Engelhauptite: A variant of S=12 kagome antiferromagnet

Abstract

We have investigated the crystal structure and magnetic properties of the synthetic copper mineral engelhauptite, $\mathrm{KC}{\mathrm{u}}_{3}{\mathrm{V}}_{2}{\mathrm{O}}_{7}{(\mathrm{OH})}_{2}\mathrm{Cl}$, which possesses a kagome lattice made of $\mathrm{C}{\mathrm{u}}^{2+}$ ($3{d}^{9}$) ions. Unlike the hexagonal structure with a perfect kagome lattice reported in the natural mineral, a synthetic crystal has a monoclinic structure with a distorted kagome lattice. We observe a magnetic transition at 6 K and an anomaly in the magnetization curve around 50 T. Engelhauptite represents a variant of the $S=1/2$ kagome antiferromagnet and we discuss the structure-property relationship by comparing engelhauptite and its relative compound volborthite, $\mathrm{C}{\mathrm{u}}_{3}{\mathrm{V}}_{2}{\mathrm{O}}_{7}{(\mathrm{OH})}_{2}\ifmmode\cdot\else\textperiodcentered\fi{}2{\mathrm{H}}_{2}\mathrm{O}$.