Description of current-driven torques in magnetic tunnel junctions

TL;DR

This paper presents a quantum mechanical analysis of spin-dependent transport and torques in magnetic tunnel junctions, highlighting the origins of transverse spin density, oscillatory behaviors, and bias asymmetries.

Contribution

It introduces a free electron model for non-collinear magnetizations in MTJs, analyzing quantum interference effects and the impact of s-d exchange coupling on spin transfer torque.

Findings

Identification of oscillatory torques due to quantum interference

Discovery of bias asymmetry in spin transfer torque

Influence of s-d exchange coupling on torque in half-metallic MTJs

Abstract

A free electron description of spin-dependent tranport in magnetic tunnel junctions with non collinear magnetizations is presented. We investigate the origin of transverse spin density in tunnelling transport and the quantum interferences which give rise to oscillatory torques on the local magnetization. Spin transfer torque is also analyzed and an important bias asymmetry is found as well as a damped oscillatory behaviour. Furthermore, we investigate the influence of the s-d exchange coupling on torque in particular in the case of half-metallic MTJ in which the spin transfer torque is due to interfacial spin-dependent reflections.