High‐Efficiency Spin–Orbit Torque Switching Using a Single Heavy‐Metal Alloy with Opposite Spin Hall Angles

Spin–orbit torque (SOT) induced perpendicular magnetization switching in Pt1‐xGdx/Co/Al2O3 heterostructure with x = 0, 0.02, 0.14, 0.30, and 0.33 is investigated. With in‐plane charge current flowing through the Pt1‐xGdx layer, field‐free current‐induced magnetization switching is observed for all nonzero x due to the existence of opposite spin Hall angles (θSHA) from Pt1‐xGdx alloys. Furthermore, the large θSHA of about 0.27 is obtained in the optimal Pt0.70Gd0.30 alloy films, which is about four times larger than that of the pure Pt. This work suggests a simple and scalable method for realizing field‐free SOT switching, and provides potential candidates of spin Hall materials that can be used to produce highly efficient SOTs. Using a single layer Pt1‐xGdx alloy with opposite spin Hall angle θSHA of Pt and Gd gives a source of spin–orbit torque. The electron scattering on the impurity centers of Pt1‐xGdx results in out‐of‐plane competing spins due to opposite θSHA. Therefore, the structural symmetry is broken and the field‐free current‐induced magnetization switching in a Pt1‐xGdx/Co/Al2O3 heterostructure is observed.