Anisotropies and magnetic phase transitions in insulating antiferromagnets determined by a Spin-Hall magnetoresistance probe

TL;DR

This study uses spin-Hall magnetoresistance to determine magnetic anisotropies and Dzyaloshinskii-Moriya fields in hematite, revealing surface-sensitive insights into antiferromagnetic properties across various temperatures.

Contribution

It introduces an analytical model combined with SMR measurements to identify magnetic parameters in antiferromagnetic hematite over a broad temperature range.

Findings

SMR response depends on current direction relative to anisotropy axes

Anisotropies can be extracted across the Morin transition

Surface sensitivity enables analysis of thin films' magnetic properties

Abstract

We demonstrate that we can determine the antiferromagnetic anisotropies and the bulk Dzyaloshinskii-Moriya fields of the insulating iron oxide hematite, {\alpha}-Fe2O3, using a surface sensitive spin-Hall magnetoresistance (SMR) technique. We develop an analytical model that in combination with SMR measurements, allow for the identification of the material parameters of this prototypical antiferromagnet over a wide range of temperatures and magnetic field values. Using devices with different orientations, we demonstrate that the SMR response strongly depends on the direction of the charge current with respect to the magneto-crystalline anisotropies axis. We show that we can extract the anisotropies over a wide temperature range including across the Morin phase transition. We observe that the electrical response is dominated by the orientation of the antiferromagnetic N\'eel order parameter, rather than by the emergent weak magnetic moment. Our results highlight that the surface sensitivity of the SMR allows accessing the magnetic anisotropies of antiferromagnetic crystals and in particular thin films where other methods to determine anisotropies such as bulk-sensitive magnetic susceptibility measurements do not provide sufficient sensitivity.