Stability and magnetism of infinite atomic chains Jaime Ferrer.
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Transcript of Stability and magnetism of infinite atomic chains Jaime Ferrer.
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Stability and magnetism of infinite atomic chains
Jaime Ferrer
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Three questions that will be addressed:– Which elements may produce atomic chains in MCBJ?– Which chains display magnetic behavior?– What is the anisotropy of magnetic atomic chains?
OUTLINE
Infinite Atomic Chains
– Motivation: zigzag versus linear chains– Set-up of the simulations– The case of Ir and Pt– Stability of Transition Metal atomic chains– Magnetism and magnetic anisotropy of atomic chains
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ACKNOWLEDGMENTS
DISCUSSIONS SIESTA team
C. Untiedt AlicanteJ. J. Palacios Alicante
A. Vega ValladolidF. Flores Madrid
C. J. Lambert Lancaster S. Sanvito Dublin
P. Major BudapestJ. Cserti BudapestS. Sirichantaropass Lancaster
L. Fernández-Seivane - Oviedo
V. M. García-Suárez - Lancaster
Infinite Atomic Chains
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Conductance oscillations in atomic chains - The experiments
R. H. Smit et al. PRL 87, 266102 (2001); 91, 076805 (2003)
MotivationInfinite Atomic Chains
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The SMEAGOL method for spin- and molecular electronics
A. RochaS. Sanvito
S pin and
M olecular
E lectronics in
A tomically
G enerated
O rbital
L andscapes
S. BaileyC. Lambert
V. García-Suárez J. Ferrer
PRB 73, 085414 (06) http://www.smeagol.tcd.ie
Infinite Atomic Chains Motivation
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Stability and conductance of infinite Pt chains
Zigzag vs linear chainsSame bond distance d = 2.38 ÅAngle with z-axis = 25º
Conductance of zigzag chains as function of dz
Energy of zigzag and linear chains as function of dz
dz
dz
Infinite Atomic Chains Motivation
García-Suárez et al. PRL 95, 256804 (2005)
For Gold chains, see Sánchez-Portal, PRL 83 (99)
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Stability of finite length Pt chains attached to electrodes
Atomic configuration of the constriction1-, 2- and 4- atom chainsFull Molecular Dynamics relaxation for fixed dz
Cohesion energy of relaxed chains as function of dz2-, 3-, 4- and 5- atoms chains
Infinite Atomic Chains Motivation
García-Suárez et al. PRL 95, 256804 (2005)
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Conductance oscillations in zigzag Pt chains
Smit et al, PRL (2003)
Conductance averaged over distances ~ 1 A about equilibrium distance
Conductance of 2, 3, 4 and 5 atoms chains as function of dz
Infinite Atomic Chains MotivationMotivation
García-Suárez et al. PRL 95, 256804 (2005)
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Zigzag versus linear chains: maybe Spin-Orbit interaction?
Infinite Atomic Chains MotivationMotivation
Spin-Orbit hamiltonian
TheoryExperiments
SLrV=H
S>L<rVE
Magnetic anisotropy
>S<LrVE
Chain stiffnessFrustration
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Infinite Atomic Chains Simulations set-up
dz
dz
Simulations performed with SIESTA + Spin-Orbit
Soler et al. JPCM (2002)Fernández-Seivane et al. JPCM (2006)
Unit cells with 2 atoms to allow for zigzags(tests with 4, 6 atoms for Ir) Full relaxation of forces
HgAuPtIrOsReWTaHfLa
CdAgPdRhRuTeMoNbZrY
ZnCuNiCoFeMnCrVTiSc
Al, Pb
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Infinite Atomic Chains The case of Ir & Pt
Ir Pt
Zigzag
Ladder
Zigzag
Ladder
Linear chains Delin & Tossati, PRB 68 (2003)
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Infinite Atomic Chains Stability of atomic chains
All chains have the absolute minimum that corresponds to ladders
Few chains have the zigzag local minimum ( & its accompanying maximum)
Look at the chain tension (slope)
Tosatti et al., Science 291 (2001)
T =∂ E∂ d z
Zigzag minimum exists if T becomes negative
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Infinite Atomic Chains Stability of atomic chains
Importance of Spin polarization & Spin-Orbit interaction for the stability
Paramagnetic simulations tend to overestimate stability
Spin-Orbit interaction does not affect much the stability of chains
Ir Pt
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Infinite Atomic Chains Stability of atomic chains
Importance of Spin polarization & Spin-Orbit interaction for the stability
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Infinite Atomic Chains Stability of atomic chains
Elements that make chains – experimental evidence
Length histograms of chains of different TM elements
From quantum point contacts to monatomic chains: fabrication and characterization of the ultimate nanowireRHM Smit Thesis manuscript, Leiden (2003)
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Infinite Atomic Chains Stability of atomic chains
Elements that make chains – experimental evidence
From quantum point contacts to monatomic chains: fabrication and characterization of the ultimate nanowireRHM Smit Thesis manuscript, Leiden (2003)
Plots of average return lengths
Stretch until breaking point (BP)and bring electrodes back to contact (C)
Return length = length from BP to C
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Infinite Atomic Chains Stability of atomic chains
Tension of chains of different TM elements
Only Ir, Pt & Au have energy minima
AuPtIr
AgPdRh
CuNiCo
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Infinite Atomic Chains Stability of atomic chains
Tension of chains of different TM elements
W & Os (and possibly Re) should form atomic chains
Hg may make long atomic chains
Pb (and Al) should not form chains
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Infinite Atomic Chains Magnetic anisotropies
Magnetism & magnetic anisotropies
Magnetism (& Spin-Orbit effects) in gold are negligible
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Infinite Atomic Chains Magnetic anisotropies
Magnetism of Os
W displays similar behavior
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Infinite Atomic Chains Summary
Summary
Ab-initio simulations of infinite zigzag chains of TM elements Co, Ni, Cu, Rh, Pd, Ag, Al & Pb do not form stable zigzag chains Ir, Pt & Au form stable chains W, Os (and possibly Re) are predicted to form stable chains Hg may form long chains Ir & Pt chains are magnetic and show sizable MAEs W, Os, Au & Hg chains show no magnetic behavior.