A study of strongly correlated electron behavior in the filled skutterudites.

摘要

In the search for new and interesting strongly correlated electron phenomena, a detailed study has been underway of the rare earth-based filled skutterudite compounds. This work has been driven by the rich variety of strongly correlated electron phenomena exhibited by the filled skutterudites such as metal insulator transitions, heavy fermion behavior, quadrupole ordering, non-Fermi liquid behavior, and heavy fermion superconductivity. The filled skutterudite compounds have the chemical formula MT4X 12 where M = alkali metal, alkaline-earth, lanthanide, or actinide; T = Fe, Ru, or Os; and X = P, As, or Sb. To improve the general understanding of these systems and to look for other strongly correlated electron behavior, single crystals of Pr 0.87Fe4Sb12, PrOs4As12, PrOs4P12, SmOs4Sb12, and NdOs 4Sb12 were grown and characterized with X-ray diffraction, magnetization, electrical resistivity and specific heat measurements.; Measurements of the filled skutterudite compound Pr0.87Fe 4Sb12 reveal long range magnetic ordering below 4.1 K with indications of ferromagnetic ordering. Features in the magnetization of the filled skutterudite PrOs4As12 are consistent with antiferromagnetic ordering below 2.3 K. The specific heat, electrical resistivity, and magnetization measurements on PrOs4As12 also show features consistent with at least 2 to 3 ordered phases. Strong crystalline electric field effects were observed in PrOs4P12 and SmOs4Sb 12, with both systems exhibiting Schottky anomalies in specific heat measurements. Magnetic ordering was observed in SmOs4Sb12 below 2.6 K with a ferromagnetic component as indicated by hysteresis in the magnetization as a function of field at 2 K. Magnetic ordering was also observed in the filled skutterudite compound NdOs4Sb 12 below 0.9 K. Analysis of the specific heat measurements on Pr 0.87Fe4Sb12, PrOs4As12, SmOs4Sb12, and NdOs4Sb12 reveal an enhanced electron effective mass, with SmOs4Sb12 showing the largest enhancement.