Specific Heat of a Dense-Kondo System Ce_xLa_1-xCu₆

Specific heat of a dense-Kondo system, Ce_xLa_1-xCu₆, has been systematically measured between 2 and 80 K in order to clarify the transition from dilute-Kondo to dense-Kondo behavior as the cerium concentration, x, increases. We have found that the magnetic specific heat per molar cerium, C_m, is nearly independent of x and is explained by a simple sum of the Kondo specific heat and the Schottky specific heat, with the x-independent energy separation between the ground and the first excited states (65 K). However, due to the interaction between the cerium ions, the first excited state tends to be broadened as x increases, and the width of the first excited state for the dense limit of CeCu₆ (T_K=3.9 K) is estimated to be about 20 K. At low temperatures, C_m increases as x is decreased. This tendency is qualitatively interpreted as due to the decrease in T_K caused by the increase of unit cell volume.