Non-Fermi-liquid behaviour at the pressure-induced antiferromagnetic to nonmagnetic transition in a heavy-fermion compound, Ce7Ni3

High-pressure studies of transport. magnetic and thermal properties of a heavy-fermion antiferromagnet. Ce7Ni3. are reviewed. At ambient pressure, the Ce ions in the three nonequivalent sites in this compound are found to be very close to trivalent from L(III)-XANES (x-ray absorption near-edge structure) spectra and magnetic susceptibility measurements. With increasing pressure, T-N (1.8 K at P = 0) of Ce7Ni3 is suppressed and vanishes near P-c approximate to 0.32 GPa. Non-Fermi-liquid (NFL) behaviour appears around 0.4 GPa in both the specific heat and AC magnetic susceptibility: C-m/T proportional to - In T and X(AC) proportional to (1-alpha T-1/2). Above 0.62 GPa, the normal Fermi liquid state recovers as indicated by the T independence of C-m/T and the T-2 dependence of magnetic resistivity. The variation of C-m(T) with pressure is analysed in terms of two models: the impurity Kondo model with three Kondo temperatures and the self-consistent renormalization (SCR) theory of spin fluctuations (SFs). We find that the crossover in C-m/T is better described by the SCR theory. The characteristic SF temperature T-0 increases by a factor of 20 for 0.33 GPa less than or equal to P less than or equal to 0.75 GPa, yielding a large Gruneisen parameter Gamma(e) = 220 around 0.4 GPa.