Anisotropic magnetic property of single crystals RV6Sn6 (R=Y, Gd−Tm, Lu)

${R\mathrm{V}}_{6}{\mathrm{Sn}}_{6}$ $(R=\mathrm{Y}, \mathrm{Gd}\text{\ensuremath{-}}\mathrm{Tm}, \mathrm{Lu})$ single crystals are synthesized by the Sn-flux method and their physical properties are characterized by magnetization, resistivity, and specific heat measurements. Powder x-ray diffraction patterns of all samples can be well indexed with the hexagonal ${\mathrm{HfFe}}_{6}{\mathrm{Ge}}_{6}$-type structure, where rare-earth atoms form hexagonal layers and vanadium atoms form kagome layers. At high temperatures, magnetic susceptibility measurements of moment-bearing rare-earth ions $(R=\mathrm{Gd}\text{\ensuremath{-}}\mathrm{Tm})$ follow Curie-Weiss behavior. Effective moments estimated from the polycrystalline average of magnetic susceptibility curves are consistent with the values for free ${R}^{3+}$ ions. Strong magnetic anisotropy due to crystalline electric field effects is observed for moment-bearing rare-earth ions, except ${\mathrm{GdV}}_{6}{\mathrm{Sn}}_{6}$. The easy magnetization direction is determined to be the $c$ axis for $R=\mathrm{Tb}\text{\ensuremath{-}}\mathrm{Ho}$ and $ab$ plane for $R=\mathrm{Er}$ and Tm. The vanadium ions in ${R\mathrm{V}}_{6}{\mathrm{Sn}}_{6}$ possess no magnetic moment. The compounds for $R=\mathrm{Y}$ and Lu exhibit typical characteristics of paramagnetic metals. At low temperatures, the magnetic ordering is confirmed from magnetization, specific heat, and resistivity: the highest ${T}_{N}=4.9$ K for ${\mathrm{GdV}}_{6}{\mathrm{Sn}}_{6}$ and the lowest ${T}_{N}=2.3$ K for ${\mathrm{HoV}}_{6}{\mathrm{Sn}}_{6}$. No magnetic ordering is observed down to 1.8 K for $R=\mathrm{Er}$ and Tm. A slight deviation of the magnetic ordering temperature from the de Gennes scaling suggests the dominant Ruderman-Kittel-Kasuya-Yosida exchange interaction between rare-earth moments in metallic ${R\mathrm{V}}_{6}{\mathrm{Sn}}_{6}$ compounds.