New Nabokoite-Like Phases ACu7TeO4(SO4)5Cl (A = Na, K, Rb, Cs) with Decorated and Distorted Square Kagome Lattices.

A new family of compounds ACu7TeO4(SO4)5Cl (A = Na, K, Rb, Cs) isostructural to mineral Nabokoite (K species) was synthesized by solid state and gas transport reactions in sealed ampoules and characterized in measurements of magnetization and specific heat in a wide temperature range. These complex compounds are of the utmost interest as a testing playground to study the properties of a quasi-two-dimensional magnets with a square kagome lattice geometry. A quantum ground state of such a corner-sharing network is a spin liquid. Unlike idealized grid analyzed in numerous models, the square kagome lattice in nabokoites is wavy and distorted being composed by the versatile triangles. Moreover, it contains "excessive" decorating magnetic ions, which makes magnetism of these objects even more complicated. The interaction of these decorating ions through virtual excitations of the square kagome lattice is accompanied by the formation of a long-range magnetic order coexisting with the spin liquid.