Origin of Weak Ferromagnetism in YbxFe4Sb12, Relationship between Weak Ferromagnetism and Filling Ratio x

Abstract

The magnetization and specific heat of single-crystalline samples of filled-skutterudite compounds Yb x Fe 4 Sb 12 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 x Fe 4 Sb 12 appearing at low temperatures was found to strongly correlate with x ; with increasing x from 0.875 to 0.910, the transition temperature, T C , decreases from 17 to 5 K and the weak-ferromagnetic moment, m 0 , decreases from 0.066 to 0.005 µ B /Fe. From these trends, both T C and m 0 were expected to reach zero at the critical concentration, x c =0.93. In the temperature dependence of the specific heat, no anomaly at T C was observed, reflecting that m 0 is extremely small compared with the effective Bohr magneton number. With the application of pressure, the T C of the sample with x =0.882 increases rapidly, with the ratio of d T C /d P =+5.27 K/GPa. This weak ferromagnetism of Yb x Fe 4 Sb 12 originates from the itinerant 3d electrons of Fe in anions [Fe 4 Sb 12 ].