Defect-Controlled Magnetic Anisotropy in Alloys

技术：本项目描述了一项研究计划，旨在阐明无序效应支配磁性材料各向异性的条件和机制。传统上认为磁性各向异性是由晶体结构决定的，无序性在微观理论中作用很小。然而，最近的研究结果表明，在很大一类合金中自然存在的不均匀性可能会共同作用，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重大影响，本项目试图使用以下技术在整个适用范围内测试该模型：(1)合金的结构将通过中子衍射研究；(2)利用穆斯堡尔光谱研究材料的局部化学性质；(3)晶体和磁性结构将通过常规和洛伦兹透射电子显微镜同时进行研究，以系统地建立模型的适用范围，将研究以下材料体系：铁磁形状记忆合金（fsma）的高温（非铁弹性）相，如NiMnGa和FePd；FeCo合金。一种具有相似磁性和不太清楚的结构紊乱的模型系统。非技术：低各向异性和大磁致伸缩的材料在传感器或换能器的应用中变得越来越重要。这些研究的结果可能会通过这些应用对经济产生重大影响。此外，通过这项研究，许多学生将在材料合成和表征技术方面得到培训。与摩根州立大学（一所历史悠久的黑人大学）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-阿姆斯学校（一所女子学校）的外展项目，将确保该项目与HBCU大学和潜在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)教育效益将扩展到本科生（HBCU）和高中生，他们将在研究中合作/作为pi实验室的实习生，(3)结果的国内和国际传播将有助于一般的知识话语，最后，(4)该项目具有基础和技术利益。后者是基于磁性固态执行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.