Ultraviolet Magneto-Optical Properties of Single-Crystal Orthoferrites, Garnets, and Other Ferric Oxide Compounds

The ultraviolet and visible linear magneto-optical properties of representative ferric oxide compounds were measured by reflection methods between 1.7 and 5.64 eV at room temperature. The experimental technique, based on the complex polar Kerr effect (rotation and ellipticity), was applied to all available single-crystal rare-earth orthoferrites and to representative rare-earth iron garnets, nickel spinel ferrite, and magnetoplumbite. For representative orthoferrites and yttrium iron garnet, the magneto-optical results were reduced, with the aid of additional straight (nonmagnetic) reflectivity data, to obtain the magnetically induced off-diagonal elements of the dielectric tensor. Presentation of the magneto-optical results in the form of the tensor elements facilitates comparison with microscopic theories because of the difference in energy dependence between the tensor elements and the experimental observables. The observed spectra are analyzed in terms of a molecular-orbital theory that elaborates on an earlier calculation by Clogston. For the orthoferrites, explicit calculation of the dielectric-tensor elements has made it possible to identify the most prominent features in the magneto-optical spectra in terms of explicit charge-transfer and crystal-field transitions. The magneto-optical effects in the orthoferrites are approximately the same order of magnitude as in the garnets, although a simple theory would have them an order of magnitude smaller. This is interpreted as evidence for an anisotropic orbital quenching that follows from the low symmetry of the Fe ion in the orthoferrites. Magneto-optical measurements on gallium-substituted europium iron garnet has made it possible to differentiate between the magneto-optical structure that arises from Fe ions on octahedral and tetrahedral sites.