XANES study and rietveld refinement for the nanometer sized polycrystalline ferrite, AFe12O19 (A=Sr, Ba)

Summary form only given. Nanometer sized (/spl tilde =/ 50nm) hexagonal strontium and barium ferrite (AFe/sub 12/O/sub 19/, A=Sr, Ba) have been prepared from metal citrate complexes. X-ray absorption near edge structure and Rietveld refinement were performed in order to investigate the structural feature and the magnetic origin of magnetoplumbite type ferrite. The increase of covalency or the presence of higher oxidation state (Fe/sup 4+/) could not be observed in XANES. The peak shapes of Fe K-edge XANES spectra of hexagonal ferritte is similar to that in the spinel, Fe/sub 3/O/sub 4/. The pre-edge peak (/spl tilde =/ 7111.5 eV) with large intensity could be observed due to the coexistance of local symmetries such as octahedral, tetrahedral and trigonal bipyramidal. According to the Rietveld refinement, the Sr-ferrite has shorter bond distances and smaller cell volume than the Ba-ferrite because of the ionic size difference. The larger magnetic value (H/sub C/=6500 Oe) of Sr-ferrite might be due to the reduced Fe-O-Fe bond distance which leads to a stronger ferromagnetic coupling between the Fe/sup 3+/ ions in the lattice.