Paramagnetic spin Hall magnetoresistance

TL;DR

This paper demonstrates spin Hall magnetoresistance (SMR) in a paramagnetic insulator Gd₃Ga₅O₁₂ (GGG) with a Pt film, revealing new mechanisms of spin transport at metal/paramagnetic interfaces and enabling spintronic control without magnetic order.

Contribution

It reports the first observation of SMR in a paramagnetic insulator, showing spin-transfer torque effects and tunability with magnetic fields, expanding the understanding of spin transport in paramagnetic systems.

Findings

SMR observed in paramagnetic GGG without spontaneous magnetization

Spin-transfer torque acts on localized spins in GGG

Spin torque and spin-flip scattering efficiencies are tunable with magnetic fields

Abstract

Spin Hall magnetoresistance (SMR) refers to a resistance change in a metallic film reflecting the magnetization direction of a magnet attached to the film. The mechanism of this phenomenon is spin exchange between conduction-electron spins and magnetization at the interface. SMR has been used to read out information written in a small magnet and to detect magnetization dynamics, but it has been limited to magnets; magnetic ordered phases or instability of magnetic phase transition has been believed to be indispensable. Here, we report the observation of SMR in a paramagnetic insulator Gd$_{3}$Ga$_{5}$O$_{12}$ (GGG) without spontaneous magnetization combined with a Pt film. The paramagnetic SMR can be attributed to spin-transfer torque acting on localized spins in GGG. We determine the efficiencies of spin torque and spin-flip scattering at the Pt/GGG interface, and demonstrate these quantities can be tuned with external magnetic fields. The results clarify the mechanism of spin-transport at a metal/paramagnetic insulator interface, which gives new insight into the spintronic manipulation of spin states in paramagnetic systems.