Thickness dependence of the degree of spin polarization of the electrical current in permalloy thin films

TL;DR

This study examines how the degree of spin polarization in permalloy thin films varies with thickness, revealing a decrease due to surface-induced spin depolarization, supported by a comprehensive scattering model.

Contribution

It introduces a model accounting for various scattering sources affecting spin polarization in permalloy thin films, highlighting the impact of film surfaces.

Findings

Spin polarization decreases from 0.72 to 0.46 as thickness reduces from 20nm to 6nm.

Surface effects significantly contribute to spin depolarization in thin films.

A scattering model explains the thickness dependence of spin polarization.

Abstract

Spin-polarized electrical transport is investigated in $ Al_{2}O_{3}/Ni_{80}Fe_{20}/Al_{2}O_{3}$ thin films for permalloy thickness between 6 and 20nm. The degree of spin-polarization of the current flowing in the plane of the film is measured through the current induced spin wave Doppler shift. We find that it decreases as the film thickness decreases, from 0.72 at 20nm to 0.46 at 6nm. This decrease is attributed to a spin depolarization induced by the film surfaces. A model is proposed which takes into account the contributions of the different sources of electron scattering (alloy disorder, phonons, thermal magnons, grain boundaries, film surfaces) to the measured spin-dependent resistivities.