Magneto-optic Properties of Co$_{1+x}$Ge$_{x}$Fe$_{2-2x}$O$_{4}$

Recently, cobalt ferrite composites and their modifications based on chemical substitution have been actively investigated as part of the development of materials for highly sensitive non-contact stress and torque sensors. Research into the magneto-optic properties of cobalt ferrites and their modifications has also been undertaken because of their potential application to magneto-optic recording media. In the present study, the polar Kerr rotations for a series of Ge-substituted cobalt ferrite Co$_{1+x}$Ge$_{x}$Fe$_{2-2x}$O$_{4}$ samples have been investigated. The samples were prepared by standard powder ceramic techniques and the photon energy range of the magneto-optic polar Kerr spectra was measured between 1.5 and 3.0 eV with increments of 0.05 eV. Comparison the polar Kerr rotation spectra for Co$_{1+x}$Ge$_{x}$Fe$_{2-2x}$O$_{4 }$with those of recently reported CoFe$_{2-x}$Ga$_{x}$O$_{4}$ samples and the analyses of the origin of the peaks in the polar Kerr spectra and the observed shift of peak position resulting from Ge-substitution using the intervalence charge-transfer (IVCT) transition, in which an electron from a metallic cation is transferred to a neighboring cation through an optical excitation, will be presented.