Electron and spin transport in an ultrathin Al film

Abstract

The effects of surface and bulk scattering on electronic and spin transport in aluminum-based ultrathin films are predicted using the Landauer-B\"uttiker formalism and a recursive Green's function technique. The effects of surface roughness, grain boundaries, vacancies, and surface reconstruction on resistivity, spin diffusion length, and Elliott-Yafet constant $\ensuremath{\beta}$ are investigated for a 3.6-nm-thickness Al film. It is demonstrated that for a thin sputtered film, point vacancies are the dominant contribution to the momentum relaxation, and spin relaxation is dominated by the combined effect of surface reconstruction and point vacancies, which yields a reasonable spin diffusion length and the Elliot-Yafet constant. Calculations reveal that the presence of surface corrugations results in a clear departure from Matthiessen's rule and the Elliott-Yafet prediction of $\ensuremath{\beta}$, as shown by introducing random surface corrugations. It is also found that spin diffusion length induced by surface roughness is proportional to the inverse square root of the ratio between root mean square height $\ensuremath{\delta}h$ and lateral correlation length $\ensuremath{\xi}$ of a given rough surface, i.e., ${(\ensuremath{\delta}\ensuremath{\xi})}^{\ensuremath{-}1/2}$ as opposed to ${(\ensuremath{\delta}\ensuremath{\xi})}^{\ensuremath{-}1}$ as is the mean free path; this can be attributed to the interference of extended surface features.