ODMR AND EPR INVESTIGATIONS OF FE CENTERS IN KTAO3

The analysis of EPR spectra obtained from iron doped KTaO3 crystals in the as-grown state revealed three dominant iron centers: Fe3+-O-I, ax ial Fe-centers with spin S = 3/2 and rhombic Fe3+. By comparison with data from literature possible assignments for the center with S = 3/2 are discussed. For the rhombic species the temperature dependence of t he main parameters of the Spin- Hamiltonian was measured. The result m akes it most plausible that only one rhombic iron center exists in KTa O3, in contrast with literature. The understanding of the EPR spectra allows us to assign transitions, observed at very low magnetic fields by optically detected magnetic resonance (ODMR), to this rhombic Fe ce nter. On this basis, the magnetic circular dichroism (MCD) of this def ect could be identified using the method of tagged-MCD. This spectrum is compared to the tagged-MCD of Fe3+-O-I and of axial Fe4+ centers, w hich may be generated metastably by optical charge transfer. Considera bly different structures in the MCD spectra of both Fe3+ centers indic ate different local surroundings and electronic states.