  Magnetization and specific heat measurements have been carried out on
Cs$_2$Cu$_3$ZrF$_{12}$ and Cs$_2$Cu$_3$HfF$_{12}$ single crystals, in which
Cu$^{2+}$ ions with spin-1/2 form a regular Kagom\'{e} lattice. The
antiferromagnetic exchange interaction between neighboring Cu$^{2+}$ spins is
$J/k_{\rm B}\simeq 360$ K and 540 K for Cs$_2$Cu$_3$ZrF$_{12}$ and
Cs$_2$Cu$_3$HfF$_{12}$, respectively. Structural phase transitions were
observed at $T_{\rm t}\simeq 210$ K and 175 K for Cs$_2$Cu$_3$ZrF$_{12}$ and
Cs$_2$Cu$_3$HfF$_{12}$, respectively. The specific heat shows a small bend
anomaly indicative of magnetic ordering at $T_\mathrm{N}= 23.5$ K and 24.5 K in
Cs$_2$Cu$_3$ZrF$_{12}$ and Cs$_2$Cu$_3$HfF$_{12}$, respectively. Weak
ferromagnetic behavior was observed below $T_\mathrm{N}$. This weak
ferromagnetism should be ascribed to the antisymmetric interaction of the
Dzyaloshinsky-Moriya type that are generally allowed in the Kagom\'{e} lattice.

Strongly Correlated Electrons