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

热电材料可以在存在温差的情况下发电，或者在电流通过材料时以提供冷却的反向模式工作。热电技术过去主要基于用于珀尔帖冷却模块的碲化铋合金，或用于NASA航天器中使用的放射性同位素热电发电机的硅锗，在过去二十年中已扩展到用于发电，冷却或红外探测和成像应用的广泛材料。从低品位热源（例如工业废热、环境热、建筑物或身体热）发电特别受到关注。余热回收可以显著减少化石燃料的使用，并有助于防止全球能源危机。因此，热电材料的研究是目前研究的热点。到目前为止，大部分的努力和进展都集中在将热能直接转化为电能方面，进展接近停滞。该提案研究了一种基于将热量转换为磁化的热波动的替代途径，该热波动可以反过来转换为电力。这种方法提供了一条并行的路径来提高能量转换效率，从而朝着低成本，高效率，该项目团队计划设计和合成一类新的热电材料，该材料可以通过利用顺磁-玻色子准-可以作为新的独立变量的粒子不限于进入zT的参数的平衡性质。正如在发现自旋塞贝克效应，这导致了自旋电子学的新领域，其中自旋角动量转移到电子，项目团队设计的材料，在顺磁状态下的磁化的局部热波动（即，顺磁子）将它们的线性动量传递给电子并增加热电势。该提案设想了三个主要目标：（i）理解电子-顺磁相互作用的物理学，并通过多尺度建模确定关键材料参数，（ii）设计多相磁性材料，并根据理论理解和可用的实验数据合成它们，（iii）合成此类材料，表征和研究它们，并为优化设计过程提供反馈。重点将放在工程这些影响和设计高性能的商业可扩展的化合物。这项跨学科的工作将为设计高性能热电器件开辟一条新的途径。与此同时，该研究将为处于自旋动力学理论发展前沿的短寿命局部磁序的动力学研究提供重要的数据和信息。该奖项反映了NSF的法定使命，并通过使用基金会的智力价值和更广泛的影响审查标准进行评估，被认为值得支持。

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.