Spin transmission in IrMn through measurements of spin Hall magnetoresistance and spin-orbit torque

Abstract

Understanding the transport of spin current in antiferromagnetic materials is indispensable to develop antiferromagnetic spintronic devices. In this work, we study the spin current transmission through an antiferromagnetic IrMn insertion layer in a W/IrMn($t$)/CoFeB structure by measuring the spin Hall magnetoresistance (SMR) and spin-orbit torque (SOT). The temperature dependences of SMR and SOT effective fields indicate that the spin current transmission reaches its maximum at the N\'eel temperature of IrMn. The enhancement is ascribed to the increase in the interfacial spin mixing conductance, which is related to the maximum magnetic susceptibility of the IrMn layer at the N\'eel temperature. The spin transmission decreases monotonically as a function of the IrMn thickness, which is different from the case with an insulating antiferromagnetic NiO insertion layer in previous works. In addition, we found that the spin transmission through an antiferromagnetic IrMn layer is independent of the exchange bias orientation. Our results suggest that the spin current transmission through the IrMn layer (from W layer to CoFeB layer) is mainly mediated by spin-polarized electrons rather than magnons, which is likely due to the absence of the effective excitation of magnons in the IrMn layer by the spin-polarized current.