Tunneling Studies of Ferromagnetic Junctions and Interfaces

铁磁结和界面的隧道研究

• 批准号: 9730908
• 负责人: Jagadeesh Moodera
• 金额: $ 33万
• 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: 1998
• 资助国家: 美国
• 起止时间: 1998-09-01 至 2002-03-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=9730908&HistoricalAwards=false
• 关键词: Tunneling; Studies; Ferromagnetic; Junctions; Interfaces

9730908 Moodera This experimental research project is concerned with electron tunnel junctions with electrodes of magnetic metals conceived in such a way that the tunneling current is controlled in a sensitive fashion by an applied magnetic field. Well characterized ferromagnetic tunnel junctions and interfaces will be prepared under clean and ultra high vacuum conditions to allow accurate and reproducible tunneling measurements, particularly on structures with 3d and 4f ferromagnetic metals. Spin polarization of the same films that make up the tunnel junction will also be measured by superconducting tunneling spectroscopy. The main thrust is to understand the physical mechanisms responsible for the observed magnetic field sensitivity. It is expected that this research will additionally lead to new results and techniques in condensed matter physics and new applications for magnetic technology.This research program is interdisciplinary in nature and has typically involved several undergraduate and high school students in its activities. These involvements are beneficial in the preparation of students for further study and for careers in industry, government laboratories or academia. %%% This experimental research project is concerned with a new class of electronic devices that the PI has discovered in his previously supported work, which are highly sensitive to magnetic field. The electrical resistance of the device, which is called a tunnel junction, changes when the device is placed in a magnetic field, and is said to exhibit magnetoresistance. This discovery has created interest worldwide because of the potential for improvements in technology. The main technological applications may be in magnetic sensors for computer hard drives, possibly for magnetic computer memory or logic elements, and for miscellaneous applications s uch as sensors to measure rotational speeds, eg, a tachometer. The basic tunnel junction is a capacitor-like device with a thin insulating oxide between two metal plates. In this case the oxide layer is so thin that electrons can transfer from one plate to the other by the quantum mechanical tunneling process. This process was firmly established and understood in detail in the late 1960's by basic physics researchers who realized that a tunnel junction device, if it could be fabricated with a sufficiently thin and homogeneous oxide layer, could be instrumental to understanding the nature of superconductivity. Ivar Giaever won the Nobel Prize in Physics in 1973 for his experiments on superconductivity which were based on his development of improved fabrication techniques and a more complete understanding of the physical behavior of tunnel junctions. The present PI has gone on from these earlier basic research results to find the magnetic effects which are very promising for applications in computers and other technologies. As in the earlier case, the PI here has perfected new and more careful experimental methods to clearly reveal the theoretically expected physical effects, in this case magnetic in nature. This project focuses on careful and systematic measurements on junction structures with metal electrodes of different ferromagnetic compositions, in order to better understand and maximize the sensitivity to magnetic field. This research program is interdisciplinary in nature and has typically involved several undergraduate and high school students in its activities. These involvements are beneficial in the preparation of students for further study and for careers in industry, government laboratories or academia. ***

9730908 Moodera 该实验研究项目涉及带有磁性金属电极的电子隧道结，其设计方式是通过施加的磁场以灵敏的方式控制隧道电流。 特征良好的铁磁隧道结和界面将在洁净和超高真空条件下制备，以实现精确且可重复的隧道测量，特别是在具有 3d 和 4f 铁磁金属的结构上。构成隧道结的相同薄膜的自旋极化也将通过超导隧道光谱进行测量。 主要目的是了解导致观测到的磁场敏感性的物理机制。预计这项研究还将带来凝聚态物理领域的新成果和技术以及磁技术的新应用。该研究项目本质上是跨学科的，通常有几名本科生和高中生参与其活动。这些参与有利于学生为进一步学习以及在工业界、政府实验室或学术界的职业生涯做好准备。 %%% 该实验研究项目涉及 PI 在其之前支持的工作中发现的一类新型电子设备，这些设备对磁场高度敏感。该器件称为隧道结，当器件置于磁场中时，其电阻会发生变化，据说会表现出磁阻。由于技术改进的潜力，这一发现引起了全世界的兴趣。主要技术应用可能是用于计算机硬盘驱动器的磁传感器，可能用于磁性计算机存储器或逻辑元件，以及用于诸如测量旋转速度的传感器（例如转速计）的各种应用。基本的隧道结是一种类似电容器的器件，在两个金属板之间有一层薄薄的绝缘氧化物。在这种情况下，氧化层非常薄，电子可以通过量子力学隧道过程从一个板转移到另一块板。 这一过程在 20 世纪 60 年代末被基础物理研究人员牢固地建立和详细理解，他们意识到隧道结器件如果可以用足够薄且均匀的氧化物层制造，将有助于理解超导的本质。 Ivar Giaever 因其改进的制造技术和对隧道结物理行为的更全面理解而进行的超导实验荣获 1973 年诺贝尔物理学奖。 目前的 PI 从这些早期的基础研究成果出发，发现了在计算机和其他技术中非常有前景的应用的磁效应。 与之前的案例一样，这里的 PI 完善了新的、更仔细的实验​​方法，以清楚地揭示理论上预期的物理效应，在本例中本质上是磁性的。 该项目的重点是对具有不同铁磁成分的金属电极的结结构进行仔细和系统的测量，以便更好地理解和最大化对磁场的敏感性。该研究项目本质上是跨学科的，通常有多名本科生和高中生参与其活动。 这些参与有利于学生为进一步学习以及在工业界、政府实验室或学术界的职业生涯做好准备。 ***