Collaborative Research: Size-effect driven nanoparticle ferromagnetism

非技术摘要：磁尺寸效应与所研究的磁性材料的尺寸对磁性的依赖有关。像金这样的贵金属传统上不被认为是磁性材料，因为它们的块状结构缺乏永久磁性。然而，最近的研究表明，纳米材料可能具有截然不同的物理性质，事实上，贵金属可能会在某些关键特征尺寸以下变得有磁性。目前的研究项目是一项综合研究和教育计划，旨在了解贵金属磁性的尺寸相关性。这是首次详细研究贵金属纳米颗粒的大小和形状对磁性的影响。人们正在使用各种技术来确定贵金属纳米颗粒的组成、尺寸和尺寸分布以及磁性。从幼儿园到高中的学生和来自不同背景的本科生都参与了这项研究，这是一个基于研究的指导计划。技术摘要：这项提议的研究目标是验证这样一种假设，即将某些正常抗磁性金属的尺寸减小到纳米级可以导致铁磁性。有关金等贵金属纳米粒子具有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。激光加工技术正被用于在氧化物薄膜中合成所需尺寸的金、银和钯等贵金属的纳米颗粒样品。在非磁性氧化物薄膜中沉积纳米粒子同时提供了纳米粒子的合成、抑制团聚以及氧化物薄膜(氧化镁、氧化铝等)对纳米粒子的原位钝化。正在使用详细的原子级结构表征和高分辨率物理性质测量以及元素特定磁化研究来彻底表征样品。磁性研究包括静态和动态测量，以及纳米颗粒的铁磁和电子顺磁共振研究。了解这些材料的尺寸依赖行为将有助于阐明贵金属和近贵金属纳米颗粒铁磁性的起源。该项目资助2名研究生，涉及几名本科生。这项建议的教育目标是：指导一群不同的优秀学生进入STEM职业生涯，并为K-12 STEM招生工作做出贡献。来自不同背景的本科生将参与我们的研究型指导计划：通过材料工程研究(蒸汽机项目)的热情和意识取得成功。将对所有教育和外联活动进行评估，以监测方案编制的效果，并为以STEM为基础的教育的文献作出贡献。

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.