Anisotropy of the Complex Permittivity of the Kagome-Staircase Compounds Co3V2O8 and Ni3V2O8: Experiment and Ab Initio Calculations

Abstract

The anisotropy of the components of the complex permittivity of vanadate Co3V2O8 and Co3V2O8 single crystals in the paramagnetic phase are studied by optical ellipsometry in the spectral region 0.5–5.0 eV. Our experimental results support the weak anisotropy of the optical response detected earlier for axes a and c. The optical properties are also investigated along axis b. The properties of both compounds are compared. The optical spectra of both compounds along axis b are shifted toward low energies as compared to axes a and c. The maximum of the main interband absorption band of Co3V2O8 is shifted toward low energies by 0.25–0.3 eV as compared to Co3V2O8. The electronic structure parameters of both compounds are determined. Optical function spectra are analyzed using the results of ab initio band calculations.