Theoretical study of Mn K-edge in La1-xCaxMnO3

Effects of (i) local magnetic ordering, (ii) lattice distortions, and (iii) Mn 3d - O 2p hybridization on the shape of Mn K- edge XANES spectra of La1 -xCaxMnO3 have been evaluated numerically and compared with available exper imental data. We calculated the spin-polarized Mn K- edge spectra. An energ y splitting between spin-up and spin-down XANES of 0.5-1.1 eV contributes t o the broadening of the total XANES below T-N(T-c). To simulate lattice pol aronic distortions across a MI transition the Mn K-edge spectra were calcul ated twice: assuming R-3c (R=1.96 Angstrom) and Pbnm (R-1=1.91, R-2=1.97, a nd R-3=2.16 Angstrom) symmetries. Results could qualitatively reproduce the observed energy "shift" across the transition. A pre-edge peak at E simila r to 6542 eV and feature B-3 at similar to6 eV above the main peak were fou nd to be related to the Mn 3d - O 2p hybridization. The feature B-3 should be assigned to a shake-up transition. The calculated K-edge spectrum was ob tained as a convolution product of the single-electron XANES and the spectr um of many-body excitations in the Mn-O electronic states in the presence o f the 1s core-hole.