We synthesized single crystals of the new hexagonal compounds A$_2$Cu$_3$SnF$_{ 12}$ with A=Cs and Rb, and investigated their magnetic properties. These compounds are composed of Kagom\'{ e} layers of corner-sharing CuF$_6$-octahedra. Cs$_2$Cu$_3$SnF$_{ 12}$ has the proper Kagom\'{ e} layer at room temperature, and undergoes structural phase transition at $T_\mathrm{ t}\simeq 185$ K. The temperature dependence of the magnetic susceptibility in Cs$_2$Cu$_3$SnF$_{ 12}$ agrees well with the result of the numerical calculation for $S=1/2$ two-dimensional Heisenberg Kagom\'{ e} antiferromagnet down to $T_\mathrm{ t}$ with the nearest exchange interaction $J/k_\mathrm{ B}\simeq 240$ K. Although the magnetic susceptibility deviates from the calculated result below $T<T_\mathrm{ t}$, the rounded maxima were observed at approximately $T\simeq (1/6)J/k_\mathrm{ B}$ as predicted by the theory. Cs$_2$Cu$_3$SnF$_{ 12}$ undergoes three-dimensional magnetic ordering at $T_\mathrm{ N} = 20$ K.
Categories: cond-mat.str-el