Quantifying Spin-Orbit Coupling in Rare-Earth Metals via Inverse Spin Hall Effect

Ohio State University, The, Columbus OH

Investigators

Abstract

Non-technical description: Rare earth metals and alloys are strategically important materials for several technologies that have significantly impacted society, including electric and hybrid vehicles, permanent magnets, catalysts, energy-efficient lightings, and lasers. The unique characteristics of rare earths arise from their electronic structure and properties. Understanding special aspects of these in rare-earth metals can provide guidance for future transformative technologies based on rare-earth materials. In addition, yttrium iron garnet (YIG) is an important magnetic material widely used in microwave applications such as telecommunication and radar technologies, and recently in spin pumping. The YIG films with state-of-the-art quality grown in the principal investigator's group improve the spin pumping efficiency and therefore the probability for future application of pure spin transport devices. The ability to produce top-quality materials is essential for enhancing the global competitiveness of the United States. This project also includes an effort toward improving diversity in Science, Technology, Engineering and Mathematics fields, including: advising an underrepresented minority student in the American Physical Society Bridge Program at the Ohio State University, promoting participation of a diverse group of graduate and undergraduate students in cutting-edge research, and building superconductor magnetic levitation experiments for a local high school in encouraging young students to pursue a career in the STEM fields. Technical description: The objective of this research project is to investigate the inverse spin Hall effect and spin-orbit coupling in the lanthanide rare-earth metals and understand the systematic behavior of spin Hall physics in this group of fundamentally intriguing and technologically important materials. One major focus of the spintronics field is the pursuit of materials with large spin Hall effect as characterized by the spin Hall angle. This has led to quantitative determination of spin Hall angles in a broad range of materials, including the systematic measurements on the 3d and 5d transition metals by the principle investigator?s group. In fact, transition metals exhibits some of the largest spin Hall angles due to the large orbital moment of the d electrons, which points toward the possibility of finding even larger spin Hall effect in rare-earth metals due to their giant f-orbital moments and large atomic numbers as predicted by theory. However, the spin Hall effect in rare-earth metals is essentially unexplored to date. Ferromagnetic resonance spin pumping of pure spin currents from YIG thin films into metals is a versatile and reliable technique for characterizing the inverse spin Hall effect and extracting spin Hall angle. This project has the following goals: (1) understand the intrinsic inverse spin Hall effect in pure lanthanide rare-earth metals and uncover the role of 4f electrons in spin Hall effect; (2) investigate the extrinsic inverse spin Hall effect arising from rare-earth impurities in copper and gold; (3) characterize the interfacial spin conductances between the rare earth metals and other materials to understand spin transfer efficiency across interfaces. The expected outcome of this research is the systematic and quantitative understanding of the spin Hall physics in rare earth metals, which, in principle, possess all the attributes for the emergence of exceptionally large spin Hall effect.