Evolution of the Spin Hall Magnetoresistance in Cr$_2$O$_3$/Pt bilayers close to the N\'eel temperature

TL;DR

This study investigates how the spin Hall magnetoresistance in Cr$_2$O$_3$/Pt bilayers changes with temperature near the Néel temperature, revealing the role of magnetic moments at the interface in spin transport.

Contribution

It provides new insights into the temperature-dependent evolution of spin Hall magnetoresistance in antiferromagnetic insulator/metal bilayers near the Néel temperature, highlighting the influence of interfacial magnetic moments.

Findings

Large spin Hall magnetoresistance observed in the paramagnetic phase.

Magnetoresistance vanishes below the Néel temperature.

Paramagnetic field-induced magnetization alone does not explain the effect.

Abstract

We study the evolution of magnetoresistance with temperature in thin film bilayers consisting of platinum and the antiferromagnet Cr$_2$O$_3$ with its easy axis out of the plane. We vary the temperature from 20 - 60{\deg}C, close to the N\'eel temperature of Cr$_2$O$_3$ of approximately 37{\deg}C. The magnetoresistive response is recorded during rotations of the external magnetic field in three mutually orthogonal planes. A large magnetoresistance having a symmetry consistent with a positive spin Hall magnetoresistance is observed in the paramagnetic phase of the Cr$_2$O$_3$, which however vanishes when cooling to below the N\'eel temperature. Comparing to analogous experiments in a Gd$_3$Ga$_5$O$_{12}$/Pt heterostructure, we conclude that a paramagnetic field induced magnetization in the insulator is not sufficient to explain the observed magnetoresistance. We speculate that the type of magnetic moments at the interface qualitatively impacts the spin angular momentum transfer, with the $3d$ moments of Cr sinking angular momentum much more efficiently as compared to the more localized $4f$ moments of Gd.