Tunable Magnetic Nanostructures: Property Characterization and Modeling

本研究计划为期三年，主要研究方向为：（1）合成和加工电子可调的磁性纳米结构，并利用先进的表征工具和理论建模来表征其磁性随材料变量和外加电场的变化;（2）利用这些结果，从根本上了解电场、化学和微观结构对性能的影响;（3）推动它们在广泛的技术应用中的应用，包括磁数据存储和磁传感器。可调纳米结构被定义为具有高比表面积的金属或导电氧化物材料系统，其磁性能可以通过施加静电场进行“调谐”。该计划是德美联合努力的结果，涉及乔治华盛顿大学（GWU），华盛顿，DC的协助下，国家标准与技术研究所（NIST），盖瑟斯堡，MD，和纳米技术研究所（INT），卡尔斯鲁厄，德国。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的协助下，GWU和INT研究机构提供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开展的不同研究任务的结构将根据各机构的专门知识和经验以及现有的研究工具进行分配。因此，INT将合成和处理可调纳米结构，采用其开创性的新颖和通用的制造策略，并利用其内部的穆斯堡尔光谱专业知识来检查每个可调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SQUID VSM，配备空间加热器，允许从1.8 K到1000 K测量到高达7 T的外加磁场）来表征磁特性（MS，MR，HC，Hb和TC和FORC可逆曲线）。GWU在NIST的协助下还将使用先进的电光技术来表征化学，结构和微观结构，包括配备Lorentz显微镜和电子断层扫描功能的Titan扫描透射电子显微镜，以及使用电化学电池进行Kerr磁光光谱;建模工作将由美国团队进行，利用Preisach方法。该项目选择的可调纳米结构是：Fe 1-xRhx和FeRh 1-xPtx合金。选择这些合金的理由将在提案的正文中给出。该项目的规划和执行已经并将在美国和德国团队成员之间进行高度互动。将通过电子邮件和电话实时商定和协调执行不同项目任务的规划。美国和德国团队成员之间的互访将在需要时安排。由于外展部分将是该项目的一个重要组成部分，学生交流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研究员将在美国研究机构度过一段时间（三到六个月），反之亦然，对于INT的美国学生来说，这个项目成功的机会得到了组合团队的增强，该团队的主要成员已经相互认识了多年，并且在过去的许多研究项目中进行了合作。这个拟议的项目是一个高度综合的合作努力，涉及纳米技术，磁学和磁性材料领域的三个领先的研究机构。该项目从NSF寻求的资金将用于GWU，而INT将从德国的DFG寻求资金。在提案的以下部分中，给出了科学动机的细节，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.