Spin supercurrents in ferromagnetic and antiferromagnetic films

University Of California-Irvine, Irvine CA

Investigators

Abstract

Nontechnical abstract: Electric currents in electronic devices such as cell phones and computers typically lose a large fraction of their power supply's energy to the device heating. However, electric currents in some materials can flow without generating heat if the material's temperature is low enough. Such materials called superconductors are used, for example, in magnetic resonance imaging scanners to create large magnetic fields. The aim of this research project is to discover a magnetic analog of superconductivity, which is called spin superfluidity, and to study its stability at room temperature. Spin superfluids can transport magnetic currents with minimal losses similar to electric currents in superconductors. The nearly lossless magnetic currents may find use in the next generation of computers that employ magnetic materials for information storage and processing. The principal investigator and the graduate students involved in this research develop hands-on demonstrations on magnetism and superconductivity for middle school students that stimulate the students' interest in science and engineering. Technical abstract The main goal of the proposed research is to experimentally realize a new state of magnetic matter called spin superfluid, which has been predicted to exist in ferromagnets and antiferromagnets with easy plane magnetic anisotropy. The name "spin superfluid" stems from the similarity of its properties to those of superfluid liquid helium and Cooper pair condensate in superconductors. In particular, the spin superfluid is expected to support spin supercurrents that transport spin angular momentum over distances orders of magnitude longer than those achievable with spin waves. The goal of this project is to induce the spin superfluid state in thin films and nanowires of ferromagnets and antiferromagnet via injection of pure spin currents polarized perpendicular to the easy plane of magnetic anisotropy. The spin superfluid state can be detected electrically via a unique low-frequency supercurrent mode predicted to propagate over microscopic distances in easy-plane magnetic materials. The scope of work also includes studies of a chiral spin superfluid state induced by Dzyaloshinskii-Moriya interaction in ferromagnetic nanowires. Stability of the spin superfluid state against thermally induced magnetic vortex formation is investigated both experimentally and via large-scale micromagnetic simulations.