A fully relativistic description of the hyperfine interaction in magnetic systems

Based on the spin-polarized version of the multiple scattering theory, a relativistically correct formulation for the Green’s function describing the electronic structure of magnetic metallic systems has been derived. By this way, orbital contributions to the magnetic moment and, for the first time, to the hyperfine fields, which are caused by an unquenching of the orbital momentum due to spin-orbit coupling, were accessible to a calculation. In the case of Fe, Co and Ni, it has been found, that the corresponding non-s-contributions to the hyperfine field of the conduction electrons stem nearly exclusively from the d-electrons, are positive and of the same order of magnitude as the s-part of the conduction band contribution to the total hyperfine field. In all three cases these large non-s-hyperfine fields compensate the relativistic enhancement of the (Fermi contact) s-hyperfine field compared to a non-relativistic calculation, leading to theoretical hyperfine fields which are below the experimental ones. At the moment, it cannot be decided whether this discrepancy is caused by the neglect of the non-s-contributions of the core electrons or shortcomings of the local spin density approximation.