Interaction of Coherent Electronic Spin Current with Antiferromagnetic Order

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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.