Anomalous Spin Hall Effect in Iron Rhodium for Driving Spin Torque Oscillators*

Ferromagnetic materials can generate spin currents with controllable spin polarization via the anomalous spin Hall effect, a property potentially useful for driving spin torque oscillators (STOs), which have recently found applications for performing neurotrophic tasks. Iron rhodium (FeRh) exhibits a transition between a low-temperature antiferromagnetic (AFM) state and a high-temperature ferromagnetic (FM) state. For appropriate growth parameters, this transition can be found close to 300K, such that both the FM and AFM states are stable at room temperature, making it an ideal material to compare the effectiveness of FM and AFM spin sources for STOs. The transition also provides a high level of versatility for device design. We present measurements of the spin torque efficiency in iron rhodium as the temperature is varied to drive the FeRh through its magnetic transition. We compare FeRh's efficiency for driving STOs in the stable AFM and FM states at the same temperature, and compare the effectiveness of FeRh as a spin source with ordinary spin Hall materials.