Exotic Heavy-Fermion State in Filled Skutterudite SmOs4Sb12

Specific heat and transport measurements have revealed an unconventional heavy-fermion (HF) state in SmOs 4 Sb 12 single crystals. The electronic specific-heat coefficient (γ=0.82 J/K 2 mol) and the coefficient ( A ) of the quadratic temperature dependence of electrical resistivity are largely enhanced, although the ratio A γ -2 is reduced from the Kadowaki–Woods ratio of HF materials. Both γ and A do not show any significant decrease in applied field in contrast with Ce-based HF compounds, suggesting an unconventional origin of the heavy quasiparticles. A weak ferromagnetic ordering sets in below ∼3 K, probably originating in the itinerant quasiparticles.

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