Electronic structure of La_1-xCa_xMnO₃ determined by spin-polarized x-ray absorption spectroscopy: Comparison of experiments with band-structure computations

A model was developed to predict the temperature dependent changes in the local magnetic ordering based on spin-polarized Mn K-edge measurements of La_1-xCa_xMnO₃. With this model, one can ascertain the change in local ordering that occurs on transiting the magnetic ordering temperature. Parallel local density approximation (LDA) and LDA+U computations are used to label the symmetries of the unoccupied bands, determine the degree of electron correlation and to provide a direct comparison with the band ordering predicted by the temperature dependent spin-polarized measurements. The spin magnetic moment and ordering of the t_2g and e_g states are also determined. We find that the occupied t_2g orbitals are always ordered with lobes near 45° to the local Mn-O directions. The Mn K-edge main line splitting is discussed in terms of the effective spin-polarized charge density. The oxygen hole contribution to the net magnetic moment is seen to be important. We survey the spin-polarized x-ray absorption near-edge spectra of a large group of manganese oxides and show the general trends in the main line spin splitting as a function of valence.