DMREF: Collaborative Research: Design and synthesis of novel materials for spin caloritronic devices

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Non-technical Description: Microelectronics, which has propelled modern technologies to unprecedented levels, has been severely hampered by the intense Joule heating generated by the motion of electrical charge carriers. A new approach exploits pure spin currents in devices that use a minimum of electrical charge carriers, thus generating minimal heat in metals and virtually no heat in magnetic insulators, which are charge-carrier free. The spin Seebeck effect (SSE) allows one to generate a pure spin current from a temperature gradient in a magnetic insulator. The SSE, experimentally discovered only a few years ago, has lead to a burgeoning new field known as spin caloritronics, which offers new strategies for the conversion of waste heat to electricity as well as thermal management in electronic devices. This project, through close theory/experiment interactions, will focus on the fundamental understanding of the SSE effect and will explore new ferromagnetic and antiferromagnetic insulators for advancing spin caloritronic phenomena and devices. Technical Description: The proposed project will combine theory, characterization, and materials synthesis efforts to better understand spin caloritronic phenomena and devices. The effort will be built on three key and interlocking elements. These include a theoretical understanding of the physics and issues associated with the spin caloritronic phenomena, measurement of spin caloritonic properties of a broad variety of single crystals of magnetic and antiferromagnetic insulators, and the fabrication of spin caloritronic thin films devices exploiting materials with superior properties. By extending the fruitful research on topological insulators where the spin-orbit coupling is a critical factor and the theory of phonon-magnon interaction, Fiete will develop a microscopic theory for understanding physics associated with spin caloritronic phenomena. He will also develop computational tools for screening and designing new materials for fabrication of spin caloritronic devices. The simulation work will cover the materials for generating spin current and metallic materials to convert spin current into electric potential with a high efficiency as well as the interface design. The project will capitalize on the extensive experience and expertise of Zhou in growing a broad range of bulk single crystals including ferrimagnetic rare earth iron garnets, double perovskites, spinels, antiferromagnetic layered materials with peculiar magnetic properties like uniaxial, easy-plane, biskyrmion, and pyrochlores. Earth abundant elements are prioritized in the computational screening and design for the spin caloritronic devices. The most challenging problems in the material synthesis, especially with Earth abundant elements, could be overcome by high-pressure synthesis. The procedures, the fabrication, and measurement techniques for spintronic devices developed in Chien's laboratory will be used to study the performance of spin caloritronic devices made from these new materials. The experimental results will be compared with the computational model and provide new inputs to further refine the model. An iterative feedback loop will be formed among the co-PIs.