Fully relativistic theory for the magnetic extended x-ray absorption fine structure

A fully relativistic theoretical description of the magnetic extended x-ray absorption fine structure (MEXAFS) is presented that has been set up within the framework of relativistic multiple scattering theory on the basis of the Dirac equation for spin-polarized, magnetic solids. The multiple scattering processes in the final state are treated using the scattering path expansion technique for finite atomic clusters. Results of the approach for the Fe KK and the Gd LL edges are presented and are compared with experiment. An analysis of the theoretical spectra clearly shows that the MEXAFS spectra can be interpreted on the basis of the so-called sum rules in a way completely analogous to the case of near-edge x-ray magnetic circular dichroism. This means that the KK- and L1L1-edge spectra directly reflect the orbital polarization of the final states with pp character. The L2,3L2,3-edge spectra, on the other hand, give, after suitable superposition, access to the spin and orbital polarization of the dd states