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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.

By making a comparison between the Mn K-edge absorption of (MnOq) and [Mn(H20)6]'+ complexes in aqueous solution we obtain an experimental determination of the energy extent of the type-II multiple-scattering (MS) regime that is substantially wider than expected. Theoretical calculations based on the MS formalism support this conclusion. We also recognize three energy regions in the absorption spectra of these complexes: a full MS region, where numerous or an infinite number of MS paths of high order contribute (depending on whether the MS series converges or not), an intermediate MS region, where only a few MS paths of low order are relevant, and a singlescattering region where the photoelectron is backscattered only once by the ligands [extended x-rayabsorption fine-structure (EXAFS) regime]. Theoretical considerations show that this must be a general situation in x-ray-absorption spectra and opens the way to a unified scheme for their interpretation. The energy extent of the three regions is obviously system dependent. We also show how to generalize to MS contributions the usual EXAFS analysis using curved-wave propagators and indicate how to extract geometrical information from the spectra of the two clusters investigated. In particular the method is used to derive the Mn -0 -0 -Mn path length in the (Mn04) complex.

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