Spin Polarized Transport Properties in Tunnel Structures

两个具有重要技术前景的重要科学领域涉及金属和半导体隧道结构中的自旋输运。磁隧道结异质结构的制备已成为一项成熟的技术，但仍存在与隧道磁电阻的偏置依赖性、噪声和结构-性能关系相关的重要科学问题。这个个人研究者奖支持一个项目，重点是发展对自旋极化隧道传输的透彻理解。研究内容包括：应用电子全息技术对隧道势垒进行成像；从理论和实验两方面研究了态密度、势垒高度和势垒形状对隧穿磁电阻偏置依赖性的影响；考察电荷输运和自旋输运引起的不同长度尺度之间的相互作用；利用噪声光谱技术探测隧道势垒中的磁化反转和波动、缺陷以及势垒中电导通道的分布；开发室温铁磁半导体。这些问题直接影响了将隧道结结构用于非易失性磁随机存取存储器和场传感应用的技术前景，例如使用磁阻传感器阵列的磁记录读取头和生物分析。有鉴于此，资讯科技署与业界保持合作关系。该项目还旨在为两种截然不同的需求变得明显的科学教育带来相关性。首先，高等教育必须明确解决课程中可转换工作技能的问题。第二是科学和磁电子技术对美国竞争力和经济增长的重要性。这两个需求将在一个跨越地方、区域和国际层面的项目中得到解决。纳米制造方法和异质外延的现代技术进步极大地促进了磁性的研究，并提供了在纳米尺度上设计磁性现象的能力。基础研究的新领域也出现了——一个显著的例子是“自旋电子学”或“自旋电子学”。这些进步的应用使创造全新的磁电子器件结构成为可能，并推动了一种革命性的新型电子器件的发展，这种电子器件是基于电子自旋（与电子的磁性行为有关的数量），或者取代电子电荷。金属隧道结系统中的自旋输运和半导体是两个具有重要技术前景的重要科学领域。在本提案中，我们专注于通过以下协同组合来全面了解自旋极化隧道输运：一种用于揭示隧道势垒特性如何影响器件对外加磁场的电阻响应的新型显微镜技术（磁电阻）；考察电荷输运和自旋输运引起的不同长度尺度之间的相互作用；利用噪声光谱技术探测磁化反转与波动、隧道势垒中的缺陷以及势垒中电导通道的分布，开发室温铁磁半导体。这些问题直接影响了隧道结结构用于非易失性磁随机存取存储器和磁场传感应用的技术前景，例如磁记录读磁头。鉴于此，pi与领先行业合作以优化设备性能。该项目还旨在为科学教育带来相关性。两种截然不同的需求已经变得明显。首先，高等教育必须明确解决可转移工作技能在课程中的作用问题。第二是科学和磁电子技术对美国竞争力和经济增长的重要性。这两个需求将在一个跨越地方、区域和国际层面的项目中得到解决。

Two vital scientific areas with important technological prospects involve spin transport in tunneling structures made of metals and semiconductors. The fabrication of magnetic tunnel junction heterostructures is becoming a mature technology, and yet there still remain important scientific issues related to the bias dependence of the tunneling magnetoresistance, noise, and structure-property relationships. This individual investigator award supports a project that focuses on developing a thorough understanding of spin-polarized tunneling transport. The studies involve: applying electron holography to profile the tunnel barrier; investigating, both in theory and in experiment, how the density-of-states, the barrier height, and the barrier shape affect the bias dependence of the tunneling magnetoresistance; examining the interplay among different length scales arising from charge and spin transport; using noise spectroscopy to probe magnetization reversal and fluctuations, defects in the tunnel barrier, and the distribution of conductance channels in the barrier; and developing room temperature ferromagnetic semiconductors. These issues directly impact the technological prospects of using tunnel junction structures for nonvolatile magnetic random access memory and field sensing applications, such as magnetic recording read heads and biological assays that use magnetoresistive sensor arrays. In view of this, the PIs maintain collaborations with industry. The program also aims to bring relevance to science education where two distinct needs have become apparent. The first is that higher education must address explicitly the issue of transferable job skills in the curriculum. The second is the importance of science and magneto-electronic technology to U.S. competitiveness and economic growth. These two needs will be addressed in a program that spans local, regional, and international levels.Modern technological advances in nanofabrication methods and heteroepitaxy have greatly invigorated the investigation of magnetism and are providing the capability to engineer magnetic phenomena at the nanoscale. New fields of basic research have also emerged - a notable example is "spin-electronics" or "spintronics". Applications of these advances are enabling the creation of entirely new magneto-electronic device structures and driving the development of a revolutionary new class of electronics based on electron's spin (a quantity related to electron's magnetic behavior) in addition to, or in place of, electronic charge. Two vital scientific areas with important technological prospects involve spin transport in metallic tunnel junction systems and semiconductors. In this proposal, we concentrate on developing a thorough understanding of spin-polarized tunneling transport through a synergistic combination of: a novel microscopy technique used to reveal how the properties of the tunnel barrier affect a device's resistive response to an applied magnetic field (magnetoresistance); examining the interplay among different length scales arising from charge and spin transport; using noise spectroscopy to probe magnetization reversal and fluctuations, defects in the tunnel barrier, and the distribution of conductance channels in the barrier, and developing room temperature ferromagnetic semiconductors. These issues directly impact the technological prospects of using tunnel junction structures for nonvolatile magnetic random access memory and field sensing applications, such as in magnetic recording read heads. In view of this the PIs collaborate with leading industries towards optimizing device performance. The program also aims to bring relevance to science education. Two distinct needs have become apparent. The first is that higher education must address explicitly the issue of the role of transferable job skills in the curriculum. The second is the importance of science and magneto-electronic technology to U.S. competitiveness and economic growth. These two needs will be addressed in a program that spans local, regional, and international levels.