Spin Polarized Tunneling Studies in Transition Metals, Alloys and Heavy Fermions

过渡金属、合金和重费米子的自旋极化隧道研究

• 批准号: 0137632
• 负责人: Jagadeesh Moodera
• 金额: $ 37.5万
• 依托单位: Massachusetts Institute of Technology
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2002
• 资助国家: 美国
• 起止时间: 2002-01-01 至 2005-12-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0137632&HistoricalAwards=false
• 关键词: Spin; Polarized; Tunneling; Studies; Transition; Spin; Polarized; Tunneling; Studies; Transition

This project will explore electron spin properties, from both the fundamental physics point of view and from the viewpoint of the technologically important area of spintronics. The emphasis will be on surfaces and interfaces that form the basis of spin transport phenomena. The intention is also to extend the technique of spin-polarized tunneling into new areas: (1) Determination of its relation to crystalline direction, barrier interface, and bulk magnetic moment, (2) Analytical study of tunnel barriers. Though having been addressed for nearly thirty years by many theoretical approaches, the origin and the magnitude of the polarization values measured by tunneling remain an open question. This work will investigate the poorly understood relation between spin polarization of tunneling electrons on crystallographic orientation and surface band structure. This includes spin-polarized tunneling from epitaxial ferromagnetic films, interfacial-bonding effects and tunnel barrier properties. Fabrication techniques will manipulate the interfaces and barriers in planar thin film magnetic tunnel junctions in efforts to maximize the spin polarization values. Spin tunneling is influenced by delta dopants (with or without magnetic moment) in the tunnel barriers - mostly flipping the spins and, except for the case of Fe dopants, even enhancing the spin tunneling probability. This area is yet to be understood and will be well investigated. A state of the art MBE system makes it feasible to engineer thin films with new types of interface materials leading to unique electronic and magnetic properties. The theoretical support comes from Prof. William H. Butler of Oak Ridge National Lab whose expertise is in band structure calculations, interface effects as well as ferromagnetic tunnel junction structures. Spin tunneling studies will possibly be initiated, a first of its kind study in heavy Fermion systems, wherein temperature-induced changes and pressure-induced changes of the magnetic transitions occur. Students of all levels and postdocs will be involved in this investigation thus creating a pool of technical experts particularly in the future field of information technology - spintronics, and in general magnetism as well as thin film science.This condensed matter physics project broaden our fundamental understanding of electron spin properties (a topic in magnetism) by using the unique tool of spin polarized tunneling technique (a quantum phenomenon). The results will contribute to the knowledge base needed for possible future spin-based information technologies. The project will build on earlier successful work in spin tunneling plus transport, and at a later stage of the program will push toward the new frontiers by examining a new class of magnetic materials, so-called heavy Fermion metals. A major goals is to expand a new and promising interaction between theorists who are now working to analyze the spin tunneling experiments. In addition, the fabrication methods, using state of the art molecular beam epitaxy tools will manipulate the material interfaces and tunnel barriers to create novel materials and to maximize the spin polarization values. Measurements will be made in ambient as well as liquid helium temperatures in the presence of a small or large magnetic field. Some of the earlier results of this project have generated worldwide interest, both experimentally and theoretically, with many major companies involved in developing nonvolatile memory elements as well as sensors for ultrahigh-density recording. The project integrates research with the education and training of high-school students, undergraduate students, graduate students and post-doctoral fellows. The training will be in spin transport and in specialized areas such as nanotechnology. The highly educated and trained people will be well prepared for careers as educators and workers in the area of spin-based information storage technology.

该项目将从基本物理学的角度以及从技术重要的旋转区域的角度来探索电子自旋特性。 重点将放在构成自旋转运现象基础的表面和界面上。 目的是将自旋偏振隧穿的技术扩展到新区域：（1）确定其与晶体方向，屏障界面和块状磁矩的关系，（2）隧道屏障的分析研究。 尽管已经通过许多理论方法解决了将近三十年的时间，但通过隧道测量的极化值的起源和幅度仍然是一个悬而未决的问题。 这项工作将研究隧道电子在晶体学方向和表面带结构上的自旋极化之间的关系不足。 这包括来自外部铁磁膜，界面束缚效应和隧道屏障特性的自旋偏振隧道。 制造技术将操纵平面薄膜磁性隧道连接中的界面和障碍，以最大程度地提高自旋极化值。 自旋隧道受隧道屏障中的三角洲掺杂剂（带有或没有磁矩）的影响 - 主要是翻转旋转，除了Fe掺杂剂的情况外，甚至增强了自旋隧道的概率。 该区域尚未理解，并且将经过充分的研究。 最先进的MBE系统使具有新型界面材料的工程薄膜可行，从而呈现出独特的电子和磁性。 理论支持来自Oak Ridge National Lab的William H. Butler教授，其专业知识是在乐队结构计算中，界面效应以及铁磁隧道结构。 可能会启动自旋隧道研究，这是在重型费米昂系统中进行的首次研究，其中温度引起的变化和压力诱导的磁转变发生变化。 各个层次和博士后的学生将参与这项调查，从而创造了一批技术专家，尤其是在未来的信息技术领域 - 旋转技术，一般磁性以及薄膜科学。通过使用Spin Polarlized Tunnelning技术的独特工具（一种磁性工具），该凝结物理学项目扩大了我们对电子旋转特性（A主题）的基本了解（一种主题）。 结果将有助于可能将来基于旋转的信息技术所需的知识库。 该项目将基于较早的Spin Tunneling Plus Transport的成功工作，在该计划的后期，该项目将通过检查新的磁性材料，即所谓的重型费米昂金属，将其推向新的边界。 一个主要目标是扩大正在努力分析旋转隧道实验的理论家之间的新且有希望的互动。 此外，使用最先进的分子束外延工具的制造方法将操纵材料界面和隧道屏障，以创建新型材料并最大化自旋极化值。 在存在小或大磁场的情况下，将在环境和液体温度下进行测量。该项目的一些早期结果在实验和理论上都引起了全球范围的兴趣，许多主要公司参与了开发非挥发性记忆元素以及超高密度记录的传感器。 该项目将研究与高中生，本科生，研究生和博士后研究员的教育和培训相结合。 该培训将在自旋运输和纳米技术等专业领域进行。 受过良好教育和训练的人将为职业做好充分的准备，作为基于旋转的信息存储技术领域的教育者和工人。