Interplay between the Kondo effect and the Ruderman-Kittel-Kasuga-Yosida interaction in the two-impurity model

The applicability of the Kondo Hamiltonian as a microscopic model for some Ce-based magnetic alloys such as CexLa1−xPb3 and CexLa1−xCu6 where the specific heat and the magnetic suceptibility increase linearly in x for a wide range of x is discussed. The results of the phenomenological analysis of formulating the magnetic impurities as scattering centres would suggest that the impurities in these alloys are near the unitary limit. On the other hand, a perturbation analysis for the two-impurity Kondo model indicates that the zero-temperature magnetic suceptibility for two impurity spins differs significantly from those of the independent impurities owing to the Ruderman-Kittel-Kasuga-Yosida (RKKY) interaction. This suggests that the Kondo Hamiltonian may not be appropriate for these alloys even in the dilute limit. The meaning of the Rkky interaction at low temperatures is also discussed.