Quantifying Spin-Orbit Torques in Antiferromagnet/Heavy Metal Heterostructures

TL;DR

This study measures and models spin-orbit torques in antiferromagnet/heavy metal heterostructures, revealing that field-like torques dominate over damping-like torques, which is different from ferromagnetic systems.

Contribution

It provides a comprehensive method to quantify and distinguish between field-like and damping-like spin-orbit torques in AFM/HM interfaces, highlighting the significance of out-of-plane measurements.

Findings

Field-like torques are larger than damping-like torques in AFM/HM heterostructures.

Out-of-plane field scans are crucial for accurately determining damping-like torques.

Large imaginary component of spin-mixing conductance explains the torque behavior.

Abstract

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 (SOT) 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 $\alpha$-Fe$_2$O$_3$ films, with an interface to Pt. By modeling the harmonic Hall signals together with the $\alpha$-Fe$_2$O$_3$ magnetic parameters, we determine the amplitudes of field-like and damping-like SOT. Out-of-plane field scans are shown to be essential to determining the damping-like component of the torques. In contrast to ferromagnetic/heavy metal heterostructures, our results demonstrate that the field-like torques are significantly larger than the damping-like 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 SOT in AFM/HM heterostructures.