics, Emory University, Atlanta, Georgia 30322, USA

4Institute of Metal Physics, Ural Division of RAS, Yekaterinburg 620108, Russia

Injection of spin current into a ferromagnetic (FM) layer can influence the static and the dynamic

magnetization states of the latter. A particularly notable aspect of spin-orbit interaction induced effects in

FM/NM bilayers is their unidirectionality. For instance, for a given direction of the static magnetization, one

polarity of the electrical current results in strong enhancement of magnetic fluctuations in the FM layer, while

the opposite polarity results in their moderate suppression [1]. This dependence is reversed if the direction of

the magnetization is reversed.

The spin Hall magnetoresistance is believed to originate from the backflow of spin current from FM to

NM. While the dependence of resistance on the magnetization direction for this effect differs from AMR, both

are uniaxial – the resistance is symmetric with respect to the reversal of the magnetization or the current

direction. In contrast, the recently discovered unidirectional spin Hall magnetoresistance (USMR) [2] is

determined by the product (j × ��)𝐌, where j is the density of the electric current, M is the magnetization of

the FM layer, and �� is the unit vector normal to the plane of the bilayer. Consequently, USMR changes sign

when either the magnetization or the electric current is reversed.

We perform electronic measurements of unidirectional spin Hall magnetoresistance (USMR) in a

Permalloy/Pt bilayer, in conjunction with magneto-optical Brillouin light spectroscopy of spin current-driven

magnon population. We show that the current dependence of USMR closely follows the dipolar magnon

density, and that both dependencies exhibit the same scaling over a large temperature range of 80-400 K. These

findings demonstrate a close relationship between spin current-driven magnon generation and USMR, and

indicate that the latter is likely dominated by the dipolar magnons [3].

[1] V. E. Demidov, S. Urazhdin, E. R. J. Edwards, M. D. Stiles, R. D. McMichael, and S. O. Demokritov,

Phys. Rev. Lett. 107, 107204 (2011).

[2] C. O. Avci, K. Garello, A. Ghosh, M. Gabureac, S. F. Alvarado & P. Gambardella, Nat. Phys. 11, 570

(2015).

[3] I. V. Borisenko, V. E. Demidov, S. Urazhdin, A. B. Rinkevich, and S. O. Demokritov Appl. Phys. Lett.

113, 062403 (2018).


P25 98

Signature of impurity scattering in the spin susceptibility of

topological insulator thin film Mahroo Shiranzaeia, Jonas Franssona, Fariborz Parhizgara

a Uppsala University, Uppsala, Sweden

Spin-orbit coupling (SOC) together with ferromagnetism can give rise to quantum anomalous Hall effect

(QAHE) which is a significant topological phenomenon and a key to the next generation of spintronic devices.

Topological insulators (TI) with a large SOC are reported as a good promising host material for the realization

of QAHE. Many studies have been done on QAHE but fundamental questions about the origin of

ferromagnetism in TI thin film have remained. An important proposal is that such ferromagnetism can come

from the Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction between unavoidable magnetic impurities

inside the systems but the controversial question is why such alignment has been seen for some magnetic

impurities and not for all of them. Since the different terms of the RKKY interaction in TI thin film read from

the response function of spin susceptibility of the system, in our work, we generalize the conventional

definition of the spin susceptibility by using the T-matrix approach to capture how the impurity states can

affect the spin susceptibility [1]. To do that, we consider a single impurity as H=u σ0+m⋅ σ where u and m

are electrostatic and magnetic scattering potentials of an impurity. As a consequence of these scattering

potentials, at least two spin-polarized peaks induce inside the gap which their properties depend on the strength

of scattering potentials and are tunable with respect to the applied electric potential [2].

Figure 1: Heisenberg-like coupling as a function of scattering potentials (u, m). Panels (a-f) relate to V=0,

R=30 Å and different Fermi energies; -35, -30, -25, -10, 0, 35 meV respectively.

Our results argue the importance of going further linear response theory to obtain magnetic susceptibility.

According to pop up induced peaks in spin local density of states, the jump behaviour of coupling occurs for

the energy range between these two peaks which shows an inter-band behaviour of the response function.

Moreover, for some critical value of impurity’s potentials, a transition of anti-ferromagnetic to ferromagnetic

order happens which is a necessary requirement for the realization of Quantum anomalous Hall experiment in

this system. Figure (1) illustrates one of our results of Heisenberg-like coupling between two impurities in the

plane of u and m for different values of Fermi energy which experience AFM to FM transition.

In the next step, we want to use our previous results on the interaction between magnetic impurities and obtain

magnon dispersion describing spin deviation on the surface of the topological insulator by using the Schwinger

boson transformation.

[1] M. Shiranzaei, et. al., Phys. Rev. B 97, 180402(R).

[2] M. Shiranzaei, et. al., Phys. Rev. B 95, 235429.


P26 99

Domain wall dynamics driven by currents along strips formed by

antiferromagnetically coupled systems

E. Martíneza, V. Raposoa, Ó. Alejosb

a Dpto. Física Aplicada, University of Salamanca, Plaza de los Caídos S/N, 37007, Salamanca, Spain b Dpto. Electricidad y Electrónica, University of Valladolid, E-47011 Valladolid, Spain

The development of racetrack memories has attracted much interest in the recent times. [1] Many efforts

have been addressed in that way, particularly, the finding of optimal systems allowing fast displacement of

domain walls along them. Interfacial effects such as the Dzyaloshinskii-Moriya interaction, along with the

generation of spin currents through the Spin-Hall effect constituted a major step to this target. Furthermore,

recent experimental evidence shows that domain wall velocities as fast as 1km·s–1 can be achieved along strips

formed by antiferromagnetically coupled bilayers. [2] Additionally, it has been found under certain conditions

a linear relationship between domain wall speeds and current magnitudes, as also occurs in the case of certain

ferrimagnetic alloys, where spins interact antiferromagnetically. [3]

Based on these promising experimental results, we provide full micromagnetic studies dealing with such

antiferromagnetically coupled systems. Our micromagnetic simulations treat them as constituted by two

subsystems, either two ferromagnetic layers or two ferromagnetic sublattices in alloys, coupled by means of

an additional intersystem exchange interaction. Some other interactions are accounted for in different manners

within each subsystem, depending on its considered physical structure. As major findings of these simulations,

we can quote the dragging mechanism in bilayers, resulting in a vanishing domain wall tilting, a mechanism

that allows synchronous tracking of domain walls, even along curved paths. Besides, the angular moment

compensation in ferrimagnetic alloys is confirmed as responsible for the linear increase with current of domain

wall velocities in these compounds.

Our micromagnetic simulations are also backed up with the help of an extended one-dimensional model,

[4] that, differently from previous approaches to these systems, based on effective parameters, also considers

systems as formed by two coupled subsystems with experimentally definite parameters. Such approach permits

to infer results not achievable from the mentioned effective models, that can be of relevance in the development

of future experimental setups.

[1] Parkin, S. S. P., Hayashi, M., Thomas, T. Science 320, 90 (2008)

[2] S. H. Yang. Nat Nanotechnology, 10, (3), 221-6 (2015).

[3] Saima A. Siddiqui. Phys. Rev. Lett. 121, 057701 (2018).

[4] O. Alejos et al. Journal of Applied Physics 123, 013901 (2018)


P27 100

Broadband transverse magnetic properties in multiferroic Co-Y hexaferrite

Pablo Hernández-Gómeza, Daniel Martín-Gonzáleza,. Carlos Torresa, José María Muñoza

a University of Valladolid, Valladolid, Spain

Noncollinear spin systems have attracted significant interest in recent research activities, as they show

several unusual physical phenomena like electric excitation of magnon or magnetic skyrmions, especially the

compounds with magnetically induced ferroelectricty from changes in spiral magnetic ordering within the

crystal because they can present remarkable magnetoelectric effects at room temperature, with potential

applications in ultra-dense magnetic storage devices as well as low power spintronic devices [1,2]..

Single phase multiferroics are of great interest for this new multifunctional devices, being Y-type

hexaferrites good candidates. Transverse susceptibility is obtained when applying a bias DC magnetic field,

while AC applied field and response is measured in a transverse direction. It has been proved to be a versatile

tool to study singular properties of bulk and nanoparticle magnetic systems, especially to obtain their

anisotropy and switching fields. We have developed a fully automated, broadband system based on a LCR,

that allows this measurement in varying ranges of DC and AC applied fields, temperature and frequency with

enhanced sensitivity. Transverse susceptibility measurements have been carried out on Y type hexaferrites

with composition Ba0.5Sr1.5Co2Fe2O22, optimal to exhibit multiferroic properties. Polycrystalline ferrites with

this composition were sintered in 1050º C-1250º C range. Transverse susceptibility measurements in the

temperature range 80-350 K and fields up to ±0.5 T reveal different behaviour depending on the sintering

temperature, and the peak related with anisotropy field exhibit four regions with different slopes: positive in

80-130 K, negative in 130-200 K, constant in 200-280 K and negative in 280-350 K, which can be considered

a signature of spin transitions in this compound.

This work was supported by the Spanish Ministerio de Ciencia Innovación y Universidades, (AEI with

FEDER), project id. MAT2016-80784-P.

[1] T. Kimura, Magnetoelectric hexaferrites, Annu. Rev. Condens.Matter Phys. 3 (2012) 93–110.

[2] K. Zhai, Y. Wu, S. Shen, W. Tian, H. Cao, Y. Chai, B. C. Chakoumakos, D. Shang, L. Yan, F. Wang,

Y Sun, Giant magnetoelectric effects achieved by tuning spin cone symmetry in Y-type hexaferrites,

Nature Communications 8, 519 (2017).

Figure 1: Transverse magnetic susceptibility in Co-Y hexaferrite.


P28 101

Microwave rectification in magnetic tunnel junctions with perpendicular

anisotropy

A. Sidi Elvallia V. Iurchuka, N. Lamarda, A. Chaventa, J. Langerb, J. Wronab, B. Dienya, I. L. Prejbeanua, L.

Vilaa, R. Sousaa and U. Ebelsa

aUniv. Grenoble Alpes, CEA, CNRS, Grenoble INP*, IRIG-Spintec,

38000 Grenoble, France. * Institute of Engineering Univ. Grenoble Alpes bSingulus Technologies AG, Kahl, Germany

Perpendicular magnetic tunnel junctions (pMTJs) are considered as key elements for the development

of the spin transfer torque magnetic memories (STT-MRAM) with high storage density. pMTJs exploit the

interfacial perpendicular magnetic anisotropy (iPMA) which forces the out of plane orientations of the free

(FL) and reference layers (RL) [1]. Meanwhile these junctions are also expected to be suitable for the

microwave spintronic functions (i.e. rf signal generation and detection) [2, 3] providing added value for

multifunctional operation.

Here we report on the microwave signal rectification in MTJs with perpendicular RL and FL induced

by iPMA. The rectified dc voltage Vdc signal arises from the nonlinear coupling between an injected rf

current and the dynamic resistance (induced by the precession of the FL and/or RL magnetization) when the

frequency of the rf current approaches the intrinsic resonance frequency of the FL or RL modes.

Measurements without and with dc current Idc (i.e. passive and active operation regimes) are performed in

the presence of an in-plane static magnetic field (≤1.4 kOe) for the pMTJs with different FL thicknesses

(1.4, 1.6 and 1.8 nm). In the active regime and for moderate currents Idc≤1 mA, the output Vdc voltage lies

in the mV range for all devices indicating the rectification of the STT-induced precession mode. In the

passive regime (Idc≈0) the rectified voltage Vdc increases from ~0.02 mV for 1.4 nm FL to ~2 mV for 1.8 nm

FL (at -5 dBm of external rf power) indicating the crucial role of the effective perpendicular anisotropy of

the oscillating layer given by the competition between the iPMA and the demagnetizing field. Since the

magneto-resistive response is determined by the dynamic out-of-plane magnetization component mz, large

signals are expected when the effective iPMA is small, allowing large variations of mz. In addition we

demonstrate a strong dependence of Vdc on the device size. Upon reducing the diameter of the pMTJs from

150 to 20 nm the rectified Vdc increases by a factor of 3 corresponding to ~7 mV in the passive and ~28 mV

in the active regime at -5 dBm of external power.

These findings give a prospect to utilize pMTJs as nanoscale microwave detectors for power harvesting

and/or wireless sensor networks applications.

The authors acknowledge funding support from the Fondation Nanosciences, Grenoble; from ERC

MagiCAL (N° 669204) and the EU Horizon 2020 project GREAT (No. 687973).

[1] Ikeda, S., et al. Nature Materials 9.9 (2010): 721.

[2] B. Fang, et al, AIP Adv. 6 125305 (2016).


P29 102

Ultra-fast spectrum analysis using spin-torque nano-oscillator

A. Litvinenkoa, V. Iurchuka, P. Sethia, , S. Louisb, V. Tiberkevichb, A. Jenkinsc, R. Ferreirac, B.

Dienya, A. Slavinb and U. Ebelsa

a Univ. Grenoble Alpes, CEA, CNRS, Grenoble INP*, IRIG-Spintec,

38000 Grenoble, France. * Institute of Engineering Univ. Grenoble Alpes

b Oakland University, Rochester, USA c International Iberian Nanotechnology Laboratory (INL), Braga, Portugal

Spin torque nano-oscillators (STNO) are promising for wireless communication schemes due to their

nano-scale size, as well as their broadband and fast (nanosecond range) frequency tunability. So far, only few

system-level applications were experimentally demonstrated using STNOs, such as operation within a phase

locked loop [1] for frequency stabilization or communication using amplitude modulation [2].

Here we have implemented, and experimentally verified a novel application for STNOs which is a fast

spectrum analyser (SA) technique that was proposed in [3] (see Fig.1). The STNO is used as a frequency

tunable local oscillator whose frequency is swept periodically by injecting a saw-tooth signal. The STNO

output (a) is then mixed with the input signal (b) that is to be measured. The mixed signal (c) is processed by

a low pass filter and a matched filter compresses it into a peak (d). The temporal position of the peak is

proportional to the frequency of the measured input signal. For the demonstration of the STNO-SA based on

the mixing principle we have chosen a magnetic-tunnel-junction-based vortex STNO, because of its relatively

fast frequency tuning [4], low phase noise [5] and signal stability. We performed a systematic study on the

STNO-SA performance, demonstrating a maximum scanning rate of 1.5 MHz and a resolution bandwidth

(RBW) that is close to the theoretically predicted one, limited only by the STNO phase noise. To demonstrate

real-time parallel processing at this scanning rate, a matched filter is designed using direct finite impulse

response (FIR) topology and implemented in FPGA Xilinx XC6SLX9.

Financial support is acknowledged from the EC program ERC MAGICAL 669204, the French space

agency CNES, the enhanced EUROTALENT program, as well as from the NSF of the USA Grants Nos.

EFMA-1641989 and ECCS-1708982.

[1] M. Kreißig et al., 2017 IEEE 60th MWSCAS, Boston, MA, 910-913 (2017).

[2] H. S. Choi et al., Sci. Rep. 4, 5486 (2014).

[3] S. Louis et al, Applied Physics Letters 113, 112401 (2018).

[4] M. Manfrini et al, Journal of Applied Physics 109, 083940 (2011).

[5] R. Lebrun et al. Phys. Rev. Lett. 115, 017201 (2015).

Figure 1: Schematic of the ultra-fast spectrum analyzer.


P30 103

Injection locking of spintorque oscillators to arbitrary driving signals

J. Hema, L. D. Buda-Prejbeanua, U. Ebelsa

a Univ. Grenoble Alpes, CEA, CNRS, Grenoble INP*, IRIG-Spintec, 38000 Grenoble, France; * Institute of

Engineering Univ. Grenoble Alpes

Spintorque nano-oscillators (STNO) are frequency tunable, nanoscale devices that will find applications as

integrated microwave signal sources. In order to overcome the problems associated with signal stability

(linewidth and phase noise) a common technique is to mutually synchronize the devices or to injection lock

them to an external rf source. One can distinguish locking to an rf current signal via spin transfer effects and

locking to an rf field. Both concepts have been demonstrated experimentally for different STNO devices and

for different orders n ωg=nωo, with ωg the frequency of external source and ωo the frequency of the STNO [1].

Theoretically, injection locking of STNOs has been addressed by numerical simulations [2] as well as in the

general framework of spinwave theory applied to STNOs [3]. Here we extend the theoretical description of [3]

to determine the exact form of the driving force for the most general cases of injection locking. They are found

to differ depending on (i) conservative and dissipative driving (e.g. via field or current), (ii) the direction of

spin polarization p and field orientation h and (iii) on the harmonic order n. The most general form is an

elliptical driving force ℱ ∝ 𝜀1𝑐𝑜𝑠𝜓 + 𝑖𝜀2𝑠𝑖𝑛 𝜓 with unequal amplitudes of the real and imaginary parts |ε1|

|ε2| and with ψ the phase difference between the signal source and the STNO. Special cases are circular forcing

|ε1|=|ε2|, phase forcing (ε1=0) or power forcing (ε2=0). We demonstrate at the example of a uniform in-plane

magnetized STNO, that all the different cases can occur, for instance elliptical forcing under current and field

at n=1, circular forcing under field at n=2, 3 and power forcing under current for n=2,3. Here ε1 and ε2 depend

only on the free running power po as well as on the ellipticity of the STNO precession orbit. Furthermore, ε1

and ε2 together with the two non-linear parameters ν (non-linear frequency shift) and Γp (amplitude relaxation

rate) determine the four locking parameters that fully describe the injection locked state: locking range 𝛥𝛺,

locking power 𝛥𝛱, phase difference 𝜓0, power angle 𝜓𝑝. ΔΠ and 𝜓𝑝 are new parameters that we introduce for

the full description of injection locking properties. Furthermore, it is demonstrated that the ratio of the power

to phase forcing ε1/ε2 scales the enhancement of the locking range of non-isochronous oscillators as well as

the phase difference ψo at zero detuning and the power angle 𝜓𝑝. Finally, we demonstrate that the derived

equations provide a straightforward means to analyze injection locking to two simultaneous driving signals

such as the damping like aj and field like bj spin transfer torque. In this case the phase difference ψo has a

contribution given by the ratio of the two torque components 𝜓0 = 𝑎𝑟𝑐𝑡𝑎𝑛 (𝜀1,𝑏𝑗

𝜀1,𝑎𝑗

𝑏𝐽

𝑎𝐽) similar to what was found

for vortex STNOs [4].

