Magnetic State of Layered Cobalt Chalcogenides Co7Se8 and Co7Te8.

The structural and magnetic properties of the Co₇Te₈ layered compound have been studied for the first time using X-ray diffraction, measurements of the magnetic susceptibility, and nuclear magnetic resonance spectroscopy on ⁵⁹Co nuclei. The nuclear magnetic resonance study of Co₇Se₈ selenide with the same structural type (NiAs) as Co₇Te₈ has also been performed for the first time. In contrast to Co₇Se₈, the ordering of vacancies and Co atoms in cation layers is absent in the Co₇Te₈ compound, and its crystal structure is more planar and is characterized by a significantly smaller ratio c₀/a₀ compared to Co₇Se₈ (a₀ and c₀ are the basic lattice parameters of NiAs). The components of the magnetic shift and electric field gradient tensors at the location of Co nuclei have been determined. A significant local charge and spin inhomogeneity of the co-mpounds has been revealed. The hyperfine coupling constant in Co ions has been estimated from the te-mperature dependences of the shift and susceptibility in Co₇Te₈. An anisotropic increase in the interatomic distances does not increase the localization of electrons and does not lead to the appearance of magnetic moments on Co atoms in Co₇Te₈. This compound remains a Pauli paramagnet down to the lowest tempe-ratures. [ABSTRACT FROM AUTHOR]