Cation distribution in MFe2O4 (M = Ni, Co): X-ray diffraction, electron spectroscopy, Raman, and magnetization studies

Abstract

We report the structural, vibrational, surface composition, and magnetic properties of as-prepared and annealed (600-1200 degrees C) MFe2O4 (M = Ni, Co) samples to investigate the cation distribution. Rietveld refinement of X-ray diffraction data indicated a spinel structure for all samples. Raman and X-ray photoelectron analyses suggest the presence of an inverse spinel structure in the samples. Furthermore, the mixed valence states (Fe2+, Fe3+, Ni2+/ Co2+) of the cations and their occupancies over tetrahedral and octahedral sites have been evaluated. We have noticed a systematic increase in saturation magnetization (MS) (10.7-43.5 emu/g for NiFe2O4, 36.1-83 emu/g for CoFe2O4) with increasing annealing temperature up to 1000 degrees C, and then MS slightly decreased for the samples annealed at 1200 degrees C. Furthermore, the values of coercivity (HC) varied over the ranges 15-125 Oe for NiFe2O4 and 300-1644 Oe for CoFe2O4, suggesting that these materials are promising candidates for biomedical and high-frequency applications.