Magnetic susceptibility, magnetization, specific heat, and electrical resistivity studies on single crystals of Ce4Pt12Sn25 reveal an antiferromagnetic transition at T(N) = 0.19 K, which develops from a paramagnetic state with a very large specific heat coefficient (C/T) of 14 J mol(-1) K(-2)-Ce just above T(N). On the basis of its crystal structure and these measurements, we argue that a weak magnetic exchange interaction in Ce4Pt12Sn25 is responsible for its low ordering temperature and a negligible Kondo-derived contribution to physical properties above T(N). The anomalous enhancement of specific heat above T(N) is suggested to be related, in part, to weak geometric frustration of f-moments in this compound.

We report specific heat (C) and magnetization (M) of single crystalline Ce4Pt12Sn25 at temperature down to 50 mK and in fields up to 3 T. C/T exhibits a sharp anomaly at 180 mK, with a large jump in a Sommerfeld coefficient γ C/T of Δγ 30 J/molK2-Ce, which, together with corresponding cusp-like magnetization anomaly, indicate antiferromagnetic (AFM) ground state with Nel temperature TN 0.18 K. Numerical calculations based on Heisenberg model reproduce well zero field specific heat data, and point to a very small Kondo scale TK, clearly placing Ce4Pt12Sn25 in the weak exchange coupling J < Jc limit of the Doniac diagram. Magnetic field suppresses AFM state at H* 0.7 T, much more rapidly than indicated by theoretical calculations. © Published under licence by IOP Publishing Ltd.