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.

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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.