Thermodynamic properties of CeCu6-xAux: Fermi-liquid vs. non-Fermi-liquid behaviour

We report on a detailed comparison of the thermodynamic properties of the heavy-fermion system CeCu₆ which can be described as a Fermi liquid at low temperatures T < 0.1 K, and CeCu_5.9Au_0.1 where strong deviations from the Fermi-liquid behaviour were found previously in the T dependence of the specific heat C, magnetization M and electrical resistivity p. The specific heat, magnetization and elastic constants are investigated in a large range of magnetic fields, corroborating the idea that the non-Fermi-liquid behaviour arises from low-lying spin excitations. For the elastic constants, a striking linear T dependence is found for CeCu_5.9Au_0.1 in contrast to the T² Fermi-liquid behaviour of CeCu₆.