SPINCATS, an investigation of Spin Caloric Transport in magnetic Semiconductors

Ohio State University, The, Columbus OH

Investigators

Abstract

Proposal # 1133589 PI: Roberto C. Myers, Co-PI Joseph P. Heremans Like thermoelectricity is the study of the direct conversion of heat into electricity, the new field of spin caloric transport (SPINCATS) that will be studied here is the direct conversion of heat into magnetism, more specifically into a magnetic polarization. Experiments will be carried out to understand how this effect occurs by exploring its properties in various types of materials. Particularly important questions that will be addressed are: (1) Can this effect be reversed (i.e. is there a heat pumping activity associated with magnetic polarization)? (2) Is the effect is accompanied by an additional dissipation of waste heat? The spin-Seebeck effect is a spin-polarization induced by a temperature gradient, and was recently discovered in ferromagnetic metals, semiconductors, and insulators. This is a new thermal transport phenomenon, the first mixed effect that involves spins rather than charge. While the effect is real, it is not understood. The project will lead to the fundamental understanding of the classical and irreversible thermodynamic properties of the transport of magnetic polarization. Three material classes will be studied, MnAs/GaMnAs, EuO and GdGaN. Spin-Seebeck measurements as a function of position, temperature, thermal gradient, and longitudinal conductivity will be carried out. The broad technological impacts will come from the fact that these questions have a direct technological impact on the use of spin polarization as the basis for computer logic (spintronics). Indeed, one of the main limitations on the further miniaturization of computer logic circuits is the fact that they heat up, and waste heat management becomes overwhelming at small dimensions. While spin-polarization indeed can be the basis of logic circuits, it is crucial to know how much waste heat they will produce, if any. Other technological applications may be in the recovery of waste heat or in spin-caloric heat ?engines? and refrigerators. Further broad impact arises from the training and research experience for undergraduates and graduate students in the field of fundamental and irreversible thermodynamics, molecular beam epitaxy growth of compound semiconductor heterostructures, lithographic processing, electronic, magnetic, and thermoelectric / thermomagnetic characterization. Students will be recruited into a strongly interdisciplinary research environment spanning Mechanical Engineering, Materials Science, and Physics.