Interaction of Coherent Electronic Spin Current with Antiferromagnetic Order

电子带有一个小的角动量，叫做自旋。许多电子自旋的流动，或自旋电流，可能是用最小的电阻加热传输信息或翻转磁记录介质中存储的信息的有效方法。为了设计实用的基于自旋的信息技术设备，了解(1)自旋电流在衰减前传播的时间和(2)自旋电流如何与记录介质中的磁矩相互作用是很重要的。该项目针对一种特殊的优势磁性材料——反铁磁体——回答了这两个问题。反铁磁体的磁矩在原子长度尺度上是反平行（交替）排列的。由自旋电流操作的反铁磁体可能比传统的磁性材料（具有平行排列磁矩的铁磁体）实现更快和更稳定的磁记录设备，但反铁磁体中自旋电流的基本物理学尚未得到很好的理解。该项目通过确定定制反铁磁体中自旋电流衰减长度的补充实验，以及通过揭示自旋电流与不同磁性原子相互作用的强大x射线实验，填补了这一知识空白。技术摘要：当自旋电流的载流子（如电子）的自旋极化被锁定在一个均匀的方向或进动相位时，我们说自旋电流是相干的。自旋电流如何失去相干性，特别是当它与磁序相互作用时，是自旋电子学和量子信息科学中的一个关键的基本问题。本实验项目的目标是了解与交变磁矩相互作用的电子携带的自旋电流的退相干机制，即反铁磁序。该项目填补了对反铁磁金属中自旋退相干的基本理解的空白，反铁磁金属最近作为下一代自旋电子器件的平台获得了相当大的关注。具体目标是：(1)确定反铁磁金属中结构无序和电子散射如何影响横向极化自旋电流的相干长度；(2)确定电子自旋电流如何将自旋角动量传递给铁磁合金中化学上不同的反铁磁亚晶格。这些目标是通过利用模型系统的独特组合（例如，外延薄膜，纳米结构自旋阀）和薄膜结构，磁有序，微波自旋泵和磁输运的互补特性来实现的。此外，利用泵浦探针x射线同步加速器方法，对多层反铁磁系统中的自旋流物理进行了前所未有的时间和元素分辨。该项目中阐明自旋退相干的独特方法将对反铁磁自旋电子学的发展产生变革性影响。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 AbstractAn electron carries a small angular momentum called spin. A flow of many electron spins, or spin current, may be an efficient way to transport information with minimal resistive heating or to flip stored information in magnetic recording media. To design practical spin-based information-technology devices, it is important to understand (1) how long a spin current travels before decaying and (2) how a spin current interacts with magnetic moments in recording media. This project answers these two questions for a specific advantageous type of magnetic materials, antiferromagnets, where magnetic moments are aligned anti-parallel (alternating) at the atomic length scale. Antiferromagnets operated by spin current potentially enable faster and more stable magnetic recording devices than conventional magnetic materials (ferromagnets, with parallel-aligned magnetic moments), but the basic physics of spin current in antiferromagnets is not well understood. This project fills this gap in knowledge through complementary experiments that determine spin-current decay lengths in tailored antiferromagnets, as well as through a powerful X-ray experiment that reveals the interaction of spin current with different magnetic atoms. Technical AbstractA spin current is said to be coherent when the spin polarization of its carriers (e.g., electrons) is locked in a uniform orientation or precessional phase. How a spin current loses its coherence, particularly as it interacts with magnetic order, is a crucial fundamental question in spintronics and quantum information science. The goal of this experimental project is to understand decoherence mechanisms of spin current carried by electrons that interact with alternating magnetic moments, i.e., antiferromagnetic order. This project fills a gap in basic understanding of spin decoherence in antiferromagnetic metals, which have recently gained considerable attention as platforms for next-generation spintronic devices. The specific objectives are: (1) to determine how the coherence length of transverse-polarized spin current is impacted by structural disorder and electronic scattering in antiferromagnetic metals, and (2) to determine how an electronic spin current transfers spin angular momentum to chemically distinct antiferromagnetic sublattices in ferrimagnetic alloys. These objectives are met by leveraging a unique combination of model systems (e.g., epitaxial thin films, nanostructured spin valves) and complementary characterization of film structure, magnetic order, microwave spin pumping, and magnetotransport. Furthermore, a pump-probe X-ray synchrotron method is utilized to gain an unprecedented time- and element-resolved insight into spin-current physics in multilayered antiferromagnetic systems. The distinct approach in this project to elucidate spin decoherence will have transformative impact on the growing discipline of antiferromagnetic 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.