Quantitative structural refinement of Mn K edge XANES in LaMnO₃ and CaMnO₃ perovskites

Abstract

The special magnetotransport properties of hole doped manganese perovskites originate from a complex interplay among structural, magnetic and electronic degree of freedom. In this picture the local atomic structure around Mn ions plays a special role and this is the reason why short range order techniques like X-ray absorption spectroscopy (XAS) have been deeply exploited for studying these compounds. The analysis of near edge region features (XANES) of XAS spectra can provide very fine details of the local structure around Mn, complementary to the EXAFS, so contributing to the full understanding of the peculiar physical properties of these materials. Nevertheless the XANES analysis is complicated by the large amount of structural and electronic details involved making difficult the quantitative interpretation. This work exploits the recently developed MXAN code to achieve a full structural refinement of the Mn K edge XANES of LaMnO₃ and CaMnO₃ compounds; they are the end compounds of the doped manganite series La_xCa_1−xMnO₃, in which the Mn ions are present only in one charge state as Mn³⁺ and Mn⁴⁺ respectively. The good agreement between the results derived from the analysis of near edge and extended region of the XAS spectra demonstrates that a quantitative picture of the local structure can be obtained from structural refinement of Mn K edge XANES data in these crystalline compounds. The XANES analysis offers, in addition, the possibility to directly achieve information on the topology of local atomic structure around the absorber not directly achievable from EXAFS.