Coexistence of heavy fermion and intermediate valence behaviour in Ce24Co11

Low temperature specific heat, magnetic susceptibility andL_III-XAS measurements on Ce₂₄Co₁₁ are reported. The electronic specific heat can be decomposed into two contributions: a low temperature one (arising atT<5 K), with a maximum of 2.2 J/Kmole at 0.9 K, and another one becoming dominant atT>5 K, characterized by a _HT = 1.8 J/K² mole coefficient. The ·T product changes continuously with temperature, from 0.48 emu K/mole at 2 K to 7.85 emu K/mole at 200 K. TheL_III-mean valence is =3.15.As the 24 Ce atoms are distributed in ten unequivalent crystalline sites, we interpret the experimental results as due to: one atom which behaves as a Heavy Fermion and the rest as Kondo and Intermediate Valent, with a distribution of characteristic energies governed by nine different environments. Qualitatively, the specific heat behaviour under applied field and the =3.15 value are in agreement with this interpretation.