Comparative study on spin-orbit torque efficiencies from W/ferromagnetic and W/ferrimagnetic heterostructures

It has been shown that W in its resistive form possesses the largest spin-Hall ratio among all heavy transition metals, which makes it a good candidate for generating efficient dampinglike spin-orbit torque (DL-SOT) acting upon adjacent ferromagnetic or ferrimagnetic (FM) layer. Here we provide a systematic study on the spin transport properties of W/FM magnetic heterostructures with the FM layer being ferromagnetic Co₂₀Fe₆₀B₂₀ or ferrimagnetic Co₆₃Tb₃₇ with perpendicular magnetic anisotropy. The DL-SOT efficiency |ξDL|, which is characterized by a current-induced hysteresis loop shift method, is found to be correlated to the microstructure of W buffer layer in both W/Co₂₀Fe₆₀B₂₀ and W/Co₆₃Tb₃₇ systems. Maximum values of |ξDL|≈0.144 and |ξDL|≈0.116 are achieved when the W layer is partially amorphous in the W/Co₂₀Fe₆₀B₂₀ and W/Co₆₃Tb₃₇ heterostructures, respectively. Our results suggest that the spin-Hall effect from resistive phase of W can be utilized to effectively control both ferromagnetic and ferrimagnetic layers through a DL-SOT mechanism.