J. Hem acknowledges financial support from DGA

[1] S. Urazhdin, et al., Phys. Rev. Lett. 105, 104101 (2010) and Phys. Rev. B 82, 020407 (2010); B. Georges,

et al., Phys. Rev. Lett. 101, 017201 (2008) ; M. Quinsat et al., Appl. Phys. Lett. 98, 182503 (2011) ; A.

Hamadeh, et al., Phys. Rev. B 85, 140408 (2012).

[2] M. d’Aquino, et al. Phys. Rev. B 82, 064415 (2010); G. Finocchio, et al., Phys. Rev. B 86, 014438 (2012).

[3] A. Slavin and V. Tiberkevich, IEEE Trans. Magn. 45, 1875 (2009); Y. Zhou, et al., Phys. Rev. B 82, 012408

(2010).

[4] R. Lebrun et al. Phys. Rev. Lett. 115, 017201 (2015).


P31 104

Nanomagnetic Writing for Reconfigurable Magnonic Crystals

Jack C. Gartside1, Daan M. Arroo2, Alexander L. Vanstone1, Kilian Stenning1, Lesley F. Cohen1 &

Will R. Branford1

1 Imperial College London, United Kingdom 2 University College London, United Kingdom

correspondence: [email protected]

Much of the intrigue and utility of magnonic crystal systems arises from the exquisite correspondence between

the high-frequency dynamics and the system-wide magnetic configuration, or microstate.

The number of functional behaviours exhibited by a system is essentially defined by the range of

distinguishable microstates it can support and reliably access. Existing reconfigurable magnonic systems

typically perform very well on the first point, with 2N states common in an N-body system, but stumble at the

second – with often just 2 or 3 microstates reliably accessible.

Nonetheless, impressive results have been demonstrated in these few-state magnonic crystals, but the concept

is prevented from realising its full potential unless reliable means to access the entire microstate space are

developed.

Historically, microstate preparation methods have been somewhat limited – relying on globally-applied or

stripline-generated magnetic fields or stochastic thermalisation protocols to access a limited range of states.

Groups have recently demonstrated that a scanning MFM tip may be used to write all conceivable microstates,

though with the cumbersome caveat that the sample is situated within expensive and cumbersome SPM

hardware.

We present developments and applications of the dynamic magnetic-charge writing method ‘Topological

Defect-Driven Magnetic Writing’ (TMW), outlining a fully solid-state and current-addressable SPM-free

solution replacing the MFM tip with alternative magnetic charge sources.

This improved technique is leveraged to realise novel reconfigurable magnonic circuit elements,

implemented within strongly-interacting nanomagnetic networks.

Top row: MFM images showing hexagonal permalloy nanowire array

before (left) and after (right) nanomagnetic writing

Bottom row: Example microstates (left) and their corresponding spin-

wave spectra (right)


P32 105

Two spin-transfer-torque nano-oscillators coupled via magnetostatic fields

D. Mancilla-Almonacida, Alejandro O. Leonb, R. E. Ariasc, S. Allendea, and D. Altbira

a Departamento de Física, CEDENNA, Universidad de Santiago de Chile, Santiago, Chile b Instituto de Física, Pontificia Universidad Católica de Valparaíso, Valparaíso, Chile c Departamento de Física, CEDENNA, FCFM, Universidad de Chile, Santiago, Chile

During the past years, a great deal of attention has been focused on the study of spin- transfer-torque nano-

oscillators (STNOs), due to their several potential applications in telecommunications, in the implementation

of magnetic field sensors, and recently in neuromorphic computing [1]. While the dynamics of a single

oscillator has been well characterized by the experimental, analytic, and numerical points of view, the behavior

of several coupled elements is not fully understood yet.

In our work, an analytical and numerical study of the nonlinear dynamics of two magnetostatically coupled

spin valves driven by spin-transfer-torques [2] is presented under the macrospin approximation, i.e.,

considering uniform magnetization in each oscillator. In particular, we study the role that the position of the

oscillators plays in the synchronization phenomenon. We observe that for most values of the current density,

the system exhibits a synchronized motion of the magnetizations. In this regime, the difference between the

oscillation phases of the free layers remains nearly zero for an in-phase mode and π for an antiphase mode.

The transition between the two modes is characterized by a mixed-mode state in which both the antiphase and

in-phase modes participate with a finite amplitude of oscillation [3]. These results can be used as one step in

the quest for the design and control of arrays of STNOs.

We acknowledge financial support in Chile from FONDECYT 1161018, 1160198, and 1170781,

Financiamiento Basal para Centros Científicos y Tecnológicos de Excelencia FB 0807 and AFOSR FA9550-

18-1-0438. D. M.-A. acknowledges Postdoctorado FONDECYT 2018, No. 3180416.

[1] N. Locatelli, V. Cros, and J. Grollier, Nat. Mater. 13, 11 (2013).

[2] D. C. Ralph and M. D. Stiles, J. Magn. Magn. Mater 320, 1190 (2008).

[3] D. Mancilla-Almonacid, R. E. Arias, Alejandro. O. Leon, D. Altbir, and S. Allende, Phys. Rev E 99,

032210 (2019).

Figure 1: Two nano-oscillators driven by a spin-polarized current density J and coupled via magnetostatic

fields [3].


P33 106

Tunable Snell’s law for spin waves in heterochiral magnetic films

Jeroen Mulkersa,b, Bartel Van Waeyenbergea, Milorad V. Milloševićb

a Department of Solid State Sciences, Ghent University, Ghent, Belgium b Department of Physics, Antwerp University, Antwerp, Belgium

Thin ferromagnetic films with an interfacially-induced DMI exhibit nontrivial asymmetric dispersion

relations that lead to unique and useful magnonic properties. Here we present an analytical expression for the

magnon propagation angle within the micromagnetic framework and show how the dispersion relation can be

approximated by circular isofrequencies to provide a comprehensible geometrical interpretation in k-space of

the propagation of spin waves.

This comprehensible interpretation is then used to investigate and understand the behavior of spin-wave

packets in heterochiral magnets, such as the reflection and refraction at an interface between regions with

different DMI strengths. We derive a generalized Snell’s law for the non-trivial refraction, which turns out to

be tunable by an applied in-plane magnetic field. In addition to the analytical derivations, we present the results

of full-blown micromagnetic simulations in which spin-waves reflect and refract at DMI interfaces. These

simulation results, which agree strongly with the analytical results, show that the refraction is asymmetric

around the interface normal, leading to the occurrence of negative refraction and asymmetric Brewster angles

(see Fig. 1). The found asymmetric Brewster angles, which are adjustable by magnetic field, support the

conclusion that heterochiral ferromagnetic structures are an ideal platform for versatile spin-wave guides.

[1] J. Mulkers, B. Van Waeyenberge, M. V. Milošević, Phys. Rev. B. 97, 104422 (2018).

Figure 1: Refraction and reflection of wave packets for different incident angles at an

interface with a strong DMI on the left and no DMI on the right, with an applied in-plane

field perpendicular to the interface. The contour plots show the results of micromagnetic

simulations, whereas the analytically predicted propagation directions are depicted by solid

lines.


P34 107

Antiferromagnetic oscillators driven by spin currents with arbitrary spin

polarization directions

Dong-Kyu Leea, Byong-Guk Parkb, Kyung-Jin Leea,c

a Department of Materials Science and Enginnering, Korea University, Seoul 02841, Korea b Department of Materials Science and Engineering and KI for Nanocentury, KAIST, Daejeon 34141, Korea c KU-KIST Graduate School of Converging Science and Technology, Korea University, Seoul 02841, Korea

The spin Hall effect (SHE) describes interconversion between charge currents and spin currents through

the spin-orbit interaction. Previous studies on antiferromagnetic oscillators [1,2] have focused on

antiferromagnet/heavy metal bilayers in which spin current is generated by SHE. Recently, various spin-

current generation mechanisms in addition to SHE have been studied. They include the anomalous Hall effect

[3], spin swapping [4], planar Hall current [5], and interface-generated spin current [6,7]. Spin currents

generated by these mechanisms carry a spin polarization whose direction differs from that originating from the

bulk SHE.

We theoretically and numerically investigate antiferromagnetic oscillators induced by a spin current

carrying an arbitrary spin polarization direction. We find that depending on the spin polarization direction, the

threshold current to excite antiferromagnetic oscillations show a non-monotonic dependence [Fig. 1(a)] and

the oscillation frequency generally increases with current density but shows a slightly different dependence

[Fig. 1(b)]. Moreover, we investigate that how material parameters and imperfections affect properties of

antiferromagnetic oscillators. In the presentation, we will discuss details of oscillating properties.

[1] R. Cheng. et al., Phys. Rev. Lett. 116, 207603 (2016).

[2] R. Khymyn. et al., Sci. Rep. 7, 43705 (2017).

[3] T. Taniguchi. et al., Phys. Rev. Applied. 3, 044001 (2015).

[4] H. B. M. Saidaoui and A. Manchon. Phys. Rev. Lett. 117, 036601 (2016).

[5] C. Safranski et al., Nat. Nano. 14, 27 (2019).

[6] S.-h. C. Baek. et al., Nat. Mater. 17, 509 (2018).

[7] V. P. Amin. et al., Phys. Rev. Lett. 121, 136805 (2018).

Figure 1 : (a) Threshold current density as a function of spin polarization direction. (b) Oscillation

frequency as a function of the current density for different spin polarization direction


P35 108

Quantum spin transfer torque induced by spin shot noise

Alireza Qaiumzadeh and Arne Brataas

Center for Quantum Spintronics, Department of physics, Norwegian University of Science and Technology,

NO-7491 Trondheim, Norway

Recent measurements in current-driven spin valves demonstrate magnetization fluctuations that deviate from

semiclassical predictions. [1] We posit that the origin of this deviation is spin shot noise. On this basis, our

theory predicts that magnetization fluctuations asymmetrically increase in biased junctions irrespective of the

current direction. At low temperatures, the fluctuations are proportional to the bias, but at different rates for

opposite current directions. Quantum effects control fluctuations even at higher temperatures. Our results are

in semiquantitative agreement with recent experiments and are in contradiction to semiclassical theories of

spin-transfer torque. [2]

[1] A. Zholud, R. Freeman, R. Cao, A. Srivastava, and S. Urazhdin, Phys. Rev. Lett. 119 (2017), 257201.

[2] A. Qaiumzadeh and A. Brataas, Phys. Rev. B 98 (2018), 220408(R).


P36 109

Trimming of permalloy stripes to enhance the localized edge mode spectrum

probed by ferromagnetic resonance

Kilian Lenza, Tobias Schneidera,b, Gregor Hlawaceka, Ryszard Narkowicza, Sven Stienena, Attila

Kákaya, Miriam Lenza, Jürgen Fassbendera, Jürgen Lindnera

a Helmholtz-Zentrum Dresden-Rossendorf, Institute of Ion Beam Physics and Materials Research, Dresden,

Germany b Technische Universität Chemnitz, Department of Physics, Chemnitz, Germany

Finite-size effects in ultrathin magnetic films are a well-known feature, i.e., when the surface or interfaces

dominate the volume of the sample due to different roughness, texture, hybridization, modified magnetic

moment, or dipolar fields. For nanostructures these effects could arise at the side walls as well. This leads to

localized spin wave modes (edge modes).

It has been shown that the quality of the side walls (angled side walls or roughness) influence these modes

[1]. During preparation of samples by lithography a certain edge roughness and side wall slope are sometimes

inevitable. Nevertheless, in micromagnetic simulations these contributions are usually excluded from the

model. We show, how successive trimming the sides of a 5 μm x 1 μm Permalloy stripe by a focused Ne ion

beam improves the spin wave spectrum and enhances the edge mode spectrum as probed by planar

microresonator ferromagnetic resonance (FMR) [2,3] as depicted in Figure 1. Including an rms edge roughness

of ~2 nm (within the order of the permalloy grain size) in the simulations is enough to match the FMR data.

Hence, we attribute the residual roughness to the ion induced damage by the lateral penetration during

trimming of the side walls, and a small remaining edge roughness due to changes in the sputter yield for

differently oriented Permalloy grains.

[1] R.D. McMichael et al., Phys. Rev. B 74,024424 (2006).

[2] A. Banholzer et al., Nanotechnology 22, 295713 (2011).

[3] R. Narkowicz et al., Rev. Sci. Instrum. 79, 084702 (2008).

Figure 1: (a) SEM top view of the trimmed Permalloy stripe. (b,c) FMR azimuthal angular

dependence before (b) and after (c) trimming the 4 sides by HIM. Arrows and lines mark

the prominent changes of the edge modes.


P37 110

Oblique spin wave propagation in periodic and quasiperiodic sequences of

stripes

Justyna Rychły, Szymon Mieszczak, Grzegorz Centała, Jarosław W. Kłos

Adam Mickiewicz University in Poznań, Poland

We study how to tune the intrinsic anisotropy of dipolar spin waves in planar geometry by introducing the one-

dimensional (quasi)periodic modulation of material or structural parameters. We investigate numerically the

spin wave propagation in the sequence of stripes ordered in a plane in a periodic or quasiperiodic manner. The

general case of oblique propagation where each spin wave eigenmode can be decomposed to plane wave and

Bloch wave for two orthogonal directions (parallel and perpendicular to the direction of stripes) is considered.

The Plane Wave Method is used to find the dispersion relation which gives us the information about

the magnonic band gaps and allowed directions of propagation. With the aid of the Finite Element Method, we

calculate the spin wave spectrum in the finite sequences of stripes and looked for the surface states.

We are going to show the inverse proportionality between the tangential component of the wave vector

k|| and the spin waves eigenfrequency f (f ~1/ k||) and for lowest eigenfrequency – between k|| and group

velocity vg (vg~1/ k||). While increasing the k|| the spin waves bands become more wide, which is usually

connected with the increase of the interactions between the elements composing the structure. To show this

the additional study for the stripes separated by air gaps of different widths would be presented, in which by

reducing the distance between two stripes, the enhanced coupling between them would be achieved. Similarly,

this tunable interaction effect, which is easily spotted in the bandwidth change, could be obtained in our studied

(quasi)periodic structures by adjusting the k||. Additionally, the existence of surface states in the band gap

regions of spin wave spectra for (quasi)periodic structures in dependence on the value of a tangential

component of wave vector k|| would be shown.

This work has received funding from the National Science Centre Poland grant UMO-2016/21/B/ST3/0452;

J.R. would like to acknowledge the National Science Centre Poland grant - UMO-2017/24/T/ST3/00173.

[1] J. Rychły, J. W. Kłos, M. Mruczkiewicz, and M. Krawczyk, Spin waves in one-dimensional

bicomponent magnonic quasicrystals, Phys. Rev. B 92, 054414 (2015).


P38 111

Configurational entropy of magnetic skyrmions as an ideal gas

R. Zivieria, R. Tomasellob, M. Carpentieric, O. Chubykalo-Fesenkod,

V. Tiberkeviche, G. Finocchioa

a University of Messina, Italy b IACM-FORTH, Greece c Politecnico di Bari, Italy

d ICMM-CSIC, Spain e Oakland University, Rochester, MI, USA

Magnetic skyrmions have a leading role in low-dimensional magnetic systems for their suitable physical

properties and potential applications. New techniques in ferrimagnets and micromagnetic simulations show

that skyrmions exhibit changes of size and deformations with time [1]. The purpose of this study is thus the

determination of configuration entropy due to skyrmion changes of size and deformations as observed in

micromagnetic simulations using a statistical thermodynamic approach. This approach is different from the

ones of previous studies based on classical thermodynamics [2,3].

The method is based on two main ansatz: 1) the skyrmion energy is fitted via a parabola in the vicinity of the

minimum and 2) the skyrmion diameters population follows a Maxwell-Boltzmann (MB) distribution.

Concerning 1), the skyrmion energy is written as E = a (Dsky -D0sky)2 +b and has a parabolic dependence on

skyrmion diameter Dsky, with D0sky the equilibrium diameter, a the curvature and b = Emin the minimum energy.

Regarding 2), from the comparison between micromagnetic and analytical results, we have found that the

skyrmion diameters distribution is of the form dn/dDsky = C Dsky2 exp(-a(Dsky- D0sky)

2/kBT) with C a constant,

kB the Boltzmann constant and T the temperature. This has allowed us to make a strict analogy between the

skyrmion diameters population and the MB distribution of particles in an ideal gas to calculate the skyrmion

entropy S = -kB H0 from the Boltzmann H0 order function at thermodynamic equilibrium. In the special case,

the configuration entropy of a magnetic Néel skyrmion in a Co circular nanodot with out-of- plane

magnetization of radius Rd = 200 nm and thickness t = 0.8 nm has been computed.

We will show the analytically calculated skyrmion configuration entropy as a function of T using the

following parameters at T = 0 K: saturation magnetization MS=600 kA/m, exchange stiffness A=20 pJ/m, i-

DMI parameter D=3.0 mJ/m2, uniaxial anisotropy constant Ku=0.60 MJ/m3, Gilbert damping coefficient

=0.01. Magnetic parameters are scaled with T [4]. S increases with increasing T and decreases with increasing

the external bias field at fixed temperature.

[1] Woo et al., Nat. Comm. 8, 15573 (2017)..

[2] J. Wild et al., Sci. Adv. 3, e1701704 (2017)..

