Spin Filter with Polarized Superfluid: Effects of Surface and Interface

Rutgers University New Brunswick, New Brunswick NJ

Investigators

Abstract

This research is focused on experimental investigations of the spin fluid dynamics in ferromagnetic superfluid He-3. The spin-polarized He-3 constitutes a pure, nearly ideal, material system for studying fundamental processes governing spin transport, diffusion and relaxation. Earlier experiments indicated that an "interface" between the magnetic and non-magnetic fluid He-3 could present a new channel for spin relaxation. It is proposed to provide a direct test of the importance of the interface by eliminating the interface altogether. A new spin filter experiment is proposed to create a much greater polarization than heretofore possible by inducing ferromagnetic fluid flows through a "superleak". The hydrodynamics and spin dynamics properties of such a fluid state with large non-equilibrium polarization will be studied for the first time. Experiments will be carried out with liquid He-3 cooled down to 0.5 mKelvin, in magnetic fields up to 15 Tesla. These studies of spin fluid dynamics are closely related to current research in the field of "spintronics". The proposed research has certain advantages, in that simpler macroscopic structures are involved, it is relatively easy to alter material conditions and parameters, and the relaxation or decoherence time scales are longer. The proposed work will be carried out in collaboration with the Institute for Solid State Physics of the Tokyo University. The graduate students will participate in international cooperative research. They will gain experience in the state-of-the-art technology in ultra low temperature physics and in materials physics. They will acquire a solid foundation for scientific careers in industry, academia or government laboratories. Undergraduate students will also participate in the research. This project is directed at understanding of the nature of ferromagnetic fluid dynamics. The ferromagnetic fluid state occurs when an isotope of helium, He-3, is specially cooled to ultralow temperatures. The motivation for the experiments is that novel changes in the magnetic fluid properties may occur when the fluid is made to flow through a small structure called a spin filter. The model material system is ferromagnetic liquid He-3 cooled to nearly absolute zero: about 0.0005 degrees Kelvin. In addition, a very large magnetic field, up to 15 Tesla, is required. These "extreme conditions" are only available in ultra low temperature laboratories. The work will be carried out via an international collaboration involving the Institute for Solid State Physics of the Tokyo University. The ferromagnetic He-3 is attractive because it is an ideal pure substance, free from impurities, and its magnetic relaxation properties can be related to more common or "spintronic" materials. The spin fluid dynamics provides a novel analog for spintronics device research where the spin degree of freedom of the electron is used to carry information. Hence the proposed research may ultimately contribute to spintronics device technology. The graduate students participate in international cooperative research and gain experience in the state-of-the-art technology in ultra low temperature physics and materials physics. They receive rigorous training that prepares them for careers in industry, academia or government. Undergraduate students will also participate in the research.