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 K and the Gd L 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 K- and L-1-edge spectra directly reflect the orbital polarization of the final states with p character. The L-2,L-3-edge spectra, on the other hand, give, after suitable superposition, access to the spin and orbital polarization of the ci states. (C) 1998 American Institute of Physics. [S0021-8979(98)51711-2].