Magnetic Behavior of Nanoengineered Lithographic Particles and Arrays in the Single Domain Limit

技术概述：这项建议的基本目标是首次解决金属、纳米工程异质结构在单畴极限和尺寸范围30-300 nm范围内的静态和动态磁性行为，包括形状控制的单层、三层合成反铁磁体以及具有交换偏置和交换弹簧行为的异质结构。它将强调依赖于尺寸的标度定律，通过消除较长的长度-尺度效应、大型系综阵列的集体行为和具有包括旋转在内的完全自由度的自由浮动元件来研究真正的纳米尺度的磁交换现象。中心焦点将集中在对磁反转行为、层间耦合、交换作用、老化和记忆效应以及弛豫动力学的基本理解上，所有这些都是在单畴极限和最近的理论模型的背景下进行的。这项新的科学将通过最近建立的高通量纳米印迹程序和一系列仔细和专门的磁性测量来实现。纳米压印技术可以在几平方厘米的面积上制造出横向尺寸在30到300纳米之间的相同的、定制形状的薄膜元件-足以进行宏观整体测量。与电子束光刻不同，构图时间长达数小时，纳米压印光刻可以在短短几分钟内为整个基板构图。此外，所提出的合成方法克服了湿化学方法的两个主要局限性，即制备介观尺寸范围内的单分散粒子和产生异质结构元素。最后，纳米尺度的NLP的物理/磁性微结构将在所有阶段与使用粒子系综测量的磁性相关联。非技术摘要：材料的性能严重依赖于尺寸，特别是纳米尺度。磁性最显著地表现了这一行为。在宏观尺度上，磁性材料分解成多个磁区，以使其静磁能量最小化。随着材料的尺寸变小，它不再能够支持多个域，而成为单域材料。在这种长度尺度下，可以探索基本的和内在的磁性行为，而不会受到来自磁场壁的外在特性的干扰。人们提出了一种新的方法，通过一种新开发的纳米压印光刻技术-一种类似于橡胶冲压但具有纳米级特征的方法--来合成大量在尺寸、形状、形态和磁性方面都是均匀的这种设计粒子。这将使我们能够研究足够大数量的“粒子”的磁响应及其时间依赖性，以提供统计上有意义的数据和对这种长度尺度上的磁行为的理解。这项基础性工作也对信息存储、自旋电子学、磁逻辑、用于能源的硬磁体和生物传感技术产生了潜在的影响。发现与教学、培训和学习同步推进将是一体化的。这些活动包括为纳米技术本科课程和磁性材料研究生课程开发新的授课模块。将为一年一度的UW工程学院开放日开发一个新的互动展览；来自当地学校的4000多名学生将参加。PI计划做出额外努力，向威斯康星大学招收少数族裔/女性学生，并将具体与斯佩尔曼学院合作，斯佩尔曼学院是亚特兰大的一所历史悠久的非裔美国人文理学院，它与威斯康星大学有一个联合的科学/工程项目。还计划与日本的一个领导小组在电子全息术方面进行国际合作。

TECHNICAL SUMMARY: The fundamental goal of this proposal is to address, for the first time, the static and dynamic magnetic behavior of metallic, nanoengineered heterostructures in the single-domain limit and in the size-range of 30-300 nm, that include shape-controlled single layers, tri-layers of synthetic anti-ferromagnets, and heterostructures with exchange-bias and exchange-spring behavior. It will emphasize size-dependent scaling laws, with studies of true nanoscale magnetic exchange phenomena by eliminating longer length-scale effects, collective behavior of large ensemble arrays and free-floating elements with complete degrees of freedom, including rotation. The central focus will be on the fundamental understanding of magnetic reversal behavior, interlayer coupling, exchange interactions, aging and memory effects and relaxation dynamics, all in the single domain limit and in the context of recent theoretical models. This new science will be enabled by high-throughput recently established nanoimprinting routines and by a series of careful and specialized magnetic measurements. Nanoimprinting allows the fabricate of identical, custom-shaped thin-film elements in the lateral size range between 30 and 300 nm over areas as large as several square centimeters---sufficient for macroscopic ensemble measurements. Unlike electron-beam lithography, with patterning times of many hours, nanoimprint lithography can pattern a whole substrate in just a few minutes. Moreover, the proposed synthesis method overcomes two principal limitations of wet-chemistry approaches, i.e. preparing monodisperse particles in this mesoscopic size range and creating heterostructured elements. Finally, the physical/magnetic microstructure at the nanometer length scale of the NLPs will be correlated at all stages with the magnetic properties measured using particle ensembles. NON-TECHNICAL SUMMARY: The properties of materials depend critically on size, especially on the nanometer length scale. Magnetic properties express this behavior most prominently. At the macroscopic scale a magnetic material breaks down into domains to minimize its magnetostatic energy. As the size of the materials is made smaller it is no longer able to sustain multiple domains and becomes a single domain material. At this length scale, it becomes possible to explore fundamental and intrinsic magnetic behavior without the interference of extrinsic characteristics arising from domain walls. It is proposed to use a novel method to synthesize large numbers of such "designer particles" that are homogeneous in size, shape, morphology and magnetic characteristics by a newly developed technique of nanoimprint lithography---a method similar to rubber-stamping but with nanoscale features. This will enable the study of the magnetic response, as well as its time dependence, of sufficiently large number of "particles" to provide statistically significant data and understanding of magnetic behavior on this length scale. This fundamental work also has potential impact on the technologies of information storage, spin electronics, magnetic logic, hard magnets for energy applications and biological sensing. The simultaneous advancement of discovery with teaching, training and learning will be integrated. These activities include developing new lecture modules for an undergraduate course in Nanotechnology and a graduate class on Magnetic Materials. A new interactive exhibit for the annual UW, College of Engineering open house will be developed; is attended by more than 4000 students from local schools. The PI plans to make the extra effort to recruit minority/women students to UW and will specifically work with Spelman College, a historical African-American liberal arts college in Atlanta, which has a joint science/engineering program in place with UW. International collaborations on electron holography with a leading group in Japan are also planned.