Large Spin‐Orbit Torque with Multi‐Directional Spin Components in Ni₄W

Abstract

Abstract Spin‐orbit torque (SOT) offers an efficient mechanism for manipulating the magnetization of ferromagnetic materials in spintronics‐based memory and logic devices. However, conventional SOT materials, such as heavy metals and topological insulators, are limited by high crystal symmetry to generating and injecting only in‐plane spins into the ferromagnet. Low‐symmetry materials and symmetry‐breaking strategies have been employed to generate unconventional spin currents with out‐of‐plane spin polarization, enabling field‐free deterministic switching of perpendicular magnetization. Despite this progress, the SOT efficiency of these materials has typically remained low. Here, a large SOT efficiency of 0.3 in the bulk Ni 4 W at room temperature is reported, as evaluated by second harmonic Hall measurements. In addition, due to the low crystal symmetry of Ni 4 W, unconventional SOT from the out‐of‐plane and Dresselhaus‐like spin components are observed. Notably, a large SOT efficiency of 0.73 is observed in W/Ni 4 W (5 nm), potentially resulting from additional interfacial contributions or extrinsic effects. Furthermore, field‐free switching of perpendicular magnetization has been achieved using the multi‐directional SOT of Ni 4 W, highlighting its potential as a low‐symmetry SOT material for energy‐efficient spintronic devices.