1
Current-induced magnetic domain wall motion -Effect of the Dzyaloshinskii–Moriya interaction
on the magnetic domain-wall dynamics-
Institute for Chemical Research, Kyoto University Teruo Ono
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Collaborators
Kab-Jin Kim, Kohei Ueda, Yoko Yoshimura Institute for Chemical Research, Kyoto University
Yoshinobu Nakatani University of Electro-communications
Hiroshi Kohno Nagoya University
Gen Tatara RIKEN
H. Tanigawa, T. Suzuki, N. Ohshima Renesas Electronics Corporation
S. Fukami, F. Matsukura, H. Ohno Tohoku University
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3
Institute for Chemical Research Nanospintronics Lab.
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Magnetic domain-wall (DW) • Boundary between two different magnetization regions
DW motion
MFM image
MOKE image
DW and DW motion
B
e-
Magnetic field-driven DW motioin
Electric current-driven DW motion
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Prediction of current-induced domain wall motion
Change in spin direction of conduction electron
Rotation of
local magnetic moment
Static domain wall
Domain wall
Current
Conservation of spin angular momentum
Luc Berger Professor Emeritus,
Carnegie Mellon University
J. Appl. Phys. 55, 1954 (1984).
x
mu j
t
mmHm
t
meff
jPeM
gu
s
Bj
2
Adiabatic spin transfer torque
DW motion along electron flow
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Successive images of DW motion by current pulse injections (7×1011 A/m2, 0.5 µs)
DW position can be controlled by current pulsed.
Phys. Rev. Lett., 92 (2004) 077205. NiFe, w = 240nm, t = 10nm
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Magnetic Racetrack Memory proposed by IBM
A novel three-dimensional spintronic storage memory
Magnetic nanowires: Information stored in the domain
-Capacity of a hard disk drive -Reliability and performance of solid state memory (DRAM, FLASH, SRAM...)
Courtesy of Stuart Parkin (IBM)
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Race-track memory Demo. Writing, Shifting, Reading
Applied Physics Express 3 (2010) 073004.
Shift operation (3DWs)
Back & forth operation (2DWs)
Mult-DWs motion with the same velocity as a single DW.
Co/Ni with perpendicular magnetization
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Mechanisms of current-induced DW motion
(1)DWM by spin transfer torque
Tatara and Kohno, Phys. Rev. Lett. (2004).
(2)DWM by spin Hall torque
Thiaville et al., Europhys. Lett. 100, 57002 (2012).
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Bloch DW
Energy
<
To drive a DW by current,
spin torque has to overcome the barrier of Neel wall!
DWM by adiabatic spin torque
P
KeJ
B
th2
Tatara and Kohno, Phys. Rev. Lett. (2004).
Neel DW
+ -
DW moves with precessional motion.
Direction of DW motion is along electron flow.
Jth is given by
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Bloch DW Neel DW
Energy
< + -
+ -
Energy
>
Energy
=
How to prove the intrinsic pinning?
For current-driven DW motion by adiabatic torque, Spin torque has to overcome the barrier of Neel wall!
Spin torque has to overcome the barrier of Bloch wall!
Resulting in Jth minimum
By changing wire width,
(1) Existence of minimum of Jth for DW motion
(2) Change of DW structure from Bloch to Neel
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Neel Wall
Neel Wall + Bloch Wall
Bloch Wall
Bloch Wall
Bloch Wall
Evidence for intrinsic pinning!
Jth & DW resistance v.s. wire width
Bloch DW Neel DW
Nature Materials 10 (2011) 194.
・Jth minimum
・Change of DW structure
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Spin Hall torque-driven DW motion
SH
NoSH
No
J
Bloch DW
No spin Hall torque!
No DW motion…
J
14
SH
SH
J J
spin Hall torque on Neel wall!
DW motion…
Spin Hall torque-driven DW motion
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Heff Heff
Heff
Heff
Chiral Neel wall is necessary!
What is the origin of the chiral Neel wall?
Spin Hall torque-driven DW motion
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Chiral Neel wall stabilized Dzyaloshinskii–Moriya interaction
Dzyaloshinskii-Moriya interaction (DMI)
HDMI= -D12 • (S1 × S2)
Observation of chiral DW by SPLEEM
Wu, Schmid et al., Nat. Comm. (2013)
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Co/Ni multilayers
• Perpendicular magnetic anisotropy (interfacial anisotropy btw Co and Ni) • Multilayer only with magnetic materials • High tunneling magnetoresistance (TMR) • Low threshold current with high thermal stability
PRL, 68, 682 (1992) APL, 97, 072513 (2010) Nat. Mater. 10, 194 (2011) Nat. Nanotechnol. 7, 635 (2012) Nat. Comm. 4, 2011 (2013)
Promising material for spintronic application
Effect of the Dzyaloshinskii–Moriya interaction on DW dynamics Co/Ni multilayers with broken structural inversion symmetry
…
Co/Ni multilayer
Insert MgO layer to break structural inversion symmetry
Our sample structure
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Thickness dependence of current-induced DW motion
-3 -2 -1 0 1 2 30
1
J ( 1012
Am-2
)
PD
W
t = 1.2 nm
t = 2.1 nm
t = 3.0 nm
t = 3.9 nm
t = 4.8 nm
t = 5.7 nm
t = 6.6 nm
t = 7.5 nm
t = 8.4 nm
APEX 7, 053006 (2014).
[electron direction] [current direction]
current flow direction
electron flow direction
Me
ch
an
ism
tra
ns
itio
n
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Thickness dependence of current-induced DW motion
-3 -2 -1 0 1 2 30
1
J ( 1012
Am-2
)
PD
W
t = 1.2 nm
t = 2.1 nm
t = 3.0 nm
t = 3.9 nm
t = 4.8 nm
t = 5.7 nm
t = 6.6 nm
t = 7.5 nm
t = 8.4 nm
APEX 7, 053006 (2014).
Adiabatic spin transfer torque (STT)
e- Adiabatic STT-driven DW motion
Nat. Mater. 10, 194 (2011).
Spin Hall torque
e- Spin Hall torque-driven DW motion
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Dzyaloshinskii–Moriya interaction
-3 -2 -1 0 1 2 30
1
J ( 1012
Am-2
)
PD
W
t = 1.2 nm
t = 2.1 nm
t = 3.0 nm
t = 3.9 nm
t = 4.8 nm
t = 5.7 nm
t = 6.6 nm
t = 7.5 nm
t = 8.4 nm
APEX 7, 053006 (2014).
Spin Hall torque + Dzyaloshinskii–Moriya interaction
SH
J
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Summary
We investigated the DW dynamics in Co/Ni multilayered structure which is promising candidate for spintronic applications.
From the thickness dependence of the DW motion, we found that the DW driving mechanim shows transition from SH torque in thinner layers to adiabaitic STT in thicker layers.
We found that the DMI influences the structure of DW, which gives a crucial effect on the DW dynamics.
We developed several methods to quantify the DMI and estimated the DMI-induced effective field in various thicknesses of Co/Ni multilayers.
Using a real-time detection method, we found that the strength of DMI increases as decreasing the temperature.
Supported by Scientific Research(S) of JSPS and the R&D Project for IC
T Key Technology to Realize Future Society of MEXT.
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