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

技术支持：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部磁场对纳米结构和磁各向异性的作用，以及（2）开发一个唯象模型来理解外部磁场依赖效应。PI将实现这些目标，通过一个综合的活动，涉及纳秒激光诱导自组织实验，测量纳米磁性，并在这些纳米系统的磁化现象学建模。控制纳米尺度的磁各向异性，促使磁化强度指向所需的方向，可以被视为实现功能性纳米磁性材料的基本要求。到目前为止，磁各向异性主要通过两种贡献的操纵来实现：（i）形状各向异性，即具有大纵横比结构;以及（ii）通过外延或织构化生长经由晶体取向的磁晶各向异性。最近，PI发现，通过快速激光诱导自组织产生的近半球多晶单畴纳米磁体在各个方向上表现出稳定的和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旨在通过以下活动实现对纳米材料中的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流体静压力对快速激光自组织纳米颗粒中磁各向异性的作用。(ii)研究外磁场对磁各向异性、微结构、形核和生长的作用。(iii)发展快速雷射自组织奈米结构之奈米磁性唯象模型。这一综合实验和理论活动的智力价值将源于以下特点：（a）这将是探索快速激光自组织、热应变、外部磁场与纳米级磁各向异性的成核和生长之间的耦合的第一项决定性工作。这将导致？纳米粒子相图精确地描述了这种耦合以及由此产生的微结构和磁各向异性。(b)PI预计新型磁性材料的设计和合成可能会影响数据存储，传感和信息处理领域。非技术性：这项活动的更广泛影响将通过致力于扩大研究生、本科生和高中生的研究和教育经验来实现。具体影响包括：（a）在材料科学、激光材料加工、凝聚态物理学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允许研究人员和创新者进行基于设计和发现的计划来合成新材料。(c)大学和高中学生的积极参与（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，从而帮助美国继续保持其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.