Optical properties of thulium orthoferrite TmFeO3

Optical properties of the orthorhombic thulium orthoferrite TmFeO3 were studied in the spectral range from 0.64 to 5.4 eV. In the weak absorption region, below 2.2 eV, the energies of localized optical transitions in the Tm3+ and Fe3+ ions were determined. The dispersion relations of the real and imaginary parts of the principal refractive indices along three crystallographic axes were found. In the region of strong absorption, above 2.2 eV, the energies of six charge-transfer transitions were determined. The experimental data fit well to the concept of charge-transfer transitions in the FeO69- octahedral complexes providing a dominant contribution to the optical properties of the orthoferrites. Optical birefringence and its temperature dependence were measured for the three principal directions of light propagation, and the anisotropic magnetic contribution to birefringence in the region of spin-orientational transitions was isolated. (c) 2005 Pleiades Publishing, Inc.