  The physical properties of the very heavy fermion YbCu$_4$Ni were
characterized through structural, magnetic, thermal and transport studies along
nearly four decades of temperature ranging between 50 milikelvin and 300 K. At
high temperature, the crystal electric field levels splitting was determined
with $\Delta_1 (\Gamma_6)= 85$ K and $\Delta_2 (\Gamma_8) \approx 200$ K, the
latter being a quartet in this cubic symmetry. An effective magnetic moment
$\mu_{eff} \approx 3\mu_B$ is evaluated for the $\Gamma_7$ ground state, while
at high temperature the value for a Yb$^{3+}$ ion is observed. At low
temperature this compounds shows the typical behavior of a magnetically
frustrated system undergoing a change of regime at a characteristic temperature
$T^*\approx 200$ mK into a sort of Fermi-liquid type 'plateau'of the specific
heat: $C_m/T|_{T\to 0}$ = const. The change in the temperature dependence of
the specific heat coincides with a maximum and a discontinuity in respective
inductive and dissipative components of the ac-susceptibility. More details
from the nature of this ground state are revealed by the specific heat behavior
under applied magnetic field.
