X-ray-absorption near-edge spectroscopy and circular magnetic x-ray dichroism at the Mn<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>K</mml:mi></mml:math>edge of magnetoresistive manganites

A thorough study of Mn $K$-edge x-ray-absorption near-edge spectroscopy (XANES) on several manganites has been performed. The spectra of ${\mathrm{La}}_{1\ensuremath{-}x}{\mathrm{Ca}}_{x}{\mathrm{MnO}}_{3}$ 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 $3+$ and $4+$ states. We have also collected XANES spectra of magnetoresistive perovskites $(x\ensuremath{\approx}0.33)$ 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.