Impact of unidirectional magnetoresistance on spin-orbit torque analysis

The second-harmonic Hall technique is a widely used, sensitive method for studying the spin-orbit torques generated by charge current. It exploits the dependence of the Hall resistance on the magnetization direction, although thermal phenomena also contribute. Historically, deviations from the expected magnetic field dependence have usually been neglected. Based on our studies on permalloy/platinum bilayers, we show that a unidirectional magnetoresistance - known to appear in the second-harmonic longitudinal resistance - also appears in the Hall data, and that describing the results in a wide field range with these contributions is essential to accurately estimate the torques.