Theoretical study of Mn K ‐edge in La 1‐ x Ca x MnO 3

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 experimental data. We calculated the spin‐polarized Mn K‐edge spectra. An energy splitting between spin‐up and spin‐down XANES of 0.5‐1.1 eV contributes to the broadening of the total XANES below TN(Tc). To simulate lattice polaronic distortions across a MI transition the Mn K‐edge spectra were calculated twice: assuming R‐3c (R=1.96 Å) and Pbnm (R1=1.91, R2=1.97, and R3=2.16 Å) symmetries. Results could qualitatively reproduce the observed energy "shift" across the transition. A pre‐edge peak at E~ 6542 eV and feature B3 at ~6 eV above the main peak were found to be related to the Mn 3d ‐ O 2p hybridization. The feature B3 should be assigned to a shake‐up transition. The calculated K‐edge spectrum was obtained as a convolution product of the single‐electron XANES and the spectrum of many‐body excitations in the Mn‐O electronic states in the presence of the 1s core‐hole.