Spin Transport in Metals and Oxides

University Of Minnesota-Twin Cities, Minneapolis MN

Investigators

Abstract

Non-technical description: Magnetism in thin layers or films of materials, and at interfaces between multiple layers, has attracted attention for many years. This is due to basic scientific interest, but also technological importance, as magnetic films enable such devices as the hard disk drives that now power cloud storage. Despite the maturity of such "spintronic" technologies there remain surprising gaps in the understanding of such materials, as well as major obstacles to next generation devices. One example is the manner in which magnetism can be induced in otherwise non-magnetic metals by injecting electrons across an interface with a magnetic metal. This is termed "spin injection", the subsequent motion of the electrons enabling "spin transport". Despite the fact that working technologies rely upon these effects, many fundamental questions remain unanswered, including what limits how far injected spin currents can persist. The goal of this project is to understand exactly this, focusing on the all-important role of imperfections in the materials. In addition to elucidating the poorly understood basic physics, this also contributes to the development of next generation hard drive read heads. This project does this not only with conventional magnetic metals, but also in the new realm of conductive oxide materials. In addition to impact in both science and technology, these activities train undergraduate and graduate students in an active, interdisciplinary research field, directly contributing to a skilled US workforce. Outreach to the public is also achieved, primarily through an educational program developed by the principal investigator that can impact up to 500 school students a year. Technical description: This project uses the separation of charge and spin currents enabled by the nanoscopic lateral non-local spin valve to dramatically improve the understanding of spin injection and relaxation in metals and oxides. The goal is to develop a general physical understanding of the factors that limit spin diffusion lengths and lifetimes in non-magnetic metals and oxides, thus directly contributing to the exploration of low resistance-area product sensor technologies for next generation hard disk drive read heads. The factors inducing spin relaxation in non-magnetic metals are being systematically deconvoluted in this work, providing a full understanding of the role of magnetic impurities, spin-orbit scattering centers, grain boundaries, surfaces, interfaces, and phonons. The research additionally includes novel experiments aimed at understanding the role of local magnetic moments, Kondo physics, and even magnetic interactions and fluctuations on spin transport in metals with magnetic impurities. The work will gradually move from conventional metals to conductive oxides, exploring the opportunities provided by highly spin polarized complex oxide spin injectors, the prospects to understand the fundamentals of spin injection, diffusion and relaxation in oxide metals, and the potential for fascinating new physics combining spin transport with electronic phase transitions.