We present depth-resolved experimental results on the atomic and electronic structures of the Co-Cr interface on four IrMn/Cr/Co thin films with variable thickness of the Cr layer. Grazing incidence X-ray absorption near edge structure near the Cr K-
edge was used, and an Angstrom resolved depth-profile for this layer was obtained. An interdiffusion between chromium and cobalt layers was observed in all films, being more pronounced for samples with thinner Cr layers, where Cr behaves as an amorphous material. This causes a contraction in coordination distances in Cr near the interface with Co. In this region, a change in the electronic structure of chromiums 3d orbitals is also observed, and it appears that Cr and Co form a covalent bond resulting in a CrCo alloy. Ab initio numerical simulations support such an interpretation of the obtained experimental results.
The pressure-dependent relation between Eu valence and lattice structure in model compound EuO is studied with synchrotron-based x-ray spectroscopic and diffraction techniques. Contrary to expectation, a 7% volume collapse at $approx$ 45 GPa is accom
panied by a reentrant Eu valence transition into a $emph{lower}$ valence state. In addition to highlighting the need for probing both structure and electronic states directly when valence information is sought in mixed-valent systems, the results also show that widely used bond-valence methods fail to quantitatively describe the complex electronic valence behavior of EuO under pressure.
In order to probe the changes in the valence state and magnetic properties of Eu metal under extreme pressure, x-ray absorption near-edge spectroscopy, x-ray magnetic circular dichroism and synchrotron Mossbauer spectroscopy experiments have been car
ried out. The Mossbauer isomer shift exhibits an anomalous pressure dependence, passing through a maximum near 20 GPa. Density functional theory has been applied to give insight into the pressure-induced changes in both Eus electronic structure and Mossbauer isomer shift. Contrary to previous reports, Eu is found to remain nearly divalent to the highest pressures reached (87 GPa) with magnetic order persisting to at least 50 GPa. These results should lead to a better understanding of the nature of the superconducting state found above 75 GPa and of the sequence of structural phase transitions observed to 92 GPa.
