  Co$_3$O$_4$, ZnFe$_2$O$_4$, CoFe$_2$O$_4$, ZnCo$_2$O$_4$, and Fe$_3$O$_4$
thin films were fabricated by pulsed laser deposition at high and low
temperatures resulting in crystalline single-phase normal, inverse, as well as
disordered spinel oxide thin films with smooth surface morphology. The
dielectric function, determined by spectroscopic ellipsometry in a wide
spectral range from 0.5 eV to 8.5 eV, is compared with the magneto-optical
response of the dielectric tensor, investigated by magneto-optical Kerr effect
(MOKE) spectroscopy in the spectral range from 1.7 eV to 5.5 eV with an applied
magnetic field of 1.7 T. Crystal field, inter-valence and inter-sublattice
charge transfer transitions, and transitions from O$_{2p}$ to metal cation 3d
or 4s bands are identified in both the principal diagonal elements and the
magneto-optically active off-diagonal elements of the dielectric tensor.
Depending on the degree of cation disorder, resulting in local symmetry
distortion, the magneto-optical response is found to be strongest for high
crystal quality inverse spinels and for disordered normal spinel structure,
contrary to the first principle studies of CoFe$_2$O$_4$ and ZnFe$_2$O$_4$. The
results presented provide a basis for deeper understanding of light-matter
interaction in this material system that is of vital importance for
device-related phenomena and engineering.