[3] H. Han et al., Mater. Res. Bull. 94, 500 (2017).

[4] R. Tomasello et al., Phys Rev. B 97, 060402 (R) (2018).


P39 112

Analysis of switching times statistical distributions for perpendicular spin-

torque magnetic memories

Massimiliano d’Aquinoa, Valentino Scalerab, Claudio Serpicob

aEngineering Department, University of Naples “Parthenope”, I-80143 Napoli, ITALY

bDepartment of Electrical Engineering and ICT, University of Naples Federico II, I-80125 Napoli, ITALY

Magnetization switching in nanomagnets is the fundamental issue to deal with in order to obtain high

speed and energy-efficient recording devices[1].

To realize fast magnetization switching with greater efficiency, strategies as microwave-assisted

switching[2] and precessional switching[3] have been proposed. In particular, the latter occurs by applying a

field transverse to the initial magnetization and yields much smaller switching times than conventional

switching. However, extremely precise design of the field pulse is required for successful switching. Then, the

equilibrium magnetization is reached after quasi-random relaxation from a high-to low-energy state. This

mechanism is probabilistic even when thermal fluctuations are neglected, but the stochasticity is much more

pronounced when the latter are considered[3]. On the other hand, magnetic recording devices must fulfill strict

reliability requirements in terms of very low write-error rates, which can be realized at expense of the write

process speed.

In this paper, we theoretically analyze the magnetization switching for a single magnetic bit cell subject to

applied field/spin-polarized current pulses and room temperature thermal fluctuations. By using analytical

techniques, we derive expressions for the switching times distribution functions in terms of material,

geometrical and external current/field properties[4]. Numerical simulations (macrospin and full

micromagnetic) are performed to validate the analytical predictions. Fig. 1 reports an example of comparison

between analytical approach, numerical macrospin and full micromagnetic simulations in the case of a

perpendicular spin-torque magnetic random access memory cell.

Figure 1: Switching times probability and cumulative distributions as function of applied current pulse amplitude

computed by analytical theory, macrospin and micromagnetic simulations.

[1] J.-P. Wang, Nature Mater. 4, 191, (2005)

[2] C. Thirion et al., Nature Mater. 2, 524, (2003)

[3] S. Kaka et al., Appl. Phys. Lett. 80, 2958, (2002)

[4] M. d’Aquino et al., J. Magn. Magnet. Mater. 475, 652 (2019)


P40 113

Injection and annihilation of micromagnetic topological defects through domain

walls in cylindrical nanowires

Alexis Wartellea, Beatrix Trappa, Michal Staňoa‡, Christophe Thiriona, Sebastian Bochmannb, Julien

Bachmannb,c, Michael Foersterd, Lucía Aballed, Tevfik O. Menteşe, Andrea Locatellie, Alessandro Salae,

Laurent Cagnona, Jean-Christophe Toussainta, and Olivier Fruchartf

a Univ. Grenoble Alpes, CNRS, Institut Néel, F-38000 Grenoble, France b Friedrich-Alexander Universität Erlangen-Nürnberg, Erlangen 91058, Germany

c Institute of Chemistry, Saint-Petersburg State University, Universitetskii pr. 26, 198504 St. Petersburg,

Russia d Alba Synchrotron Light Facility, CELLS, E-08290 Barcelona, Spain

e Elettra-Sincrotrone Trieste, S.C.p.A., Trieste I-34012, Italy f Univ. Grenoble Alpes, CNRS, CEA, INAC-Spintec, F-38000 Grenoble, France

Topology has awoken a large interest in micromagnetics, but so far, simulations and especially

experimental works have focused on topologically non-trivial textures like skyrmions, and not on

micromagnetic topological defects. There exists only one: the Bloch point, where magnetization vanishes.

While elusive, it is present at rest in a domain wall (DW) type hosted by cylindrical nanowires, the so-called

Bloch point wall (BPW).

In this work, we use shadow XMCD-PEEM to probe the magnetic-field-driven response of BPWs. While

simulations have so far predicted that this DW retains its topology even under large fields, our experimental

results [1] indicate that Bloch points can be created into, or expulsed from DWs under moderate inductions

(below 20 mT). In the latter case, the BPW transforms into the topologically trivial transverse-vortex wall

(TVW), see Fig. 1. This DW’s transverse magnetic moment features a vortex resp. antivortex texture at its

ends.

These transformations challenge the widespread notion of topological protection, and raise the question of

their mechanism, so far undisclosed. In order to answer this question, we performed finite-element-based

micromagnetic simulations of BPWs and TVWs under field, in cylindrical permalloy nanowires. Though we

do not reproduce the BPW-to-TVW transition even at high fields, we do observe the Bloch point’s injection

into the domain wall (initially TVW) above a well-defined threshold in field. Monitoring the simulated

configuration’s topology via its winding number as well as the vortex and antivortex features, we reveal a

dynamical path for the Bloch point’s injection, involving their merging [1].

†Present address: Technical University of Munich, Germany, Department of Physics, Experimental Physics

of Functional Spin Systems, Chair C. Back ‡Present address: CEITEC – Central European Institute of Technology, Brno University of Technology, 612

00 Brno, Czech Republic

[1] A. Wartelle et al., Phys. Rev. B 99 (2019) 024433.

Figure 1: Transmission XMCD-PEEM (only shadow visible) of a NiFe nanowire. a1-2)

BPW pushed to a pinning site with a field Hm without transformation. b1) Same initial

state. b2) A larger field HM leads to motion, pinning, and transformation into a TVW.


P33 114

Excitation of short-wavelength spin waves via spin wave conversion

Takuya Taniguchia, Stefan Mändla, Matthias Kronsederb, Christian Backa, b

a Physik-Department, Technische Universität München, Garching, Germany b Department of Physics, Regensburg University, Regensburg, Germany

Short-wavelength spin waves (SSW) are required to realize nanometer scaled magnonic devices. Since

using coplanar waveguide methods to excite spin waves (SWs) is technically difficult to implement for SSWs,

many alternative methods have been reported [1-3]. However, the investigation of the interaction of SSW and

spin textures is still challenging , which is one of the target topicsof magnonics. We show that the SW

conversion technique is a possible and easy to implement method for the investigation of SSW related

phenomena.

For this, a T-shaped device is designed as shown in figure 1. By locally applying a rf field, a Damon-

Eshbach SW (DESW) is excited and propagates in the DE area. The DESW lead to a precessional motion of

the magnetization in the conversion area and the precession works as secondary antenna for SWs propagating

in the BVW area, which has backward volume SW (BVSW) geometry. Since the dispersion relations of the

two excited SWs are different [4], it is expected to excite shorter-wavelength SWs from longer-wavelength

SW via SW conversion (inset of figure 1).

Micromagnetic simulations are performed using mumax3 [5] by using typical material parameters of

permalloy in the simulation. Typical results are shown in Fig. 2. It is found that the SW is converted in the

conversion area and the wavelength of the BVSW is shorter than that of the DESW. Moreover, we observe

that the node of BVSW depends on the number of nodes of the DESW in the conversion area.

[1] A. V. Chumak et al., Nat. Phys. 11, 453 (2015). [2] S. Neusser and D. Grundler, Adv. Mater. 21, 2927 (2009). [3] S. Wintz et al.,

Nat. Nanotechnol. 11, 948 (2016). [4] B. A. Kalinikos and A. N. Slavin J. Phys. C 19, 7013 (1986). [5] A. Vansteenkiste et al., AIP

Adv. 4, 107133 (2014).

Figure 1: Schematic illustration of SW conversion.

Figure 2: Results of simulations using different structures: the width of DE area is 500 nm

and that of BVW area is (a) 100 nm and (b) 500 nm. Red and blue colour respectively

indicate the positive and negative perpendicular component of magnetization.


P42 115

Magnetic actuated tuning of Winter magnons propagation

D. Osuna Ruiz, A. P. Hibbins, F.Y. Ogrin

University of Exeter, Exeter, UK

Controlling spin wave propagation along domain walls is key to steer them along magnonic circuitry. In

the past, the path of spin waves in confined structures has been successfully controlled by using external

biasing currents or confining them along the edges of shaped nanodots [1] [2]. Confined spin waves along

Bloch domain walls, or so-called Winter Magnons [3], are of special interest due to the natural localization

and uni-directionality of their propagation. The arising and displacement of magnetic inhomogeneities, such

as vortex core and domain walls, allow to steer the spin waves inside the shape, giving more degrees of

freedom. In this work, we use Mumax3 to explore the dynamics of these spin waves under the effects of

external biasing magnetic fields in magnetic thick nano-patches of different common shapes in the vortex state.

We also show how the instantaneous k-vector of the confined spin wave at different positions in the domain

wall is modified moving away from the core. In rounded-corner shapes, we show that an interesting spatial

“down-chirping” effect for spin waves can be enhanced in contrast to sharp corner shapes, and can also be

tuned by applying external biasing magnetic fields. We relate this effect to the inhomogeneous demagnetizing

field transversal to the wall as a consequence of shape anisotropy. The calculation of an expression for the

demagnetizing factors in a non-uniform magnetized and non-ellipsoidal element can be extremely tedious and

non-trivial and therefore, numerical results on particular shapes are preferred. From our numerical results on

very basic thick shapes (squares and triangles), we deduce a simple model that can be used as first

approximation to predict and control all the mentioned effects in these particular but commonly used elements.

Figure 1: Numerical results for the normalized demagnetizing factor transversal to the diagonal upper-right

Bloch wall for different biasing external magnetic fields (solid lines) and our analytical fitting model (dashed

lines). Inset shows the shape of the nano-patch and the direction of the applied field.

[1] K. Vogt et al, Nat. Comm. 5 (2014), 3727.

[2] A. J. Lara et al, Sci. Rep. 7 (2017), 5597.

[3] J. M. Winter, Phys. Rev. 124 (1961), 452.


P43 116

Frequency selective spin-wave valve and phase-shifter

in Damon-Eshbach geometry

Kevin G. Frippa, Fedor B. Mushenoka, Vlad D. Poimanovb, Volodymyr V. Kruglyaka

a University of Exeter, Exeter, United Kingdom b Donetsk National University, Donetsk, Ukraine

The promise of creation of spin-wave based logic devices rests on our ability to excite spin waves with

nanoscale wavelength and then to control their amplitude and / or phase, all on the nanoscale. Au et al

demonstrated that a magnetic nano-element formed above a longitudinally magnetised magnonic waveguide

can act as an efficient spin-wave transducer, valve and phase shifter, each reprogrammable through switching

of the magnetisation in the element [1,2]. Here, we use micromagnetic simulations to extend the concept of

Au et al to the case of a similar system but magnetised orthogonal to the direction of spin-wave propagation,

i.e. Damon-Eshbach geometry. This system demonstrates the ability to control the propagation of spin waves

along the waveguide via magneto-dipolar coupling to the overlaid magnetic nano-element [1,2]. Depending

upon the direction of the magnetisation of the nano-element and waveguide by the bias magnetic field, the spin

waves either can be transmitted or reflected, or absorbed in a controlled manner.

Our observations are explained in terms of the coupling of the discrete spectrum of precessional modes of

the nano-element to the spin-wave continuum in the waveguide, where a frequency dependent non-reciprocity

in transmission is observed when the spin-wave wavelength becomes comparable to the width of the nano-

element. The switching of the confinement region of the magnetic field above or below the waveguide

depending upon the direction of spin-wave propagation leads to a difference in coupling strength to the nano-

element from the stray field, in a rather non-trivial way.

The research leading to these results has received funding from the EPSRC of the UK Project No.

EP/L019876/1 and from the European Union’s Horizon 2020 research and innovation program under Marie

Sklodowska Curie Grant Agreement No. 644348 (MagIC).

[1] Y. Au, M. Dvornik, O. Dmytriiev, and V. V. Kruglyak, Appl. Phys. Lett. 100 (2012), 172408.

[2] Y. Au, E. Ahmad, O. Dmytriiev, M. Dvornik, T. Davison, and V. V. Kruglyak, Appl. Phys. Lett. 100

(2012), 182404.

Figure 1: (a) Transmission coefficient obtained from the micromagnetic simulations is

shown for a waveguide – element separation of 12 nm. (b-c) The system’s dynamics is

shown for a spin wave at 18.8 GHz incident from the left (b) and right (c) hand sides. In

each panel, the top and bottom images show the x-component of the magnetisation and the

z-component of the magnetic field, respectively, at the same instance of time.


P44 117

A fully implicit integration method of the Landau-Lifshitz equation for finite

difference time domain micromagnetics

Kevin G. Frippa, Volodymyr V. Kruglyaka

a University of Exeter, Exeter, United Kingdom

The use of numerical simulations to approximate realistic magnetic materials has been increasing steadily

with improving computational power. In particular, time domain numerical micromagnetic simulations are

used in research fields where time domain dynamic behaviour of the magnetisation is inherent to the studied

phenomena. An example of such a field is magnonics, wihtin which the excitation, propagation, control and

detection of spin waves in structured and / or graded magnetic media and devices are of primary interest.

Furthermore, the error control and intrinsic numerical stability of methods used in micromagnetic simulations

are of importance to ensure the viability of the produced numerical results. Typical studied systems are highly

complex due to the non-linearity of the Landau-Lifshitz equation and the effective magnetic field implicitly

including both the short-range exchange and long-range magnetostatic dipole-dipole interactions. This leads

to a so-called ‘stiffness’ in the numerical integration of the Landau-Lifshitz equation. This effect is

compounded with broadband excitations such as sinc magnetic pulses, a common occurrence in

micromagnetics for computing magnonic dispersion relations. Such problems would benefit from an implicit

integration method. However, in a finite-difference method for the Landau-Lifshitz equation, an efficient fully

implicit scheme is not obvious to implement [1]. Here, we present results for the implementation of an efficient

implicit integration scheme using the trapezoidal method for the solution of the Landau-Lifshitz equation

utilising its Jacobian, optimised with the properties of the finite-difference method.

The research leading to these results has received funding from the Engineering and Physical Sciences

Research Council of the United Kingdom Project No. EP/L019876/1 and from the European Union’s Horizon

2020 research and innovation program under Marie Sklodowska Curie Grant Agreement No. 644348 (MagIC).

[1] Y. Nakatani, Y. Uesaka, N. Hayashi, Jap. J. Appl. Phys. 28 (1989), 2485-2507.

[2] https://www.ctcms.nist.gov/~rdm/mumag.org.html

Figure 1: Our solution of muMAG standard problem 4, field 1, is shown in comparison with

that produced using OOMMF [2].

https://www.ctcms.nist.gov/~rdm/mumag.org.html


P45 118

Performance of Co25Fe75 magnon conduits under the presence of four-magnon

scattering

Tobias Hulaa, Katrin Schultheissa , Aleksandr Buzdakova, Lukas Liensbergerb,c, Luis Flackeb,c,

Mathias Weilerb,c and Helmut Schultheiss a

a Helmholtz-Zentrum Dresden-Rossendorf, Dresden, Germany bPhysik-Department, Technische Universität München, Garching, Germany

c Walther-Meißner Institute, Bayrische Akademie der Wissenschaften, Garching, Germany

We present results on spin-wave transport in ultra-low damping Co25Fe75 magnon waveguides measured

by Brillouin light scattering microscopy (µBLS) [1]. The material`s small Gilbert damping favors both long

propagation distances of spin waves and the excitation of nonlinear processes in a similar range of the applied

excitation power. Using the capability of µBLS to measure incoherent contributions to the spin wave spectrum,

we can link the power dependence of the waveguides transmission coefficient to the occurrence of four-

magnon scattering.

In our experiments, these nonlinear processes can be observed in terms of a broadening of the directly

excited spin waves at the microwave frequency ωRF due to energy redistribution [2]. Line scans acquired along

the waveguide show that the measured linewidth decreases with increasing distance to the antenna which

indicates that the four-magnon scattering is most important above a certain amplitude threshold close to the

antenna. Above this threshold, the transmission coefficient reduces with increasing amplitude of the RF

excitation. By experimental determination of the dispersion relation via phase resolved µBLS for the entire

range of applied pumping powers, no significant changes in the group velocity were observed.

Our results reveal the impact of nonlinear interactions on the spin wave transmission through a metallic

ferromagnet which can be crucial when designing waveguides for magnon based computing.

Financial support from the Deutsche Forschungsgemeinschaft within programme SCHU 2922/1-1 is

gratefully acknowledged. Samples were prepared at the Nanofabrication Facilities (NanoFaRo) at the Institute

of Ion Beam Physics and Materials Research at the Helmholtz-Center Dresden-Rossendorf (HZDR). K.S.

acknowledges funding within the Helmholtz PostDoc Programme.

[1] M. A. W. Schoen et al., Nature Physics 12 (2016), 839-842.

[2] H. Schultheiß et al., Phys. Rev. B 86 (2012), 054414.


P46 119

Spin wave propagation in CoNi multilayer systems

M. Sushrutha, M. Grassib, K. Ait-Oukacic, Y. Henryb, M. Bailleulb, S. Petit-watelotc, D. Lacourc, M.

Hehnc, J.-V. Kima, T. Devoldera, J.-P. Adama

a C2N, CNRS, University of Paris-Sud, University of Paris-Saclay, 91120 Palaiseau b IPCMS, University of Strasbourg, Strasbourg, France

c IJL, University of Lorraine, Nancy, France

Magnonics is an emerging technology for low-power signal transmission and data processing based on spin

waves (SWs) propagating in magnetic materials. Nowadays such SW-based computing concept is discussed

and undergoes benchmarking in the framework of beyond-CMOS strategies, due to its nanometer wavelengths

and Joule-heat-free transfer of spin information over macroscopic distances. Majority of the SW studies has

been conducted using insulators or in-plane magnetized metallic thin films. Compared to insulators, the

metallic magnetic thin films are of main interest because of well controlled properties in the thin films and

easier coupling to CMOS integrated circuits. However despite these obvious advantages, the studies on SW

propagation in metallic PMA films are still rather scarce. One of the main reason is due to higher damping in

PMA systems resulting in shorter SW propagation lengths.

