A Comparative Study on Spin-Orbit Torque Efficiencies from W/ferromagnetic and W/ferrimagnetic Heterostructures.
Ting-Chien Wang1*, Chi-Feng Pai1, Hung-Wei Yen1
1Department of Materials Science and Engineering, National Taiwan University, Taipei 10617, Taiwan
* Presenter:Ting-Chien Wang
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, 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 DL-SOT efficiency = 0.144 and 0.10 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.

Keywords: MRAM, perpendicular magnetic anisotropy, spin-orbit torque efficiency, CoFeB/CoTb, W buffer layer