Understanding Spin Diffusion Lengths in Metals and Oxides

University Of Minnesota-Twin Cities, Minneapolis MN

Investigators

Abstract

Non-technical abstract: High performance magnetic devices are ubiquitous in our society, the magnetic hard disk drives that power cloud data storage serving as one example. Underpinning technological advancement in this area is the ongoing progress in fundamental understanding of magnetism and magnetic materials. In this project, a fundamental problem relevant to "spin electronics" is being tackled, specifically how electron spins relax after being pumped from magnetic to non-magnetic materials. This is a poorly understood issue in magnetism, despite many scientific efforts and high importance for next generation devices. In this work, a particular type of nanomagnetic device is being used to understand, quantitatively, and for the first time, how specific materials defects control the relaxation of spins. In addition to advancing basic scientific knowledge, broader impact is being achieved through societal benefits from device applications, through education of students, and through outreach to the public. The latter involves collaboration with the Science Museum of Minnesota, developing exhibits and performances on the science of materials in our everyday lives, thus raising awareness of the role of materials research in our society. Technical abstract: Central to many spintronic phenomena and devices is the flow of a pure spin current, or a spin-polarized charge current, in a non-magnetic metal. A fundamental question in such a situation is over what distance does a non-equilibrium spin population relax in a non-magnetic metal, or: what is the spin diffusion length? Remarkably, while the basic mechanism governing metallic spin relaxation, the Elliot-Yafet mechanism, is known, there remain massive gaps in our understanding of this process. The individual effects of specific defects remain unknown, preventing quantitative or predictive understanding of spin transport. Addressing this problem, with its obvious technological relevance, would constitute a transformative advance. The essence of this project is to use non-local lateral spin valves to determine spin diffusion lengths in a variety of conventional and oxide-based metals. Elemental metals such as Al are being studied to separately quantify spin relaxation due to phonons, impurities, grain boundaries, surfaces, and interfaces, thus determining Elliott-Yafet constants for each defect. Metallic perovskite oxides are also being studied. These materials offer tremendous potential for spintronics, although an understanding of their spin diffusion lengths remains elusive. A progression from conventional metal-based devices to perovskite metals is being followed in this research, providing the first understanding of spin diffusion lengths in oxide ferromagnets and non-magnetic metals, a critical step in the development of oxide spintronics. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.