Effects of Co substitution on magnetic and thermoelectric properties of BaFe4Sb12

The effects of electron doping on the low-temperature thermoelectric properties of the nearly ferromagnetic compound BaFe4Sb12 have been studied by measuring the magnetic and transport properties of BayFe4-xCoxSb12 (x = 0,1,2,2.5,3). Both the magnetic susceptibility and thermopower for x = 0 exhibit maxima at 50 K, which disappear for x = 1. With increasing x to 2.5, resistivity markedly increases and both magnetic susceptibility and electronic specific heat coefficient decrease. A diamagnetic behavior for x = 2.5 indicates that Co substitution leads to a marked decrease in the electronic density of states at the Fermi,level. The positive thermopower of 135 mu V/K at 500 K for x = 2.5 changes to a negative one, - 120 mu V/K, for x = 3.0. The Hall coefficient at 290 K also changes from positive for x = 2.5 to negative for x = 3.0. These results indicate that electron carriers doped by Co substitution overcompensate for hole carriers in this alloy system.