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经成为自旋电子器件的原型，其应用于数据存储、存储器和传感器。最近已经表明，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。这种效应是由于磁致弹性耦合到光学产生的，传播的表面声波。这种热致磁致弹性耦合对于诸如热辅助磁记录和全光磁化切换之类的新兴技术可能特别重要。本项目的目标是充分了解这些现象，最大限度地发挥它们的作用，并探索它们在节能全光交换中的应用。这项研究直接影响了我们对纳米磁体材料和性质的基本理解，特别是磁性和弹性自由度之间的耦合。该项目还具有多个教育组成部分，包括纳米磁学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）计划参与代表性不足的群体的本科生，以及高中生和当地K-6学校的外展活动。技术概要：磁弹性耦合到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，即使对于相对弱的磁弹性材料。周期性阵列是新兴自旋电子器件的原型布局，但它们也充当声子晶体，其共振影响磁化。这种影响需要仔细考虑，特别是对于新兴的光学辅助技术，激发声子模式，由于涉及到大的热能。该项目包括一个全面的调查，磁致弹性控制的纳米磁体动力学在密集的阵列，以获得一个完整的理解的程度，纳米结构阵列的几何形状可以确定其磁性能的目标。这个项目的变革性影响将是回答这个问题，并展示几个科学第一。该项目围绕三个重点进行设计：第一个重点是磁性材料的参数优化。纳米磁体材料、形状和阵列几何形状被系统地改变，以证明磁化旋进的频率可以完全由阵列几何形状确定，而与施加的场无关。重点是纳入大磁弹性系数的材料。第二个推力的重点是探索和优化非局部激励的磁化动力学通过光学产生的表面声波。我们的目标是展示选择性激发和检测一个单一的纳米磁体与表面声波（SAW）。这代表了第一次观察到的单一纳米磁体动态阵列下的非热，定义明确的激励与磁弹性产生的外部场。最终推力的重点是通过证明SAW提供的机械能可以帮助磁化切换来探索通往设备的路径。我们的目标是显示减少所需的全光开关的FeTb纳米磁体的光通量。能够非热影响光开关的要求可能会对全光开关在数据存储和其他应用中的潜在用途产生重大影响。

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.