Theoretical study of Mn K-edge in La_1-xCa_xMnO₃

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.