Magnetoelastic Control of Magnetization Dynamics in Nanomagnet Arrays

非技术总结：磁性是许多日常应用的核心。最近，密集排列的纳米磁体阵列已成为自旋电子器件的原型，应用于数据存储、内存和传感。最近的研究表明，这些阵列的几何设计可以影响动态磁响应，因为磁性与纳米元件的物理振动相互作用。这种效应是由于磁弹性耦合光学产生的，传播表面声波。这种热诱导磁弹性耦合对于热辅助磁记录和全光磁化开关等新兴技术尤其重要。该项目的目标是充分了解这些现象，最大限度地利用它们，并探索它们在节能全光开关中的应用。这项研究直接影响了我们对纳米磁铁材料及其特性的基本理解，特别是磁性和弹性自由度之间的耦合。该项目还有多个教育组成部分，包括纳米磁性和超快光学领域的研究生培训，通过UC LEADS和CAMP（加州少数民族参与联盟）项目让来自代表性不足群体的本科生参与，以及向高中生和当地K-6学校开展的推广活动。技术概述：磁弹性耦合传播的表面声波可以强烈地影响纳米磁体阵列的磁化动力学，即使是相对弱磁弹性材料。周期阵列是新兴自旋电子器件的原型布局，但它们也作为声子晶体，其共振影响磁化。这种效应需要仔细考虑，特别是对于新兴的光学辅助技术，由于涉及到很大的热能，激发声子模式。该项目包括对密集阵列中纳米磁体动力学的磁弹性控制的全面研究，目的是全面了解纳米结构阵列的几何形状在多大程度上决定其磁性能。这个项目的变革性影响将是回答这个问题，并展示几个科学上的第一。该项目围绕三个推力进行设计：第一个推力针对磁性材料的参数优化。系统地改变了纳米磁体的材料、形状和阵列几何形状，以证明磁化进动的频率可以完全由阵列几何形状决定，而与外加磁场无关。重点是结合具有大磁弹性系数的材料。第二个重点是探索和优化通过光产生的表面声波磁化动力学的非局部激励。目的是演示用表面声波（SAW）选择性激发和检测单个纳米磁铁。这代表了在非热的、明确定义的、具有磁弹性产生的外场的激励下，阵列中单个纳米磁体动力学的第一次观察。最终推力的重点是通过证明saw传递的机械能有助于磁化开关来探索通向器件的路径。我们的目标是要降低FeTb纳米磁体全光开关所需的光能量。能够对光交换的要求产生非热影响，可能会对数据存储和其他应用中全光交换的潜在使用产生重大影响。

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.