Development of Thermoelectric Materials using Magnetic Interaction

Thermoelectric conversion is expected to be useful for improving energy efficiency. Developments of high-performance thermoelectric materials, however, are challenging because of the trade-off between electrical and thermal properties. Here, we show our studies of enhancing thermoelectric power factor by using the interaction of carriers and magnetism. The first example is the antiferromagnetic semiconductor CuFeS2. A high power-factor of 1 mW/K2m is achieved for the CuFeS2-based alloys, where the antiferromagnetic ordering of Fe magnetic moment is coupled with the carrier electrons, leading to large Seebeck coefficients. This finding motivated us to the second example, dilute magnetic semiconductors CuGa1-xMnxTe2. Enhanced power factor and ZT are obtained for slight Mn-doping with x = 0.01 to 0.03. Strong coupling of carriers and magnetic moments was clarified by the magnetic and transport measurements. Finally, the case of itinerant-electron ferromagnet is described. Magnetization studies demonstrate that the Heusler alloys Fe2V1-xMxAl1-ySiy (M = Cr, Fe) are classified as itinerant-electron weak ferromagnetic metals. Distinct increase in the Seebeck coefficient around the Curie temperature is observed, indicating the contribution of spin fluctuation. Increase in thermopower due to magnetic interaction occurs in a wide temperature range, thereby is helpful for the application of thermoelectric devices near room temperature.