Evidence for 3dnto 3dn-14s transitions in magnetite and in lithium and magnesium ferrites

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Abstract
Optical reflectivity and magneto-optical polar Kerr effect measurements in the photon energy ranges from 0.006 to 12 eV and 0.5 to 5 eV, respectively, are reported for magnetite and for Li and Mg ferrites. The diagonal and off-diagonal elements of the dielectric tensor are derived. From a comparison of the experimental results with the cation distribution formulae of the materials the excitations occurring below 2 eV can be assigned to transitions from Fe2+in octahedral sites and the excitation at about 3.9 eV to Fe3+in tetrahedral sites. Energy level schemes are deduced and are supported by a model describing the shape and the sign of the various magneto-optical transitions. In this model 3dnto 3dn-14s orbital promotion processes for the three kinds of iron ions are considered. Above 5 eV oxygen 2 p band to iron 4 s band charge-transfer transitions are shown to be responsible for the very strong optical absorption.