Magnetoelastic Control of Magnetization Dynamics in Nanomagnet Arrays

非技术摘要：磁性是众多日常应用的核心。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，在数据存储、存储和传感方面有着广泛的应用。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到光产生的、传播的表面声波。这种热致磁弹性耦合对于诸如热辅助磁记录和全光磁化切换等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，最大限度地利用它们，并探索它们在节能全光交换中的应用。这项研究直接影响到我们对纳米磁性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。该项目还包括多个教育组成部分，包括纳米磁学和超快光学领域的研究生培训，通过加州大学领导小组和CAMP(加州少数群体参与联盟)计划让来自代表性不足群体的本科生参与，以及面向高中生和当地K-6学校的外联活动。技术摘要：磁弹性耦合到传播的表面声波可以强烈地影响纳米磁阵列的磁化动力学，即使对于相对较弱的磁弹性材料也是如此。周期阵列是新出现的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。这种效应需要仔细考虑，特别是对于由于所涉及的大热能而激发声子模的新兴光学辅助技术。该项目包括对密集阵列中纳米磁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可以决定其磁性的程度。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。该项目围绕三个推力进行设计：第一个推力解决磁性材料的参数优化问题。系统地改变了纳米磁体的材料、形状和阵列的几何形状，以证明磁化进动的频率可以完全由阵列的几何形状决定，而不受外加磁场的影响。重点放在结合具有大磁弹性系数的材料上。第二个重点是探索和优化通过光学产生的表面声波的磁化动力学的非局部激发。其目标是演示用声表面波(SAW)选择性地激发和检测单个纳米磁体。这是首次观察到阵列中的单个纳米磁动力学在非热的、定义明确的、带有磁弹性产生的外场的激励下的动力学。最后的重点是通过证明SAW提供的机械能可以帮助磁化转换来探索一条通向设备的道路。其目标是显示减少FeTb纳米磁体全光开关所需的光通量。能够以非热方式影响对光交换的需求可能会对全光交换用于数据存储和其他应用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.