E. Matsuoka

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 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.

Magnetic and Thermoelectric Properties of Ce2NiB10-δ (\(\delta\cong 0.3\)), a Ni-incorporated Variant of CeB6

Magnetic susceptibility, electrical resistivity, thermopower, specific heat, and thermal conductivity measurements were made on Ce 2 NiB 10-δ . The crystal structure is derived from that of CeB 6 by replacing two B atoms in the B 6 –B 6 network with one Ni atom. The sample prepared by arc melting is deficient in the boron composition, (deltacong 0.3). The magnetic susceptibility, electrical resistivity, and specific heat show no sign of magnetic ordering down to 0.5 K, but exhibit non-Fermi liquid (NFL) behavior, i.e., χ∝- T 0.5 , ρ∝ T and C / T ∝-ln T . This behavior of C ( T ) in zero field and its suppression by external magnetic fields are explained qualitatively by the Kondo disorder model with the average Kondo temperature of 26 K. Atomic disorder induced by boron defects is the most probable origin of the NFL behavior. The thermal conductivity of Ce 2 NiB 9.7 is much reduced from that for CeB 6 , which is ascribed to the increase of phonon scattering by the lattice defect.