Spin Seebeck Devices for Thermoelectric Power Generation

在过去几年中，对可持续的“绿色”技术的开发和理解一直是研究和商业化的主导动力。其中一项技术是热电发电，它可以用来将我们日常环境中的环境热量转化为有用的电能。这些热电发电机有潜力在各种远程应用中驱动低功率传感器，如监测桥梁结构健康、安全系统、医疗诊断等。然而，目前可用的热电发电机表现出非常低的热电转换效率。该项目建议利用电子的自旋来提高这些发电机的效率。影响传统热电器件效率的基本限制不适用于这些器件。因此，基于自旋的发电机原则上可以比传统设备更有效。如果取得成功，研究成果将有助于减少温室气体排放，并使整个社会受益。本项目将为不同学科的研究生和本科生提供学习机会。将作出特别努力，鼓励女性和代表性不足的少数民族学生参与该计划。该项目的目标是通过利用最近发现的自旋塞贝克效应（SSE）和逆自旋霍尔效应的现象，实现一类新的能量收集设备。SSE是指当磁性材料置于温度梯度中时，其自旋电压的产生。提出的研究是基于这样的假设，即这种热产生的自旋电压可以利用逆自旋霍尔效应转换成电压。利用这两种效应，在初步研究中，PI的小组已经证明了设计一种室温自旋电流驱动的热电发电机的可行性，该发电机采用磁性绝缘体薄膜和高自旋轨道耦合金属，直接涂覆在非磁性基板上。上述演示为打造一种全新的能量收集技术开辟了一条道路。然而，目前SSE器件的效率远低于传统的热电器件。对于任何实际应用，这些设备的效率都需要提高。在这个项目中，PI提议进行深入的科学调查，以实现上述目标。提出的方法有四个方面：(a)了解磁绝缘体中自旋波输运的机制；(b)通过提高自旋混合电导来增强磁绝缘体/正常金属界面处的热驱动自旋电流；(c)发现具有大自旋霍尔角的金属；(d)器件制造和优化。

The development and understanding of sustainable, "green" technologies has been a dominant, driving force for research and commercialization over the last several years. One such technology is thermoelectric power generation, which can be used to convert the ambient heat present in our day-to-day environment into useful electric power. These thermoelectric power generators have potential to drive low powered sensors in variety of remote applications such as monitoring the structural health of bridges, security systems, medical diagnostics, etc. However, presently available thermoelectric power generators exhibit very low heat-to-electricity conversion efficiencies. The proposed project proposes to improve the efficiency of these generators by using the spin of electrons. The fundamental limitations which affect traditional hermoelectric device efficiencies do not apply for these devices. Therefore, spin-based generators can in principle be significantly more efficient than the traditional devices. If successful, the research outcomes will help in reducing greenhouse gas emissions and benefit the society at large. Graduate students and undergraduate students from various disciplines will be provided with learning opportunities within this project. Special efforts will be made to encourage the participation of female and underrepresented minority students in the program. The goal of this project is to enable a new class of energy harvesting devices by utilizing the recently discovered phenomena of the spin Seebeck effect (SSE) and the inverse spin Hall effect. The SSE refers to the generation of a spin voltage in a magnetic material when it is placed in a temperature gradient. The proposed research is based on the hypothesis that this thermally generated spin voltage can be converted into an electrical voltage using the inverse spin Hall effect. Making use of these two effects, in preliminary studies, PI's group has demonstrated the feasibility of designing a room temperature spin-current driven thermoelectric generator that employs a thin film of a magnetic insulator and a high spin-orbit coupled metal, directly coated on a non-magnetic substrate. The above demonstration opens a path to crafting an entirely new class of energy harvesting technologies. However, at present the efficiency of SSE devices is much lower than the traditional thermoelectric devices. For any practical application, efficiency of these devices needs to be enhanced. In this project, PI is proposing to perform in-depth scientific investigations to achieve the above goal. The proposed approach is four-fold: (a) Understanding the mechanism of spin wave transport in magnetic insulators, (b) Enhancing the thermally driven spin-current at the magnetic insulator/normal metal interface by improving the spin mixing conductance (c) Discovering metals with large spin-Hall angles, (d) Device fabrication and optimization.