Spin Hall magnetoresistance in metallic bilayers

TL;DR

This study investigates spin Hall magnetoresistance in metallic bilayers, revealing a significant enhancement in W/CoFeB systems and developing a model to explain the temperature and thickness dependence of SMR.

Contribution

The paper introduces a model for SMR in metallic bilayers that accounts for spin current absorption and temperature effects, providing quantitative estimates of spin transport parameters.

Findings

SMR is nearly ten times larger in W/CoFeB than in HM/FI systems.

SMR increases as temperature decreases despite stable resistivity.

The model accurately describes thickness and temperature dependence of SMR.

Abstract

Spin Hall magnetoresistance (SMR) is studied in metallic bilayers that consist of heavy metal (HM) layer and a ferromagnetic metal (FM) layer. We find nearly a ten-fold increase of SMR in W/CoFeB compared to previously studied HM/ferromagnetic insulator (FI) systems. The SMR increases with decreasing temperature despite the negligible change in the W layer resistivity with temperature. A model is developed to account for the absorption of the longitudinal spin current to the FM layer, one of the key characteristics of a metallic ferromagnet. We find that the model not only quantitatively describes the HM layer thickness dependence of SMR, allowing accurate estimation of the spin Hall angle and the spin diffusion length of the HM layer, but also can account for the temperature dependence of SMR by assuming a temperature dependent spin polarization of the FM layer. These results illustrate the unique role a metallic ferromagnetic layer plays in defining spin transmission across the HM/FM interface.