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，也可以在电流通过材料时以相反的方式提供冷却。热电技术过去主要基于用于珀尔梯冷却模块的碲化铋合金，或用于美国宇航局航天器的放射性同位素热电发电机的硅锗合金，在过去二十年中已经扩展到用于发电，冷却或红外探测和成像应用的广泛材料。低品位热源发电，如工业废热、环境热、建筑热或体热，特别受到关注。废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是在将热直接转化为电，这一进展接近停滞。该提案研究了一种基于将热量转化为磁化的热波动的替代路线，而磁化热波动又可以转化为电能。这种方法为提高能量转换效率提供了一条平行的途径，从而为低成本、高效率和多用途热电技术的发展指明了方向。该项目团队计划设计和合成一类新的热电材料，这种材料可以利用顺子（玻色子准粒子）来克服费米-狄拉克统计对载流子施加的基本限制，顺子可以作为一个新的自变量，而不限于进入zT的参数的平衡性质。正如自旋塞贝克效应的发现，导致了自旋角动量转移到电子的自旋电子学的新领域，项目团队设计的材料在顺磁状态（即顺磁子）磁化的局部热波动将其线性动量转移到电子并增加热功率。该提案设想了三个主要推力：(i)通过多尺度建模了解电子-顺磁子相互作用的物理特性并确定关键材料参数；（ii）基于理论认识和现有实验数据设计多相磁性材料并合成它们；（iii）合成这些材料，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途径。同时，本文提出的研究将为短期局部磁序动力学研究提供重要的数据和信息，这是目前自旋动力学理论发展的前沿。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识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.