Current-Induced magnetization switching by the high spin Hall conductivity $α$-W

Abstract

The spin Hall effect originating from 5d heavy transition metal thin films such as Pt, Ta, and W is able to generate efficient spin-orbit torques that can switch adjacent magnetic layers. This mechanism can serve as an alternative to conventional spin-transfer torque for controlling next-generation magnetic memories. Among all 5d transition metals, W in its resistive amorphous phase typically shows the largest spin-orbit torque efficiency ~ 0.20-0.50. In contrast, its conductive and crystalline $α$ phase possesses a significantly smaller efficiency ~ 0.03 and no spin-orbit torque switching has yet been realized using $α$-W thin films as the spin Hall source. In this work, through a comprehensive study of high quality W/CoFeB/MgO and the reversed MgO/CoFeB/W magnetic heterostructures, we show that although amorphous-W has a greater spin-orbit torque efficiency, the spin Hall conductivity of $α$-W ($|σ_{\operatorname{SH}}^{α\operatorname{-W}}|=3.71\times10^{5}\operatornameΩ^{-1}\operatorname{m}^{-1}$) is ~3.5 times larger than that of amorphous-W ($|σ_{\operatorname{SH}}^{\operatorname{amorphous-W}}|=1.05\times10^{5}\operatornameΩ^{-1}\operatorname{m}^{-1}$). Moreover, we demonstrate spin-orbit torque driven magnetization switching using a MgO/CoFeB/$α$-W heterostructure. Our findings suggest that the conductive and high spin Hall conductivity $α$-W can be a potential candidate for future low power consumption spin-orbit torque memory applications.