Optical and magneto-optical polar Kerr spectra of ${\mathrm{Fe}}_3{\mathrm{O}}_4$ and ${\mathrm{Mg}}^{2+}$- or ${\mathrm{Al}}^{3+}$-substituted ${\mathrm{Fe}}_3{\mathrm{O}}_4$

The diagonal elements of the dielectric tensor, between 0.5 and 5.0 eV, and the magneto-optical polar Kerr spectra, between 0.7 and 4.0 eV, have been determined for a synthetic crystal of magnetite, ${\mathrm{Fe}}_3{\mathrm{O}}_4$ and a systematic investigation of these properties for ${\mathrm{Mg}}^{2+}$ and ${\mathrm{Al}}^{3+}$ substitutions has been carried out. From these spectra the off-diagonal elements of the dielectric tensor was calculated between 0.7 and 4.0 eV. Through fitting simultaneously both the diagonal and the off-diagonal elements of this tensor with one set of parameters and consistently for all partially substituted ferrite samples, we were able to resolve the magneto-optical spectrum of ${\mathrm{Fe}}_3{\mathrm{O}}_4$ between 0.7 and 4.0 eV. The observed trends in the major transitions upon substitution provide the experimental evidence for intervalence charge transfer and intersublattice charge transfer transitions in ${\mathrm{Fe}}_3{\mathrm{O}}_4.$