Moderate Positive Spin Hall Angle in Uranium

TL;DR

This study measures spin pumping and inverse spin Hall effect in Ni80Fe20/uranium bilayers, revealing a moderate positive spin Hall angle and suggesting f-electron orbitals influence spin-charge conversion.

Contribution

First measurement of spin Hall effect in uranium showing a positive spin Hall angle, highlighting the role of electronic configuration over atomic number.

Findings

Spin Hall angle of 0.004 in uranium

Comparable spin mixing conductance to transition metals

Electronic configuration influences spin pumping and spin Hall effects

Abstract

We report measurements of spin pumping and the inverse spin Hall effect in Ni80Fe20/Uranium bilayers designed to study the efficiency of spin-charge interconversion in a super-heavy element. We employ broad-band ferromagnetic resonance on extended films to inject a spin current from the Ni80Fe20 (permalloy) into the uranium layer, which is then converted into an electric field by the inverse spin Hall effect. Surprisingly, our results suggest a spin mixing conductance of order 2x10 e19 m-2 and a positive spin Hall angle of 0.004, which are both merely comparable to those of several transition metals. These results thus support the idea that the electronic configuration may be at least as important as the atomic number in governing spin pumping across interfaces and subsequent spin Hall effects. In fact, given that both the magnitude and the sign are unexpected based on trends in d-electron systems, materials with unfilled f-electron orbitals may hold additional exploration avenues for spin physics.