Abstract
We report the evolution of magnetic properties and thermopower ( S) of the La 1− x Sr x CoO 3 ( 0 ⩽ x ⩽ 0.5 ) system with doping and temperature in order to investigate the relationship between the spin state of cobalt ions and the thermopower. The paramagnetic-to-ferromagnetic transition temperature ( T C ) increases with x for x ⩾ 0.2 , and the temperature dependence of magnetic susceptibility can be fitted to the Curie–Weiss law for T > T C . Assuming that the Co 3+ ions are in the intermediate spin (IS) state, the spin of Co 4+ ions is 2.25 determined from DC magnetic susceptibility, which means that the most Co 4+ ions should be in the high spin (HS) state. The room-temperature thermopower, S (300 K), can be described by the modified Heikes formula assuming that the Co 3+ ions are in the IS state, and the most Co 4+ ions are in the HS state. The results suggest that both the degeneracy of charge carriers and the strong electron correlation play important roles in determining the thermopower in cobalt oxides.
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