Abstract
Ruthenium-doped γ-Fe2O3has been synthesized and examined by x-ray powderdiffraction, XANES, EXAFS and by 57 Fe Mössbauerspectroscopy. Ruthenium K-edge x-ray absorption spectroscopy shows that rutheniumadopts a fully occupied octahedral site in the spinel related γ-Fe2O3 structureas Ru4+.The 57 FeMössbauer spectra recorded in the presence of a longitudinal magnetic field of 6 T confirmedthe octahedral coordination of the tetravalent ions and canting angles for the Fe3+ ions weredetermined as 24°for those in octahedral sites and 33°for those in tetrahedral sites. The 57 FeMössbauer spectra recorded in situ from ruthenium-doped γ-Fe2O3showed parameters typical of maghemite up to 600 K but with amagnetic hyperfine field distribution suggesting an inhomogeneousdistribution of ruthenium within particles of varied size around about15 nm. At 700 K a phase transition from γ-Fe2O3 to α-Fe2O3was observed and further studies showed the ruthenium-doped α-Fe2O3to have a Morin transition temperature of about 400 K.
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