In this work we demonstrate SW propagation in PMA systems having a potential towards energy efficient

low power option. We develop an all electrical experiment to perform the phase-resolved spectroscopy of

propagating magneto-static forward volume spin waves (MSFVSW) in micrometer sized Co (0.2nm) Ni

(0.6nm) (61 repetitions) 50nm thick SW conduits with perpendicular magnetic anisotropy. Using FMR

technique, the damping parameter of the blanket film was determined to be 0.015. The MSFVSW are excited

and detected by 200 nm wide CPW antennas. We also developed an analytical model which accounts for the

main features of the apparatus transfer functions.

Figure 1: (a) Experimentally obtained FMR trace at 10GHz for a blanket CoNi multilayer

film. (b) Analytically calculated dispersion relation (wavevector vs frequency) for

magnetostatic forward volume spin waves in CoNi multilayer system for different given

magnetic field values. (c) Macroscopic view of the fabricated device showing the contacts,

CPW antennae and CoNi SW conduits.


P47 120

Spin-wave phase shifter on the YIG-VO2 structure

Aleksei A. Nikitin, Vitaliy V. Vitko, Andrey A. Nikitin, Alexey B. Ustinov,

Boris A. Kalinikos

St.-Petersburg Electrotechnical University “LETI”, St.-Petersburg, Russia

For a long time, the microwave devices utilizing excitation and propagation of spin waves (SW) in ferrite

films and layered structures attract a considerable attention. This attention is particularly determined by a

possibility to electronically tune SW dispersion. One possible way to tune the SW dispersion utilizes an

influence of perfectly conductive plane on propagation characteristics of surface magnetostatic waves.

However, the key issues inherent to microwave applications of the above-mentioned tuning mechanism are

associated with a necessity of precise control of a conductor position and a slow time response. In order to

tackle the problems, the investigations of an influence of conductivity on the microwave properties of magnetic

multilayers are relevant [1, 2]. Our recent work [3] was devoted to a novel SW tuning mechanism, which was

achieved owing to the controllable variation of the VO2 conductivity in the ferrite-dielectric-VO2 structures.

The purpose of the present work is to enhance a tunability efficiency and decrease the insertion losses of a

miniature microwave phase shifter utilizing a metal-insulator transition (MIT) that is shown in Fig. 1а.

A ferrite waveguide consists of an yttrium iron garnet (YIG) film (2) on a gadolinium gallium garnet

substrate (1). A dielectric-metal structure is composed of a SiO2 layer (3) and a VO2 film (4) on a sapphire

substrate (5).

In order to

obtain the

MIT in the

VO2, the

laser pulses

with enough

energy heat

the film and

provide a

drastic

change in the

conductivity

σ4 across the transition range (see Fig. 1b). It is worth mentioning that a thermal insulation of the ferrite film

is achieved due to the intermediate dielectric layer. The dispersion characteristics calculated for various

conductivities of VO2 denoted by the circles are shown in Fig. 1c. The colours of the curves in Figs. 1c and 1d

correspond to the colours of these circles. As is seen, a variation of conductivity provides a shift of the SW

dispersion, which produces wavenumber variation. In addition, it is found that the VO2 conductivity determines

an operating bandwidth of the proposed phase shifter, which broadens with increasing in the VO2 conductivity

(see Fig. 1d). The influences of the physical parameters and geometry of the YIG-VO2 structure on the

tunability efficiency and the damping decrement will be presented at the conference.

[1] M. Mruczkiewicz and M. Krawczyk, J. Appl. Phys., 115 (2014), 113909.

[2] J. Trossman et al., J. Appl. Phys., 125 (2019), 053905.

[3] A. A. Nikitin et al., IEEE Magn. Lett., 9 (2018), 1-5.

Figure 1: Sketch of the ferrite-dioxide vanadium layered structure (a); dependence of VO2

conductivity versus temperature (b); dispersion characteristics (c) and damping decrements

(d) for various VO2 conductivities.


P48 121

Nonlinear frequency response of spin-wave optoelectronic active ring resonator

Aleksei A. Nikitin, Vitalii V. Vitko, Andrey A. Nikitin, Ilya A. Ryabcev, Alexey B. Ustinov, and

Boris A. Kalinikos

St.-Petersburg Electrotechnical University “LETI”, St.-Petersburg, Russia

An interaction of intensive electromagnetic radiation with different nonlinear resonance systems leads to

appearance of a bistable phenomenon. It has attracted a lot of attention due to a variety of the fundamentally

important effects and practical applications. Naturally, the phenomenon manifests itself in the ring systems,

an electrical length of which is large compared to the wavelength of the circulating signal. Nowadays the main

attention has been given to the optical rings. Among them, two nonlinear systems, namely, optical fiber rings

and micro-rings, have been studied (see, e.g. [1, 2]). Only Janantha [3] investigated the “foldover” phenomenon

representing bistable behaviour of the microwave spin-wave rings. It is physically clear that a combination of

the spin-wave and optical waveguides in a feedback ring provides a new type of the nonlinear systems with

various nonlinear phenomena. In this work, the microwave bistability in the active ring resonators (RRs) with

dual spin-wave and optical nonlinearities was investigated. The theory for the nonlinear transfer function of

the active RRs consisting of a spin-wave delay line and a highly nonlinear optical fiber was developed taking

into account both the dispersion and nonlinear properties of the ferrite film as well as the nonlinear properties

of an optical fiber. The bistable behavior of the transmission characteristics of the active RR was analyzed

using the developed theory for the two types of the spin-wave delay lines based on the forward volume spin

waves (FVSWs) and surface spin waves (SSWs). It is shown that an introduction of the highly nonlinear optical

fiber in the active RR based on the FVSW delay line provides compensation of the spin-wave nonlinearity.

However, exactly the same nonlinear optical fiber in the active RR based on the SSW delay line enhanced the

bistability. The transmission characteristics of the particular case of the active RRs consisted of the nonlinear

FVSW or SSW delay lines and linear optical single mode fiber were experimentally measured. It is found out

that a decrease in the attenuation for the FVSW/optical RR resulted in a nonlinear upper-shift of the resonant

frequency. Its maximum value is 71 kHz. In contrast to this, the SSW/optical RR demonstrated a nonlinear

down-shift of the resonant frequency, which was 10.8 kHz. The obtained theoretical results are in good

agreement with the experiment.

[1] S. Li et al., Scientific Reports, 7 (2017), 8992.

[2] V. R. Almeida and M. Lipson, Optics letters, 29 (2004), 2387-2389.

[3] P. A. P. Janantha et al., Physical Review B, 95 (2017), 064422.


P49 122

Spin-wave phase shifter upon a single linear defect

O.V. Dobrovolskiy1,2, R. Sachser1, S.A. Bunyaev3, D. Navas3, V.M. Bevz2,4,

M. Zelent5, J. Rychly5, M. Krawczyk5, R.V. Vovk2,4, M. Huth1, and G.N. Kakazei3

aPhysikalisches Institut, Goethe University, 60438 Frankfurt am Main, Germany bPhysics Department, V. N. Karazin Kharkiv National University, 61077 Kharkiv, Ukraine

cDpto de Fisica e Astronomia, University of Porto IFIMUP-IN, 4169-007 Porto, Portugal dICST Faculty, Ukrainian State University of Railway Transport, 61050 Kharkiv, Ukraine

eNanomaterials Physics Division, Adam Mickiewicz University in Poznań, Poznań, Poland fSynopsys Ltd., Bradninch Hall, Castle Street, EX4 3PL, Exeter

Local modification of magnetic properties in nanoelement is a key to design new-generation of magnonic

devices, in which information is carried and processed via spin waves. One of the big challenge here is to

fabricate simple and miniaturized phase-controlling element with broad tunability. Here, we successfully

realize spin wave phase shifter upon a transmission through a single nanogroove milled by focused ion beam

in a CoFe microsized magnonic waveguide. By varying the groove depth and the in-plane bias magnetic field

we continuously tune the spin wave phase and experimentally evidenced a complete phase inversion. The

microscopic mechanism of the phase shift is based on the combined action of the nanogroove as a geometrical

defect and the lower spin wave group velocity in the waveguide under the groove where the magnetization is

reduced due to the incorporation of Ga ions during the ion-beam milling. Micromagnetic simulations revealed

that the modification of magnetization under the groove should be taken into account to explain such a large

phase shift. Our findings are relevant for a fine tuning of the spin wave phase in magnonic circuits and logic

devices as well as for the generation of spin wave beams by phased-array antennas in spin wave nano-optics.

Fig. 1. Calculated phase shift at 20 GHz as a function of the nanogroove depth for a 45 nm-thick film with the

magnetization Ms in comparison with the cases when a 10 nm thick slice under the groove has a reduced magnetization,

as indicated. The solid line is an average of the calculated curves.

The project is financed by the European Union Horizon 2020 Research and Innovation Program under

Marie Sklodowska- Curie grant agreement No. 644348.


P50 123

Dynamics of a magnon Bose-Einstein condensate in inhomogeneous magnetic

fields

Alexander J. E. Kreila, Pascal Freya, Alexander A. Sergaa, Burkard Hillebrandsa


67663 Kaiserslautern, Germany

A supercurrent is a macroscopic quantum phenomenon, which appears when many bosons (real- or

quasiparticles) are being self-assembled in one quantum state with minimum energy and zero group velocity—

a Bose-Einstein condensate (BEC)—and move as a whole due to a phase gradient imposed on their joint wave

function. This phenomenon is commonly associated with resistant-free electric currents of Cooper pairs in

superconductors, and superfluidity of liquid Helium. For example, in in-plane magnetized Yttrium Iron Garnet

(YIG) ferrimagnetic films a Bose-Einstein condensate (BEC) of spin-wave quasiparticles, magnons, can be

formed even at room temperature if the quasiparticle density exceeds a critical value [1, 2]. The possibility of

supercurrents in such a BEC has been recently reported: a phase gradient, being induced in the BEC wave

function by local optical heating of the YIG-film sample [2–4], propels the long-distance supercurrent transport

of the magnon condensate density over the distance of several hundred micrometres [4].

Here we present another approach to induce magnon supercurrents and to control the transport properties

of a magnon BEC. By applying a direct electric current, which flows through a microstrip line placed near the

surface of the parametrically pumped YIG film, the bias magnetic field is locally modified. Depending on the

current direction, a potential wall or well can be formed in the BEC along the direction of the external magnetic

field Hext. By means of time- and space-resolved Brillouin light scattering spectroscopy, we investigate the

influence of this inhomogeneous magnetic field on the temporal and two-dimensional spatial dynamics of the

magnon BEC with emphasis on the behaviour of a freely evolving BEC, formed after the termination of the

external microwave pumping. The stability of the magnon condensate in magnetically formed potential wells

and the excitation of two-dimensional supercurrents is discussed.

Financial support by the European Research Council within the Advanced Grant 694709

“SuperMagnonics” is gratefully acknowledged.

[1] S. O. Demokritov et al., Nature 443, 430-433 (2006).

[2] A. J. E. Kreil et al., Phys. Rev. Lett. 121, 077203 (2018).

[3] D. A. Bozhko et al., Nat. Phys. 12, 1057-1062 (2016).

[4] D. A. Bozhko et al., arXiv:1808.07407.


P51 124

Slow wave based magnonic diode

M. P. Grassia, M. Geilenb, D. Louisa, M. Mohsenib, M. Hehnc, D. Stoefflera,

T. Brächerb, Y. Henrya, P. Pirrob, M. Bailleula

a Institut de Physique et Chimie de Matériaux de Strasbourg, University of Strasbourg-CNRS, Strasbourg,

France b Fachbereich Physik and Landesforschungszentrum OPTIMAS, Technische Universität Kaiserslautern,

Kaiserslautern, Germany c Institut Jean Larmour, Université de Loraine-CNRS, Nancy, France

In most wave physics systems, dispersion relations are reciprocal, i.e., f(k)=f(-k). The magnetic systems

have the particularity of breaking the time-inversion symmetry and could present, inversely, strong non-

reciprocities [1]. It is the case of spin waves that propagate perpendicularly to the direction of the magnetization

in ferromagnetic asymmetric thin films [2]. We will expose how we have exploited this non-reciprocity in the

case of a ferromagnetic bilayer to fabricate a slow wave based magnonic diode, where the spin waves can

propagate only in one direction because their group velocity is null in the opposed direction.

To prove this particular effect, two antennas have been deposited on a CoFeB/Py bilayer thin film (Fig.

1a). The change of mutual inductance associated to the spin wave propagation has been measured as a function

of the frequency for the two opposite propagation directions (Figs. 1b and 1d). The dispersion relation has

been extracted from this data and compared to micromagnetic simulations (Fig. 1c) and to Brillouin Light

Scattering (BLS) measurements. It is possible to identify a plateau only for the waves traveling to the right

(k>0). Consequently, at higher frequencies the wave propagation is possible only to the left (k<0). This

magnonic diode behaviour is due to the chiral character of the dipolar interaction, which is dominant in this

system. It could be used as a base component in future magnonic devices.

[1] R. E. Camley, Surface Science Reports 7, 103-187, (1987).

[2] O. Gladii et al., Phys. Rev. B 93, 054430, (2016).

Figure 1: (a) Schematic representation of the device used for the inductive measurements.

(b),(d) The spin wave propagation signal between the two antennas depends on its direction.

For frequencies higher than 13 GHz, spin wave propagation signal is measured at the left

(b), but not at the right (d). (c) Dispersion relation extracted from the signal phase (symbols);

the color map shows the results of a micromagnetic simulation.


P52 125

Nonlinear nanoscale spin-wave directional coupler

Q. Wanga, M. Keweniga, M. Schneidera, R. Verbab, B. Heinza,c, M. Geilena, M. Mohsenia, P. Pirroa,

B. Lägeld, C. Dubse, T. Brächera, and A. V. Chumaka

a Fachbereich Physik and Landesforschungszentrum OPTIMAS, Technische Universität Kaiserslautern, D-

67663 Kaiserslautern, Germany b Institute of Magnetism, Kyiv 03680, Ukraine

c Graduate School Materials Science in Mainz, Staudingerweg 9, 55128 Mainz, Germany d Nano Structuring Center, Technische Universitat Kaiserslautern, D-67663 Kaiserslautern, Germany

e INNOVENT e.V., Technologieentwicklung, Prüssingstraße 27B, 07745 Jena, Germany

Magnonics is a promising alternative in view of more-than-Moore computing in which information is

carried by magnons, the quanta of spin waves, instead of electrons [1-2]. The advantages of magnons are

ultrashort wavelengths down to tens of nanometers, ultrahigh frequency up to THz, ultralow losses due to the

absence of Joule heating, as well as their abundant nonlinear phenomena.

In this work, we report on the fabrication of a nanoscale directional coupler from a 85 nm thick Yttrium

Ion Garnet (YIG) film grown by liquid phase epitaxy. A SEM micrograph of the structure with the sizes are

shown in Fig. 1a. The main part of the directional coupler is two adjacent spin-wave waveguides that are

coupled due to the dipolar interaction. Micro-focused Brillouin light scattering (BLS) spectroscopy is used to

detect the spin-wave intensities in the directional coupler and to demonstrate its functionality. Figure 1b shows

that 91% of the output spin-wave energy of frequency f = 3.465 GHz is transferred from the first waveguide,

in which spin wave is excited using U-shaped antenna, to the second waveguide. The output spin-wave energy

of a directional coupler strongly depends on the spin-wave frequency and external field, which imply that it

can be used as a connector, power splitter and frequency multiplexer. Furthermore, a power-dependent

nonlinear switching of the spin-wave path is observed experimentally, which paves the way for all-magnon

data processing, e.g. for the realization of a magnonic half-adder [3].

Fig. 1 a. SEM image of the nanoscale directional coupler with U-shaped microwave antenna under investigation. b. Two-

dimensional spatial map of the BLS intensity at a frequency of 3.465 GHz. The right column shows the spin-wave intensity integrated

over the red dashed rectangular region at the end of directional coupler

[1] A. V. Chumak, V. I. Vasyuchka, A. A. Serga, and B. Hillebrands, Nat. Phys. 11 (2015), 453-461.

[2] Q. Wang, P. Pirro, R. Verba, A. Slavin, B. Hillebrands, and A. V. Chumak, Sci. Adv. 4 (2018),

e1701517.

[3] Q. Wang, R. Verba, T. Brächer, P. Pirro, A. V. Chumak, ArXiv: 1902.02855 (2019).

https://www.physik.uni-kl.de/hillebrands/members/philipp-pirro/


P53 126

Enhancement of the spin pumping effect by magnon confluence process in

YIG/Pt bilayers

Vitaliy I. Vasyuchkaa, Timo B. Noacka, Dmytro A. Bozhkoa,d, Björn Heinza,e, Pascal Freya, Denys

V. Slobodianiukb, Oleksandr V. Prokopenkob, Gennadii A. Melkovb, Peter Kopietzc, Burkard

Hillebrandsa, and Alexander A. Sergaa

a Fachbereich Physik and Landesforschungszentrum OPTIMAS,

Technische Universität Kaiserslautern, Kaiserslautern, Germany b Faculty of Radiophysics, Electronics and Computer Systems,

Taras Shevchenko National University of Kyiv, Kyiv, Ukraine c Institut für Theoretische Physik, Universität Frankfurt, Frankfurt, Germany d School of Engineering, University of Glasgow, Glasgow, United Kingdom

e Graduate School Materials Science in Mainz, Johannes Gutenberg-Universität Mainz, Mainz, Germany

We present the experimental investigation of the spin pumping process by dipolar-exchange magnons

parametrically excited in in-plane magnetized Yttrium Iron Garnet / Platinum (YIG/Pt) bilayers. When the

microwave parametric pumping is applied to the sample, the electric voltage generated in the platinum layer

via the inverse spin Hall effect (ISHE) results from contributions of two opposite spin currents formed by the

longitudinal spin Seebeck effect and by the spin pumping from parametric magnons. In our field-dependent

measurements of the spin pumping induced component of the ISHE-voltage, a clearly visible sharp peak is

detected at high pumping powers. It is found that the peak position and the corresponding magnetic field are

determined by the process of confluence of two parametrically exited magnons into one magnon possessing

twice the frequency and the sum of the wavevectors of the initial magnons. The experimentally measured ISHE

peak fields for different parametric pumping frequencies perfectly correspond to the calculated dependence

without additional fitting parameters.

