Relativistic N\'eel-Order Fields Induced by Electrical Current in Antiferromagnets

Relativistic Néel-Order Fields Induced by Electrical Current in Antiferromagnets

J. Železný, H. Gao, K. Výborný, J. Zemen, J. Mašek, Aurélien Manchon, J. Wunderlich, Jairo Sinova, and T. Jungwirth

Phys. Rev. Lett. 113, 157201 – Published 6 October 2014

Abstract

We predict that a lateral electrical current in antiferromagnets can induce nonequilibrium Néel-order fields, i.e., fields whose sign alternates between the spin sublattices, which can trigger ultrafast spin-axis reorientation. Based on microscopic transport theory calculations we identify staggered current-induced fields analogous to the intraband and to the intrinsic interband spin-orbit fields previously reported in ferromagnets with a broken inversion-symmetry crystal. To illustrate their rich physics and utility, we consider bulk ${Mn}_{2} Au$ with the two spin sublattices forming inversion partners, and a 2D square-lattice antiferromagnet with broken structural inversion symmetry modeled by a Rashba spin-orbit coupling. We propose an antiferromagnetic memory device with electrical writing and reading.

Received 2 June 2014

DOI:https://doi.org/10.1103/PhysRevLett.113.157201

Authors & Affiliations

J. Železný^1,2, H. Gao³, K. Výborný¹, J. Zemen⁴, J. Mašek⁵, Aurélien Manchon⁶, J. Wunderlich^1,7, Jairo Sinova^8,1,3, and T. Jungwirth^1,9

¹Institute of Physics ASCR, Cukrovarnická 10, 162 53 Praha 6, Czech Republic
²Faculty of Mathematics and Physics, Charles University in Prague, Ke Karlovu 3, 121 16 Prague 2, Czech Republic
³Department of Physics, Texas A&M University, College Station, Texas 77843-4242, USA
⁴Department of Physics, Blackett Laboratory, Imperial College London, London SW7 2AZ, United Kingdom
⁵Institute of Physics ASCR, Na Slovance 2, 182 21 Praha 8, Czech Republic
⁶Physical Science and Engineering Division, King Abdullah University of Science and Technology (KAUST), Thuwal 23955-6900, Kingdom of Saudi Arabia
⁷Hitachi Cambridge Laboratory, Cambridge CB3 0HE, United Kingdom
⁸Institut für Physik, Johannes Gutenberg Universität Mainz, 55128 Mainz, Germany
⁹School of Physics and Astronomy, University of Nottingham, Nottingham NG7 2RD, United Kingdom

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Vol. 113, Iss. 15 — 10 October 2014

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Figure 1
(a) ${Mn}_{2} Au$ crystal structure and antiferromagnetic ordering. The two spin sublattices have broken inversion symmetry as illustrated by the red and purple colors. The full crystal is centrosymmetric around the Au atom as also highlighted in the figure. (b) Total, sublattice, and spin projected density of states from the ab initio calculation and for the tight-binding Hamiltonian model.
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Figure 2
(a) 2D AFM square lattice model with Rashba spin-orbit coupling. (b),(c) Band structure and the spin-resolved density of states projected in each sublattice for the AFM state. (d),(e) Band structure and the spin-resolved density of states for the FM state. Here the hopping parameter $t_{N} = 3.0 eV$ , $J_{s d} = 1.0 eV$ , and $V_{SO} = 0.1 eV$ .
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Figure 3
(a) Schematics of the intraband, inverse spin galvanic effect in a model Rashba system. The left panel represents the equilibrium distribution of spins (red arrows); the right panel shows the nonequilibrium redistribution resulting in a net in-plane spin polarization (thick red arrow) perpendicular to the current (green arrow). (b) Intraband NSOT field in ${Mn}_{2} Au$ as a function of the in-plane spin-axis angle. The sublattice index $A$ or $B$ and component of the field $x$ , $y$ , or $z$ ([100], [010], [001]) are shown for each curve. (c) Same as (b) for the out-of-plane spin-axis angle. (d) Schematics of the intrinsic interband contribution to the nonequilibrium spin polarization. In equilibrium all spins are approximately aligned with the exchange field, which is considered to be stronger than the Rashba field. A nonequilibrium in-plane Rashba field (purple arrows) aligned perpendicular to the applied current causes an out-of-plane tilt of the carrier spins on the shifted Fermi surface. (e),(f) Interband NSOT fields as a function of spin-axis angles in the 2D Rashba AFM for $Γ = 0.01 eV$ and $E_{F} = - 2 eV$ . Other parameters of the model are as in Fig. 2 In all panels the current is along the [100] axis.
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Figure 4
(a) The $z$ component of the NSOT field in the 2D square-lattice Rashba AFM for $ϕ = 0$ as a function of the Fermi energy. (b) Same as (a) for the FM state of the 2D Rashba square lattice. (c) Schematics of the AFM dynamics in a staggered field generating the fieldlike torque. (d) Schematics of the electrical writing scheme via the NSOT in a memory device built in an AFM with cubic easy axes. Black arrows represent the cross-wire writing currents and either of the current lines can be also used for reading by the AMR. Red-blue arrows show the current-induced AFM spin-axis reorientation.
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Physical Review Letters

Relativistic Néel-Order Fields Induced by Electrical Current in Antiferromagnets

J. Železný, H. Gao, K. Výborný, J. Zemen, J. Mašek, Aurélien Manchon, J. Wunderlich, Jairo Sinova, and T. Jungwirth

Phys. Rev. Lett. 113, 157201 – Published 6 October 2014

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