Large Spin-Orbit Torque with Multi-Directional Spin Components in Ni₄W.

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 Ni₄W at room temperature is reported, as evaluated by second harmonic Hall measurements. In addition, due to the low crystal symmetry of Ni₄W, 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/Ni₄W (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 Ni₄W, highlighting its potential as a low-symmetry SOT material for energy-efficient spintronic devices.