Amorphous Tungsten Driving Extraordinary Long‐Range Interlayer Exchange Coupling and Large Spin‐Orbit Torque

Abstract

Artificially‐designed magnetic hetero‐structures with an antiferromagnetic alignment of magnetization in magnetic layers, which exploit the interlayer exchange coupling (IEC) through a non‐magnetic layer, are called synthetic antiferromagnets (SyAF) and are a treasure trove of functionalities for spintronics applications. In SyAF spintronics, a non‐magnetic layer simultaneously providing IEC and large electric current‐induced torque originating from spin‐orbit interaction, called spin‐orbit torque (SOT), has been eagerly desired for efficient magnetization manipulation by current injection. Here we report that amorphous tungsten (W) is a promising non‐magnetic interlayer. Amorphous W shows clear antiferromagnetic coupling at thicknesses from 1.2 to 2.0 nm, which is thicker than other crystallized non‐magnetic interlayers at the first peak thicknesses of IEC oscillation. In addition, the amorphous W generates large SOT based on the intrinsic process of the spin Hall effect, which allows magnetization vector switching in SyAF. Amorphous W does not possess a well‐defined crystal symmetry. Considering this fact, the long‐range IEC and large SOT originating from the electronic structure in amorphous W are counterintuitive findings. The present study revisits what phases are stabilized in thin W layers, and provides a new avenue for utilizing the amorphous phase as a spintronic material.