Collaborative Research: The Magnetic Properties of Disordered Rare-Earth Nanostructures

*非技术摘要*纳米级无序是非常不同类别的技术重要材料的共同线索，例如用于永久磁体和信息存储的材料。这个合作项目使用模型稀土合金系统来理解磁性对纳米级结构和化学无序的依赖。模型体系将通过不同的制备方法制备，并利用X射线衍射、电子显微镜和同步加速器技术对其结构进行表征。原子水平和宏观磁性测量将与特定类型的无序相关联。这些结果将提高我们对更复杂材料中纳米级无序和磁性之间关系的理解，从而使我们能够为现有和未来的应用开发更好的材料。这个合作项目涉及来自内布拉斯加大学林肯分校和北爱荷华大学、阿贡国家实验室高级光子源和洛斯阿拉莫斯国家实验室的研究人员。该项目在国家迫切需要的领域为博士后研究员、研究生和本科生提供跨学科培训(包括使用国家实验室的设施)。为数理学生、初高中教师和高中生开设的工作坊和暑期活动将有助于教育未来的劳动力有关纳米材料的重要性。纳米尺度的不均匀性是巨磁电阻(CMR)材料和高温超导体等系统的许多基本特性的基础。这个合作项目使用纳米结构的稀土(RE)系统来研究磁性和原子级无序之间的关系。特别是，无序RE Laves相材料将通过机械球磨、惰性气体冷凝和熔体纺丝来制备。稀土Laves相材料具有类似于CMR和高T_c材料的磁特性，但结构更简单。无序度(配位数、平均原子间距离和原子间距离的变化)将通过X射线衍射和X射线吸收精细结构谱(XAFS)来确定。原子水平和宏观磁性测量，包括磁性XAFS、XMCD以及交流和直流磁化，将与特定类型的无序相关。了解矫顽力等外在性质是如何依赖于无序的，将改进用于永磁体和信息存储的材料。样品制作、直流磁测量和结构表征将在内布拉斯加-林肯大学进行，而北爱荷华大学将负责交流磁化率测量和分析。该奖项的更广泛影响包括博士后、研究生和本科生的跨学科研究培训。初中和高中教师和高中生将通过研讨会和暑期项目受到影响，这些研讨会和暑期项目展示了材料在社会中发挥的作用。

****NON-TECHNICAL ABSTRACT****Nanoscale disorder is a common thread in very different classes of technologically important materials such as those used for permanent magnets and information storage. This collaborative project uses model rare-earth-alloy systems to understand the dependence of magnetic properties on nanometer-scale structural and chemical disorder. The model systems will be prepared by different fabrication methods and structurally characterized using x-ray diffraction, electron microscopy and synchrotron techniques. Atomic-level and macroscopic magnetic measurements will be correlated to specific types of disorder. These results will improve our understanding of the relationship between nanoscale disorder and magnetic properties in more complex materials, thus allowing us to develop improved materials for existing and future applications. This collaborative project involves researchers from the University of Nebraska at Lincoln and the University of Northern Iowa, the Advanced Photon Source at Argonne National Laboratory, and Los Alamos National Laboratory. The project provides postdoctoral fellows, graduate students and undergraduate students with interdisciplinary training (including the use of facilities at national laboratories) in an area of critical national need. Workshops and summer activities with Upward Bound math & science students, middle and high school teachers, and high-school students will help educate the future workforce about the importance of nanoscale materials.****TECHNICAL ABSTRACT****Nanoscale inhomogeneity underlies many of the fundamental properties of systems such as colossal magnetoresistance (CMR) materials and high-Tc superconductors. This collaborative project uses nanostructured rare-earth (RE) systems to investigate the relationship between magnetic properties and atomic-level disorder. In particular, disordered RE Laves-phase materials will be prepared by mechanical milling, inert-gas condensation, and melt spinning. RE Laves-phase materials have magnetic characteristics similar to CMR and high-Tc materials, but are structurally simpler. Disorder (coordination number, mean interatomic distances, and variations in the interatomic distances), will be determined by x-ray diffraction and X-Ray Absorption Fine-Structure Spectroscopy (XAFS). Atomic-level and macroscopic magnetic measurements, including magnetic XAFS, XMCD, and ac and dc magnetization, will be correlated to specific types of disorder. Understanding how extrinsic properties such as coercivity depend on disorder will improve materials such as those used for permanent magnets and information storage. Sample fabrication, DC magnetic measurements, and structural characterization will be done at the University of Nebraska-Lincoln, while the University of Northern Iowa will be responsible for ac susceptibility measurements and analysis. The broader impacts of this award include interdisciplinary research training for postdocs, graduate students and undergraduates. Middle and high school teachers and high-school students will be impacted through workshops and summer programs that illustrate the role materials play in society.