Defect-Controlled Magnetic Anisotropy in Alloys

技术：本项目描述了一项研究计划，旨在阐明无序效应主导磁性材料各向异性的条件和机制。传统上，磁各向异性被认为是由晶体结构决定的，而无序在微观理论中所起的作用很小。然而，最近的结果表明，在一大类合金中自然存在的不均匀可能共同作用于完全消除磁晶各向异性。如果这被证明是正确的，它可能会对该领域的未来发展产生很大的影响，这个项目试图使用以下技术来测试这个模型的整个适用范围：(1)用中子衍射来研究合金的结构；(2)用穆斯堡尔谱来研究材料的局部化学性质；(3)用常规电子显微镜和洛伦兹电子显微镜同时研究晶体和磁结构。为了系统地确定模型的适用范围，将研究以下材料系统：铁磁形状记忆合金(FSMA)的高温(非铁弹性)相，如NiMnGa和FEPD；FeCo合金--具有相似磁性和鲜为人知的结构无序的模型系统。非技术性：具有低各向异性和大磁致伸缩的材料在传感器或换能器等应用中变得越来越重要。通过这些应用，这些研究的结果可能会对经济产生很大影响。此外，通过这项研究，许多学生将接受材料合成和表征技术方面的培训。与摩根州立大学(一所历史上的黑人学校)的合作，以及与马里兰州霍华德县的河山高中和马里兰州蒙哥马利县的霍尔顿武器学校(一所女子学校)的外联计划，将确保该计划与HBCU大学和潜在的感兴趣的高中人口部分联系起来。这项工作将产生以下影响：(1)明确的假设将为博士论文提供同样明确的主题，(2)教育效益将扩大到在研究中合作的本科生和高中生/在私人投资机构的实验室实习，(3)在国内和国际上传播结果将有助于普遍的知识论述，最后，(4)该项目具有基本和技术意义。后者基于磁性固态驱动器所需的低各向异性/高磁致伸缩组合。

TECHNICAL: This project describes a research program to elucidate the conditions and mechanisms under which disorder effects can dominate the anisotropy of magnetic materials. Traditionally, the magnetic anisotropy is understood to be determined by the crystal structure, and disorder plays little role in the microscopic theory. However, recent results indicate that inhomogeneities naturally present in a large class of alloys may conspire to completely eliminate the magneto-crystalline anisotropy. If this proves correct, it will likely have a large impact on the future development of the field, and this project seeks to test this model throughout its range of applicability using the following techniques: (1) The structure of alloys will be studied by neutron diffraction; (2) The local chemical nature of the materials will be studied by Mossbauer spectroscopy; (3) The crystal and magnetic structure will be studied simultaneously by conventional and Lorentz transmission electron microscopy To systematically establish the range of applicability of the model, the following material systems will be studied: The high-temperature (non-ferroelastic) phase of ferromagnetic shape-memory alloys (FSMAs), e.g. NiMnGa and FePd; FeCo alloys - A model system with similar magnetic properties and poorly understood structural disorder. NON-TECHNICAL: Materials with low anisotropy and large magnetostriction have become increasingly important for applications as sensors or transducers. The results of these studies could have large impact on the economy through such applications. Additionally, many students will be trained in materials synthesis and characterization techniques through this research. The cooperation with Morgan State University (a historically black institution) and the outreach programs with River Hill High School, Howard County, MD and The Holton-Arms School (a girls-only school), Montgomery County, MD will ensure that the program connects with HBCU Universities and the potentially interested segment of the high school population. The following impacts will result from this work: (1) the clear hypotheses will provide equally clear themes for Ph.D. theses, (2) the educational benefits will extend to undergraduate (HBCU) and high-school students that will cooperate in the studies/serve as interns in PIs' laboratories, (3) the national and international dissemination of the results will contribute to the general intellectual discourse, and, finally, (4) the project is of fundamental and technological interest. The latter is based on the low anisotropy/high magnetostriction combination needed for magnetic solid state actuators.