Spektroskopie besetzter und unbesetzter Zustände intermetallischer Verbindungen mit Röntgenphotoemission und Bremsstrahlung-Isochromat-Spektroskopie

Abstract

This thesis reports an extensive investigation of the electronic structure of intermetallic alloys. The experimental techniques used were X-ray photoemission and Bremsstrahlung isochromat spectroscopy (BIS). BIS was performed with a newly developed high current electron gun especially adapted to the geometry of Johann-type soft X-ray monochromators.-The combination of these two techniquesyields a complete picture of the electronic structure of a solid, both for the occupied and unoccupied states. Applying these methods to alloys of transition metals,one of which has a nearly full d-band, whereas the d-band of the other metal is nearly empty, led to a description of such alloys in terms of a molecular orbital picture : In analogy to the hydrogen molecule, the interaction between the two "d-states" leads to bonding and antibonding states which are narrower than, and slightly shifted with regard to the parent d-states, and a lowering of the density of states at the Fermi level. While the previous studies were concerned with the extended states in ametallic solid, a second set of experiments was aimed at elucidating the interaction between extended states and the localized 4f states of rare earths, and, in particular, Ce. BIS is very well suited to study this problem since in many cases the d-states of the transition metal ligands contribute only negligibly to the density of states above E F , whereas the contribution of the 4f states can be clearly recognized. The unoccupied 4f-states are drastically different for magnetic and nonmagnetic Ce compounds. Comparing with various other experiments one finds significant discrepancies, especially with regard to the average f occupation, which can only be caused by a sizeable hybridization between f-states and conduction states. Therefore, this hybridization is identified as the most important factor for the loss of magnetism in Ce intermetallics