Tunable Magnetic Nanostructures: Property Characterization and Modeling

本项目为期三年，主要研究方向为可调谐磁性纳米结构的特性表征与建模：(1)利用前沿表征工具并辅以理论建模，合成和加工电子可调谐磁性纳米结构，并表征其磁性作为材料变量和外加电场的函数；(2)利用结果对电场、化学和微观结构对性能的影响有一个基本的认识；(3)推动其在包括磁数据存储和磁传感器在内的广泛技术应用中的应用。在本计划的背景下，可调谐纳米结构被定义为那些具有高比表面积的金属或导电氧化物材料系统，其磁性可以通过施加的静电场“调谐”。该项目由德美两国联合开展，包括华盛顿特区的乔治华盛顿大学（GWU），马里兰州盖瑟斯堡的国家标准与技术研究所（NIST）和德国卡尔斯鲁厄的纳米技术研究所（INT）。这个多学科项目的结构是为了明智地利用不同小组的互补和加强的专业知识和经验，以及在NIST的帮助下，在GWU和INT研究机构可用的先进材料合成和表征工具。具体而言，为实现项目目标和目的而进行的不同研究任务的结构将根据各机构各自的专门知识和经验以及可用的研究工具进行分配。因此，INT将合成和处理可调谐纳米结构，采用其开创性的新颖和通用的制造策略，并利用其内部专业知识Mössbauer光谱来检查每个可调谐样品的局部晶体结构和电荷状态。同样，GWU和NIST将通过先进的测量工具（包括配备空间加热器的SQUID VSM）表征磁性（MS， MR， HC, Hb， TC和FORC可逆曲线），允许从1.8 K到1000 K的测量到高达7 t的应用领域，GWU在NIST的帮助下还将使用先进的电光技术表征化学，结构和微观结构。包括Titan扫描透射电子显微镜，配备洛伦兹显微镜和电子断层扫描功能，以及使用电化学电池进行Kerr磁光谱学；建模工作将由美国团队使用Preisach方法进行。本项目选择的可调谐纳米结构是：Fe1-xRhx和FeRh1-xPtx合金。选择这些合金的理由将在提案正文中说明。在美国和德国团队成员之间，这个拟议项目的规划和执行已经并将高度互动。执行不同项目任务的计划将通过电子邮件和电话实时商定和协调。根据需要安排美国和德国团队成员互访。由于外联部分将是项目的重要组成部分，学生交换将在双方同意的基础上安排。也就是说，德国研究生或博士后将在美国研究机构度过一段时间（三到六个月），而INT的美国学生反之亦然。该小组的主要成员彼此认识多年，并在过去的一些研究项目中进行过合作，这增加了这个项目成功的机会。该项目是一个高度整合的合作项目，涉及纳米技术、磁学和磁性材料领域的三家领先研究机构。为该项目向NSF寻求的资金将用于GWU，而INT将向德国DFG寻求资金。在提案的以下部分中，详细介绍了科学动机，实验技术和相关设备的概述以及程序结构的描述。

The objectives of this proposed three year research project on Tunable Magnetic Nanostructures: Property Characterization and Modeling are: (1) to synthesize and process electronically tunable magnetic nanostructures and characterize their magnetic properties as a function of material variables and applied electric field using leading-edge characterization tools and complemented by theoretical modeling; (2) to use the results to gain a fundamental understanding on the effects of electric field, chemistry, and microstructure on properties; and (3) to advance their use in a wide range of technological applications, including magnetic data storage and magnetic sensors. Within the context of this proposed program, tunable nanostructures are defined as those metal or conducting oxide material systems that are characterized by high specific surface areas and whose magnetic properties can be “tuned” by an applied electrostatic field.This program is proposed as a German-American joint effort, involving George Washington University (GWU), Washington, DC with the assistance of National Institute of Standards and Technology (NIST), Gaithersburg, MD, and the Institute of Nanotechnology (INT), Karlsruhe, Germany. This multidisciplinary project is structured so as to judiciously exploit the complimentary and reinforcing suite of expertise and experience of the different groups as well as the advanced material synthesis and characterization tools that are available at the GWU and INT research institutions with the assistance of NIST. Specifically, the structure of the different research tasks to achieve the project goals and objectives will be distributed based on the respective expertise and experience as well as the research tools available in each establishment. Accordingly, INT will synthesize and process the tunable nanostructures, employing its pioneering novel and versatile fabrication strategies and use its in-house expertise on Mössbauer spectroscopy to examine the local crystallographic structure and charge state of each tunable sample. Similarly, GWU and NIST will characterize the magnetic properties (MS, MR, HC, Hb, and TC and FORC reversible curves) by the advanced measurement tools, including a SQUID VSM, equipped with a space heater, allowing measurements from 1.8 K to 1000 K to an applied field up to 7 T. GWU with assistance of NIST will also characterize the chemistry, structure, and microstructure, using advanced electro-optical techniques, including a Titan scanning transmission electron microscope equipped with Lorentz microscopy and electron tomography capabilities as well conduct Kerr magneto-optical spectroscopy with an electro-chemical cell; the modeling effort will be carried out by the US team, utilizing a Preisach approach. The tunable nanostructures selected for this project are: Fe1-xRhx and FeRh1-xPtx alloys. The rationale for selecting these alloys will be given in the body of the proposal. The planning and execution of this proposed project has been and will be highly interactive among the US and German team members. The planning for carrying out the different project tasks will be agreed upon and coordinated in real-time via e-mail and telephone calls. Exchanged visits between the US and German team members will be arranged when they are needed. Being that the outreach component will be an essential element of the project, student exchanges will be arranged on a mutually agreeable basis. That is, a German graduate student or a post-doctoral fellow would spend a period of time (three to six months) at the US research institutions and vice versa for American students at INT. The chances for success of this project are enhanced by the mix of the assembled team whose key members have known each other for a number of years and have collaborated in the past in a number of research projects. This proposed project is a highly integrated collaborative effort involving three leading research institutions in the areas of nanotechnology, magnetism, and magnetic materials. The funding sought for the project from NSF will be for GWU, whereas INT will seek its funding from DFG in Germany. In the following sections of the proposal the details of scientific motivation, an overview of the experimental technique and associated equipment are given as well as a description of the program structure.