AB2X4 compounds and other new thermoelectric materials studied at JPL

Magneto-thermoelectric effects of the layered cobalt oxides

I. Terasaki^1,2,3, T. Fujii^1,2

^{1Department of Applied Physics, Waseda University, Tokyo 169-8555, Japan
^{2PRESTO, Japan Science and Technology Corporation, Tokyo 108-0075, Japan
^{3CREST, Japan Science and Technology Corporation, Tokyo 103-0027, Japan}}}

The layered cobalt oxides having the CdI₂-type hexagonal CoO₂ layer exhibit good thermoelectric properties especially at high temperatures. This is attributed to the fact that large entropy of k_Blog 6 is carried by the low-spin-state Co⁴⁺. Since the entropy of k_Blog 6 comes from the spin and orbital degrees of freedom, it is sensitive to the external magnetic field. Magnetic field can release the spin degeneracy through the Zeeman effect, and also release the orbital degeneracy through the high-spin-low-spin transition. Here we report on measurement and analysis on the field dependence of the thermoelectric properties of the Bi-based layered cobalt oxide [(Bi,Pb)₂Sr₂O₄]_yCoO₂. Magnetic field significantly suppresses the thermopower, resistivity and thermal conductivity. The magnetic field effects on the electronic states will be quantitatively discussed.