Origins of the unidirectional spin Hall magnetoresistance in metallic bilayers

TL;DR

This paper investigates the origins of unidirectional spin Hall magnetoresistance in metallic bilayers, identifying three key mechanisms and demonstrating how their interplay influences resistance asymmetry.

Contribution

It reveals the specific mechanisms—interface and bulk spin-dependent scattering, and electron-magnon scattering—that cause UMR in Co/Pt and CoCr/Pt bilayers, providing a comprehensive understanding.

Findings

UMR can be positive or negative depending on scattering mechanisms.

Resistance asymmetry depends on current, magnetic field, and temperature.

The study offers a unified description of UMR behavior in metallic bilayers.

Abstract

Recent studies evidence the emergence of asymmetric electron transport in layered conductors owing to the interplay between electrical conductivity, magnetization, and the spin Hall or Rashba- Edelstein effects. Here, we investigate the unidirectional magnetoresistance (UMR) caused by the current-induced spin accumulation in Co/Pt and CoCr/Pt bilayers. We identify three competing mechanisms underpinning the resistance asymmetry, namely interface and bulk spin-dependent electron scattering and electron-magnon scattering. Our measurements provide a consistent description of the current, magnetic field, and temperature dependence of the UMR and show that both positive and negative UMR can be obtained by tuning the interface and bulk spin-dependent scattering terms relative to the magnon population.