The filled skutterudite compound $\mathrm{Sm}{\mathrm{Os}}_4{\mathrm{Sb}}_{12}$ was prepared in single-crystal form and characterized using x-ray diffraction, specific-heat, electrical resistivity, and magnetization measurements. The $\mathrm{Sm}{\mathrm{Os}}_4{\mathrm{Sb}}_{12}$ crystals have the $\mathrm{La}{\mathrm{Fe}}_4{\mathrm{P}}_{12}$-type structure with lattice parameter $a=9.3085\mathrm{\AA }$. Specific-heat measurements indicate a large electronic specific-heat coefficient of $\approx 880\mathrm{mJ}∕\mathrm{mol}{\mathrm{K}}^2$, from which an enhanced effective mass $m^{*}\approx 170m_e$ is estimated. The specific-heat data also suggest crystalline electric field (CEF) splitting of the ${\mathrm{Sm}}^{3+}J=5∕2$ multiplet into a ${\Gamma }_7$ doublet ground state and a ${\Gamma }_8$ quartet excited state separated by $\sim 37\mathrm{K}$. Electrical resistivity $\rho \left(T\right)$ measurements reveal a decrease in $\rho \left(T\right)$ below $\sim 50\mathrm{K}$ that is consistent with CEF splitting of $\sim 33\mathrm{K}$ between a ${\Gamma }_7$ doublet ground state and ${\Gamma }_8$ quartet excited state. Specific-heat and magnetic susceptibility measurements display a possible weak ferromagnetic transition at $\sim 2.6\mathrm{K}$, which could be an intrinsic property of $\mathrm{Sm}{\mathrm{Os}}_4{\mathrm{Sb}}_{12}$ or possibly due to an unknown impurity phase.

• Received 9 March 2004

DOI:https://doi.org/10.1103/PhysRevB.71.104402