Voltage Asymmetry of Spin-Transfer Torques

TL;DR

This paper introduces a Non-Equilibrium Green's Function model for spin-transfer torque devices that accurately matches experimental data across various parameters, highlighting the role of multiple transverse modes and contact polarization.

Contribution

The paper presents the first comprehensive theoretical model that quantitatively explains diverse experimental observations in spin-transfer torque devices using a unified approach.

Findings

Model matches experimental differential resistances, MR, and torques.

Inclusion of multiple transverse modes is crucial for accuracy.

Explains bias asymmetry of in-plane torque via contact polarization.

Abstract

We present a Non-Equilibrium Green's Function based model for spin torque transfer (STT) devices which provides quantitative agreement with experimentally measured (1) differential resistances, (2) Magnetoresistance (MR), (3) In-plane torque and (4) out-of-plane torque over a range of bias voltages, using a single set of three adjustable parameters. We believe this is the first theoretical model that is able to cover this diverse range of experiments and a key aspect of our model is the inclusion of multiple transverse modes. We also provide a simple explanation for the asymmetric bias dependence of the in-plane torque, based on the polarization of the two contacts in energy range of transport.