Magnetic Nanostructures through Metallic Dewetting

非技术摘要：这项研究计划将研究一种新的战略，使不同的金属和合金的纳米粒子，并表征其大小依赖的属性。当材料在纳米长度尺度上结构化时，许多电子、磁性和光学性质变得依赖于尺寸。闪存、计算机硬盘中的磁记录介质以及数字视频播放器中的二极管激光器都是使用纳米结构材料的技术的例子。 该研究计划中感兴趣的材料是尚未制备成具有良好尺寸控制的纳米颗粒的金属和合金。重点将放在已知具有有趣的磁电子或磁光特性的合金上，或在节能应用中作为永磁体的潜在用途。该方法将使用具有规则凹坑阵列的纳米图案模板来控制颗粒大小。在沉积所需材料的薄膜后，将其加热，直到薄膜去湿并填充凹坑。均匀的凹坑尺寸将导致均匀的颗粒尺寸。这种制造方法将能够探索尺寸依赖行为。磁性、磁阻和磁光特性的表征将提供可用于工程纳米结构材料的有价值的新数据。技术摘要：该研究计划将研究通过纳米图案模板上的薄金属膜的润湿和去湿产生的单分散磁性纳米颗粒的形成，并研究其磁性、磁阻和磁光特性。虽然L10 FePt将是目标材料之一，但由于其氧化敏感性或复杂的晶体结构，尚未通过化学方法制成的磁性金属合金将特别感兴趣。挑战是克服对氧化的敏感性，这使得许多这些颗粒不可能通过溶液化学方法制备，并实现晶体取向以测量其各向异性磁性。将有三种策略用于制备磁性合金纳米颗粒阵列，每种策略都具有优势和局限性：1）在纳米颗粒单层上的阴影沉积，2）在纳米孔阵列中接种后沉积，以及3）使用纳米柱阵列作为磁性合金薄膜的硬掩模。在所有情况下，快速热退火将用于探索合金纳米颗粒的晶体取向方法。模板将是介电材料（SiOx、SiNx、MgO）和导电TiNx。磁性合金将包括L10合金，既有熟悉的（FePt），也有研究较少的（FeNi，MnAl，MnBi），用于自旋电子学的材料（Heusler合金Co2FeSi和Ni2MnGa，加上FeCoB），以及用于磁光的材料（非晶材料GdFeCo和TbFeCo）。结果将导致更好地理解金属润湿和去湿纳米。纳米图案化工艺将适用于广泛的复杂材料，而不仅仅是磁性金属合金。制备单分散、钝化的磁性金属合金纳米颗粒将能够进行定量的尺寸依赖性测量。磁化行为将揭示在颗粒表面的表面化学和减少交换相互作用的作用。新的电阻，磁阻测量将在个别纳米粒子。纳米粒子的光滑单层阵列将通过光学和磁光光谱来表征。这个项目将涉及一个研究生的博士论文研究，沿着几个本科生的研究项目。也将通过与磁性社区相关的许多教育活动对广大观众产生影响。

Non-technical Abstract:This research program will investigate a new strategy for making nanoparticles of different metals and alloys, and characterize their size-dependent properties. Many electronic, magnetic, and optical properties become size-dependent when the material is structured on the nanometer length scale. Flash memory, magnetic recording media in computer hard disks, and diode lasers in digital video players, are examples of technology using nanostructured materials. The materials of interest in this research program are metals and alloys that have not yet been prepared as nanoparticles with good size control. The emphasis will be on alloys known to have interesting magneto-electronic or magneto-optical properties, or potential use as permanent magnets in energy-saving applications. The approach will use nanopatterned templates with regular arrays of pits to control the particle size. After depositing a thin film of the desired material, it will be heated until the film dewets and fills the pits. The uniform pit size will lead to a uniform particle size. This fabrication method will enable exploration of size-dependent behavior. Characterization of the magnetic, magnetoresistive, and magneto-optical properties will provide valuable new data that can be used in engineering nanostructured materials.Technical Abstract:This research program will investigate the formation of monodisperse magnetic nanoparticles created by the wetting and dewetting of thin metal films on nanopatterned templates, and to investigate their magnetic, magnetoresistive, and magneto-optical properties. While L10 FePt will be one of the target materials, there will be particular interest in magnetic metal alloys that have not yet been made by chemical methods, due to their oxidation sensitivity or complex crystal structures. The challenges are to overcome the sensitivity to oxidation that makes many of these particles impossible to prepare by solution chemistry methods, and to achieve crystallographic orientation to measure their anisotropic magnetic properties. There will be three strategies for preparing the magnetic alloy nanoparticle arrays, each with strengths and limitations: 1) shadow deposition on a nanoparticle monolayer, 2) deposition after seeding in nanohole arrays, and 3) using nanopillar arrays as a hard mask for a magnetic alloy thin film. In all cases rapid thermal annealing will be used to explore methods for crystallographically orienting the alloy nanoparticles. The templates will be dielectric materials (SiOx, SiNx, MgO) and conducting TiNx. The magnetic alloys will include L10 alloys, both familiar (FePt), and less studied (FeNi, MnAl, MnBi), materials for spintronics (the Heusler alloys Co2FeSi and Ni2MnGa, plus FeCoB), and for magneto-optics (the amorphous materials GdFeCo and TbFeCo). The results will lead to an improved understanding of metallic wetting and dewetting on the nanoscale. The nanopatterning process will be applicable to a wide range of complex materials, not only magnetic metal alloys. The preparation of monodisperse, passivated magnetic metal alloy nanoparticles will enable quantitative size-dependent measurements. The magnetization behavior will reveal the roles of surface chemistry and reduced exchange interactions at the particle surface. Novel resistance, magnetoresistance measurements will be made on individual nanoparticles. Smooth monolayer arrays of nanoparticles will be characterized by optical and magneto-optical spectroscopy. This project will involve the doctoral thesis research of a graduate student, along with several undergraduate research projects. There will also be impact to a broad audience through numerous educational activities associated with the magnetics community.