Physical properties of $R$Mg$_{2}$Cu$_{9}$ ($R$ = Y, Ce-Nd, Gd-Dy)

$R$Mg$_{2}$Cu$_{9}$ is a family of hexagonal compounds with a single rare earth site that has a $\bar{6}$m2 local symmetry. In this talk, magnetic, electric transport and specific heat data measured on single crystals of $R$Mg$_{2}$Cu$_{9}$ synthesized using Ta crucible will be presented and discussed. Due to a strong CEF effect, all local moment bearing members (except for isotropic GdMg$_{2}$Cu$_{9}$) in the present study show a higher magnetic susceptibility when external field is applied along the ab-plane than along the c-axis. For $R$ = Ce, Nd, Gd-Dy, the compounds order antiferromagnetically above 2 K. The ordering temperature deviates from de Gennes scaling with GdMg$_{2}$Cu$_{9}$ ordering at a lower temperature than TbMg$_{2}$Cu$_{9}$. PrMg$_{2}$Cu$_{9}$ does not order magnetically down to 2 K and might have a singlet ground state. This series of compounds offer an opportunity to study in-plane anisotropy of rare earth in a hexagonal CEF configuration, following our previous work on in-plane 4-state clock model in a tetragonal system, for example: HoNi$_{2}$B$_{2}$C (P.C. Canfield et al. PRB 55, 970) and DyAgSb$_{2}$ (K.D. Myers et al. PRB 59, 1121).