Temperature dependent changes of the Mn 3d and 4p bands near Tc in colossal magnetoresistance systems: XANES study of La1−xCaxMnO3

Abstract

We report high-resolution x-ray-absorption near-edge structure measurements at the Mn K edge as a function of temperature, for ${\mathrm{La}}_{1-x}{\mathrm{Ca}}_x{\mathrm{MnO}}_3$ samples, with a focus mainly on the pre-edge region. Small peaks labeled $A_1–A_3$ are observed which correspond to $1s-3d$ dipole transitions, made weakly allowed via a hybridization of Mn $4p$ states with Mn $3d$ states on neighboring atoms. Adjusting the parameters in a local spin-density approximation calculation to approximately match the experimental $A_1-A_2$ splitting yields $U=4\mathrm{}$ eV and $J_H=0.7\mathrm{}$ 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 significantly as T moves through $T_c.$ There are also small changes in the shape of the main edge $(1s-4p$ transitions).