Thermal properties of various Kondo ground states in the heavy-fermion system CeNi1-xCoxGe2

We report results of the specific heat of the heavy-fermion compounds of the alloying series CeNi1-xCoxGe2. With increasing x, hybridization between the localized 4f and conduction band electrons is enhanced. The magnetic order observed for the x = 0 composition is completely suppressed at a critical concentration of x(c) = 0.3, yielding Fermi-liquid behaviour for x > 0.3. We observe significant deviations from the Fermi-liquid behaviour at x(c) = 0.3. Anomalies found in the specific heat are well explained by the Kondo model for a degenerate impurity spin J = 1/2, 3/2, and 5/2 in the Coqblin-Schrieffer limit for the Co concentration ranges of x <= 0.6, 0.7 <= x <= 0.8, and x >= 0.9, respectively.