Interaction of Coherent Electronic Spin Current with Antiferromagnetic Order

电子携带一个小的角动量，称为自旋。许多电子自旋或自旋电流的流动可以是以最小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式。为了设计实用的基于自旋的信息技术设备，重要的是要了解（1）自旋电流在衰变之前的传播时间以及（2）自旋电流如何与记录介质中的磁矩相互作用。这个项目回答了这两个问题，一个特定的有利类型的磁性材料，反铁磁体，其中磁矩在原子长度尺度上反平行排列（交替）。由自旋电流操作的反铁磁体可能比传统磁性材料（铁磁体，具有平行排列的磁矩）更快，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还没有得到很好的理解。该项目通过互补实验填补了这一知识空白，这些实验确定了定制反铁磁体中的自旋电流衰减长度，并通过一个强大的X射线实验揭示了自旋电流与不同磁性原子的相互作用。当自旋电流的载流子的自旋极化（例如，电子）被锁定在均匀的取向或旋进相位。自旋电流如何失去其相干性，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基础问题。这个实验项目的目标是了解与交变磁矩相互作用的电子所携带的自旋电流的退相干机制，即，反铁磁序该项目填补了反铁磁金属中自旋退相干的基本理解的空白，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，以及（2）确定电子自旋电流如何将自旋角动量转移到亚铁磁合金中化学性质不同的反铁磁子晶格。这些目标是通过利用模型系统的独特组合来实现的（例如，外延薄膜、纳米结构自旋阀）和膜结构、磁序、微波自旋泵浦和磁输运的补充表征。此外，泵浦-探测X射线同步加速器方法被用来获得一个前所未有的时间和元素分辨洞察多层反铁磁系统中的自旋电流物理。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这一日益发展的学科产生变革性的影响。该奖项反映了NSF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.