Role of chemical pressure on the electronic and magnetic properties of the spin- 12 kagome mineral averievite

We investigate the electronic and magnetic properties of the kagome mineral averievite $(\mathrm{Cs}\mathrm{Cl}){\mathrm{Cu}}₅{\mathrm{V}}₂{\mathrm{O}}₁₀$ and its phosphate analog $(\mathrm{Cs}\mathrm{Cl}){\mathrm{Cu}}₅{\mathrm{P}}₂{\mathrm{O}}₁₀$ using first-principles calculations. The crystal structure of these compounds features ${\mathrm{Cu}}²⁺$ kagome layers sandwiched between ${\mathrm{Cu}}²⁺\ensuremath{-}{\mathrm{P}}⁵⁺$/${\mathrm{Cu}}²⁺\ensuremath{-}{\mathrm{V}}⁵⁺$ honeycomb planes, with pyrochlore slabs made of corner-sharing Cu tetrahedra being formed. The induced chemical pressure effect upon substitution of V by P causes significant changes in the structure and magnetic properties. Even though the in-plane antiferromagnetic (AFM) coupling ${J}₁$ within the kagome layer is similar in the two materials, the interplane AFM coupling ${J}₂$ between kagome and honeycomb layers is five times larger in the P variant, increasing the degree of magnetic frustration in the constituting Cu tetrahedra.