Spin Polarized Transport Properties in Tunnel Structures

具有重要技术前景的两个重要科学领域涉及金属和半导体隧道结构中的自旋输运。磁性隧道结异质结的制备技术日趋成熟，但在隧道磁阻与偏置的关系、噪声和结构-性质关系等方面仍存在一些重要的科学问题。这一个人研究人员奖支持一个项目，该项目专注于发展对自旋极化隧道传输的彻底理解。这些研究包括：应用电子全息术来描绘隧道势垒的轮廓；从理论和实验上研究态密度、势垒高度和势垒形状如何影响隧道磁阻的偏置关系；考察由电荷和自旋输运引起的不同长度尺度之间的相互作用；使用噪声光谱来探测磁化反转和涨落、隧道势垒中的缺陷以及势垒中电导通道的分布；以及开发室温铁磁半导体。这些问题直接影响将隧道结结构用于非易失性磁随机存取存储器和现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检测。有鉴于此，私人投资促进机构与工业界保持合作。该计划还旨在为科学教育带来相关性，因为在科学教育中，两种不同的需求已经变得明显。首先，高等教育必须在课程中明确解决可转让工作技能的问题。其次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、地区和国际层面的计划中得到解决。在纳米制造方法和异质外延方面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”。这些进展的应用正在创造全新的磁电子设备结构，并推动基于电子自旋(与电子的磁性行为有关的量)以及电子电荷或电子电荷替代的革命性新型电子设备的开发。具有重要技术前景的两个重要科学领域涉及金属隧道结系统和半导体中的自旋传输。在这一提议中，我们专注于通过以下各项的协同作用来彻底理解自旋极化的隧道输运：一种新的显微技术，用于揭示隧道势垒的性质如何影响器件对外加磁场(磁阻)的阻性响应；研究电荷和自旋输运引起的不同长度尺度之间的相互作用；使用噪声光谱来探测磁化反转和涨落、隧道势垒中的缺陷以及势垒中电导通道的分布，以及开发室温铁磁半导体。这些问题直接影响将隧道结结构用于非易失性磁随机存取存储器和场感测应用的技术前景，例如在磁记录读取头中。有鉴于此，PI与领先行业合作，以优化设备性能。该计划还旨在将其与科学教育联系起来。两种截然不同的需求已经变得显而易见。首先，高等教育必须明确解决可转让工作技能在课程中的作用问题。其次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、地区和国际层面的计划中得到解决。

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.