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, for La$_{1-x}$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-3d dipole-transitions, made weakly allowed via a hybridization of Mn 4p states with Mn 3d states on {\it neighboring} atoms. Adjusting the parameters in an LSDA calculation to approximately match the experimental A$_1$-A$_2$ splitting yields 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 shows that the 3d bands change significant as T moves through T$_c$. There are also small changes in the shape of the main edge (1s-4p transitions).