Temperature dependent changes of the Mn 3d and 4p bands near T-c 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 La1-xCaxMnO3 samples, w ith a focus mainly on the pre-edge region. Small peaks labeled A(1)-A(3) ar e observed which correspond to 1s-3d dipole transitions, made weakly allowe d via a hybridization of Mn 4p states with Mn 3d states on neighboring atom s. Adjusting the parameters in a local spin-density approximation calculati on 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) decreas es with T while A(2) increases with T below T-c, which shows that the 3d ba nds change significantly as T moves through T-c. There are also small chang es in the shape of the main edge (1s-4p transitions).