Negative spin Hall magnetoresistance in Mn3Ir/Co bilayers induced by interfacial spin-orbit coupling

Understanding the interconversion between charge current and spin current in antiferromagnetic materials is crucial for advancing antiferromagnetic spintronic devices. In this work, we utilize the second harmonic technique and the spin Hall magnetoresistance method to investigate the spin current generation in Mn3Ir/Co bilayers. The angular dependence of the second harmonic Hall voltage shows that only a y-polarized spin current is generated, which exerts spin-orbit torques on Co magnetic moments. Contrary to the positive spin Hall magnetoresistance induced by y-polarized spin current, we observe the anomalous negative spin Hall magnetoresistance in Mn3Ir/Co bilayers. By further investigating the Mn3Ir thickness dependence of the negative spin Hall magnetoresistance and spin-orbit torque, we demonstrate that the negative spin Hall magnetoresistance originates from the interconversion between charge current and spin current driven by interfacial spin-orbit coupling. Our findings provide compelling evidence for interfacial spin-orbit coupling conversion at the antiferromagnetic/ferromagnetic bilayer interface. This indicates that the interface engineering is essential for optimizing non-collinear antiferromagnetic spintronic devices.