Anomalous Bias Dependence of Spin Torque in Magnetic Tunnel Junctions

TL;DR

This paper predicts an unusual bias dependence of spin transfer torque in magnetic tunnel junctions, showing sign reversals and quadratic behaviors due to the interplay of spin currents and barrier symmetry.

Contribution

It introduces the concept of anomalous bias dependence of spin torque in MTJs, highlighting the role of exchange splitting and barrier symmetry in this behavior.

Findings

T_{||} can reverse sign without bias sign change

Spin torque exhibits quadratic bias dependence

Mechanism involves interplay of spin currents in different magnetic configurations

Abstract

We predict an anomalous bias dependence of the spin transfer torque parallel to interface, $T_{||}$, in magnetic tunnel junctions (MTJ), which can be selectively tuned by the exchange splitting. It may exhibit a sign reversal {\it without} a corresponding sign reversal of the bias or even a quadratic bias dependence. We demonstrate that the underlying mechanism is the interplay of spin currents for the ferromagnetic (antiferromagnetic) configurations, which vary linearly (quadratically) with bias, respectively, due to the symmetric (asymmetric) nature of the barrier. The spin transfer torque perpendicular to interface exhibits a quadratic bias dependence.