Ferromagnetic Transition at 2.5K in the Hexagonal Kondo-Lattice Compound CeRh6Ge4

Magnetization, specific heat, and electrical resistivity measurements have been performed for polycrystalline samples of hexagonal CeRh6Ge4 and CeRh6Si4. The Ce ions in CeRh6Ge4 are trivalent above 100 K, while those in CeRh6Si4 display an intermediate-valence state below room temperature. We discovered that CeRh6Ge4 is a new ferromagnetic (FM) compound with the transition temperature T-C = 2.5 K. The -lnT dependence of the magnetic part of the electrical resistivity, the small magnetic entropy released at TC (0.19Rln2), and the relatively large electronic specific-heat coefficient (0.25 J.mol(-1).K-2) imply that CeRh6Ge4 is a Kondo-lattice compound. We argue that CeRh6Ge4 is a rare Ce-based FM compound with a proximity to a quantum critical point.