Defect-Rich Quasi Two Dimensional Metal Oxides with Strong Ferromagnetism

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Nontechnical DescriptionMaterials that form permanent magnets or are attracted to magnets are called ferromagnetic. Such materials have many uses, ranging from data storage to power systems. However, ferromagnetism is an unusual property that occurs only in a few substances such as iron, nickel, cobalt and their alloys, and some rare earth materials. This project aims to understand how strong ferromagnetism can arise from ultrathin, two-dimensional (2D) materials, that are not magnetic in bulk form. Vacancies, a type of defect arising from “missing” atoms, appear to play a crucial role in stabilizing magnetism in 2D semiconductors. The investigators will perform a combined experimental and theoretical study to determine the concentration of vacancies that can be formed in these nanosheets and quantify how they impact magnetic properties. This research has the potential to realize low-dimensional ferromagnetic materials with a broad range of applications, including memory devices and quantum computing. This project offers opportunities to provide research experiences to underrepresented minority undergraduate and provides education and training on experimental and computation materials research. This project enriches the Informatics Skunkworks to engage undergraduates in research at the interface of data science and materials science and engineering. The research project and results will be integrated into outreach to high school teachers and students.Technical DescriptionThe objective of this project is to understand the formation and stabilization mechanisms of massive cation vacancy concentrations in quasi two-dimensional (2D) transition metal oxides and demonstrate that strong ferromagnetism can be induced in non-ferromagnetic oxides by dimension confinement and point defect engineering. This project is based on an overarching hypothesis that cation vacancies can be created and stabilized at a high level in oxides when their thickness is reduced to the nanometer level, which in turn introduces a strong ferromagnetism to the 2D material. The PIs discovered orders of magnitude enhancement of room temperature ferromagnetism from zinc vacancy-rich 2D ZnO nanosheets. A strong cooperative coupling phenomenon stabilized a vacancy concentration greater than 30% in ZnO nanosheets, enabled by ionic layer epitaxy. The combined experimental and theoretical research project consists of three specific research tasks. Task 1 is a theoretical study to understand the fundamental mechanisms of massive cation vacancy concentration stabilization and associated strong ferromagnetism in 2D oxide lattices. Task 2 is an experimental investigation of zinc vacancy evolution and stabilization mechanisms in ZnO nanosheets to understand the cation vacancy formation and stabilization mechanisms in correlation to the nanoscale thickness, surfaces and grain boundaries. In task 3, the extraordinary magnetic properties rising from the cation vacancies in ultrathin nanosheets are quantified in cerium and manganese oxides, as representative examples to reveal vacancy ordering contribution, and cation vacancy and transition metal moment coupling effects, respectively. Success of this project brings transformative knowledge for the design and synthesis of a new family of ferromagnetic 2D nanomaterials with high magnetization and multi-functionality.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.