Length scale of spin-orbit torques and efficient switching in magnetic insulators*

Magnetic insulators (MIs) attract tremendous interest for spintronic applications due to low damping and absence of Ohmic loss. The efficient manipulation of magnetization in MIs via current-induced spin-orbit torques (SOTs) promises future development of low-power spintronics based on MIs. Here, we report a systematic study of MI layer thickness dependent SOTs and current-driven switching behaviors by using tungsten/thulium iron garnet (W/TmIG) bilayers. Our results reveal a characteristic increase of the damping SOT efficiency with the TmIG thickness, which is linked to the exchange coupling strength at the interface. The characteristic length of TmIG is around 8 nm, which is much larger than the case of around 1 nm in ferromagnetic metals. We then demonstrate the current-induced SOT switching in the W/TmIG bilayers with a TmIG thickness up to 15 nm, where the switching direction is opposite to that of Pt/TmIG. The switching current density is significantly lower than that of Pt/TmIG, which is attributed to a larger spin Hall angle and stronger thermal effect. Our results about length scale of SOTs and efficient switching in MIs shed light on the future development of low power MI-based spintronics.