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 |xi DL|, 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 |xi DL| approximate to 0.144 and |xi DL| approximate to 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.