Magnetoelastic Control of Magnetization Dynamics in Nanomagnet Arrays

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NON-TECHNICAL SUMMARY: Magnetism is at the heart of numerous every-day applications. Recently, arrays of densely packed nanomagnets have emerged as the prototype vision for spintronic devices with applications in data storage, memory, and sensing. It has recently been shown that the geometric design of these arrays can impact the dynamic magnetic response because the magnetism interacts with the physical vibrations of the nanoelements. This effect is due to magnetoelastic coupling to optically generated, propagating surface-acoustic waves. Such thermally induced magnetoelastic coupling can be particularly important for emerging techniques such as heat-assisted magnetic recording and all-optical magnetization switching. The goal of this project is to fully understand these phenomena, maximize them, and to explore their utilization for energy-efficient all-optical switching. This research has direct impact on our fundamental understanding of nanomagnet materials and properties, specifically the coupling between magnetic and elastic degrees of freedom. The project also has multiple educational components, including graduate student training in the fields of nanomagnetism and ultrafast optics, involvement of undergraduate students from underrepresented groups through the UC LEADS and CAMP (California Alliance for Minority Participation) programs, and outreach activities to high school students and local K-6 schools. TECHNICAL SUMMARY: Magnetoelastic coupling to propagating surface-acoustic waves can strongly affect the magnetization dynamics of a nanomagnet array, even for relatively weakly magnetoelastic materials. Periodic arrays are the prototype layout for emerging spintronic devices, but they also act as phononic crystals whose resonances affect the magnetization. Such effects need to be carefully considered, especially for emerging optically assisted techniques that excite phononic modes due to the large thermal energies involved. This project comprises a comprehensive investigation of magnetoelastic control of nanomagnet dynamics in dense arrays with the goal of obtaining a complete understanding of the extent to which the geometry of the nanostructured array can determine its magnetic properties. The transformative impact of this project will be to answer this question and to demonstrate several scientific firsts. The project is designed around three thrusts: The first thrust addresses parameter optimization of magnetic materials. Nanomagnet material, shape and array geometry are systematically varied in order to demonstrate that the frequency of the magnetization precession can be completely determined by the array geometry, independent of applied field. The focus is on incorporation of materials with large magnetoelastic coefficients. The second thrust focuses on exploring and optimizing nonlocal excitation of magnetization dynamics via optically generated surface acoustic waves. The goal is to demonstrate selective excitation and detection of a single nanomagnet with a surface-acoustic wave (SAW). This represents the first observation of single nanomagnet dynamics in an array under non-thermal, well-defined excitation with a magnetoelastically generated external field. The focus of the final thrust is to explore a path towards devices by demonstrating that SAW-delivered mechanical energy can assist in magnetization switching. The goal is to show a reduction in the optical fluence required for all-optical switching of FeTb nanomagnets. Being able to non-thermally affect the requirements for optical switching could have significant impact on the potential use of all-optical switching for data storage and other applications.