Multifunctional composite magnet for practical transverse thermoelectrics

Permanent magnets are used in various products and essential for human society. If omnipresent permanent magnets could directly convert heat into electricity, they would lead to innovative energy harvesting and thermal management technologies. However, achieving such "multifunctionality" has been difficult because of the poor thermoelectric performance of conventional magnets. Here, we develop a multifunctional composite magnet that enables giant transverse thermoelectric conversion. The proposed composite material, comprising alternately and obliquely stacked SmCo₅/Bi0.2Sb1.8Te₃ multilayers, exhibits large remanent magnetization and coercivity as well as an excellent figure of merit of 0.32 for transverse thermoelectric conversion around room temperature. While having versatile transverse geometry and high mechanical durability, the thermopile module based on these composite magnets generates 204 mW at a temperature difference of 152 K owing to extremely low interfacial electrical and thermal resistances. The corresponding power density per heat transfer area of 56.7 mW/cm² is not only record-high among all the transverse thermoelectric modules but also comparable to those of commercial longitudinal thermoelectric modules based on the Seebeck effect. The novel functional material enables the integration of thermoelectric conversion capabilities wherever permanent magnets are currently used.