Anisotropic tunneling magnetoresistance and tunneling anisotropic magnetoresistance: Spin-orbit coupling in magnetic tunnel junctions

Abstract

The effects of the spin-orbit coupling ͑SOC͒ on the tunneling magnetoresistance of ferromagnet/ semiconductor/normal-metal tunnel junctions are investigated. Analytical expressions for the tunneling anisotropic magnetoresistance ͑TAMR͒ are derived within an approximation in which the dependence of the magnetoresistance on the magnetization orientation in the ferromagnet originates from the interference between Bychkov-Rashba and Dresselhaus SOCs that appear at junction interfaces and in the tunneling region. We also investigate the TAMR effect in ferromagnet/semiconductor/ferromagnet tunnel junctions. The conventional tunneling magnetoresistance ͑TMR͒ measures the difference between the magnetoresistance in parallel and antiparallel configurations. We show that in ferromagnet/semiconductor/ferromagnet heterostructures, because of the SOC effects, the conventional TMR becomes anisotropic-we refer to it as the anisotropic tunneling magnetoresistance ͑ATMR͒. The ATMR describes the changes in the TMR when the axis along which the parallel and antiparallel configurations are defined is rotated with respect to a crystallographic reference axis. Within the proposed model, depending on the magnetization directions in the ferromagnets, the interplay of Bychkov-Rashba and Dresselhaus SOCs produces differences between the rates of transmitted and reflected spins at the ferromagnet/semiconductor interfaces, which results in an anisotropic local density of states at the Fermi surface and in the TAMR and ATMR effects. Model calculations for Fe/GaAs/Fe tunnel junctions are presented. Finally, based on rather general symmetry considerations, we deduce the form of the magnetoresistance dependence on the absolute orientations of the magnetizations in the ferromagnets.

Spin precession and inverted Hanle effect in a semiconductor near a finite-roughness ferromagnetic interface

“…A difference is, however, observed, attributed to anisotropy of the tunneling process. [39][40][41] Apart from some quantitative differences, the results for GaAs-and Si-based devices are remarkably similar.…”

Current-induced spin–orbit torques

“…Indeed, a metal/oxide bilayer is already half of an MTJ, which could be used as a readout element of a magnetic bit where the write functions are performed by the SO torque [15]. Moreover, several studies have pointed out the interplay between SO coupling and tunnelling anisotropic magnetoresistance in MTJs [99][100][101] and explicitly considered the dependence of the tunnelling conductance on interfacial Rashba spin splitting in metal systems [102,103] as well as the coexistence of Dresselhaus and Rashba fields in metal/semiconductor heterojunctions [31,65,104], providing additional functionalities to layers displaying strong SO effects. Further, as noted by Obata & Tatara [59], DW manipulation can be achieved by means of an SO torque, depending on the type of DW involved and easy axis magnetization direction, which may be useful in, for example, shift register or random access memory applications based on DW motion.…”

“…Together with other forms of spin accumulation and spin currents that can be excited in semiconductors by electrical or optical means, this has generated considerable interest in a 'magnetfree' approach to spintronics [14]. Moreover, several proposals have been made to exploit the intrinsic SO fields in semiconductors to control or modulate spin injection into FM electrodes through a semiconductor channel [62][63][64] or tunnel junction [31,65,66]. It has been realized as well that the mechanism described in §3 could be used to exert a torque on the magnetization of an FM layer in contact with a semiconducting channel by absorption of the SO-induced spinpolarization component perpendicular to the FM magnetization at the interface between the two materials [67,68].…”

Antiferromagnetic spintronics

“…Hence, by varying the ferromagnetic orientation (e.g., by applying an external magnetic field H), the resistance (R) of the trilayer can be changed. Some of the explanations for tunnel anisotropic magnetoresistance are based on Rashba-or Rashba and Dresselhaus-induced spin-orbit coupling (Shick et al, 2006;Matos-Abiague and Fabian, 2009). The effect was first experimentally shown to exist in (Ga,Mn)As-based tunnel junctions (Gould et al, 2004) and has been widely studied since then for various ferromagnetic-based tunnel junctions.…”