X-RAY-ABSORPTION AND DICHROISM OF TRANSITION-METALS AND THEIR COMPOUNDS

This review presents an overview of the X-ray absorption spectra of 3d transition metals and their compounds. The emphasis is on the description of the X-ray absorption process and the various routes to interpret the results within the framework of their electronic structure. This also includes the use of polarization dependent measurements which are particularly used for the study of the magnetic structure. Emphasis will be given to the metal 2p spectra for which the obtainable resolution has been greatly improved over the last 10 years. The interpretation of 2p core spectra, photo-emission as well as absorption, is dominated by short range models, such as the Anderson impurity model. It has been shown that 2p X-ray absorption is relatively insensitive to charge transfer effects which simplifies the analysis. The interpretation with a ligand field multiplet model accounts well for the observed spectra and due to its simplicity this model yields accurate and well defined electronic structure parameters. For the 1s X-ray absorption spectra, of the metals as well as of the ligands, it has been shown that they correspond closely to the unoccupied density of states as determined from single particle schemes using either band structure methods or real space multiple scattering. A number of potentially important effects beyond this interpretation will be discussed. Overviews will be given of the published X-ray absorption results for the metal 2p, the metal 1s and the ligand 1s spectra.