Large Spin Hall Effect in an Amorphous Binary Alloy

TL;DR

This study explores the spin Hall effect in W-Hf thin films, revealing a maximum spin Hall angle at the amorphous phase transition, and compares experimental results with first-principles calculations to understand alloying physics.

Contribution

It provides the first detailed investigation of the spin Hall effect in amorphous W-Hf alloys and links phase transition to spin Hall angle variations.

Findings

Maximum spin Hall angle of -0.25 at 70% W composition

Spin Hall conductivity decreases from W to Hf with a weak discontinuity

Amorphous phase exhibits enhanced spin Hall effect

Abstract

We investigate the spin Hall effect of W-Hf thin films, which exhibit a phase transition from a segregated phase mixture to an amorphous alloy below 70% W. The spin Hall angle was determined with a planar harmonic Hall voltage technique. Due to the accompanying jump in resistivity, the spin Hall angle shows a pronounced maximum at the composition of the phase transition. The spin Hall conductivity does, however, reduce from W to Hf with a weak discontinouity across the phase transition. The maximum spin Hall angle of $\theta_\mathrm{SH} = -0.25$ is obtained for amorphous W$_{0.7}$Hf$_{0.3}$. A detailed comparison with spin Hall conductivities calculated from first principles for hcp, fcc, and bcc solid solutions provides valuable insight into the alloying physics of this binary system.