Observation of unidirectional spin Hall magnetoresistance in amorphous PtSn4/CoFeB bilayers

Unidirectional spin Hall magnetoresistance (USMR) is a magnetoresistance effect with potential applications to read two-terminal spin–orbit-torque (SOT) devices directly. In this work, we observed a large USMR value (up to 0.7 × 10−11 per A/cm2, 50% larger than reported values from heavy metals) in sputtered amorphous PtSn4/CoFeB bilayers. Ta/CoFeB bilayers with interfacial MgO insertion layers are deposited as control samples. The control experiments show that increasing the interfacial resistance can increase the USMR value, which is the case in PtSn4/CoFeB bilayers. The observation of a large USMR value in an amorphous spin–orbit-torque material has provided an alternative pathway for USMR application in two-terminal SOT devices.