Giant spin Hall effect with multi-directional spin components in Ni4W

TL;DR

This paper reports a giant spin-orbit torque efficiency in Ni4W/CoFeB heterostructures, featuring unconventional out-of-plane spin components due to low crystal symmetry, promising improved energy-efficient spintronic devices.

Contribution

It demonstrates a record-high SOT efficiency in Ni4W with low symmetry, revealing unconventional spin components and enhanced switching performance.

Findings

SOT efficiency of 0.85 at room temperature

Observation of out-of-plane and Dresselhaus-like spin components

Order of magnitude improvement in switching efficiency

Abstract

Spin-orbit torque (SOT) can be used to efficiently manipulate the magnetic state of magnetic materials, which is an essential element for memory and logic applications. Due to symmetry constraints, only in-plane spins can be injected into the ferromagnet from the underlying SOT layer for conventional SOT materials such as heavy metals and topological materials. Through the use of materials with low symmetries, or other symmetry breaking approaches, unconventional spin currents with out-of-plane polarization has been demonstrated and enabled field-free deterministic switching of perpendicular magnetization. Despite this progress, the SOT efficiency of these materials has typically remained low. Here, we report a giant SOT efficiency of 0.85 in sputtered Ni4W/CoFeB heterostructure at room temperature, as evaluated by second harmonic Hall measurements. In addition, due to the low crystal symmetry of Ni4W, unconventional out-of-plane and Dresselhaus-like spin components were observed. Macro-spin simulation suggests our spin Hall tensor to provide about an order of magnitude improvement in the magnetization switching efficiency, thus broadening the path towards energy efficient spintronic devices using low-symmetry materials.