Spin Hall Effect in a Thin Pt Film

TL;DR

This study uses relativistic scattering formalism to analyze charge and spin transport in thin platinum films, revealing surface effects significantly influence the spin Hall effect and related parameters.

Contribution

It develops a generalized model incorporating surface effects to accurately describe the spin Hall effect in thin Pt films, improving upon previous bulk-based approximations.

Findings

Surface roughness affects charge current suppression.

Surface enhances in-plane spin Hall effect.

Adjusted model matches first-principles transport results.

Abstract

A density-functional-theory based relativistic scattering formalism is used to study charge transport through thin Pt films with room temperature lattice disorder. A Fuchs-Sondheimer specularity coefficient $p \sim 0.5$ is needed to describe the suppression of the charge current at the surface even in the absence of surface roughness. The charge current drives a spin Hall current perpendicular to the surface. Analysing the latter with a model that is universally used to interpret the spin Hall effect in thin films and layered materials, we are unable to recover values of the spin-flip diffusion length $l_{\rm sf}$ and spin Hall angle $\Theta_{\rm sH}$ that we obtain for bulk Pt using the same approximations. We trace this to the boundary conditions used and develop a generalized model that takes surface effects into account. A reduced value of $\Theta_{\rm sH}$ at the surface is then found to describe the first-principles transport results extremely well. The in-plane spin Hall effect is substantially enhanced at the surface.