Anomalous spin Hall magnetoresistance in Pt/Co bilayers

TL;DR

This study investigates the anomalously large spin Hall magnetoresistance in Pt/Co bilayers, revealing its dependence on Co thickness and ruling out several conventional explanations, suggesting a Co-specific origin.

Contribution

The paper identifies a large SMR in Pt/Co bilayers that cannot be explained by existing models, indicating a novel Co-related mechanism.

Findings

SMR increases with Co thickness and temperature

Conventional models cannot fully explain the large SMR

The large SMR is specific to Co and not observed in W/CoFeB

Abstract

We have studied the spin Hall magnetoresistance (SMR), the magnetoresistance within the plane transverse to the current flow, of Pt/Co bilayers. We find that the SMR increases with increasing Co thickness: the effective spin Hall angle for bilayers with thick Co exceeds the reported values of Pt when a conventional drift-diffusion model is used. An extended model including spin transport within the Co layer cannot account for the large SMR. To identify its origin, contributions from other sources are studied. For most bilayers, the SMR increases with decreasing temperature and increasing magnetic field, indicating that magnon-related effects in the Co layer play little role. Without the Pt layer, we do not observe the large SMR found for the Pt/Co bilayers with thick Co. Implementing the effect of the so-called interface magnetoresistance and the textured induced anisotropic scattering cannot account for the Co thickness dependent SMR. Since the large SMR is present for W/Co but its magnitude reduces in W/CoFeB, we infer its origin is associated with a particular property of Co.