Electronic States and Optical Spectra of ErSn_1.1Ge_0.9 and TmSn_1.1Ge_0.9 Compounds

The spin-polarized electronic structure, magnetic moments, and spectra of optical conductivity of the ternary ErSn_1.1Ge_0.9 and TmSn_1.1Ge_0.9 compounds have been calculated within the GGA+U method, taking into account strong electron correlations in the 4f-shell of Er and Tm, as well as non-stoichiometry of compositions. The calculation results pointed to antiferromagnetic ordering for both intermetallics with effective magnetic moments that precisely reproduce the published experimental values. Optical properties of these compounds were measured using the ellipsometric method in the energy range of 0.078–5.64 eV. It has been shown that the main peculiarities of experimental curves are described by calculated densities of electronic states. The good agreement of magnetic moments and interband optical conductivities, which are calculated from first principles, with the experimental data indicates the importance of accounting for the strong electron correlations and non-stoichiometry of compositions in calculations of electronic structure of the RSn_1.1Ge_0.9-type compounds containing heavy rare-earth metals.