Quantifying spin Hall angles from spin pumping: Experiments and Theory

TL;DR

This paper presents a method combining experiments and theory to quantify spin Hall angles in nonmagnetic materials using spin pumping and voltage measurements in permalloy/metal bilayers.

Contribution

The authors develop a comprehensive experimental and theoretical approach to accurately measure spin Hall angles in various materials, including small-angle conductors.

Findings

Quantified spin Hall angles for Pt, Au, and Mo.

Distinguished AMR and spin Hall contributions via symmetry analysis.

Method adaptable to any conducting material with small spin Hall angles.

Abstract

Spin Hall effects intermix spin and charge currents even in nonmagnetic materials and, therefore, ultimately may allow the use of spin transport without the need for ferromagnets. We show how spin Hall effects can be quantified by integrating permalloy/normal metal (N) bilayers into a coplanar waveguide. A dc spin current in N can be generated by spin pumping in a controllable way by ferromagnetic resonance. The transverse dc voltage detected along the permalloy/N has contributions from both the anisotropic magnetoresistance (AMR) and the spin Hall effect, which can be distinguished by their symmetries. We developed a theory that accounts for both. In this way, we determine the spin Hall angle quantitatively for Pt, Au and Mo. This approach can readily be adapted to any conducting material with even very small spin Hall angles.