The three-magnon confluence process constitutes an additional damping mechanism for the group of

parametrically pumped magnons. Thus, for low pumping powers the confluence will decrease the total number

of magnons in the system that results in the decreasing of the ISHE-voltage. Nevertheless, we demonstrate by

numerical calculations that under the action of a rather strong parametric pumping field this confluence process

results in the increase of the total number of magnons in the magnetic sample. This leads to the enhancement

of the spin pumping effect in the YIG/Pt bilayer in the presence of the three-magnon confluence process.


P54 127

Spin wave propagation in sinusoidally modulated thin films

Igor Turčan a, Lukáš Flajšman a, Marek Vaňatka a, Michal Urbánek a,b

a CEITEC, Brno University of Technology, Brno, Czech Republic b Institute of Physical Engineering, Brno University of Technology, Brno, Czech Republic

Although magnonic circuits are prospective candidates for future information processing, their technical

realization is extremely challenging with conventional approaches. E.g. efficient steering of the spin waves

requires local directional control of effective magnetic fields. To achieve this directional control, one of the

most effective ways is to locally manipulate the magnetic anisotropy direction. Recent advances in 3D

nanofabrication technologies allow to fabricate structures with properties unobtainable with classical planar

lithography approaches, and the possibility to spatially control magnetic anisotropy at nanoscale control is one

of them. Via precise shaping of the 3D surface morphology at nanometre level the magnitude and direction of

the uniaxial magnetic anisotropy in thin films can be controlled [1] and at the same time it can be optimized in

a way that it has a minimal influence on spin wave decay.

We studied spin wave propagation in waveguides made from sinusoidally modulated 10 nm thick films of

Permalloy. The films were deposited on silicon dioxide mesas with sinusoidal modulation prepared by focused

electron beam induced deposition (FEBID). The period of modulation was 100 nm and the amplitudes of

modulation were changing from 0 to 20 nm. The magnetic anisotropy induced by the surface modulation was

quantified by Kerr magnetometry and the spin wave propagation length was measured by micro-focused

Brillouin light scattering. We will show that in sinusoidally modulated thin films the curvature-induced

magnetic anisotropy is strong enough to overcome the shape anisotropy of the waveguide and that the curvature

has only minor impact on spin wave propagation.

[1] K. Chen et al. Phys. Rev. B, 86, 064432 (2012).


P55 128

Antiferromagnetic domain wall motion driven by spin-orbit torques

Luis Sánchez-Tejerinaa, Vito Puliafitob, Pedram Khalili Amiric, Mario Carpentieria, Giovanni

Finocchiod

a Dipartimento di Ingegneria Elettrica e dell’Informazione, Politecnico di Bari, Bari, Italy b Dipartimento di Ingegneria, Università di Messina, Messina, Italy

c Department of Electrical and Computer Engineering, Northwestern University, Evanston, IL, USA d Department of Mathematical and Computer Sciences, Physical Sciences and Earth Sciences, University of

Messina, Messina, Italy

The nucleation and manipulation of ferromagnetic (FM) domain walls (DWs) have attracted a lot of

attention in recent years due to the promising results for the development of spintronic devices [1,2]. In

addition, it has been predicted that the velocity of DWs in antiferromagnets (AFMs) should reach tens of km/s

and it is limited by the group velocity of spin waves [3]. This ultrafast dynamics is govern by the

antiferromagnetic exchange coupling between the two sublattices forming the AFM, whose relaxation

processes lays on the ps time scale [4]. Thus, AFMs are rather appealing for of ultrafast spintronic devices

development.

Antiferromagnetic dynamics can be described by a full micromagnetic (µM) framework [4] based on the

numerical solution of two Landau-Lifshitz-Gilbert equations, each of them describing a sublattice of the AFM,

coupled through homogeneous and inhomogeneous exchange interactions. Here, we study the DW motion in

AFM by full µM simulations.

A systematic study of the role of the different exchange interactions shows a DW velocity independent of

the homogeneous interlattice exchange, and with a square root dependence on both inhomogeneous exchanges,

i.e. intralattice and interlattice. Besides, the role of the exchange interaction on the DW width parameter is also

addressed. A simplified analytical model can predict quantitatively these results allowing for a fast exploration

of a wide range of material parameters. Finally, we show that new domains can be nucleated at the edges of

the system due to the boundary conditions of the interfacial Dzyaloshinskii-Moriya interaction [5] (See Figure

1), limiting the DW velocity in an antiferromagnetic racetrack memory whose stored information would be

modified in this way.

[1] S. S. P. Parkin, M. Hayashi, and L. Thomas, Science 320, 190 (2008).

[2] S. Lequeux, et. al, Sci. Rep. 6, 31510 (2016).

[3] O. Gomonay, M. Kläui, and J. Sinova, Appl. Phys. Lett,109, 142404 (2016).

[4] V. Puliafito et. al., Phys. Rev. B 99, 024405 (2019).

[5] E. Martinez, S. Emori, and G. S. D. Beach, Appl. Phys. Lett. 103, 072406 (2013).

Figure 1: Snapshots of the first sublattice magnetization from µM simulations under a

current density 29 TA/mJ = for (a) simulations with Dzyaloshisnkii-Moriya interaction

boundary conditions and (b) without these boundary conditions.


P56 129

Nanoscale Detection of Spin Wave Deflection Angles in Permalloy

Felix Groß, Nick Träger, Johannes Förster, Gisela Schütz, Markus Weigand, Joachim Gräfe

Max Planck Institute for Intelligent Systems, Heisenbergstraße 3, 70569 Stuttgart

Since the introduction of the term magnonics4 spin waves are considered as promising approach for next

generation data transmission. However, the scaling of magnetic devices into the sub µm region is accompanied

by challenges such as the scalability of the production process, or even more fundamental, the observation of

the desired effect as optical methods are limited by their wavelength of 300 nm.

Fortunately, the MAXYMUS x-ray microscope at BESSY II routinely achieves magnetic resolutions

down to 15 nm using the XMCD effect2. A fast photon-sorting algorithm allows for an acquisition of a dynamic

spin wave video within a couple of minutes with time resolutions down to a few ps.

The video in real space and time domain yields information about spin amplitude and phase at the same

time. With temporal Fourier analysis, a ‘dynamic picture’ of such a spin wave is extracted. k-Space

transformation, allows for the separation of overlapping spin wave modes. Additionally, the absolute spin

angle of the spin wave is calibrated by measuring a XMCD spectrum of the sample and comparing it to the

contrast of a movie3.

To demonstrate the power of combining this measurement technique and analysis method for magnonics

research we measured a 50 nm permalloy film in Demon-Eshbach geometry. An exemplified result is shown

in Fig. 1. The color represents the relative phase, the amplitude is encoded in brightness. The total area

displayed is 40 x 5 µm2 with an acquisition time of less than 5 minutes. The dispersion relation is in good

agreement with literature, proving the reliability of STXM for spin wave research3. By comparing the contrast

of the video to the contrast expected from the XMCD spectrum we can calculate the absolute spin deflection

angle3 (fig. 2). Thus, STXM measurements yield a complete set of information on absolute amplitude and

phase of the spin wave.

In summary, STXM gives massive new opportunities for the time-resolved observation of nano

magnetic structures such as spin waves, skyrmion movement, or domain wall oscillations. With resolutions

down to 15 nm in space and 35 ps in time, there is an almost endless amount of opportunities to investigate

magnetic structures and their dynamic behavior.

4 V. V. Kruglyak, et al., J. Phys. D: Appl. Phys. 43 260301 (2010) 2 G. Schütz, et al., Phys. Rev. Lett. 58, 737 (1987) 3 F. Groß, et al., Appl. Phys. Lett. 114, 012406 (2019)

Figure 2: Dynamic illustration of a spin wave. Color encodes relative phase,

brightness encodes amplitude. White lines denote the position of the stripline.

Figure 2: Absolute spin wave angle. As expected the

spin wave amplitude is highest underneath the

stripline and decays the further the wave propagates.


P57 130

Spin wave propagation of ferrimagnetic GdCo

Shinsaku Funada, Tomoe Nishimura, Yoichi Shiota, Shuhei Kasukawa, Mio Ishibashi, Takahiro Moriyama,

Teruo Ono

Institute for Chemical Research, Kyoto University, Uji, Kyoto 611-0011, Japan

Rare earth (RE)-transition metal (TM) ferrimagnets are promising materials for an emerging field of

antiferromagnetic spintronics where fast magnetization dynamics and low susceptibility to magnetic fields are

key, because they exhibit compensation temperatures of magnetization (TM) and angular momentum (TA).

Recently, fast field-driven domain wall motion at the vicinity of TA has been reported [1]. Since the domain

wall motion is fundamentally governed by the precession of moments, it is interesting to investigate the

magnetization dynamics, such as propagating spin waves, in RE-TM ferrimagnets. In this study, we measured

propagating spin waves in ferrimagnetic amorphous GdCo, and evaluated the group velocity and attenuation

length in GdCo with various compositions.

The films consisting of GdxCo1-x (20 nm)/Pt (2 nm)/Ta (5 nm) were prepared on thermally oxidized Si

substrates by dc magnetron sputtering. The GdxCo1-x alloys are deposited by cosputtering of Co and Gd targets

with different sputtering power. Figure 1 shows the temperature dependence of magnetization for x = 0.22,

0.30, 0.59. Co magnetic moment dominates for x = 0.22 and 0.30, whereas Gd magnetic moment does for x =

0.59. The films were then patterned into rectangular shape and two shorted coplanar wave guides for exciting

and detecting the spin waves were fabricated. Propagating spin wave spectroscopy was performed by using a

vector network analyzer under the in-plane magnetic field transverse to the spin wave propagation direction.

We measured transmission signal (S21, S12) and reflection signal (S11, S22) at room temperature. Figure 2 shows

transmission signal S21 for x = 0.22. The group velocity was estimated to be 11 km/s for x = 0.22, 11 km/s for

x = 0.30 and 4.8 km/s for x = 0.59. Spin wave attenuation length was evaluated to be 2.1 µm for x = 0.22 and

1.65 µm for x = 0.59 from the antenna gap dependence of amplitude.

[1] K. -J. Kim et al., Nat. Mater. 16 (2017), 1187-1193.

2.5 3.0 3.5 4.0 4.5 5.0 5.5

-1.0x10-4

-5.0x10-5

0.0

5.0x10-5

1.0x10-4

1.5x10-4

Re[

S21

], Im

[S21

]

Frequency (GHz)

Gd0.22Co0.78

Re[S21]

Im[S21]

d = 10 μm

Figure 2. Transmission signal for Gd0.22Co0.78.

0 50 100 150 200 250 3000.4

0.5

0.6

0.7

0.8

0.9

1.0

1.1

1.2

1.3 Gd0.22Co0.78

Gd0.30Co0.70

Gd0.59Co0.41

Mag

netiza

tion

(MA

/m)

Temperature (K)

Figure 3. Temperature dependance of

magnetization for GdxCo1-x.


P58 131

Snell’s law for isotropically propagating spin wave

Tian Li1, Takuya Taniguchi1, 2, Yoichi Shiota1, Takahiro Moriyama1, and Teruo Ono1, 3†

1Institute for Chemical Research, Kyoto University, Uji, Kyoto 611-0011, Japan 2Deptartment of Physics, Technical University of Munich, Munich 85748, Germany

3Center for Spintronics Research Network (CSRN), Graduate School of Engineering Science, Osaka Univ.,

Osaka 560-8531, Japan

Control of spin wave (SW) propagation is one of crucial tasks in magnonics [1]. As one of the important

properties of the propagation, refraction of magnetostatic surface spin wave (MSSW) has been investigated

[2]. However, MSSW has anisotropic dispersion relation and it should be taken into count the angle dependent

wave vector of SW. Such anisotropic Snell’s law requires complex calculation and it is not easy to apply

techniques grown in optics. Regarding the dispersion relation of SW considering exchange interaction and

dipole-dipole interaction [3],

𝜔2 = (𝜔𝐻 + 𝛼𝜔𝑀𝑘2) [𝜔𝐻 + 𝛼𝜔𝑀𝑘2 + 𝜔𝑀 (1 −1−𝑒−𝑘𝑑

𝑘𝑑)] (1)

SWs propagating in-plane with out-of-plane magnetization propagate isotropically. Furthermore, Eq.1

describes the dispersion relation of magnetostatic forward volume wave (MSFVW) when𝛼𝜔𝑀𝑘2 0 is assumed.

In this study, we investigated Snell's law for both MSFVW and isotropically propagating dipole-exchange SW.

The micromagnetic simulation is performed utilizing mumax3[4]. To suppress the SW attenuation, we use

material parameters of yttrium iron garnet (YIG), which is a well-known material having low damping. In the

simulation, samples are shaped as Fig.1. The black and white areas are respectively the thicker and thinner

regions. And the thickness step, the boundary between two regions, is tilted with the angle 𝜃1. The rf magnetic

field is applied at the antenna. MSFVW is excited in the thicker(800 nm) region, passes through the thickness

step and propagates in the thinner(400 nm) region. The incident wave is refracted following Snell’s law 𝑠𝑖𝑛𝜃1

𝑠𝑖𝑛𝜃2=

𝑘2

𝑘1. The wave number is independent on the direction of propagation due to the isotropic dispersion property.

For MSFVW, a wavenumber is varied in order to keep 𝑘𝑑 constant when it passes through a thickness step.

Hence, the Snell’s law for MSFVW is independent of frequency (Fig.2). Furthermore, if we reduce the

thickness to 100nm and 50 nm, dipole-exchange SW is excited. Because of the exchange interaction,𝑘𝑑 is not

conserved, resulting in a frequency-dependent Snell’s law.

[1] A. V. Chumak et al., Nat. Phys. 11, 453 (2015).

[2] J. Stigloher et al., Phys. Rev. Lett. 117, 037204 (2016).

[3] B. A. Kalinikos and A. N. Slavin, J. Phys. C: Solid State Phys. 19, 7013 (1986).

[4] A. Vansteenkiste et al., AIP Adv. 4, 107133 (2014).

Figure1 Figure2

Figure 1: Simulation setup

Figure 2: Refraction angle versus incident angle of MSFVW


P59 132

A Magnetometer Based on a Spin Wave Interferometer

M. Balynskya, D. Gutierreza, H. Chiang a, A. Kozhevnikovb, G. Dudkob , Y. Filimonovb,c, A.A.

Balandina, and A. Khituna

aDepartment of Electrical and Computer Engineering, University of California -Riverside, Riverside,

California, USA 92521 bKotelnikov Institute of Radioengineering and Electronics of the Russian Academy of Sciences, Saratov,

Russia 410019 cSaratov State University, Saratov, Russia 410012

We describe a magnetic field sensor based on a spin wave interferometer. Its sensing element consists of

a magnetic cross junction with four micro-antennas fabricated at the edges. Two of these antennas are used for

spin wave excitation while two other antennas are used for detection of the inductive voltage produced by the

interfering spin waves. Two waves propagating in the orthogonal arms of the cross may accumulate

significantly different phase shifts depending on the magnitude and direction of the external magnetic field.

This phenomenon is utilized for magnetic field sensing. The sensitivity attains its maximum under the

destructive interference condition, where a small change in the external magnetic field results in a drastic

increase of the inductive voltage, as well as in the change of the output phase. We report experimental data

obtained for a micrometer scale Y3Fe2(FeO4)3 cross structure. The change of the inductive voltage near the

destructive interference point exceeds 40 dB per 1 Oe. The phase of the output signal exhibits a π-phase shift

within 1 Oe. The data are collected at room temperature. Taking into account the low thermal noise in ferrite

structures, we estimate that the maximum sensitivity of the spin wave magnetometer may exceed attotesla.

[1] M. Balynsky, D. Gutierrez, H. Chiang, A. Kozhevnikov, G. Dudko, Y. Filimonov, A. A. Balandin, and A.

Khitun, "A Magnetometer Based on a Spin Wave Interferometer," Scientific Reports, vol. 7, 2017. DOI:

10.1038/s41598-017-11881-y

Fig.1 (A) Experimental data showing the response of the spin wave magnetometer. The red

and the blue markers correspond to the amplitude and the phase of the output inductive

voltage. (B) Experimental data: noise power as a function of the phase difference between

the interfering spin waves. All measurements are done at room temperature.

(A) (B)


P60 133

Direct observation of unusual interfacial Dzyaloshinskii-Moriya interaction in

Graphene/NiFe/Ta heterostructure

Avinash Kumar Chaurasiya,a Akash Kumar,b Rahul Gupta,b Sujeet Chaudhary,b Pranaba Kishor Muduli,b and

Anjan Barmana,*

aDepartment of Condensed Matter Physics and Material Sciences, S. N. Bose National Centre for Basic Sciences, Block

JD, Sec. III, Salt Lake, Kolkata 700106, India bThin Film Laboratory, Department of Physics, Indian Institute of Technology Delhi, Hauz Khas, New Delhi 110016,

India ϯPresenting author; *Corresponding author’s email: [email protected]

One of the key motivations of modern spintronics research is to achieve low power consumption, faster

information processing and higher storage density. To this end, graphene and other 2-D materials have shown

promises. The interfacial Dzyaloshinskii Moriya interaction (iDMI) has drawn intense interest due to its

fundamental role in stabilizing chiral spin textures in ultrathin ferromagnets. Recently, Yang et al. have

reported the observation of significant DMI at the graphene-FM interface originating from Rashba effect [1].

