Development of ultrathin intermetallics for giant spin Hall effects

Columbia University, New York NY

Investigators

Abstract

Non-technical Summary: Certain nonmagnetic metals have been shown to behave like magnets when electrical current is passed through them. As electrical current is passed through these metals, which exhibit the so-called spin Hall effect, they can be used to control the switching and other functional properties of adjacent ferromagnetic metals, removed by a few atomic layers in a sandwich structure. This phenomenon, known as the spin Hall effect, is very exciting for applications in magnetic data storage ('spintronics'), since it enables very efficient current-controlled switching for nanoscale magnets. This project will search for chemically ordered metal alloys, up to a dozen atomic layers thick, which are expected to offer very efficient electrical-current control of magnetism. These metallic alloys will be synthesized at thicknesses of dozens of atoms; their atomic arrangements and chemical tranformations will be studied, and their functional properties in data storage will be measured at temperatures approaching absolute zero and up to room temperature. The discovery of these improved materials would have broad impact in information storage technology. Graduate students will gain broad expertise in topics ranging from classical metallurgy electronic devices. Outreach activities are planned with K-12 schools in Manhattan. Technical Summary: This project will conduct a materials search for ultrathin paramagnetic intermetallic phases, based on tungsten (W) and other heavy metals, which have the potential to convert charge current to spin current with high efficiency. Theoretical considerations indicate that intermetallic phases with a large number of atoms per unit cell should have a conversion efficiency (spin Hall angle) possibly in excess of that observed for tungsten (W), which currently has the highest spin Hall angle known. The experiments will combine epitaxial ultrathin film depositions, high-resolution transmission electron microscopy (TEM) characterization, measurements of phase transformation kinetics, and innovative measurements of the spin Hall effect using radio-frequency techniques. The discovery of phases with high spin Hall angles would have broad impact, facilitating the incorporation of spin torque in information storage technology. Graduate students will gain broad expertise in topics ranging from classical metallurgy (microstructure, phase transformations) to measurements of film-level physical properties (cryogenic magnetotransport and ferromagnetic resonance) to incorporation in spin electronic devices. Outreach activities are planned with K-12 schools in Manhattan.