Harmonic analysis is a powerful tool to characterize and quantify current-induced torques acting on magnetic materials, but so far it remains an open question in studying antiferromagnets. Inspired by the collaborative work with PI-Kent and PI-Yang, PI-Cheng’s group formulated a general theory of harmonic Hall responses of collinear antiferromagnets driven by current-induced torques including both field-like and damping-like components. By scanning a magnetic field of variable strength in three orthogonal planes, one is able to distinguish the contributions from field-like torque, damping-like torque, and concomitant thermal effects by analyzing the second harmonic signals in the Hall voltage. The analytical expressions of the first and second harmonics as functions of the magnetic field direction and strength are confirmed by numerical simulations with good agreement. The theory has been utilized directly to explain experimental observations of PI-Kent’s group, and has also been generalized to NiO, providing general guidance to future experiments.

This article has been published in the Journal of Magnetism and Magnetic Materials and is available here.