Here, we demonstrate the first direct observation of iDMI in graphene/Ni80Fe20/Ta heterostructures using

Brillouin light scattering (BLS) technique. We have used high-quality commercial CVD graphene (from

Graphenea) on a Si/SiO2 substrate. A series of samples consisting of substrate/graphene/Ni80Fe20 (t)/Ta (2),

with t = 3, 4, 6, 8, 10, 15 nm were deposited at room temperature using DC magnetron sputtering at varying

Ar working pressure and 3 μTorr base pressure. The Ar working pressure for deposition of NiFe thin films on

graphene was varied from 2 mTorr to 10 mTorr for inducing controlled defects in the graphene layer. By

measuring frequency non-reciprocity of Damon-Eshbach spin waves using BLS, we observed that iDMI

constant D scales linearly with the inverse of NiFe thickness revealing its purely interfacial origin (c.f. Fig.

1(a)). Furthermore, by controlling the defects at the interface by Ar deposition pressure during growth of

Ni80Fe20, we established that the DMI in this system arises from the defect induced extrinsic spin-orbit

coupling. This is further supported by a correlation between the DMI and spin-mixing conductance (obtained

from ferromagnetic resonance measurement), both of which are related to spin-orbit coupling (c.f. Fig. 1(b))

[2]. Our detailed FM layer thickness and Ar pressure dependent study of iDMI will enrich the understanding

of the observation and tunability of iDMI in these 2D heterostructures for controlling chiral spin structure and

magnetic domain-wall based storage, memory and logic devices.

We gratefully acknowledge the financial assistance from DST, Govt. of India [SR/NM/NS-09/2011] and

SNBNCBS [SNB/AB/12-13/96].

References:

[1] H. Yang et al., Nat. Mater. 17 (2018), 605.

[2] A. K. Chaurasiya et al., Phys. Rev. B 9 (2019), 035402.

Figure 1 (a) Variation of D as a

function of inverse of NiFe

thickness. Inset: Schematic of the

sample stack. (b) A positive

correlation between surface DMI

constant and spin-mixing

conductance


P61 134

Spin waves in a three-dimensional nanoscale Cobalt tetrapod structure

Sourav Sahoo1, Sucheta Mondal1, Gwilym Williams2, Andrew May2, Sam Ladak2 and Anjan

Barman1, *

1Department of Condensed Matter Physics and Material Sciences, S. N. Bose National Centre for Basic

Sciences, Block JD, Sector III, Salt Lake, Kolkata 700 106, India 2School of Physics and Astronomy, Cardiff University, Cardiff CF24 3AA, UK

ǂPresenting author, *Corresponding author’s email: [email protected]

Three-dimensional (3D) magnetic nanostructures are gaining huge interest because they offer exotic spin

structures and rich magnetization reversal and dynamics. They have the potential to enhance data storage

density and the functionality of magnonic devices when arranged in ordered arrays. Here, we have studied the

ultrafast magnetization dynamics of a nanoscale 3D cobalt tetrapod structure by using time-resolved magneto-

optical Kerr effect (TR-MOKE) microscopy based on a two-color collinear pump-probe technique. Each

tetrapod (shown in Fig.1(a)) structure consisting of four wires, each with dimension 657 nm × 782 nm × 10

µm, were fabricated by the combination of two-photon lithography and electrodeposition on to a glass/ITO

substrate [1]. The time-resolved dynamics (shown in Fig.1(c)) shows an ultrafast demagnetization followed by

two-step relaxation and a damped precessional motion of magnetization [2]. The fast Fourier transform (FFT)

spectra (shown in Fig.1(d)) of time-resolved precessional data obtained from the junction of the tetrapod

structure show two clear spin-wave (SW) modes at around 1 and 10 GHz along with a third less intense mode

around 30 GHz. The spatial distribution of the SW modes (shown in Fig.1 (e)) is mapped with the help of

micromagnetic simulations. The higher frequency mode (30 GHz) is found to be the most uniform precessional

mode while the others two modes are mixed quantized modes with increased quantization number with the

decrease in frequency. The knowledge of ultrafast magnetization dynamics in such complex 3D magnetic

structures will promote them as a potential candidate for spatially compact high-frequency spintronic and

magnonic devices.

The authors gratefully acknowledge the financial assistance from the Department of Science and Technology,

Govt. of India under grant no. SR/NM/NS-09/2011 and the S. N. Bose National Centre for Basic Sciences

(SNBNCBS) under project no. SNB/AB/12-13/96. SS acknowledges SNBNCBS and SM acknowledges the

DST INSPIRE scheme for financial support. SL acknowledges support from the EPSRC (EP/R009147/1).

[1] G. Williams et al., Nano Res. 11 (2018), 845-854.

[2] S. Sahoo et al., Nanoscale, 10 (2018), 9981-9986.

Figure 1: a) Scanning electron micrograph

image of a single tetrapod element. (b)

Schematic diagram of the cobalt tetrapod and

the experimental geometry. (c) Time-

resolved Kerr rotation data at bias field H =

3.92 kOe. (d) FFT spectra for time resolved

precessional data. (e) Simulated spin-wave

mode profiles of three different modes.

mailto:[email protected]


P62 135

Determining magneto-elastic coupling coefficients by anisotropic

magnetoresistance

Hasnain Ahmada, Max Kouwenhovena,b, Frederic Vandervekena,c, Davide Tiernoa, Iuliana Radua,

Florin Ciubotarua, Christoph Adelmanna

a Imec, Leuven, Belgium. b TU Delft, Delft, Nederlands

c KU Leuven, Leuven, Belgium.

Voltage-based magnetoelectric (ME) composite heterostructures offer an energy-efficient scalable

approach to control nanomagnets. Such ME composites consist of both magnetostrictive as well as

piezoelectric elements and the magnetization can be controlled by the strain induced in the piezoelectric

element via the Villari effect. Numerous studies have used ferromagnetic resonance to quantify the

magnetoelectric coefficient of various

composites consisting of thin magnetic films

on bulk macroscopic piezoelectric

substrates. However, magnetoelastic and

magnetoelectric effects at a nanoscale have

only received very scarce attention so far and

a deeper understanding of the

magnetoelectric coupling is still missing.

Here, we report on an investigation of a Ni-

PbZrTO3 magnetoelectric composite, as

shown in Figure 1 (Left). Anisotropic

magnetoresistance measurements have been

used to assess the magnetoelectric coupling

in 1-µm-wide Ni stripe patterned on top of

500-nm-thin PZT mesas. The mesa was

formed by etching 100 nm deep into PZT to

reduce clamping in the structure. Two needle-shaped 4-µm-wide Au electrodes with 750-nm-wide gaps with

respect to the Ni stripe were used to generate voltage-controlled strain in the PZT and, four additional Au

contact pads (two voltage and two current pads) were patterned on the waveguide to measure anisotropic

magnetoresistance (Figure 1 (Right)) of the device as a function of an applied dc voltage and the angle of the

external magnetic field. The application of a dc voltage to the electrodes generates electric fringing fields in

the PZT mesa, which in turn induces a change in the magnetoelastic anisotropy field in the Ni stripe. The

anisotropy field depends on both the components of the strain tensor as well as the direction of the

magnetization. This complex interplay translates into a modulation and/or a shift of the anisotropic

magnetoresistance. The observed variation of the anisotropic magnetoresistance with applied field allowed for

the quantification of the magnetoelastic coefficient in such Ni/PZT nanostructures, leads to a value of 5840

(A/m)/V, which is considerably larger than previously reported values for macroscopic devices [1]. This

indicates that large voltage responses in nanoscale ME composites are highly promising for low-voltage

spintronic applications such as spin-wave generation, control of nanomagnets, etc.

[1] M. Liu and N.X. Sun, Phil. Trans. R. Soc. A 372, 20120439 (2014).

Funding Sources: the European Union’s Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant

agreement No 794354 and within the FET-OPEN project CHIRON under grant agreement No. 801055.

(Left) (Right)

Figure 1: (Left) Schematic of the AMR Device, (Right) Perpendicular AMR

measurements vs the angle of the external magnetic field at different bias

voltages.


P63 136

Nanoscale magnetic imaging of ferritins in a single cell

Maosen Guo1,2,3†, Sanyou Chen1,2,3†, Pengfei Wang1,2,3†, Tao Xu4,5*, Jiangfeng Du1,2,3*

1CAS Key Laboratory of Microscale Magnetic Resonance and Department of Modern Physics, University of

Science and Technology of China, Hefei 230026, China.

2Hefei National Laboratory for Physical Sciences at the Microscale, University of Science and Technology

of China, Hefei 230026, China.

3Synergetic Innovation Center of Quantum Information and Quantum Physics, University of Science and

Technology of China, Hefei 230026, China.

4National Laboratory of Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing

100101, China.

5College of Life Sciences, Chinese Academy of Sciences, Beijing 100049, China.

†These authors contributed equally to this work.

*Correspondence: [email protected], [email protected].

Abstract

The in situ measurement of the distribution of biomolecules inside a cell is one of the important goals in life

science. Among various imaging techniques, the magnetic imaging (MI) based on the nitrogen-vacancy (NV)

center in diamond provides a powerful tool for the biomolecular research, while the nanometer scale MI of

intracellular proteins remains a challenge. Here we use ferritin as a demonstration to realize the MI of

endogenous proteins in a single cell using NV center as the sensor. With the scanning, the intracellular ferritins

is imaged with a spatial resolution of ca. 10 nanometers, and ferritin-containing organelles are co-localized by

correlative MI and electron microscopy. The approach paves the way for nanoscale MI of intracellular proteins.

[1]

[1] Wang et al., Sci. Adv. 2019;5: eaau8038 10 April 2019


P64 137

Structural and electrical transport studies in sputtered La0.34Pr0.31Ca0.35MnO3

thin film

Suman Kumari,1# Shital Chauhan P. K. Siwach,1 G. D. Varma2 and H. K. Singh1

1Academy of Scientific and Innovative Research (AcSIR), CSIR-National Physical Laboratory, Dr.

K. S. Krishnan Road, New Delhi-110012, India

Present study reveals the superlattice formation through the electrical transport measurements and

surface inhomogeneities of phase separated manganite (La1-yPry)1-xCaxMnO3. Thin films having

nominal composition La0.34Pr0.31Ca0.35MnO3 were deposited on single crystal LaAlO3 (100) and

SrTiO3 (100) substrate. Film were grown by RF Magnetron Sputtering in 40 mtorr of Argon oxygen

gas mixture at 870 C substrate temperature. The film thickness was 63 nm as estimated by X-ray

Reflectivity. The deposited thin films were characterized by high resolution x-ray diffraction

(HRXRD) using Cuk𝛼 radiation, temperature dependence resistance (R-T). The surface morphology

was analyzed by Atomic force microscopy (AFM). It is found that films were epitaxial grown along

[100] direction and from the XRD patterns, the out-of-plane lattice constant was deduced to be ~

0.3911, ~0.3836 nm for LPCMO/LAO, LPCMO/STO respectively, which confirms the compressive

and tensile strain (Bulk LPCMO ~0.3840 nm). The AFM results shows that both films have island

type of growth morphology which may be due to low pressure during sputtering. The R-T data of

LPCMO/LAO film shows insulating behaviour whereas LPCMO/STO shows insulator to metal

transition at TIMC ≈ 133 K & TIM

W ≈ 177 K respectively, in cooling and warming cycle. The observed

different electrical transport in these films have been explained in terms of strain relaxation as seen

in the superlattice profile and consequent oxygen deficiency.


P65 138

Investigation of magnons and phonons interactions

in CoFeB/Au multilayer for oblique geometry

Nandan K. P. Babu a, A. Trzaskowska a, S. Mielcarek a, H. Głowiński b,

P. Kuświk b, F. Stobiecki b , M. Zdunek a, P. Graczyk a, J. W. Kłos a, G. Centała a, M. Krawczyka

aFaculty of Physics, Adam Mickiewicz University, Poznań, Poland bInstitute of Molecular Physics, Polish Academy of Sciences, Poznań, Poland

Recent studies shows that the CoFeB/Au multilayers have significantly reduced effective magnetization

saturation but sustain relatively low spin wave damping. For the CoFeB layers thicker than 1 nm the shape

anisotropy dominate over the perpendicular anisotropy induced on the interfaces with gold and the system is

in-plain magnetized [1]. Such structure deposited on thick elastic substrate can be used for observation of the

interaction between surface acoustic waves with dipolar spin waves. The reduced frequencies of spin waves in

material of lowered magnetization saturation allow for (anti)crossing of spin wave dispersion branches with

the dispersion branches of Rayleigh or Sezava surface acoustic waves characterized natively by lower

frequencies. For in-plain magnetic configurations we can gain the oblique orientation of wave vector respect

to the static magnetization which is crucial for enhancement of magneto-elastic interaction with Rayleigh or

Sezava waves [2].

In our studies, we determine the dispersion relation of thermal magnons and phonons in the CoFeB/Au

multilayer deposited on silicon substrate with Ti and Au buffer layers using Brillouin light scattering

spectroscopy. We choose an oblique geometry, where the angle between magnetic field and wave vector is

45°. We found the noticeable interaction between the spin waves and Sezava mode which is observed as

splitting of Sezava mode and reducing its intensity at the (anti)crossing with spin wave.

Figure 1: (a)

The

dispersion

relation for

surface

acoustic

waves and

spin waves in

CoFeB/Au

multilayer

deposited on

silicon

substrate measured with the aid of BLS spectroscopy. (b) The Region of (anti)crossing of acoustic Sezeava

wave with spin wave marked in (a) by green circle.

[1] P. Kuświk, et al., J. Phys.: Condens. Matter 29 (2017), 435803.

[2] L. Dreher, et al. Phys. Rev. B 86 (2012), 134415.

Figure 1: Top row: hysteresis loops of samples with different thickness. Bottom row:

corresponding MFM images at remanence.


P66 139

Transport properties of antiferromagnetic CuMnAs alloy

František Mácaa, Josef Kudrnovskýa, Václav Drchala, Karel Carvab, Pavel Balážb, Ilja Turekb

a Institute of Physics, Czech Academy of Sciences, Prague, Czech Republic

b Charles University, Faculty of Mathematics and Physics, Prague, Czech Republic

Electronic, magnetic, and transport properties of the antiferromagnetic (AFM) CuMnAs alloy with

tetragonal structure, a promising material for the AFM spintronics, are studied from first principles. The alloy

is semimetal with very low density of states at Fermi level. The experiment on real samples gave the residual

resistivity around 90 cm for low temperature T ~ 5 K and 160 cm for room temperatures. This indicates

the presence of defects whose origin and concentrations are known only very approximately. Our theoretical

analysis identified the MnCu and CuMn antisites and vacancies on Mn or Cu sublattices as most probable defects

in CuMnAs.

The AFM-CuMnAs with tetragonal structure is prepared by the molecular beam epitaxy. We find that the

interactions of the growing thin film with the substrate and with vacuum are important for the phase stability

of real samples prepared as a thin film on the appropriate substrate. We estimated the in-plane resistivity of

CuMnAs with defects of low formation energies. Our numerical simulations fitted experiment very well if we

assumed concentrations 3.5-5% MnCu antisites in the samples, much larger concentrations would be needed

for CuMn antisites or Mn-vacancies.

Our transport studies employ the Kubo-Greenwood linear response theory in which the disorder-induced

vertex-corrections are included in the coherent potential approximation. In real conditions which are far from

the thermodynamical equilibrium and with possible violation of the sample stoichiometry, the resistivities

depend on the actual occupation of sublattices by the alloy constituents resulting in the presence of antisite

sublattice disorder. This is a challenging problem for the structural X-ray analysis in the present alloy because

of similar scattering cross sections of atoms forming the alloy (Cu and Mn). We compare resistivities for two

samples of experimentally obtained compositions. Calculated planar resistivities are in a good agreement with

the X-ray structural analysis of samples grown on GaP(001) substrate and also the simulations for systems

with Cu- and Mn-vacancies have the resistivity close to that found in the experiment.

Finally, we determine the exchange interactions and estimate the Néel temperature of the ideal and

disordered AFM-CuMnAs alloy using the Monte Carlo approach. The Néel temperature has been estimated

from the peak in the magnetic susceptibility or the peak in the heat capacity. We have obtained a good

agreement between experimental and calculated Néel temperatures. Specifically, the vacancies on Mn and Cu

as well as the antisite MnCu defects reduce the calculated Néel temperature (446 – 465 K) in comparison with

that for the ideal CuMnAs (495 K) while keeping a good agreement with experiment (480 K).

[1] F. Maca et al., J. Magn. Magn. Mater. 474 (2019), 467-471.


P67 140

Strain-induced perpendicular magnetic anisotropy and Gilbert damping in

Tm3Fe5O12 thin films

Oana Ciubotariua, Anna Semisalovab, Killian Lenzb, Manfred Albrechta

a Institute of Physics, University of Augsburg, Augsburg, Germany b Institute of Ion Beam Physics and Materials Research, Helmholtz-Zentrum Dresden-Rossendorf, Dresden,

Germany

In the attempt of implementing iron garnets with perpendicular magnetic anisotropy (PMA) in spintronics,

the attention turned towards strain-grown iron garnets. One candidate is Tm3Fe5O12 (TmIG) which can possess

a strain-induced out-of-plane magnetic easy axis when grown under tensile strain [1]. Possible substrate

choices are Gd3Ga5O12 (GGG) and substituted-Gd3Ga5O12 (sGGG) substrates, where the latter generates a

higher in-plane tensile strain for the growth of TmIG.

