Dependence of weak-ferromagnetic transition in Yb_x Fe₄ Sb₁₂ single crystals on the filling ratio x

Single crystals of the filled-skutterudite compound Yb_x Fe₄ Sb₁₂ were prepared by the Sb-flux method. Filling ratios, x, of Yb and chemical ratios of Fe were determined with the electron-probe micro analysis, setting the content of Sb at 12. The filling ratios of Yb ranged from 0.875 to 0.910 and the chemical ratios of Fe were determined to be 4.0 for all samples. The results of magnetization measurements of the samples indicated that all samples were weak-ferromagnets with transition temperatures, T_C, ranging between 20 and 6 K, and that T_C decreased smoothly with increasing x. A straight line fitted for the plot of T_C versus x suggests that T_C vanishes around x = 0.93.