Ferromagnetism and possible heavy-fermion behavior in single crystals of Nd Os 4 Sb 12

Single crystals of the filled-skutterudite compound $\mathrm{Nd}{\mathrm{Os}}_{4}{\mathrm{Sb}}_{12}$ have been investigated by means of electrical resistivity, magnetization, and specific heat measurements. The $\mathrm{Nd}{\mathrm{Os}}_{4}{\mathrm{Sb}}_{12}$ crystals have the $\mathrm{La}{\mathrm{Fe}}_{4}{\mathrm{P}}_{12}$-type cubic structure with a lattice parameter of $9.3\phantom{\rule{0.3em}{0ex}}\mathrm{\AA{}}$. Possible heavy-fermion behavior is inferred from specific heat measurements, which reveal a large electronic specific heat coefficient $\ensuremath{\gamma}\ensuremath{\approx}520\phantom{\rule{0.3em}{0ex}}\mathrm{mJ}∕\mathrm{mol}\phantom{\rule{0.2em}{0ex}}{\mathrm{K}}^{2}$, corresponding to an effective mass ${m}^{*}\ensuremath{\approx}98{m}_{e}$. Features related to a ferromagnetic transition at $\ensuremath{\sim}0.9\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ can be observed in electrical resistivity, magnetization, and specific heat. Conventional Arrott-plot analysis indicates that $\mathrm{Nd}{\mathrm{Os}}_{4}{\mathrm{Sb}}_{12}$ conforms to mean-field ferromagnetism.