Abstract
Fe 2+ site occupancy in iron garnets is investigated by means of optical absorption and magnetic circular dichroism. In particular measurements are carried out on bulk single crystals of yttrium iron garnet (YIG) doped with Si 4+, Nb 5+, Sn 4+, Zr 4+, Ti 4+ and Th 4+. The results are discussed in the light of the recent discovery of tetrahedral Fe 2+ in Nb-doped YIG. We find that, in general, Fe 2+ occupies both octahedral and tetrahedral sites, the actual distribution being related to site occupancy of the donor centers. This correlation may be relaxed by photoinduced charge transfer between iron sites, at low temperatures. Contrary to recent attributions, no dodecahedral component is found in the infrared spectra above 1 μm wavelength.
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