Hard x-ray emission spectroscopy: a powerful tool for the characterization of magnetic semiconductors

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This review aims to introduce the x-ray emission spectroscopy (XES) and resonant inelastic x-ray scattering (RIXS) techniques to the materials scientist working with magnetic semiconductors (e.g. semiconductors doped with 3d transition metals) for applications in the field of spin-electronics. We focus our attention on the hard part of the x-ray spectrum (above 3 keV) in order to demonstrate a powerful element- and orbital-selective characterization tool in the study of bulk electronic structure. XES and RIXS are photon-in/photon-out second order optical processes described by the Kramers-Heisenberg formula. Nowadays, the availability of third generation synchrotron radiation sources permits applying such techniques also to dilute materials, opening the way for a detailed atomic characterization of impurity-driven materials. We present the Kβ XES as a tool to study the occupied valence states (directly, via valence-to-core transitions) and to probe the local spin angular momentum (indirectly, via intra-atomic exchange interaction). The spin sensitivity is employed, in turn, to study the spin-polarized unoccupied states. Finally, the combination of RIXS with magnetic circular dichroism (RIXS-MCD) extends the possibilities of standard magnetic characterization tools.