Electron and Spin Transport in an Ultrathin Al Film for Use as a Nonlocal Spin Valve

Size effect on electron and spin relaxation in ultrathin metallic films is crucial from both scientific and technological perspectives. Our work studies the relaxation of electron and spin transport in the presence of surface and bulk defects in aluminum-based ultrathin films. The contributions from surface roughness, grain boundary scattering, vacancies and surface reconstruction to momentum and spin relaxation are investigated in the Landauer-Buttiker formalism with a Green’s function technique. Resistivity and spin diffusion length are determined assuming that both the leads and the metallic channel are made of Al with 3.6nm thickness at T=0k and embedded in vacuum. Our calculations identify that for thin sputtered films, random point vacancies and the combined effect of point vacancies and surface corrugation are the dominant contribution to momentum and spin relaxation respectively. Predicted spin diffusion lengths and Elliott-Yafet constants are found to approximately match experimental data. In addition, our work addresses the validity of the Elliott-Yafet spin relaxation mechanism and Matthiessen’s rule in the presence of surface corrugations at sub-10nm, which has not been previously reported. Violations of Matthiessen’s rule and Elliott-Yafet prediction of β are found in the presence of surface periodicity. However, when bulk scattering dominates, the Elliott-Yafet prediction and Matthiessen’s rule are obeyed because the symmetry breaking is closely dependent on the scattering length scale and concentration of random defects.