Defect-Rich Quasi Two Dimensional Metal Oxides with Strong Ferromagnetism

形成永久磁铁或被磁铁吸引的材料被称为铁磁性材料。这种材料有很多用途，从数据存储到电力系统。然而，铁磁性是一种不寻常的性质，只存在于铁、镍、钴及其合金和一些稀土材料等少数物质中。该项目旨在了解超薄的二维（2D）材料是如何产生强铁磁性的，这些材料在散装形式下没有磁性。空位，一种由“缺失”原子引起的缺陷，似乎在稳定二维半导体的磁性方面起着至关重要的作用。研究人员将进行实验和理论相结合的研究，以确定这些纳米片中可以形成的空位的浓度，并量化它们如何影响磁性。这项研究有可能实现低维铁磁材料的广泛应用，包括存储设备和量子计算。该项目为少数族裔本科生提供了研究经验的机会，并为实验和计算材料研究提供了教育和培训。该项目丰富了信息学臭鼬工厂，以吸引本科生在数据科学和材料科学与工程的界面研究。研究项目和结果将整合到高中教师和学生的推广中。本项目的目的是了解准二维（2D）过渡金属氧化物中大量阳离子空位浓度的形成和稳定机制，并证明通过尺寸限制和点缺陷工程可以在非铁磁性氧化物中诱导强铁磁性。该项目基于一个总体假设，即当氧化物的厚度降至纳米级时，阳离子空位可以在氧化物中产生并稳定在高水平，这反过来又为二维材料引入了强铁磁性。pi发现富锌空位的二维ZnO纳米片的室温铁磁性有数量级的增强。离子层外延使得ZnO纳米片的空位浓度稳定在30%以上。实验与理论相结合的研究项目包括三个具体的研究任务。任务1是一项理论研究，旨在了解二维氧化晶格中大量阳离子空位浓度稳定和相关强铁磁性的基本机制。任务2是对ZnO纳米片中锌空位演化和稳定机制的实验研究，以了解与纳米尺度厚度、表面和晶界相关的阳离子空位形成和稳定机制。在任务3中，以铈和锰氧化物为代表，量化了超薄纳米片中阳离子空位引起的特殊磁性能，分别揭示了空位有序贡献以及阳离子空位和过渡金属矩耦合效应。该项目的成功为设计和合成具有高磁化和多功能的新型铁磁二维纳米材料带来了变革性的知识。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

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.