Ab initio description of transverse transport due to impurity scattering in transition-metals

Beschreibung

This thesis attempts to shed light on various spin-orbit driven transport phenomena in materials, as a crucial for the further development of the eld of spintronics. In particular, we address the skew-scattering mechanism in dilute alloys, which gives rise to the anomalous and spin Hall eect, as well as spin-relaxation processes. We create the tools to access these quantities from ab initio calculations in the framework of the full-potential all-electron Korringa-Kohn-Rostoker Green-function method, by (a) developing and implementing a new tetrahedron method for the calculation of complicated, multi-sheeted Fermi surfaces even of complex transitionmetal compounds, and (b) developing an eciently parallelized and thus highly scalable computer program (up to thousands of processors) for the precise calculation of scattering properties. In a rst application of the new tetrahedron method, we calculate the Elliott-Yafet spin-mixing parameter on the Fermi surfaces of 5d and 6sp metals, and discover a yet unexplored dependence on the electron's spin-polarization direction. As we show, this anisotropy can reach gigantic values in uniaxial hcp crystals due to the emergence of large spin- ip hot-areas or hot-loops on the Fermi surface, supported by the low symmetry of the hcp crystal. A simple model is able to reveal an interesting interplay between the orbital character of the states at special points, lines or areas in the Brillouin zone and the matrix-elements of the spin- ip part of the spin-orbit coupling operator. We further calculate the skew-scattering contribution to the anomalous Hall eect (AHE) in dilute alloys based on a ferromagnetic host for the rst time. A systematic study of 3d impurities in bcc Fe, as well as the non-magnetic hosts Pd, Pt and Au, allows us to identify trends across the periodic table. In all our calculations, we also observe a strong correlation between the spin Hall eect and anomalous Hall eect in these materials, which is of interest for the creation and detection of strongly spin-polarized currents. A Fermi-surface analysis of the contributions to the AHE reveals a non-trivial, peaked behavior at small hot-spots around spin-orbit lifted degeneracies. We then proceed to the more complicated L10-ordered alloy FePt and address dierent kinds of disorder. We showcase the power of our method by treating the very complicated compounds FexMn1??xSi and MnSi1??xGex, based on the non-Fermi liquid manganese silicide (MnSi). Finally, we also calculate the pure spin Hall eect for 4d=5sp and 5d=6sp impurities in fcc Ir and hcp Re hosts. For the latter, we discover a strong dependence on the electron's spin-polarization direction.

Autor*in

Bernd Zimmermann

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