Optical,magneto-optical and mössbauer spectroscopy on Co3+ substituted cobalt ferrite Co2+Fe2?xCo3+xO4(0 ? x ? 2)

The magneto-optical spectra of Co_1+xFe_2?xO₄ show with increasing Co³⁺ content an increasing intensity of the 4A₂ ? 4T₁(F) and 4A₂ ? 4T₁(P) transition of Co²⁺ at 0.8 and 2.0 eV. A decrease in the Co²⁺-Fe³⁺ charge transfer transitions on octahedral sites is found. In the optical spectra a strong increase in optical absorption is found with dominant transitions at 0.8, 1.6 and 2.6 eV due to Co³⁺ crystal field transitions on octahedral sites and a Co²⁺-Co³⁺ charge transfer. Conversion Electron Mössbauer Spectroscopy has been used to determine the cation distribution in the surface layer of the samples. The results indicate a shift of Co²⁺ from octahedral to tetrahedral sites when Co³⁺ is substituted in CoFe₂O₄. This results in enhanced optical absorption, enhanced magneto-optical effects and a lower Curie temperature.