Selection of Lengthscales in Fe-based Nanochessboards to Enhance Exchange-Coupled Ferromagnetism

永磁体是各种技术的关键部件，尤其是在电动机和发电机中。它们对于磁记录也是至关重要的，而磁记录仍然是大规模数据存储设备的基础。为了提高磁体的性能，需要新的材料、新的策略和新的科学。改善磁性行为的一种方法被称为交换耦合，在这种方法中，两种不同的磁性材料在量子水平上相互作用，创造出任何一种材料本身都无法获得的新特性。然而，为了使其有效，需要材料在纳米尺度上相互缠绕，称为纳米复合材料。大多数关于纳米复合材料的研究都探索了两个极端。薄膜提供了极端的简单性，其中两种材料只是薄的平面层，彼此叠加。体积纳米复合材料提供了极端的复杂性，其中具有不规则形状，大小和界面的微小颗粒相互交织在一起。该项目研究了一种非常特殊的纳米复合材料，称为纳米棋盘，其中两种材料的规则排列是通过自组装实现的，在特定的材料组合中，只需加热它们。最终的结构看起来很像一个棋盘，但其中的单个瓷砖是纳米级的。本研究的智力价值强调改变材料组合，以阐明材料的性质如何影响其自组装成纳米棋盘，以及它们交换偶联的能力。反过来，这将为研究提供更广泛的影响——对行为的重要新理解，可用于定义创造高性能交换耦合磁铁的新策略。本项目将选择和竞争长度尺度，结构与磁性，使用先进的加工技术，在Fe-Pd和Fe-Pt系统中创建精致的纳米棋盘，以便更好地理解，控制和增强交换耦合铁磁性。这些二元体系包含A1—L10+L12形式的共析，如果处理条件得到严格控制，则通过伪旋量分解形成棋盘。智力优势是由这里使用的合金的具体选择所构成的，这决定了与l10相相关的单轴磁晶各向异性，这反过来又选择了交换耦合的临界长度尺度。棋盘是通过共析连续冷却产生的，但为了获得额外的周期性控制，将研究热机械加工和循环退火。交换耦合的程度将使用第一阶反转曲线分析来询问，该分析擅长于揭示磁相如何相互作用。除了从最初的多晶A1起始材料中生长棋盘外，还将生长单晶A1，然后在磁场或双轴应变下退火，以创建单一排列变量棋盘。这将有助于更好地理解磁化反转机制，以及棋盘变换本身。实时x射线衍射将在棋盘形成过程中使用，以更好地阐明转变的动力学和过程。所提出的研究成功的更广泛的影响将有助于我们理解大块纳米复合磁体中的交换耦合铁磁性，不仅包括层次长度尺度，还包括相形态，界面和应变的作用。改进永磁体对于提高电动机的效率具有持续的重大意义。

Non-Technical AbstractPermanent magnets are key components in a diverse range of technologies, most notablyin electric motors and electric generators. They are also critical to magnetic recording,which still forms the foundation of large-scale data storage devices. To improve theperformance of magnets, new materials, new strategies, and new science are needed. Oneapproach towards improving magnetic behavior is called exchange coupling, in whichtwo different magnetic materials interact at the quantum level to create new propertiesnot available from either material by itself. For this to be effective, however, requires thatthe materials be intertwined at the nanoscale, called a nanocomposite material. Mostresearch on nanocomposite materials has explored two extremes. Extreme simplicity isprovided by thin films, in which the two materials are simply thin, planar layers on top ofone another. Extreme complexity is provided by bulk nanocomposites, where tiny grainswith irregular shapes, sizes and interfaces, are mutually intertwined. This projectinvestigates a very special nanocomposite, called the nanochessboard, where a regulartiling of the two materials is achieved by self-assembly, in specific combinations ofmaterials, simply by heating them. The resulting structure looks much like a chessboard,but where the individual tiles are nano-sized. The Intellectual Merit of this studyemphasizes varying the materials combinations in order to illuminate how the nature ofthe materials affects both their self-assembly into nanochessboards, and their ability toexchange couple. In turn, this will provide the Broader Impacts of the study - theimportant new understanding of the behaviors that can be used to define new strategiesfor creating high-performance exchange-coupled magnets.Technical AbstractThis project will select and compete lengthscales, structural vs. magnetic, using advancedprocessing techniques to create refined nanochessboards in the Fe-Pd and Fe-Pt systems,in order to better understand, control, and enhance exchange-coupled ferromagnetism.These binary systems contain eutectoids of the form A1-- L10+L12 that result inchessboards by pseudo-spinodal decomposition, if processing conditions are carefullycontrolled. The Intellectual Merit is framed by the specific choice of alloys to be usedhere, which dictates the uniaxial magnetocrystalline anisotropy associated with the L10phase, which, in turn, selects the critical lengthscale for exchange coupling. Chessboardsare produced by cooling continuously through the eutectoid, but to gain additional controlover the periodicity, thermomechanical processing and cyclic annealing will beinvestigated. The degree of exchange coupling will be interrogated using First OrderReversal Curve analysis, which excels at revealing how magnetic phases interact. Inaddition to the growth of chessboards from an initially polycrystalline A1 startingmaterial, monocrystalline A1 will also be grown, and then annealed under magnetic fieldsor biaxial strain, to create a single-alignment-variant chessboard. This will enable betterunderstanding of the magnetization reversal mechanisms, as well as the chessboardtransformation itself. Real-time x-ray diffraction will be employed during chessboardformation to better elucidate the kinetics and progression of the transformation. TheBroader Impacts of success in the proposed research would be the contribution to ourunderstanding of exchange-coupled ferromagnetism in bulk nanocomposite magnets, notonly including hierarchical lengthscales, but the role of phase morphology, interfaces andstrain. Improving permanent magnets is of ongoing major significance with regard toincreasing the efficiency of electric motors.