Comparison of spin-orbit torques and spin pumping across NiFe/Pt and NiFe/Cu/Pt interfaces

TL;DR

This study compares spin-orbit torques and spin pumping in NiFe/Pt and NiFe/Cu/Pt interfaces, revealing the dominant role of diffusive spin current transport and interface scattering effects.

Contribution

It provides experimental evidence on how inserting a Cu layer affects spin-orbit torques and spin pumping, clarifying their origins and interface contributions.

Findings

Cu insertion reduces spin-orbit torques and spin pumping by ~1.4 times.

Spin Hall effect-driven diffusive spin current is the main source of torques.

Interface scattering at NiFe/Pt enhances damping independently of spin pumping.

Abstract

We experimentally investigate spin-orbit torques and spin pumping in NiFe/Pt bilayers with direct and interrupted interfaces. The damping-like and field-like torques are simultaneously measured with spin-torque ferromagnetic resonance tuned by a dc bias current, whereas spin pumping is measured electrically through the inverse spin Hall effect using a microwave cavity. Insertion of an atomically thin Cu dusting layer at the interface reduces the damping-like torque, field-like torque, and spin pumping by nearly the same factor of ~1.4. This finding confirms that the observed spin-orbit torques predominantly arise from diffusive transport of spin current generated by the spin Hall effect. We also find that spin-current scattering at the NiFe/Pt interface contributes to additional enhancement in magnetization damping that is distinct from spin pumping.