SOFT X-RAY ABSORPTION SPECTROSCOPY (MnL2,3 AND O K) IN MIXED VALENCE MANGANITES

Abstract

Several series of oxides with Mn in a mixed valence state were studied by means of soft X-ray absorption spectroscopy in order to understand better the nature of the electronic structure of these 3d transition metal oxides. XANES spectra of REMnO 3, RE 1-x Ca x MnO 3 (RE: La, Pr and Tb) and RE 0.5 A 0.5 MnO 3 (RE–A: La–Ca, Pr–Ca, Tb–Ca and Pr–Sr) series were recorded at both Mn L 2,3 and O K edges as a function of temperature. The Mn 2p spectra shift towards higher energies with increase of the formal valence of the Mn atom. Moreover, the spectral shape shows minor changes both with the doping ratio (x) and the variation of the RE and/or A cations. No significant changes are also found with temperature across the different magnetic and electrical phase transitions. On the other hand, the O 1s spectra are much more sensitive to the variation of RE (A) cations. The spectra show a prepeak structure at the Fermi energy corresponding to empty states in the O-2p band. This prepeak feature shifts to lower energies and increases its intensity as the formal valence of the Mn atom increases. Finally, neither O K-edge nor Mn L-edge XANES spectra of RE 1-x Ca x MnO 3 compounds can be reproduced by a weighted linear combination of REMnO 3 and CaMnO 3 spectra, indicating that these intermediate composition oxides cannot be described as fluctuating Mn 3+– Mn 4+ mixed valence systems.