Rare earth valence and paramagnetic properties of the skutterudites Ce1-zYbzFe4Sb12, BayFe4Sb12 and LayFe4Sb12

Abstract: We report on the rare earth valence and paramagnetic properties of the double filled skutterudites Ce1-yYbyFe4Sb12, BayFe4Sb12 and LayFe4Sb12. The susceptibility of all these compounds are well described by a Curie–Weiss law above 150K. BayFe4Sb12 and LayFe4Sb12 have, respectively, an effective moment of 3.0 and 2.9μB (f.u.)-1 and a paramagnetic temperature (θp) of 29K and -70K. In the Ce1-zYbzFe4Sb12 series, the paramagnetic temperature steadily increases from –80K in CeFe4Sb12 to +55K in Yb0.93Fe4Sb12, underlining a change in the character of the dominant interactions, from antiferromagnetic-to-ferromagnetic when one goes from trivalent cerium to nearly divalent ytterbium (v=2.2). The effective paramagnetic moment has been separated into three contributions, arising, respectively, from cerium, ytterbium and [Fe4Sb12]. The weak contribution of ytterbium to paramagnetism and the great similarity between the thermal variations of susceptibility in Yb0.93Fe4Sb12 and in BayFe4Sb12 seriously challenge previous scenarios for the low-temperature properties of Yb0.93Fe4Sb12. The nearly constant contribution of [Fe4Sb12] across the series (3.1μB(f.u.)-1 in CeFe4Sb12 and 3.2μB(f.u.)-1 in Yb0.93Fe4Sb12) contradicts the prediction of the “ionic model” and demonstrates the itinerant character of [Fe4Sb12] electrons. When substituting Fe by Ni in CeyFe4-xNixSb12, and θp are both affected, reflecting a change in the electronic band structure. [Copyright &y& Elsevier]