Effects of Co Substitution on Magnetic and Thermoelectric Properties of BaFe4Sb12

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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 μV/K at 500 K for $x=2.5$ changes to a negative one, $-120$ μV/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.
2006-05-15