Collaborative Research: Size-effect driven nanoparticle ferromagnetism

非技术文摘：磁性尺寸效应与磁性材料的尺寸对磁性性能的依赖性有关。传统上，像黄金这样的贵金属并不被认为是磁性材料，因为它们的体积形式缺乏永久磁性。然而，最近的研究表明，纳米材料可能具有显著不同的物理性质，而且贵金属在某些临界特征尺寸以下可能会变得磁性。目前的研究项目是一个综合的研究和教育计划，以了解贵金属磁性的大小依赖关系。本文首次详细研究了贵金属纳米颗粒磁性能的大小和形状依赖关系。各种技术被用于确定贵金属纳米颗粒的组成、尺寸、尺寸分布和磁性能。本研究以不同背景的幼稚园至高中学生及本科生为研究对象，透过研究型辅导计划进行研究。技术摘要：本提案的研究目的是验证将某些正常抗磁性金属的尺寸减小到纳米级可以产生铁磁性的假设。关于金等贵金属纳米粒子的铁磁性的报道被认为是有争议的，因为这些发现与公认的物理学相矛盾。激光加工技术被用于在氧化物薄膜中合成所需尺寸的贵金属，如金、银和钯的纳米颗粒样品。纳米颗粒沉积在非磁性氧化薄膜中，同时提供了纳米颗粒的合成、抑制团聚和氧化薄膜（氧化镁、氧化铝等）的原位钝化。详细的原子级结构表征和高分辨率物理特性测量以及元素特定磁化研究被用来彻底表征样品。磁性研究包括纳米颗粒的静态和动态测量以及铁磁和电子顺磁共振研究。了解这些材料的尺寸依赖性行为将有助于阐明贵金属和近贵金属纳米颗粒中铁磁性的来源。该项目支持2名研究生和几名本科生。该提案的教育目标是：指导不同群体的高成就学生从事STEM职业，并为K-12 STEM招聘工作做出贡献。来自不同背景的本科生将参与我们基于研究的指导计划：通过对材料工程研究的热情和意识取得成功（项目STEAMER）。所有的教育和推广活动都将被评估，以监测规划的有效性，并为stem教育的文献做出贡献。

Non-technical abstract:Magnetic size effects are related to the dependence of the magnetic properties on the dimensions of the magnetic material being studied. Noble metals like gold have not traditionally been considered as magnetic materials because of the lack of permanent magnetism in their bulk forms. However, recent research has shown that nanomaterials may have strikingly different physical properties and indeed noble metals may become magnetic below some critical feature size. The current research project is an integrated research and education program to understand the size dependence of the magnetic properties of noble metals. This is the first detailed study on the size and shape dependence of the magnetic properties of noble metal nanoparticles. A variety of techniques are being used to determine the composition, size and size distribution and magnetic properties of the noble metal nanoparticles. Students in kindergarten through high school and undergraduate students from diverse backgrounds are involved in this research via a research-based mentoring program. Technical abstract:The research objective of this proposal is to test the hypothesis that reducing the dimensions of certain normally diamagnetic metals to the nanoscale can result in ferromagnetism. Reports of ferromagnetism in noble metal nanoparticles like gold are considered controversial because the findings contradict well-established physics. Laser-processing techniques are being used to synthesize nanoparticle samples of noble metals like gold, silver and palladium of desired sizes in oxide thin films. Deposition of the nanoparticles in nonmagnetic oxide thin films simultaneously provides synthesis, suppressed agglomeration, and in-situ passivation of the nanoparticles by the oxide thin films (magnesia, alumina, etc.). Detailed atomic-level structural characterization and high-resolution physical property measurements along with element specific magnetization studies is being used to thoroughly characterize the samples. The magnetic studies include static and dynamic measurements and ferromagnetic and electron paramagnetic resonance studies of the nanoparticles. Understanding the size-dependent behavior of these materials will elucidate the origin of the ferromagnetism in noble and near noble nanoparticles. The project supports 2 graduate students and involves several undergraduate students. The educational objectives of this proposal are to: mentor a diverse group of high achieving students to STEM careers and contribute to K-12 STEM recruitment efforts. Undergraduate students from diverse backgrounds will be involved in our research-based mentoring program: Success Through Enthusiasm and Awareness of Materials Engineering Research (Project STEAMER). All of the educational and outreach activities will be assessed to monitor the efficacy of the programming and to contribute to the literature on STEM-based education.