Specific heat of Ce1-xMxCu6 (M=La, Th, Y, and Pr)

Ce1-xLaxCu6 is known to have a γ [≡C/T (T→0)] per Ce mole that increases monotonically with increasing La concentration: γ of Ce0.1La0.9Cu6 is ∼2.3 J/Ce mole K2 while that for pure CeCu6 is only 1.6 J/Ce mole K2. To investigate this behavior, unusual in comparison with, e.g., UBe13 or CeCu2Si2, the properties (including specific heat to 0.4 K, dc susceptibility to 1.8 K, and resistivity) of Ce1-xMxCu6, M=La, Th, Y, and Pr, 0≤x≤1, have been investigated, with the most extensive work being on La and Th. χ (1.8 K) remains essentially constant to x=0.4 for Th and La doping, and then rises (falls) for further La (Th) doping, with values for x=0.1 of 45.7 memu/Ce mole for La and 19.3 memu/Ce mole for Th versus 36.7 memu/mole for pure CeCu6. While the specific-heat γ values, as previously reported, increase essentially linearly upon increasing La doping, the γ values for Th doping remain essentially constant up to x=0.4, and then decrease monotonically upon further Th doping, reaching γ=500 mJ/Ce mole K2 for x=0.9