Magnetic Anisotropy in Nanoscale Systems Produced by Fast Laser Processing: Fundamental Mechanisms, Control and Novel Magnetic Materials

技术：这项高风险探索性研究的目标是：(1)确定激光诱导自组织过程中外磁场对纳米结构和磁各向异性的作用；(2)建立一个现象学模型来理解外场依赖效应。pi将通过纳秒级激光诱导自组织实验、纳米级磁性测量和这些纳米级系统磁化的现象学建模等综合活动来实现这些目标。控制纳米尺度的磁各向异性，促使磁化指向所需的方向，可以被视为实现功能纳米磁性材料的基本要求。到目前为止，磁性各向异性主要是通过操纵两个贡献来实现的：(i)形状各向异性，即具有大纵横比结构；（ii）通过外延或织构生长形成的晶体取向的磁晶各向异性。近年来，研究人员发现，激光诱导快速自组织制备的近半球形多晶单畴纳米磁体在各个方向上表现出稳定的、与尺寸相关的磁各向异性。这种行为普遍存在于所研究的所有磁性材料中，包括Co， Ni， Fe和Fe-Co合金。在这个项目中，pi的目标是通过以下活动来实现对纳米材料磁各向异性及其控制的基本理解：(i)研究热应变和单轴应变以及静水压力对快速激光自组织纳米颗粒磁各向异性的作用。（ii）研究外加磁场对磁性各向异性、微观结构、成核和生长的作用。（iii）为快速激光自组织纳米结构建立纳米级磁性的现象学模型。这一综合实验和理论活动的智力价值将源于以下特点：(a)这将是第一个探索快速激光自组织、热应变、外磁场和纳米尺度磁各向异性成核和生长之间耦合的决定性工作。这将导致什么？纳米颗粒相图？准确地描述了这种耦合以及由此产生的微观结构和磁各向异性。(b)项目计划预期设计和合成可能影响数据储存、传感和信息处理领域的新型磁性材料。非技术：这项活动的更广泛影响将是通过承诺扩大研究生、本科生和高中生的研究和教育经验。具体影响包括：(a)在材料科学、激光材料加工、凝聚态物理和磁学等多学科领域培训本科生和研究生。(b)通过这项活动开发的现象学模型可以使研究人员和革新者进行基于设计和发现的方案来合成新材料。(c)大学和高中生的积极参与（通过辉瑞/Solutia STARS计划）将有助于培养纳米科学领域的未来科学家，这是国家的核心利益，从而帮助美国继续在科学和技术方面的领导地位。

TECHNICAL: The objectives of this high-risk exploratory research are (1) To determine the role of external magnetic field during laser-induced self-organization on the nanostructure and magnetic anisotropy and (2) To develop a phenomenological model to understand the external field dependent effects. PIs will realize these goals through an integrated activity involving experiments of nanosecond laser-induced self-organization, measurement of nanoscale magnetism, and phenomenological modeling of magnetization in these nanoscopic systems. The control of nanoscale magnetic anisotropy, which prompts the magnetization to point in desired directions, can be viewed as a fundamental requirement towards realizing functional nanomagnetic materials. Thus far, magnetic anisotropy has been realized primarily through the manipulation of two contributions: (i) shape anisotropy, i.e. with large aspect ratio structures; and (ii) magnetocrystalline anisotropy via crystallographic orientation through epitaxy or textured growth. Recently, PIs have discovered that near-hemispherical polycrystalline single-domain nanomagnets created by fast laser-induced self-organization show stable and size-dependent magnetic anisotropy in various directions. This behavior was universally present in all magnetic materials investigated, including Co, Ni, Fe and an Fe-Co alloy. In this project, PIs aim to achieve a fundamental understanding of magnetic anisotropy and its control in nanoscale materials through the following activities: (i) Investigate the role of thermal and uniaxial strain, and hydrostatic pressure on magnetic anisotropy in fast laser self-organized nanoparticles. (ii) Investigate the role of external magnetic field on magnetic anisotropy, microstructure, and nucleation and growth. (iii) Develop a phenomenological model of nanoscale magnetism for fast laser self-organized nanostructures. The intellectual merit of this integrated experimental and theoretical activity will stem from the following features: (a) This will be the first definitive work exploring the coupling between fast laser self-organization, thermal strain, external magnetic field and nucleation and growth on nanoscale magnetic anisotropy. This will result in ?nanoparticle phase diagrams? that accurately describe this coupling and the resulting microstructure and magnetic anisotropy. (b) PIs anticipate the design and synthesis of novel magnetic materials that could impact areas of data storage, sensing and information processing. NON-TECHNICAL: The broader impact from this activity will be through commitments to broadening research and education experiences of graduate, undergraduate and high-school students. Specific impacts include: (a) The training of undergraduate and graduate students in a multidisciplinary area comprising materials science, laser-materials processing, condensed matter physics and magnetism. (b) The phenomenological model developed through this activity could permit researchers and innovators to undertake a design and discovery based program to synthesize new materials. (c) Active participation of university and high-school students (through the Pfizer/Solutia STARS program) will help train future scientists in the area of nanoscience, which is of core national interest, and thereby help the US continue its leadership in science and technology.