Unidirectional Spin Hall Magnetoresistance in Y₃Fe₅O₁₂/NiO/Pt Structure

The discovery of unidirectional spin-Hall magnetoresistance (USMR) in heavy metal (HM)/ferromagnetic(FM) bilayers such as Pt/Co and Ta/Co provides a means of studying spin orbit torque switching of the ferromagnetic layer without a third terminal. The USMR depends on the current density J and the magnetization direction m, as (Jxz).m implying that this effect is nonlinear, in contrast to spin-Hall magnetoresistance(SMR) which depends on m². In this work, we demonstrate that USMR is associated with antiferromagnet-HM interfaces by studying Y₃Fe₅O₁₂ (YIG)/(x) NiO/5nm Pt structures. The USMR is measured with the YIG magnetized in the x-y, x-z and y-z planes, using a lock-in technique that probes the response at 2ω. Unlike Ta/Co or Pt/Co bilayers where a current of amplitude of 10⁸A/cm² is required, the USMR signal appears at only 10⁶A/cm². The contribution of USMR has been separated from the anomalous Nernst and spin Seebeck effect by varying the current amplitude and magnetic field. We have carried out temperature dependent USMR measurements as well. We note that USMR may prove a useful probe of spin-dynamics and spin-torque switching in antiferromagnetic layers.