Domain Walls in Ferromagnetic Shape Memory Alloys

技术总结：像差校正洛伦兹透射电子显微镜（LTEM）将被用来研究磁畴壁的行为，在一些多铁性材料，表现出多个相变，每一个产生一个精细尺度的域微观结构。这些畴之间的相互作用（例如，晶体学孪晶边界和磁畴壁之间，或反相边界和磁畴壁之间）是拟议研究的主要焦点。 磁性材料是一类重要的材料，用于各种工程应用，重要的是要了解它们在变化的磁场下的行为。 当施加的场被反转时，材料中的磁化强度将试图跟随场的方向，但是这种反转过程受到其他晶体实体的存在的强烈影响，例如界面和线缺陷。 相位重建LTEM是确定局部磁化状态和畴壁与晶格缺陷之间的潜在相互作用的选择技术。 选择的合金是具有接近化学计量的Ni 2 MnGa化合物的组成的铁磁形状记忆合金和具有约30at%Pd的Fe-Pd合金。拟议的研究将包括静态和动态条件下的磁畴壁的实验观察，并由基于微磁模型的图像模拟支持。此外，磁力显微镜（MFM）和电子扫描对比成像（ECCI，在扫描电子显微镜）将被用来成像微观结构特征以及表面穿透缺陷在一些不同的长度尺度。 通过像差校正LTEM提供的改进的空间分辨率将使静态和动态畴壁过程的定量研究成为可能，并且将使通过不同观察方向进行观察来获得关于材料磁化状态的3-D信息成为可能。非技术概要：拟议的研究计划将研究当施加缓慢变化的磁场时材料的磁化状态如何变化。 一个专门的实验技术，利用透射电子显微镜，将被用来可视化的磁化模式，无论是作为一个静态的模式，或作为一个动态变化的模式时，施加一个字段。 磁性材料是先进工程应用的重要材料类别;例如，在现代汽车中，各种部件（电动机，门锁和各种传感器）都有数百个磁铁。 了解这些材料在变化的磁场中使用时的行为在能源效率方面至关重要。 拟议的研究也可能对新型磁记录介质领域产生影响。 在这项研究中使用的实验协议以及直接观察将提供给更广泛的科学界。 拟议计划的教育部分有可能影响大匹兹堡地区几所学校的初中和高中科学教育。 该计划将为当地初中和高中的学生提供几台扫描电子显微镜，并将教育一些科学教师，使他们能够在教室里使用这些显微镜。此外，拟议的计划将提供一个机会，一些本科材料的学生进行矿物鉴定领域的研究，通过与希尔曼矿物和宝石厅在卡内基自然历史博物馆位于卡内基梅隆大学旁边的合作。

TECHNICAL SUMMARY:Aberration-corrected Lorentz Transmission Electron Microscopy (LTEM) will be used to study magnetic domain wall behavior in a number of multi-ferroic materials which exhibit multiple phase transitions, each giving rise to a fine-scale domain microstructure. The interactions between these domains (for instance, between crystallographic twin boundaries and magnetic domain walls, or between anti-phase boundaries and magnetic domain walls) is the main focus of the proposed research. Magnetic materials form an important class of materials for a wide variety of engineering applications and it is important to understand how they behave under a changing magnetic field. When an applied field is reversed, the magnetization in the material will attempt to follow the direction of the field, but this reversal process is strongly influenced by the presence of other crystallographic entities, such as interfaces and line defects. Phase reconstructed LTEM is the technique of choice to determine the local magnetization state and the potential interactions between domain walls and lattice defects. The alloys of choice are the ferromagnetic shape memory alloys with compositions near the stoichiometric Ni2MnGa compound and Fe-Pd alloys with around 30 at% Pd. The proposed research will consist of experimental observations of domain walls in static and dynamic conditions, supported by image simulations based on micro-magnetic models. In addition, Magnetic Force Microscopy (MFM) and Electron Channeling Contrast Imaging (ECCI, in a scanning electron microscope) will be employed to image micro-structural features as well as surface-penetrating defects at a number of different length scales. The improved spatial resolution offered by aberration-corrected LTEM will enable this quantitative study of static and dynamic domain wall processes, and will make it possible to obtain 3-D information about the magnetization state of the material by carrying out observations with different viewing directions.NON-TECHNICAL SUMMARY:The proposed research program will study how the magnetization state of a material changes when a slowly changing magnetic field is applied. A specialized experimental technique, making use of a transmission electron microscope, will be used to visualize the magnetization pattern, either as a static pattern, or as a dynamic changing pattern when a field is applied. Magnetic materials form an important class of materials for advanced engineering applications; for instance, in a modern car, there are several hundred magnets for a variety of components (electric motors, door locks, and various sensors). Understanding the behavior of these materials while they are used in a changing magnetic field is crucial in the context of energy efficiency. The proposed research may also have an impact in the area of novel magnetic recording media. The experimental protocols used during this research as well as direct observations will be made available to the broader scientific community. The educational component of the proposed program has the potential to impact middle and high school science education in several schools in the greater Pittsburgh area. The program will make several scanning electron microscopes available to students in local middle and high schools, and will educate a number of science teachers so that they can use these microscopes in their class rooms. In addition, the proposed program will provide an opportunity to a number of undergraduate material students to carry out research in the area of mineral identification through collaboration with the Hillman Hall of Minerals and Gems in the Carnegie Museum of Natural History located right next to Carnegie Mellon University.