Ab initio theory of galvanomagnetic phenomena in random and non-random ferromagnets

Abstract:
The talk reviews recent progress in ab initio theory of transport properties of spin-polarized metallic systems in presence of spin-orbit interaction. Our approach is based on evaluation of the full conductivity tensor within the Kubo linear response theory with impurity scattering due to chemical randomness. The alloy disorder is taken into account by means of the coherent-potential approximation (CPA) implemented in the tight-binding linear muffin-tin orbital (TB-LMTO) method. The spin-orbit interaction is treated as an on-site perturbation to the scalar-relativistic TB-LMTO Hamiltonian, the velocity operators are reduced to intersite hopping elements, and the CPA-vertex corrections to the conductivity tensor are included.
The developed theory is applied to cubic binary transition-metal alloys FeCo (bcc), NiCo (fcc), NiFe (fcc) and NiMn (fcc) for which selected concentration trends are discussed: (i) a strong deviation of the isotropic resistivity from the Nordheim rule in FeCo alloys, (ii) a big anisotropic magnetoresistance in NiCo and NiFe alloys, and (iii) the change of sign of the anomalous Hall effect in Ni-based alloys. Particular attention is paid to the dilute limit (bcc Fe, fcc Ni), where the Kubo theory provides an alternative description of the anomalous Hall conductivity of non-random magnets formulated recently in terms of their band structure and the Berry curvature.
First results obtained for anisotropic magnetoresistance of Mn-doped GaAs diluted ferromagnetic semiconductors will be presented and discussed as well.