Signatures of asymmetric and inelastic tunneling on the spin torque bias dependence

TL;DR

This paper theoretically investigates how structural asymmetries and inelastic scattering affect the bias dependence of spin transfer torque in magnetic tunnel junctions, revealing distinct signatures for different scattering mechanisms.

Contribution

It introduces a theoretical model showing how asymmetries and inelastic scattering modify the bias dependence of spin transfer torque and conductance in magnetic tunnel junctions.

Findings

Asymmetries and inelastic scattering add antisymmetric bias dependence to the perpendicular torque.

Interfacial inelastic scattering produces symmetric bias dependence.

Signature analysis can identify the origin of discrepancies in measurements.

Abstract

The influence of structural asymmetries (barrier height and exchange splitting), as well as inelastic scattering (magnons and phonons) on the bias dependence of the spin transfer torque in a magnetic tunnel junction is studied theoretically using the free electron model. We show that they modify the "conventional" bias dependence of the spin transfer torque, together with the bias dependence of the conductance. In particular, both structural asymmetries and bulk (inelastic) scattering add {\em antisymmetric} terms to the perpendicular torque ($\propto V$ and $\propto j_e|V|$), while the interfacial inelastic scattering conserves the junction symmetry and only produces {\em symmetric} terms ($\propto |V|^n$, $n\in\mathbb{N}$). The analysis of spin torque and conductance measurements displays a signature revealing the origin (asymmetry or inelastic scattering) of the discrepancy.