Relationship between specific heat, valence and effective magnetic moment of Sm ions in strongly correlated Sm compounds

Strongly-correlated electron states emerging in cubic Sm-based compounds, e.g., SmOs4Sb12 and Sm Tr2Al20 (Tr: transition metal elements), have anomalous characteristics, like magnetic-field-insensitive heavy-fermion behaviors and strongly mixed valence of Sm ions. In this paper, we compare key physical parameters of these compounds. The results reveal the existence of the following novel features: (i) the electronic specific heat coefficient γ shows a significant inverse correlation with the effective magnetic moment μeff (γ∼1/μeff2), and (ii) largely enhanced γ appears in intermediate Sm valance states around ∼ +2.8. Other remarkable features are the absence of enhanced Pauli paramagnetism at low temperatures and largely suppressed μeff (down to ∼0.1 μB). These are quite different from those of Ce-based heavy-fermion compounds, pointing to an unconventional mechanism for the formation of Sm-based heavy quasiparticles, possibly caused by complex hybridization processes associated with multi-4 f-electrons of a Sm ion.