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

We report the structural, vibrational, surface composition, and magnetic properties of as-prepared and annealed (600–1200 °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 °C, and then MS slightly decreased for the samples annealed at 1200 °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.