LOW-TEMPERATURE MAGNETIC-BEHAVIOR OF CE7NI3

Low-temperature specific heat (C(P)) (70 mK < T < 30 K) and AC magnetic susceptibility (chi) (70 mK < T < 3 K) measurements on Ce7Ni3 (under applied magnetic fields up to B = 6 T) are presented. The maxima in C(P) (at 1.55 K) and in chi (at 1.85 K) are related to an antiferromagnetic (AF) type transition. The experimental results are interpreted in terms of three Ce sublattices (1Ce(I), 3Ce(II) and 3Ce(III) atoms per formula unit) of the Th7Ni3-type structure. These sublattices correspond to the three different Ce local environments. According to the entropy gain the AF order is related to the Ce(I) sublattice and the Ce(II) atoms behave as heavy fermions, with gamma(LT) almost-equal-to 2.7 J/Ce(II)-at. K2 and a characteristic temperature of T(K) almost-equal-to 4 K. The Ce(III) atoms are responsible for an intermediate valence behavior with Y(HT) almost-equal-to 0.3 J/Ce(III)-at. K2 and a characteristic temperature of T0 almost-equal-to 70 K, which is confirmed by the ln T dependence of the electrical resistivity.