Fully relativistic theory for magnetic EXAFS: Formalism and applications

A fully relativistic theory for magnetic extended x-ray absorption fine structure is presented that is based on the Dirac equation for spin-polarized systems and relativistic multiple scattering theory. This scheme not only allows one to treat spin polarization and all relativistic effects on the same level but can also be applied to go beyond the standard muffin-tin construction by using nonspherical potentials. To illustrate the application of the presented fully relativistic scheme, results for the K-edge spectra of Ni in fcc Ni and the $L_{2,3}$ edges of Pt in fcc ${\mathrm{Fe}}_3\mathrm{Pt}$ are presented. A very simple and convincing interpretation of the corresponding dichroic spectra is given on the basis of the differential form of the so-called sum rules.