Evolution of the spin hall magnetoresistance in Cr₂O₃/Pt bilayers close to the Néel temperature

Abstract

We study the evolution of magnetoresistance with temperature in thin film bilayers consisting of platinum and the antiferromagnet Cr₂O₃ with its easy axis out of the plane. We vary the temperature from 20°C to 60°C, close to the Néel temperature of Cr₂O₃ of approximately 37°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 Cr₂O₃, which however vanishes when cooling to below the N\'eel temperature. Comparing to analogous experiments in a Gd₃Ga₅O₁₂/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.