Understanding Spin Diffusion Lengths in Metals and Oxides

非技术摘要：高性能的磁性设备在我们的社会中无处不在，为云数据存储提供动力的磁性硬盘驱动器就是一个例子。这一领域的技术进步的基础是对磁性和磁性材料的基本认识的不断进步。在这个项目中，一个与“自旋电子学”相关的基本问题正在解决，特别是电子自旋在从磁性材料泵送到非磁性材料后是如何放松的。这是一个知之甚少的磁学问题，尽管许多科学努力和下一代设备的高度重要性。在这项工作中，一种特殊类型的纳米磁性装置首次被用于定量地理解特定材料缺陷如何控制自旋的弛豫。除了推进基础科学知识之外，通过设备应用的社会效益，通过对学生的教育以及与公众的接触，正在实现更广泛的影响。后者包括与明尼苏达科学博物馆合作，在我们的日常生活中发展材料科学的展览和表演，从而提高人们对材料研究在我们社会中的作用的认识。技术摘要：在非磁性金属中，纯自旋电流或自旋极化电荷电流的流动是许多自旋电子现象和器件的核心。在这种情况下的一个基本问题是，非平衡自旋居群在非磁性金属中的弛豫距离是多少，或者：自旋扩散长度是多少？值得注意的是，虽然已知控制金属自旋弛豫的基本机制，即艾略特-雅费机制，但我们对这一过程的理解仍存在巨大差距。特定缺陷的个别影响仍然未知，妨碍了对自旋输运的定量或预测性理解。解决这一问题及其明显的技术相关性，将构成一种变革性的进步。该项目的实质是使用非局部横向自旋阀来确定各种常规金属和氧化基金属中的自旋扩散长度。人们正在研究诸如Al这样的元素金属，分别量化声子、杂质、晶界、表面和界面引起的自旋弛豫，从而确定每个缺陷的艾略特-亚费常数。金属钙钛矿氧化物也在研究中。这些材料为自旋电子学提供了巨大的潜力，尽管对其自旋扩散长度的理解仍然难以捉摸。在这项研究中，从传统的金属基器件到钙钛矿金属的进展，提供了对氧化物铁磁体和非磁性金属中自旋扩散长度的首次理解，这是氧化物自旋电子学发展的关键一步。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Non-technical abstract:High performance magnetic devices are ubiquitous in our society, the magnetic hard disk drives that power cloud data storage serving as one example. Underpinning technological advancement in this area is the ongoing progress in fundamental understanding of magnetism and magnetic materials. In this project, a fundamental problem relevant to "spin electronics" is being tackled, specifically how electron spins relax after being pumped from magnetic to non-magnetic materials. This is a poorly understood issue in magnetism, despite many scientific efforts and high importance for next generation devices. In this work, a particular type of nanomagnetic device is being used to understand, quantitatively, and for the first time, how specific materials defects control the relaxation of spins. In addition to advancing basic scientific knowledge, broader impact is being achieved through societal benefits from device applications, through education of students, and through outreach to the public. The latter involves collaboration with the Science Museum of Minnesota, developing exhibits and performances on the science of materials in our everyday lives, thus raising awareness of the role of materials research in our society.Technical abstract:Central to many spintronic phenomena and devices is the flow of a pure spin current, or a spin-polarized charge current, in a non-magnetic metal. A fundamental question in such a situation is over what distance does a non-equilibrium spin population relax in a non-magnetic metal, or: what is the spin diffusion length? Remarkably, while the basic mechanism governing metallic spin relaxation, the Elliot-Yafet mechanism, is known, there remain massive gaps in our understanding of this process. The individual effects of specific defects remain unknown, preventing quantitative or predictive understanding of spin transport. Addressing this problem, with its obvious technological relevance, would constitute a transformative advance. The essence of this project is to use non-local lateral spin valves to determine spin diffusion lengths in a variety of conventional and oxide-based metals. Elemental metals such as Al are being studied to separately quantify spin relaxation due to phonons, impurities, grain boundaries, surfaces, and interfaces, thus determining Elliott-Yafet constants for each defect. Metallic perovskite oxides are also being studied. These materials offer tremendous potential for spintronics, although an understanding of their spin diffusion lengths remains elusive. A progression from conventional metal-based devices to perovskite metals is being followed in this research, providing the first understanding of spin diffusion lengths in oxide ferromagnets and non-magnetic metals, a critical step in the development of oxide spintronics.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.