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

TL;DR

This study demonstrates that crystalline $ ext{α}$-W exhibits high spin Hall conductivity and enables efficient current-induced magnetization switching, making it a promising material for low-power spin-orbit torque memory devices.

Contribution

It reveals that crystalline $ ext{α}$-W has significantly higher spin Hall conductivity than amorphous W and can achieve magnetization switching, unlike previous reports.

Findings

$ ext{α}$-W has a spin Hall conductivity of $3.71 imes 10^5 ext{Ω}^{-1} ext{m}^{-1}$.

Magnetization switching was achieved using $ ext{α}$-W in heterostructures.

Crystalline $ ext{α}$-W is a promising material for spin-orbit torque applications.

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 $\alpha$ phase possesses a significantly smaller efficiency ~ 0.03 and no spin-orbit torque switching has yet been realized using $\alpha$-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 $\alpha$-W ($|\sigma_{\operatorname{SH}}^{\alpha\operatorname{-W}}|=3.71\times10^{5}\operatorname{\Omega}^{-1}\operatorname{m}^{-1}$) is ~3.5 times larger than that of amorphous-W ($|\sigma_{\operatorname{SH}}^{\operatorname{amorphous-W}}|=1.05\times10^{5}\operatorname{\Omega}^{-1}\operatorname{m}^{-1}$). Moreover, we demonstrate spin-orbit torque driven magnetization switching using a MgO/CoFeB/$\alpha$-W heterostructure. Our findings suggest that the conductive and high spin Hall conductivity $\alpha$-W can be a potential candidate for future low power consumption spin-orbit torque memory applications.