Strong magnetic frustration in Y$_{3}$Cu$_{9}$(OH)$_{19}$Cl$_{8}$: a distorted kagome antiferromagnet (1702.01036v2)

Abstract: We present the crystal structure and magnetic properties of Y${3}$Cu${9}$(OH)${19}$Cl${8}$, a stoichiometric frustrated quantum spin system with slightly distorted kagome layers. Single crystals of Y${3}$Cu${9}$(OH)${19}$Cl${8}$ were grown under hydrothermal conditions. The structure was determined from single crystal X-ray diffraction and confirmed by neutron powder diffraction. The observed structure reveals two different Cu-positions leading to a slightly distored kagome layer in contrast to the closely related YCu${3}$(OH)${6}$Cl${3}$. Curie-Weiss behavior at high-temperatures with a Weiss-temperature $\theta{W}$ of the order of $-100$ K, shows a large dominant antiferromagnetic coupling within the kagome planes. Specific-heat and magnetization measurements on single crystals reveal an antiferromagnetic transition at T${N}=2.2$ K indicating a pronounced frustration parameter of $\theta{W}/T_{N}\approx50$. Optical transmission experiments on powder samples and single crystals confirm the structural findings. Specific-heat measurements on YCu${3}$(OH)${6}$Cl$_{3}$ down to 0.4 K confirm the proposed quantum spin-liquid state of that system. Therefore, the two Y-Cu-OH-Cl compounds present a unique setting to investigate closely related structures with a spin-liquid state and a strongly frustrated AFM ordered state, by slightly releasing the frustration in a kagome lattice.