On the origin of the magneto-optical effects in Li, Mg, Ni, and Co ferrite

A reexamination of the magneto-optical (MO) spectra of Li0.5Fe2.5O4, MgFe2O 4, NiFe2O4, and CoFe2O4 is presented. Thus far the MO spectra of these comp ounds have been explained by either orbital promotion processes, oxygen to iron charge transfer transitions or crystal field transitions and, in the c ase of CoFe2O4, a single intervalence charge transfer (IVCT) transition. Fo r Li0.5Fe2.5O4 and MgFe2O4, the major transitions in the MO-Kerr spectra be tween 0.5 and 5.0 eV are assigned to intersublattice charge transfer (ISCT) transitions. The MO-Kerr spectrum of NiFe2O4 is more complex as in this ca se both Fe3+ and Ni2+ contribute to the spectrum. In NiFe2O4 an additional IVCT transition is observed at 2.9 eV. The complex MO spectrum of CoFe2O4 c ould be resolved using the dielectric tensors of Co2+ Al-x(3+) Fe-2-x(3+) O -4 (s = 0, 0.1, 0.6, and 1) and rigorously fitting both the diagonal and th e off-diagonal elements of the dielectric tensor with one set of transition s which was consistent for all degrees of Al3+ substitution. Thus, in these ferrites a consistent assignment of all the major transitions in the 2.0 t o 5.0 eV energy range to either IVCT or ISCT transitions is made. (C) 1998 American Institute of Physics. [S0021-8979(98)22011-1].