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 of ≈0.03 and no spin–orbit torque switching is realized using α‐W thin films as the spin Hall source. Herein, through a comprehensive study of high‐quality W/CoFeB/MgO and the reversed MgO/CoFeB/W magnetic heterostructures, it is shown that although amorphous‐W has a greater spin–orbit torque efficiency, the spin Hall conductivity of α‐W is ≈3.5 times larger than that of amorphous W . Moreover, spin–orbit torque‐driven magnetization switching using a MgO/CoFeB/α‐W heterostructure is demonstrated. The findings suggest that the conductive and high spin Hall conductivity α‐W is a potential candidate for future low‐power consumption spin–orbit torque memory applications.