T. Fujino

Elastic properties of the filled and unfilled skutterudite compounds

Ultrasonic measurements were made on a single crystal of the unfilled skutterudite compounds RhSb3 and IrSb3 and compare with that of the filled skutterudite PrOs4 Sb12 to elucidate the role of the guest ions Pr. A characteristic increase was observed around 30 K in the temperature dependence of elastic constants (C11-C12)/2 and C44 which is ascribed to unusual vibration rattling of Pr ions in an atomic cage formed by Sb-icosahedron. On the other hand, the elastic constants C11, (C11-C12)/2 and C44 increase monotonically with decreasing temperature in the case of RhSb3 and IrSb3. No such a characteristic increase was observed. These results give us a piece of evidence that the guest ions would play a crucial role for rattling motion in filled skutterudite compounds.

Elastic properties of the ferromagnetic heavy fermion system SmOs4Sb12

Ultrasonic measurements were made on a single crystal of the filled skutterudite compound SmOs4Sb12. A remarkable elastic softening toward low temperature was observed in the elastic constants C11, (C11-C12)/2 and C44 as a function of temperature, followed by a sharp drop which is associated with the onset of ferromagnetic ordering, and then display a monotonic increase below Tc. The present results indicate that the crystalline electric field (CRF) effect would not support straightforward the observed elastic softening toward low temperature. We suggest that this fact is originated from valence instability of the Sm ion at low temperature in SmOs4Sb12. The 4f electronic ground state of the Sm ion and its elastic property are discussed.