GOALI: From heat to spin to electricity: Fundamental understanding and development of high-performance spin-driven thermoelectric heterostructures

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Thermoelectric materials can generate electricity in the presence of a temperature difference or work in a reverse mode providing cooling when an electric current is passed through the material. The thermoelectric technology, which used to be primarily based on alloys of bismuth telluride for Peltier cooling modules, or silicon-germanium for radioisotope thermoelectric generators used in NASA spacecraft, has expanded over the last two decades to a wide range of materials for power generation, cooling, or infrared detection and imaging applications. Power generation from low-grade heat sources, such as waste heat at industry, ambient heat, buildings, or body heat, has particularly taken much attention. Waste heat recovery can significantly reduce the use of fossil fuels and help prevent a worldwide energy crisis. As such, thermoelectric materials research is currently an area of intense research. Until now, most of the efforts and progress have been on the direct conversion of heat into electricity, with the progress approaching a plateau. This proposal investigates an alternate route based on converting heat into the thermal fluctuation of magnetization that can, in turn, convert into electricity. This approach offers a parallel path to boost energy conversion efficiency, leading to a promising direction towards low-cost, high efficiency, and versatile thermoelectric technology.The project team plans to design and synthesize a new class of thermoelectric materials that can overcome the fundamental limits imposed by Fermi-Dirac statistics on charge carriers by utilizing paramagnons - bosonic quasi-particles that can play as a new independent variable not limited to the counter-balancing nature of the parameters that enter zT. Just as in the discovery of the spin-Seebeck effect, which led to the new area of spincaloritronics, where the spin angular momentum is transferred to the electrons, the project team designs materials where the local thermal fluctuations of magnetization in the paramagnetic state (i.e., paramagnons) transfer their linear momentum to electrons and increase the thermopower. The proposal envisions three major thrusts: (i) understand the physics of electron-paramagnon interactions and identify the key material parameters through multiscale modeling, (ii) design multi-phase magnetic materials and synthesize them based on the theoretical understandings and the available experimental data, (iii) synthesize such materials, characterize and study them, and provide feedback to the design procedure for optimization. The emphasis will be placed on engineering these effects and designing high-performance commercially scalable compounds. This transdisciplinary work will open a new way to design high-performance thermoelectrics. At the same time, the study proposed here will provide data and information critical to studying the dynamics of short-lived local magnetic order, which is now at the forefront of the development of spin-dynamic theories in general.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.