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

We report high-resolution x-ray-absorption near-edge structure measurements at the Mn K edge as a function of temperature, for La_1-xCa_xMnO₃ samples, with a focus mainly on the pre-edge region. Small peaks labeled A₁-A₃ 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 A₁-A₂ splitting yields U=4 eV and J_H=0.7 eV. For colossal magnetoresistance samples, A₁ decreases with T while A₂ 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).