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.
