The effect of spin currents on the magnetic order of insulating antiferromagnets (AFMs) is of fundamental interest and can enable new applications. Toward this goal, characterizing the spin-orbit torques (SOTs) associated with AFM–heavy-metal (HM) interfaces is important. Here we report the full angular dependence of the harmonic Hall voltages in a predominantly easy-plane AFM, epitaxial c-axis oriented α-Fe₂O₃ films, with an interface to Pt. By modeling the harmonic Hall signals together with the α-Fe₂O₃ magnetic parameters, we determine the amplitudes of fieldlike and dampinglike SOTs. Out-of- plane field scans are shown to be essential to determining the dampinglike component of the torques. In contrast to ferromagnetic–heavy-metal heterostructures, our results demonstrate that the fieldlike torques are significantly larger than the dampinglike torques, which we correlate with the presence of a large imaginary component of the interface spin-mixing conductance. Our work demonstrates a direct way of characterizing SOTs in AFM-HM heterostructures.

This article has been published in Physical Review Letters and is available here.