A thorough study of Mn K-edge x-ray-absorption near-edge spectroscopy ͑XANES͒ on several manganites has been performed. The spectra of La 1Ϫx Ca x MnO 3 have a similar shape for the whole series. The chemical shift for intermediate compositions lies between the two end members of the series showing an intermediate oxidation state of the Mn atom. The analysis of the spectra indicates that the Mn atom does not fluctuate between 3ϩ and 4ϩ states. We have also collected XANES spectra of magnetoresistive perovskites (x Ϸ0.33) at different temperatures and at different external magnetic fields. Very small differences in the XANES spectrum are induced by decreasing the temperature or by applying a magnetic field showing that the electronic state of the Mn atom across the metal-insulator transition remains essentially unaltered. X-ray circular magnetic dichroism at the Mn K edge in the ferromagnetic phase also shows a unique magnetic signal.

Iridium oxohydroxide thin coatings have been prepared by a dynamic oxidation electrodeposition method from complex oxalate solutions that induce template effects in the final coating at the nanoscale. The preparation method induces the formation of a oxohydroxide with reproducible stoichiometry and sponge-like quasiamorphous open structure, high ionic mobility, and significant behavior as compared with other reported iridium oxides as derived from X-ray diffraction, XPS, and TGA. Reproducible mixed valence states are also observed and a local rutile structure that allows ion exchange and facile redox changes. Rather significant is the large affinity for organic compounds observed and the behavior as substrate for cell culture, the best observed to date. Optimal cell response seems to be related to such open structure, which suggests this coating as ideal for devices implanted in the nervous system.

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We have investigated the low temperature phase of a Nd 0.5 Sr 0.5 MnO 3 single crystal by x-ray resonant scattering at the Mn K-edge of the (3 0 0

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Resonant x-ray scattering was used to investigate electronic fluctuations of the octahedral iron atoms in magnetite. We measured the (002) and (006) "forbidden" x-ray diffraction reflections permitted by the anisotropy of the iron anomalous scattering factor. The energy and azimuthal angle dependencies of these reflections, and the polarization analysis, are shown and discussed. The results clearly show p and d iron empty states ordering in magnetite at room temperature. Moreover, the octahedral iron atoms are electronically equivalent in a time scale lower than 10(-16) sec. Therefore, magnetite should be considered as an itinerant magnet and not as a fluctuating mixed valence material.

The local structure of LaMnO3 across the Jahn-Teller (JT) transition at T(JT)=750 K was studied by means of x-ray absorption near edge structure and extended x-ray absorption fine structure at the Mn K-edge. Our results indicate a similar electronic local structure for Mn atoms above and below T(JT) and a dynamical tetragonal JT distortion of MnO6 octahedra above T(JT). The structural transition is originated by the ordering of tetragonally distorted octahedra. The entropy content of the transition is analyzed within the framework of the three-state Potts model with nearest neighbor antiferrodistortive coupling.