Single Crystal Growth of Filled Skutterudite Compounds Containing Heavy-Rare-Earth Elements

Single, crystalline samples of Yb filled-skutterudite compounds Yb_xFe_4Sb_(12) were successfully grown by the Sb self-flux method. The magnetization and specific heat of these single-crystalline samples were measured. Six single crystals with the filling ratio of Yb, x, from 0.875 to 0.910 were prepared. The weak ferromagnetism of Yb_xFe_4Sb_(12) appearing at low temperatures was found to strongly correlate with x, that is, with increasing x from 0.875 to 0.910, the transition temperature, Tc, decreases from 17 to 5 K and the weak-ferromagnetic moment, mo, decreases from 0.066 to 0.005 μB/Fe. From these trends, both Tc and m0 were expected to reach zero at the critical concentration, Xc=0.93. In the temperature dependence of the specific heat, no anomaly at Tc was observed, reflecting that ma is extremely small compared with the effective Bohr magneton number. With the application of pressure, the Tc of the sample with x=0.882 increases rapidly, with the ratio of dTc/dP =+5.27 K/Gpa. This weak ferromagnetism of Yb_xFe_4Sb_(12) is revealed to originate from the itinerant 3d electrons of Fe in anions [Fe_4Sb_(12)].