In this study, we have investigated the effect of film thickness on the structural and magnetic properties of

TmIG films including magnetic anisotropy, saturation magnetization, and Gilbert damping determined by

frequency-dependent ferromagnetic resonance (FMR) analysis. TmIG films with thicknesses between 20 and

300 nm were epitaxially grown by pulsed laser deposition on sGGG(111) substrates. For all films a saturation

magnetization MS of around 90 kA/m was measured (fig. 1 a). Structural characterization showed that films

thinner than 70 nm exhibit in-plane tensile strain. For these films, the shape anisotropy is overcome by the

strain-induced magnetoelastic anisotropy and the films show PMA (see fig. 1 b). With increasing film

thickness, a relaxation of the unit cell towards its bulk structure is observed resulting in a rotation of the

magnetic easy axis from out of the sample plane towards the sample plane due to the dominant shape

anisotropy. Furthermore, the Gilbert damping parameter extracted from FMR measurements is in the range of

0.02 ± 0.05 with no clear dependence on the film thickness (see fig. 1 c).

Figure 4: Dependence of a) saturation magnetization MS, b) magnetic anisotropy, and c) Gilbert damping α on

film thickness.

[1] M. Kubota et al., App. Phys. Exp. 5 (2012) 103002.

[2] C. N. Wu et al., Sci. Rep. 8 (2018) 11087.


P68 141

Micromagnetic analysis of THz spin-Hall oscillators based on antiferromagnetic materials

V. Puliafitoa, I. Medlejb, R. Zivieria, R. Khymync, M. Carpentierid, B. Azzerbonia, A. Slavine, G. Finocchioa

a University of Messina, Italy b Lebanese University, Hadeth Beirut, Lebanon

c Gothenburg University, Sweden d Politecnico di Bari, Italy

e Oakland University, Rochester, MI, USA

The possibility to develop terahertz spintronics by means of antiferromagnetic materials has attracted a lot of

attention from the scientific community [1]. Magnetization dynamics of antiferromagnets (AFMs) out of their

equilibrium, in fact, is mainly driven by the large antiferromagnetic exchange interaction, which is the key

ingredient for their resonance in the THz range [2].

In this field of research, a full micromagnetic framework for studying magnetization dynamics of

antiferromagnets, in particular under the influence of spin-orbit-torques, is here presented [3]. The key idea in

the modeling of those materials is considering two different sublattices which are antiferromagnetically

coupled. The magnetization dynamics of the two sublattices are calculated by solving two Landau-Lifshitz-

Gilbert equations including a torque term due to the spin-Hall effect. The coupling between the two equations

is directly connected with the exchange field, which takes into account the three main contributions, the

inhomogeneous intralattice, the homogeneous interlattice and the inhomogeneous interlattice contributions.

Within this micromagnetic framework, antiferromagnetic spin-Hall oscillators, in particular, have been fully

characterized, obtaining a successful comparison with analytical models [3,4]. The main device consists of an

AFM layer coupled to a heavy metallic layer. The AFM is square-shaped, with dimensions 40x40 nm2, its

thickness d varies from 1 to 5 nm in our study, and it is modeled with uniaxial anisotropy. Dynamics of

magnetizations is excited above a certain threshold current, and it is characterized by a precession of the two

magnetizations m1 and m2 around the spin-Hall polarization direction p. However, the same dynamics can

disappear at lower values of the driving current, highlighting a hysteretic behavior of the excitation. Such

behavior has been studied as a function of different parameters, thickness, damping, exchange contributions,

spin-Hall polarization direction [3]. The frequency of dynamics shows a blue-shift with the increase of the

applied current, from hundreds of GHz up to several THz, as expected. The antiferromagnetic resonance

frequency (AFMR) of that layer as a function of different parameters has been also studied. The most important

result is that AFMR decreases with the increase of the direct electric current applied to the heavy metal and it

converges to the self-oscillation frequency at the threshold current.

[1] Jungwirth et al. Nat. Phys. 14 200 2018.

[2] Gomonay et al. Phys. Status Solidi RRL 11 1700022 2017.

[3] Puliafito et al. Phys. Rev. B 99 024405 2019.

[4] Khymyn et al. Sci. Rep. 7 43705 2017.


P69 142

Planar optomagnonic cavities: Adiabatic description and beyond

Petros-Andreas Pantazopoulos5, and Nikolaos Stefanou

Section of Solid State Physics, National and Kapodistrian University of Athens, Panepistimioupolis, GR-157

84 Athens, Greece

Planar optomagnonic cavities, formed in judiciously designed stratified all-dielectric structures that

comprise magnetic layer(s), are able to concurrently confine light and spin waves in the same ultra-

small region of space for a long time period. Such artificial structures which exhibit dual, photonic

and magnonic, functionalities offer impressive possibilities for tailoring the inherently weak

magneto-optic coupling and provide a promising platform for fast and energy-efficient spin-optical

information-processing applications.

It has been shown that, in such optomagnonic cavities, when the spin-wave frequency is smaller than

the width of the optical resonance, the interaction effects can be described by an adiabatic quasi-static

approach to a photonic structure driven by a slowly varying magnetization field. In this case,

systematic calculations for a relatively large dynamic optical frequency shift, induced by a strong

perturbation, reveal the possibility of efficient modulation of light waves through multi-magnon

absorption and emission processes [1,2]. However, at higher spin-wave frequencies, the adiabatic

approximation breaks down and a fully dynamic treatment is required. In the present communication

we present such a rigorous new methodology based on the (space)time Floquet scattering-matrix

theory, which is ideally suited for periodically driven systems where two time scales that differ by

several orders of magnitude are involved. We show that this general description leads to the results

of the adiabatic approximation in the low-frequency limit, encompassing the weak- and strong-

coupling regimes. Moreover, it provides at the same time a consistent interpretation of some

remarkable effects, such as resonant energy transfer between the photon and the magnon fields and

enhanced inelastic light scattering under a triple-resonance condition, i.e., when the frequency of the

magnon matches a photon transition between two neighboring resonant optical modes.

[1] P.A. Pantazopoulos, N. Stefanou, E. Almpanis, and N. Papanikolaou, Phys. Rev. B 96 (2017), 104425.

[2] P.A. Pantazopoulos, N. Papanikolaou, and N. Stefanou, J. Opt. 21 (2018), 015603.

5 P.A. Pantazopoulos is supported from the General Secretariat for Research and Technology and the Hellenic Foundation for Research and Innovation through a PhD scholarship (No. 906).


P70 143

Electromagnetic field radiation and field fluctuations at wave multiple scattering

by plane periodic array of magnetic micro- and nanoelements

Sergey Nikitova,b, Yuri Barabanenkova, Mikhail Barabanenkovc

a Kotelnikov Institute of Radio-engineering and Electronics of Russian Academy of Science (RAS),

Moscow, Russia b “Terahertz spintronics” laboratory of the MIPT, 9 Instituskij per., Dolgoprudny, 141700,

Moscow Region, Russia c Institute of Microelectronics Technology of RAS, 142432 Chernogolovka, Moscow Region

Electromagnetic wave (EM) multiple scattering by a plane periodic array of magnetic microelements in free

space is considered analytically by natural subdividing of the EM wave into the averaged and fluctuation

components. Each magnetic element is characterized by magnetic susceptibility tensor and shape. An exact

Dyson integral equation is derived for the magnetic field Floquet–Bloch amplitude in-plane averaged over an

array unit cell. The mass operator of the Dyson equation is expressed via the T-scattering operator of the array

unit cell that satisfies a type of the Lippmann–Schwinger equation. We showed that magnetic field fluctuations

are generated by the Bragg–Laue diffraction of an averaged magnetic field on the periodic array and are

described inside the array as waves propagating with the Laue wave vectors equal to the difference between

the in-plane wave vector of the incident magnetic field and the reciprocal lattice wave vector. We derived, for

the first time, an exact quadrature to calculate magnetic field fluctuations from their averaged value. These

general results are illustrated by a simple Born approximation. In particular, we revealed a mechanism of

discrete waveguide excitation by an incident plane EM wave via the averaged EM wave Brag–Laue diffraction

on the magnetic microelement array in the quasi-static approach when the wavelength of incident EM is much

larger than the sizes of magnetic elements and periods of the array. The mode energy excitation coefficient at

normal incidence of the plane EM wave on the array is evaluated.

This work was supported by Russian Science Foundation, Grant No 19-19-00607.


P71 144

Efficient magnonic spin transport in insulating antiferromagnetic thin films

Andrew Rossa,b, Romain Lebruna, Asaf Kayc, David Ellisc, Daniel Gravec, Lorenzo Baldratia,

Alireza Qaiumzedahd, Camilo Ulloae, Arne Brataasd, Avner Rothschildc, Rembert Duined,e,f and

Mathias Kläuia,b,d

a Institute for Physics, Johannes Gutenberg University Mainz, D-55128 Mainz, Germany

b Graduate School of Excellence Material Science in Mainz, Staudingerweg 9, 55128, Mainz, Germany c Department of Materials Science and Engineering, Technion-Israel Institute of Technology

d Center for Quantum Spintronics, Department of Physics, Norwegian University of Science and Technology,

NO-7491 Trondheim, Norway e Utrecht University, Princetonplein 5, 3584 CC Utrecht, Netherlands

f Department of Applied Physics, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven,

The Netherlands

In contrast to ferromagnets, antiferromagnets benefit from unparalleled stability with respect to applied

external fields, magnetization dynamics at THz frequencies and a lack of stray fields [1]-[2]. Many theoretical

studies have been undertaken describing the mechanisms through which antiferromagnets could allow for the

propagation of spin current across the long distances which would be required for integration into information

transfer and logic devices [3]-[4]. Recently, we demonstrated that in antiferromagnetic insulators, a diffusive

magnonic spin current is able to propagate over tens of micrometers carried by the intrinsic Néel order using

a single crystal of the most common insulating antiferromagnet, hematite (α-Fe2O3)[5]. With low damping and

characteristic frequencies of hundreds of GHz, this compound allows for antiferromagnetic spin-waves to

propagate as far as in YIG, a ferromagnetic material with the lowest known damping that is the material of

choice for magnonic devices. Through measurements of the spin Hall magnetoresistance, the internal crystal

anisotropies can be extracted [6], allowing for a precise determination of critical fields without the need for

high frequency resonance experiments.

Here, we grow high quality antiferromagnetic thin films of hematite (< 500 nm) and show that they can

also allow pure magnonic current to propagate over long-distances, opening the way towards a development

and integration of antiferromagnetic magnonic devices. We then discuss the role of the growth orientation in

the magnetic fields required to induce transport, the stabilization of the antiferromagnetic domains, and impact

on the propagation of magnons. Finally, we discuss the temperature dependence of the magnon propagation

for magnons originating from an electrical spin-bias at the interface of hematite and platinum or from thermal

heating of the hematite layer, and demonstrate that one can even achieve zero-field, room temperature magnon

transport in insulating antiferromagnets.

[1] T. Jungwirth et al., Nat. Phys. 14, 200-203 (2018)

[2] V. Baltz et al., Rev. Mod. Phys. 90, 015005 (2018)

[3] S. Takei et al., Phys. Rev. B, 90, 94408 (2014)

[4] S. Bender et al., Phys. Rev. Lett. 19, 056804 (2017)

[5] R. Lebrun et al., Nature 561, 222-225 (2018)

[6] R. Lebrun et al., arXiv:1901.01213 (2019)


P72 145

From nonlinear interacting magnon gas to magnon Bose-Einstein condensate

and supercurrents

Halyna Musiienko-Shmarovaa, Vasyl S. Tyberkevychb, Andrei N. Slavinb,

Alexander A. Sergaa, and Burkard Hillebrandsa

a Fachbereich Physik and Landesforschungszentrum OPTIMAS, Technische Universität Kaiserslauten,

67663 Kaiserslautern, Germany b Department of Physics, Oakland University, Rochester, Michigan 48309, USA

Bose-Einstein condensate (BEC) is a fascinating quantum phenomenon that manifests itself in the

formation of a coherent macroscopic state from chaotic motions in a thermalized many-particle system. Despite

of the fact that BEC is a consequence of equilibrium Bose statistics, it also can occur in such a nonequilibrium

system as an overpopulated gas of interacting quasiparticles, for example magnons – quanta of spin waves.

Such process is a result of local quasi-equilibrium conditions near the minima of a magnon frequency spectrum.

The dynamics of incoherent magnon gas, its thermalization via four-magnon scattering processes leading to

the formation of a magnon BEC as well as the behaviour of the condensed magnon phase strongly depend on

the peculiarities of magnon-magnon interaction processes, which can be described using corresponding

nonlinear coefficients [1, 2]. Besides, the values of these coefficients crucially influence the formation of such

nonlinear spin-wave objects as solitons, bullets and droplets [3], and determine the specific scenarios of a

phase induced macroscopic quantum collective motion of a magnon condensate—supercurrent [4]. Thus,

determination of such coefficients is an important task for the understanding of dynamics of the coherent

macroscopic quantum magnon states.

In the presented research, by the use of the theoretical approach developed in Ref. [2], we calculate the

magnon spectra and the inter- and cross-quasiparticle interaction coefficients for magnon gases in yttrium iron

garnet films of different thicknesses magnetized under different angles. The obtained data are used to

investigate the behaviour of interacting magnon condensates formed in two magnon spectrum minima at

opposite wavenumbers. Particularly, we predict the conditions for the formation and stability of the magnon

BEC and analyse a supercurrent-like BEC motion in such a system under different initial conditions.

Financial support by the European Research Council within the Advanced Grant 694709

“SuperMagnonics” is gratefully acknowledged.

[1] P. Krivosik, C. E. Patton, Phys. Rev. B 82, 184428 (2010).

[2] O. Dzyapko et al., Phys. Rev. B 96, 064438 (2017).

[3] O. R. Sulymenko et al., Low Temp. Phys. 44, 602-617 (2018).

[4] D. A. Bozhko et al., arXiv: 1808.07407 (2018).


P73 146

Second Sound on magnon BEC in a normally magnetized YIG film.

Yury Bunkov

Russian Quantum Centre, Moscow, Russia

The conventional magnon Bose-Einstein condensation (BEC of magnons with k = 0) has been

observed in magnetically ordered materials with repulsive interaction between magnons, like superfluid 3He,

MnCO3, CsMnF3 ets. [1]. In particularly it was observed in Yttrium Iron Garnet (YIG) film, magnetized

perpendicular to the surface. For YIG film the critical density of non-equilibrium magnons for BEC

condensation corresponds to a deflection of precessing magnetization on an angle ≥ 2o [2]. The eigin state

of magnon BEC determines by the frequency of supported RF field and does not depend on RF power [3].

The BEC state forms at the minimum of the effective magnetic field at the center of the YIG film,as shown in

Fig. 1.

We report the observation of the Goldstoun (second sound) modes of magnon BEC oscillations, which can

be excited by frequency modulation of the RF exciting field.

Figure 1: The magnon BEC state in the minimum of effective magnetic field and the spectrum of its

oscillations, excited by a frequency modulation of supported RF field. The two modes of oscillation are

observed, is analogy with magnon second sound in superfluid 3He [4].

[1] Yu. M. Bunkov, J. Low Temp. Phys., 183, 399 (2016)

[2] Yu. M. Bunkov and V. L. Safonov, J. M. M. M. 452, 30–34 (2018).

[3] Yu. M. Bunkov et al., https://arxiv.org/abs/1810.08051

[4] . Yu.M.Bunkov, Jap. J. Appl. Phys. v.26, p.1809, (1987).

https://arxiv.org/abs/1810.08051


P74 147

Role of magnons in the spin Seebeck effect in polycrystalline YIG pellets

G. Venkat1, T.A. Rose1, C.D.W. Cox1, G.B.G Stennings2, A. J. Caruana1,2 and K. Morrison1

1 Dept. Of Physics, Loughborough University, Loughborough, United Kingdom 2 ISIS Neutron and Muon Source, Didcot, United Kingdom

The spin Seebeck effect (SSE) is defined by a spin polarized current arising in a magnetic material when

a thermal gradient is applied. It was first observed by Uchida et. al. [1] leading to the development of the

new branch of physics: spin caloritronics, which encompasses other magnetothermal effects such as the spin

Peltier and spin Nernst effects [2]. These effects can improve thermoelectric devices as well as a host of new

spintronic devices such as directional couplers and magnon logic gates [3]. Yttrium Iron Garnet (YIG) is

predominantly used in studying these effects due to its low spin wave damping and insulating nature [4].

Here we study the magnetic properties of polycrystalline bulk YIG pellets that were produced by the

solid-state method. Stoichiometric amounts of Y2O3 and Fe2O3 were mixed and calcined in air at 1050 ⁰C

before being pressed into pellets. The pellets were sintered at 1200, 1300 and 1400 ⁰C which produced

different phases of Yttrium Iron Perovskite (YIP) and YIG. We will refer to each of these pellets as P1, P2

and P3 respectively.

The magnetic hysteresis loops of the pellets show a low coercivity of 7 Oe and different switching field

regimes in the mixed phase pellets (Fig. 1(b)). This behaviour was most prominent in the P1 pellet with the

highest YIP. This behaviour is indicative of metastability, such as an antiferromagnetic -ferromagnetic or

spin-flop transition. Broadband FMR measurements were also performed and the Gilbert damping (α) was

extracted. α was largest for P1 with the lowest YIG and lowest for P3 which had the highest YIG fraction.

SSE measurements were carried out on these pellets using a setup similar to Sola et. al [5]. The SSE

coefficient has a direct correlation to the variation of 1/α in these pellets and is direct evidence of the SSE

being agnon driven in these systems (Fig. 1(c)).

[1] K. Uchida et. al., Nature, 455, (2008) 778

[2] G. Bauer et. al., Nat. Mater., 11 (2012) 391

[3] A. Chumak et. al., Nat. Phys., 11 (2015) 453

[4] A. Serga et. al., J. Phys D., 43 (2010) 264002

[5] A. Sola et. al., Sci. Rep., 7 (2017) 46752

Figure 1: (a) The P1 (1200 ⁰C), P2(1300 ⁰C) and P3 (1400 ⁰C) pellets (left to right). (b) The

magnetic hysteresis loops of the pellets. The inset shows the zoomed in positive and

negative saturation regions. P1 shows multiple steps in the high field regions. (c) Variation

of the SSE coefficient and 1/α for the pellets. The similarity in the trends is due to the SSE

being magnon driven.

