Photoemission and core-level magnetic circular dichroism studies of diluted magnetic semiconductors

An overview is given on the photoemission studies of the electronic structure of diluted magnetic semiconductors (DMS's), in particular of the prototypical ferromagnetic DMS Ga_1-xMn_xAs. Configuration-interaction cluster-model analyses of the photoemission data allow us to estimate the p-d exchange coupling constant and hence to predict how to increase the Curie temperature in new materials. Spectra near the Fermi level combined with the transport and optical properties suggest a highly incoherent metallic state for the ferromagnetic metallic phase. It is shown that new insight into the chemically and magnetically inhomogeneous states of DMS's can be gained by the temperature and magnetic field dependence of core-level magnetic circular dichroism signals.