Valence selective DAFS measurements of Mn in La_1/3Ca_2/3MnO₃

The manganese perovskite system La_1-xCa_xMnO₃ displays a complex phase diagram of structural, magnetic, and transport properties with varying Ca concentration. At x = 2/3 and at low temperature, the system is antiferromagnetic with Mn⁴⁺ and Mn³⁺ ions occupying special positions in a charge-ordered supperlattice. The charge ordering transition at about 260 K is characterized by the appearance of satellite peaks around certain strong normal lattice reflections. The normal lattice reflections are due to scattering from planes containing Mn⁴⁺ and Mn³⁺ ions in nearly stoichiometric proportion, however the superlattice reflections are due to scattering from planes containing only Mn⁴⁺ ions. By measuring Diffraction Anomalous Fine-Structure spectra on a superlattice reflection and its associated normal lattice reflection, it is possible to isolate absorption-like spectra for the two Mn sites. Due to the weak intensity of these superlattice reflections, we were unable to obtain high quality near-edge spectra for the superlattice reflection measured. However, the data offer useful information about the local electronic structures of the two Mn ions.