Three Oxidation States of Manganese in the Barium Hexaferrite BaFeMnO.

The coexistence of three valence states of Mn ions, namely, +2, +3, and +4, in substituted magnetoplumbite-type BaFeMnO was observed by soft X-ray absorption spectroscopy at the Mn-L edge. We infer that the occurrence of multiple valence states of Mn situated in the pristine purely iron(III) compound BaFeO is made possible by the fact that the charge disproportionation of Mn into Mn and Mn requires less energy than that of Fe into Fe and Fe, related to the smaller effective Coulomb interaction of Mn (d) compared to Fe (d). The different chemical environments determine the location of the differently charged ions: with Mn occupying positions with (distorted) octahedral local symmetry, Mn ions prefer octahedrally coordinated sites in order to optimize their covalent bonding. Larger and more ionic bonded Mn ions with a spherical charge distribution accumulate at tetrahedrally coordinated sites. Simulations of the experimental Mn-L XAS spectra of two different samples with x = 1.5 and x = 1.7 led to Mn:Mn:Mn atomic ratios of 0.16:0.51:0.33 and 0.19:0.57:0.24.