ERI: Compositionally modulated ferrimagnets for spin-orbitronic devices

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This award is funded in whole or in part under the American Rescue Plan Act of 2021 (Public Law 117-2).Ferrimagnetic thin films display unique properties which may enable the creation of new low power, high speed, and high-density magnetic devices. However, disorder can significantly influence device operation by modifying thin film properties. The goal of this project is to provide an understanding of the role that a specific type of disorder common to a wide range of ferrimagnetic materials - compositional nonuniformity - plays in determining the properties that make them ideal for next-generation magnetic devices. This research will provide the framework for the optimization of these effects for future technologies through controlled growth processes, and in turn, simplifying device architectures and improving performance. The research will also have a wide educational impact, including supporting one graduate from an underrepresented group in Engineering and Physics as well as exposing undergraduate and local high school students to advanced research in magnetic materials. The students participating in this research will have the opportunity to collaborate with scientists at Brookhaven National Laboratory and gain hands on imaging experience as well as experience in nanofabrication. The educational impact is amplified by the PI’s ongoing participation in outreach programs at the University of Memphis.TechnicalCurrent spintronic technologies based on ferromagnetic materials, including memory and logic devices, often incur limitations related to energy consumption, device scalability and stability, as well as speed. One promising approach to overcoming these limits is the development of ferrimagnetic spintronics, which promises the advantages of high speed and low power operation common to antiferromagnetic materials while maintaining the straightforward growth methods and device readout of common transition metal based ferromagnets. This research will further the understanding of the role of compositional modulation on the spin-orbit phenomena of the Dzyaloshinskii-Moriya Interaction (DMI) and spin-orbit torques in transition metal-rare earth ferrimagnets, key to developing high speed, low power devices. The research will address this by (1) improving our understanding of how compositional modulation allows for the generation of large spin-orbit effects in ferrimagnetic single layers through controlled sputter deposition and systematic measurements of DMI and spin-orbit effective fields, (2) quantitatively linking the variation in magnetic properties through the film thickness to the large DMI in Co-based ferrimagnets, and (3) providing a framework to develop single layer, efficient spin-orbit torque devices based on the aforementioned compositional modulation, thereby simplifying their fabrication requirements and improving performance. To achieve these goals, the strength of DMI and spin-orbit torques in compositionally varied ferrimagnetic films will be examined by Kerr microscopy measurements of static and dynamic domain configurations and measurements of asymmetric domain wall motion driven by magnetic fields and electrical currents. Electron microscopy, bulk magnetometry, and X-ray techniques will be used link these properties directly to composition non-uniformities. Electrical measurements and direct imaging of switching processes taken for standard hall cross and nanowire geometries will allow the compositional modulation to be directly linked to device performance, including switching efficiencies and the strength of effective magnetic fields, and pave the way for faster, more efficient magnetic memory, logic, and signal processing devices.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.