Temperature dependent changes of the Mn 3d and 4p bands near $T_{c}$ in Colossal Magnetoresistance systems : a XANES study of $La_{1-x}Ca_{x}MnO_{3}$

Abstract: We report high-resolution X-ray Absorption Near Edge Structure (XANES)measurements at the Mn K-edge as a function of temperature, forLa$_{1-x}$Ca$_x$MnO$_3$ samples, with a focus mainly on the pre-edge region.Small peaks labeled A$_1$-A$_3$ are observed which corresponds to 1s-3ddipole-transitions, made weakly allowed via a hybridization of Mn 4p stateswith Mn 3d states on {it neighboring} atoms. Adjusting the parameters in anLSDA calculation to approximately match the experimental A$_1$-A$_2$ splittingyields U = 4 eV and J$_H$ = 0.7 eV. For colossal magnetoresistance samples,A$_1$ decreases with T while A$_2$ increases with T below T$_c$, which showsthat the 3d bands change significant as T moves through T$_c$. There are alsosmall changes in the shape of the main edge (1s-4p transitions).