Calculating spin transport properties from first principles: spin currents

Abstract

Local charge and spin currents are evaluated from the solutions of fully relativistic quantum mechanical scattering calculations for systems that include temperature-induced lattice and spin disorder as well as intrinsic alloy disorder. This makes it possible to determine material-specific spin transport parameters at finite temperatures. Illustrations are given for a number of important materials and parameters at 300 K. The spin-flip diffusion length $l_{\mathrm{sf}}$ of Pt is determined from the exponential decay of a spin current injected into a long length of thermally disordered Pt; we find $l_{\mathrm{sf}}^{\mathrm{Pt}}=5.3\pm 0.4$nm. For the ferromagnetic substitutional disordered alloy Permalloy (Py), we inject currents that are fully polarized parallel and antiparallel to the magnetization and calculate $l_{\mathrm{sf}}$ from the exponential decay of their difference; we find $l_{\mathrm{sf}}^{\mathrm{Py}}=2.8\pm 0.1$nm. The transport polarization $\beta$ is found from the asymptotic polarization of a charge current in a long length of Py to be $\beta =0.75\pm 0.01$. The spin Hall angle ${\Theta }_{\mathrm{sH}}$ is determined from the transverse spin current induced by the passage of a longitudinal charge current in thermally disordered Pt; our best estimate is ${\Theta }_{\mathrm{sH}}^{\mathrm{Pt}}=4.5\pm 1\%$ corresponding to the experimental room temperature bulk resistivity $\rho =10.8\mu \Omega$cm.

21 pages, 14 figures

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