P1 P2 P3

0

10

20

30

S4 (

nV

m/W

)

5

10

15

20

25

M (B

=1

00

mT

) (em

u/g

))

(a) (b) (c)


P75 148

Thickness dependence of Dzyaloshinskii-Moriya interaction, magnetic

anisotropy and damping in ultrathin cobalt films

Ryszard Gieniusza, Michał Matczakb, Anuj K. Dhimana, Iosif Svekloa, Zbigniew Kuranta, Urszula

Guzowskaa, Feliks Stobieckib, Andrzej Maziewskia

aFaculty of Physics, University of Bialystok, Bialystok, Poland

bInstitute of Molecular Physics, Polish Academy of Sciences, Smoluchowskiego, Poznań, Poland

The interfacial Dzyaloshinskii-Moriya interaction (IDMI) is now known to be responsible in stabilizes

chiral spin textures such as magnetic skyrmions [1]. The IDMI and surface magnetic anisotropy are both

directly co-related with the magnitude of spin-orbit coupling. Measurements were performed on ultrathin

cobalt wedges and flat films (with Co thicknesses 0<dCo<4nm) surrounded by Ir and Pt layers. Cobalt films

were deposited by magnetron sputtering on naturally oxidized Si substrates with Ta/Au buffer. We have

employed Brillouin Light Scattering spectroscopy in backscattering geometry for DMI constant D and spectral

linewidths studies. The magnetization excitations with wave vector along in-plane direction perpendicular to

the applied magnetic field in the sample plane (Damon-Eshbach configuration) were investigated. The values

of D were calculated from measurement of frequency differences f(dCo) between Stokes and anti-Stokes

magnetization excitation frequencies. Using magnetooptical polar Kerr effect as a function of crossed in-plane

and perpendicular applied magnetic fields magnetization curves were measured. Magnetic anisotropy fields

HA(dCo) were determined fitting these curves in single domain model.

We have observed that when the Co thickness decreases, both parameters f(dCo) and HA(dCo) first

increase linearly and then after achieving the maxima (for dCo below ~1.1nm) both decreases. Result will be

discussed with ones from literature [2-6]

Acknowledgement: Supported by Polish National Science Center projects: DEC-2016/23/G/ST3/04196

Beethoven and UMO-2018/28/C/ST5/00308 SONATINA.

1. A. Fert et al, Nat. Rev. Mater. 2 (2017), 17031.

2. D-S Han et al, Nano Lett. 16 (2016), 4438-4446.

3. C. Moreau-Luchaire et al, Nat. Nanotech. 11 (2016), 731-737.

4. K. Di et al, Phys. Rev. Lett. 114 (2015), 047201-047205.

5. D. Khadka et al, J. Appl. Phys. 123, (2018), 123905-123910.

6. P. Shepley et al, Phys. Rev. B 97 (2018), 134417-134424.

https://pubs.acs.org/author/Han%2C+Dong-Soo

https://pubs.acs.org/action/showCitFormats?doi=10.1021%2Facs.nanolett.6b01593


P76 149

Modulation instability and self-action effects under magnetostatic surface

waves pulse propagation in metallized YIG-based magnonic crystals

S. Vysotskii1, A. Kozhevnikov1, G. Dudko1, E. Pavlov1, Y. Khivintsev1, Y. Filimonov1,

A. Stognij2, R. Marcelli3, S. Nikitov4

1Kotelnikov IRE of RAS, Saratov Branch, 410019, Saratov, Russia

2SPMRC National Academy of Sciences of Belarus, 220072, Minsk, Belarus

3CNR-IMM, Roma, Italy

4Kotelnikov IRE of RAS, Moscow, Russia

Spin waves modulation instability and soliton formation in magnonic crystals (MC) has been discussed

both theoretically and experimentally1-4. The same nonlinear effects are possible5-7 for magnetostatic

surface wave (MSSW) propagating in plane YIG films separated from metal screen by air gap with the

thickness h. In this work we studied nonlinear MSSW pulse propagation in the layered structure MC-

dielectric-metal (MCDM). Special attention was paid on the MSSW with wavelength λ~h for which

Lighthill criterion can be fulfilled in the MCDM structures. Experiments were performed for MC based in

YIG films thickness of ≈7.7μm and ≈8.8 μm with 1D periodic array of groves with periods L≈8, 50, 170

μm. By appropriate choice of the parameters h and L it was possible to receive overlapping of the magnonic

gap with anomalous part of MSSW dispersion in MCDM structure where λ~h. For MSSW pulses with

duration τ less than time τ*≈60 ns required for four-magnon parametric instability onset we observe soliton

formation only for MCDM structure based on subwavelength MC8,9 with L≈ 8μm. Figures a)- d) illustrates

MSSW pulses envelope at the output antenna as a function of power of incident microwave pulses duration

of 40 ns. Figure e) illustrates the four-magnon parametric instability onset for pulses with duration τ>τ*.

Figures a)-c) corresponds to MSSW propagation in single subwavelength MC. In that case we observe only

self-action effects leading to pulse width increasing with growing input power. Figure d) illustrate pulse

shrinking with increasing power at frequency 4.22 GHz corresponding to MSSW with λ~h.

This work was supported by the RFBR grant No. 18-57-00005-Bel_a, 17-07-01452_a.

[1]. M. Chen, A.N. Slavin, M.G. Cottam. Phys. Rev. B. Vol. 47, P. 8687-8671. (1993).

[2] 18A. Ustinov, N. Grigorieva, B. Kalinikos, JETP Lett. 88, 31 (2008).

[3]. Drozdovskii, A.V., Cherkasskii, M.A., Ustinov, A.B. et al. Jetp Lett. (2010) 91: 16

[4] A. Ustinov, B. Kalinikos, V. Demidov, S. Demokritov. Phys. Rev. B, 81, 180406(R) (2010)

[5]. Filimonov Y., Marcelli R., Nikitov S. IEEE Trans. on Magn., .38(5), 3105 (2002)

[6]. Marcelli R. Nikitov S., Filimonov Y. et al. IEEE Trans. On Magn..42(7), 1785 (2006)

[7]. Dudko G., Filimonov Y., Galishnikov A. et al. JMMM, V.272-275, Part 2, .999 (2004)

[8] S. Vysotskii, Y. Khivintsev, V. Sakharov et al. IEEE Magn. Lett. 8 (2017) 3706104

[9] S. Vysotskii, G. Dudko, V. Sakharov et al. Acta Physica Polonica A. 133, (2018) 508.


P77 150

A novel protocol to image magnetic field using a single spin in diamond

Cheng-Jie Wang, Pengfei Wang, Jiangfeng Du

University of Science and Technology of China, Hefei, China

Imaging the magnetic field generated by spins and currents is a powerful method to study materials and

devices. In recent years a scanning magnetometer based on the nitrogen-vacancy color center (NV center) in

diamond is emerging, which enables magnetic field imaging with high sensitivity and nanoscale spatial

resolution [1]. Measuring the Zeeman splitting of NV centers can determine the magnetic field and quantum

interference schemes can be applied to improve sensitivity. After the first experiment that demonstrates

potential nanoscale imaging magnetometry [2], NV center microscope is adopted to study non-collinear

antiferromagnetic order [3] and domain-wall hopping [4]. Spin dynamics can also be detected, such as spin

wave in a ferromagnetic microdisc [5] and magnons in a magnetic insulator [6].

In order to image a magnetic field within limited time, we introduce a microwave frequency adjustment

during scanning to record a multiple contour line image in a single scan. Furthermore, a radial basis function

is employed to reconstruct the magnetic field from contour line images. The simulation shows the

reconstructed field is in good agreement with the original field both qualitatively and quantitatively. This

protocol is applied to record the contour line image of the stray field of a frustrated magnet in experiment and

a plausible magnetic field is reconstructed. Our scheme is simple to employ in terms of both software and

hardware and adaptive for magnetic field generated by various materials.

[1] F. Casola, et al., Nature Reviews Materials. 3, 17088 (2018).

[2] G. Balasubramanian et al., Nature. 455, 648–651 (2008).

[3] I. Gross et al., Nature. 549, 252–256 (2017).

[4] J.-P. Tetienne et al., Science. 344, 1366–1369 (2014).

[5] T. van der Sar, F. Casola, R. Walsworth, A. Yacoby, Nat. Commun. 6, 7886 (2015).

[6] C. Du et al., Science. 357, 195–198 (2017).


P78 151

Tuning spin-torque nano-oscillator nonlinearity using He+ irradiation

Sheng Jianga, b, Roman Khymynb, Sunjae Chunga, c, Quang Tuan Lea, Liza Herrera Diezd, Afshin

Houshangb, e, Mohammad Zahedinejadb, Dafine Ravelosonad, f, and Johan Åkermana, b, e*

a Department of Applied Physics, School of Engineering Sciences, KTH Royal Institute of Technology,

164 40 Kista, Sweden b Physics Department, University of Gothenburg, 412 96, Gothenburg, Sweden

c Department of Physics and Astronomy, Uppsala University, 751 20 Uppsala, Sweden d Center for Nanoscience and Nanotechnology, CNRS, Universite Paris-Sud, Universite Paris-Saclay,

91405 Orsay, France e NanOsc AB, Kista 164 40, Sweden

f Spin-Ion Technologies, 28 rue du general Leclerc, 78000 Versailles Cedex, France

Spin-torque nano-oscillators (STNOs) are promising candidates for nanoscale broadband microwave

generators [1]. The STNO microwave signal properties, such as frequency, frequency tunability, linewidth, are

mainly governed by the nonlinearity N [2]. Here we use He+ irradiation to tune N of all-perpendicular [Co/Pd]-

Cu-[Co/Ni] spin-valve STNOs. As [Co/Ni] free layer has the He+ fluence-dependent perpendicular magnetic

anisotropy Hk (so as the effective magnetization µ0Meff, µ0Meff = µ0Ms- µ0Hk), we tune Meff by employing

different fluences [3]. As a consequence, current-induced frequency tunability df/dIdc are continuously

engineered in Fig.1, indicating the tuned nonlinearity as df/dIdc ∝ N [2]. We control N in an in-plane field from

strongly positive to moderately negative as summarized in Fig.1f. As the STNO linewidth is a parabolic

function of N [2], we can dramatically improve the linewidth by about two orders of magnitude by controlling

N→0. Our results are in good agreement with the theory for nonlinear auto-oscillators, confirm theoretical

predictions of the role of nonlinearity, and demonstrate a straightforward path towards improving the

microwave properties of STNOs [4].

Fig 1. (a-e) The power spectral density (PSD) as functions of current (Idc) in nano-contact(NC) STNOs with

different He+ irradiated fluences and nonirradiated NiFe free layer at in-plane field µ0H = 0.72 T. The NC radii

are 35 nm. The red dashed lines are the linear fits of the frequency. ∆f indicates the minimal linewidth. Note

that NiFe free layer in Fig.1e is utilized to provide higher Meff. (f) The df/dIdc (the slopes of linear fits in Fig.

1a-e) vs. µ0Meff.

[1] T. Chen, et al., Proc. IEEE 104, 1919 (2016).

[2] A. Slavin, et al., IEEE Trans. Magn. 45, 1875 (2009).

[3] S. Jiang, et al., AIP Advances, 8, 65309 (2018).

[4] S. Jiang, et al., Phys. Rev. Appl. under review (2019). https://arxiv.org/abs/1812.08873


P79 152

Domain wall mediated excitation of ultrashort spin waves in bi-axial

antiferromagnets driven by spin current.

Roman Khymyna,b, Roman Ovcharovc, Johan Åkermana,b,d, Boris Ivanovc,e

a University of Gothenburg, Gothenburg, Sweden

b NanOsc, Kista, Sweden c Taras Shevchenko National University of Kyiv, Kyiv, Ukraine

d KTH Royal Institute of Technology, Kista, Sweden e Institute of Magnetism, NAS and MES of Ukraine, Kyiv, Ukraine

Antiferromagnets (AFMs) have great benefits for the future spintronic applications [1] involving as high

frequencies (till THz) and high speeds (till dozens of km/s) of magnetic excitations. Also, the AFM spin-torque

nano-oscillators (STNOs), in which the applied spin current rotates the Neel vector [2-4], do not require

external magnetic field for their operation. Advanced devices will require high-speed propagating spin waves

(SWs) as signal carriers, i.e. SWs with the high k-vectors, the excitations of which remains challenging.

We demonstrate theoretically that the simple spin texture, such as an AFM domain wall (DW), driven by

spin current, can act as an emitter of the propagating spin waves with high wavevectors in AFMs with the bi-

axial anisotropy. We consider AFM with the strong anisotropy along the easy axis and the lower one in

perpendicular direction. In the proposed generator (Fig. 1a) the spin current, which polarization is directed

along the easy axis, excites the precession of the Neel vector within the DW. The threshold current is defined

by the value of the second anisotropy, and frequency ω is tuneable by the strength of spin current. We show

that the above precession of the DW leads to the excitation of magnons with the frequency 3ω, which means

a robust emission of the propagating SWs in the AFM strip in the case, when 3ω> ωAFMR (see Fig. 1c).

Consequently, the maximum achievable frequency of SWs is 3ωAFMR, which corresponds to a very short

wavelength of the SW, comparable with the exchange length of the AFM. The SW emission occurs, when the

applied current overcomes a threshold value σjth> α ωAFMR/3, where σ defines charge to spin conversion

efficiency [2] and α<<1 – damping parameter. When the frequency ω approaching ωAFMR, the emitted SWs

experience abrupt drop of the frequency with current, however, the amplitude of SWs increases significantly

in this case.

[1] E. Gomonay and V. Loktev, Low Temp. Phys. 40, 17 (2014).

[2] R. Khymyn et al., Sci. Rep. 7, 43705 (2017).

[3] O. Sulymenko et al., Phys. Rev. Applied, 8, 064007 (2017).

[4] V Puliafito et al., Physical Review B 99, 024405 (2019).

Figure 1: a) The sketch of the proposed SW generator, b) the snapshot from micromagnetic

simulations, c) the extracted frequencies of the DW precession (red) and propagating SWs

(blue) as a function of applied current.


P33 153

List of presenting authors:

Ahmad H, 135

Albisetti E, 13

Alejos Ducal O, 99

Anane A, 82

Ansalone P, 92

Arias R E, 30

Back C H, 70

Barman A, 57

Bertacco R, 53

Bhaskar U K, 42

Borisenko I V, 97

Bunkov Y, 146

Chaurasiya A K, 133

Che P, 55

Chumak A, 62

Ciubotariu O, 140

Costa J D, 94

Csaba G, 16

d’Aquino M, 26-112

de Loubens G, 35

Demidov V E, 29

Demokritov S, 67

Diaz S A, 71

Divinskiy B, 75-76

Dobrovolskiy O V, 25

Dreyer R, 92

Ebels U, 103

Filimonov Y, 15-149

Finocchio G, 111

Flacke L, 93

Flajšman L, 12

Flebus B, 47

Foerster M, 18

Fripp K G, 116-117

Fulara H, 84

Funada S, 130

Gartside J C, 104

Gieniusz R, 148

Giordano A, 90

Gräfe J, 63

Grassi M, 124

Grundler D, 8-78

Gruszecki P, 56

Guo M, 136

Han X, 54

Hernández-Gómez P, 100

Hillebrands B, 6

Hioki T, 19

Hoffman A, 32

Holländer R, 45

Hula T, 118

Ishibashi M, 61

Keatley P S, 23

Khalili P, 52

Khitun A, 60-132

Khymyn R, 151-152

P33 154

Kiechle M, 89

Kim J-V, 39

Kirilyuk A, 7

Körber L, 49

Kostylev M, 65

Kreil A J E, 123

Krivorotov I, 51

Kuepferling M, 88

Kumari S, 137

Kuttah Padi N B, 138

Landeros P, 38

Latcham O S, 74

Lee D K, 107

Lenz K, 109

Leo A, 31

Lewis K A, 79

Li T, 131

Li X, 50

Liensberger L, 41

Litvinenko A, 24-102

Ma F, 48

Máca F, 139

Madami M, 80

Malathi M, 33

Mancilla-Almonacid D, 105

Marković D, 22

Merbouche H, 83

Mikhaylovskiy R, 40

Mizukami S, 43

Mohseni M, 95-96

Moriyama T, 46

Mulkers J, 106

Muralidhar S, 66

Musiienko-Shmarova H, 145

Nikitin A A, 120-121

Nikitov S A, 143

Nozaki Y, 20

Ogrin F Y, 81

Osuna Ruiz D, 115

Pantazopoulos P-A, 142

Puliafito V, 141

Qaiumzadeh A, 108

Qin H, 37

Ross A, 144

Rychły J, 110

Sadovnikov A V, 17

Saha S, 28

Sahoo S, 134

Sánchez-Tejerina L, 128

Schäffer A F, 34

Schultheiss H, 10

Schultheiss K, 77

Seki S, 21

Serga A A, 14

Shiranzaei M, 98

Sidi Elvalli A, 101

Sushruth M, 119

Tacchi S, 68

Tanabe K, 86

Taniguchi T, 114

Träger N, 44-129

P33 155

Tyberkevich V, 69

Urazhdin S, 72

Urbánek M, 127

Van Dijken S, 11

Vanderveken F, 87

Vasyuchka V I, 126

Venkat G, 147

Wang C-J, 150

Wang H, 85

Wang Q, 125

Wartelle A, 113

Wintz S, 59

Yu H, 36

Zahedinejad M, 27

Zakeri Kh, 64

Zelent M, 58-122

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