Collaborative Research: Understanding Magnetostrictive Galfenol Physics for Micro- and Nano-scale Devices

提出的研究重点是铁镓（Galfenol）薄膜和纳米线的磁致伸缩的结构化分析和实验分析，以促进对这种尺度的磁致伸缩物理的理解，并实现新的微纳米级设备功能的变革。这种合金系统具有明显的优势，即对磁场的响应具有高应变（400ppm），同时还表现出铁的机械延展性和强度。电沉积这种活性材料的能力是可能的，因为初步的工作克服了Ga在水电解质中氧化的困难，因此使FeGa金属合金能够制成薄膜和纳米线。这项研究的智力价值包括，从所提出的微纳米级测试设备的研究中获得的见解将导致对促进在纳米尺度上利用磁致伸缩所需的激动人心的设备物理学的深刻理解，例如在模拟自然界生物换能器的人工纤毛传感器和致动器中。作为唯一可能的高响应材料，如延展性纳米线和共形（非平面）厚膜，这项研究也有望在微纳米尺度上为变革性传感器和执行器带来创造性的新概念。这项工作的最初计划是实现从材料科学到设备的飞跃，有四个重要目标。第一个目标是测量电沉积Galfenol薄膜的磁致伸缩作为组成，晶体取向和磁畴取向的函数，这是一个简单但关键的步骤。电容桥将用于测量这些薄膜的磁致伸缩，最佳沉积参数将用于后续目标。第二个目标是制作非接触式扭矩传感器作为测试装置，研究Galfenol薄膜的器件物理特性。扭矩传感器将在现有的转轴扭矩试验台进行评估。第三个目标涉及对纳米级器件（直径10-100nm的Galfenol纳米线）的磁致伸缩进行高风险、高回报的测量。以前已经制作了具有正确成分，晶体结构甚至必要分割的导线，但是由于未知的应变，非常小的磁场（来自单线）和一般尺寸限制，在这种尺度上测量磁致伸缩是困难的。在这里，测量单个纳米线中的巨磁电阻（GMR）将用于确定施加拉伸和压缩应变的影响。此外，将使用磁力显微镜观察弯曲纳米线的磁化旋转，以验证GMR结果。第四个也是最后一个目标将涉及使用Galfenol纳米线制造高分辨率触觉传感器，以了解更多关于其行为和集成到设备中的信息。这项研究将在广泛的领域产生影响，包括自旋电子学（GaAs上的FeGa），振动传感器，作为悬臂和/或纳米线的能量采集器，以及使用非接触式机械-磁耦合的各种传感器和执行器（例如保形非接触式扭矩传感器和结构健康监测传感器）。这项研究将影响两所大学通过REU项目对本科生的教育，特别是通过教师指导项目对代表性不足的学生的教育。研究生将从课程开发中受益，课程开发将包括本项目的研究成果，以及通过工业中心与行业的年度回顾、期刊俱乐部和研讨会的互动。最后，pi将培训学生拓展到k-12学生，以继续对下一代产生广泛的影响。

The proposed research focuses on structured analytical and experimental analysis of magnetostriction in iron-gallium (Galfenol) thin films and nanowires to advance understanding of the magnetostrictive physics at this scale and to enable transformative new micro- and nano-scale device functionality. This alloy system has the distinct advantage of having high strains in response to magnetic fields (400ppm) while also exhibiting the mechanical ductility and strength of iron. The ability to electrodeposit this active material is possible due to preliminary work which overcame the difficulty of Ga oxidation in aqueous electrolytes, and which therefore enabled FeGa metallic alloys to be fabricated as thin films and nanowires. The intellectual merit of this research includes that insights from study of the proposed micro- and nano-scale test devices will lead to a deep understanding of the exciting device physics needed to facilitate utilizing magnetostriction at the nanoscale such as in artificial cilia sensors and actuators that mimic biological transducers in nature. As the only highly responsive material possible as ductile nanowires and conformal (nonplanar) thick films, this research is also expected to lead to the creative, new concepts for transformative sensors and actuators at the micro- and nano-scale. This work proceeds with an original plan to make the leap from materials science to devices with four important goals. The first goal is a simple, yet critical, step of measuring magnetostriction of electrodeposited Galfenol thin films as a function of composition, crystallographic orientation and magnetic domain orientation. A capacitance bridge will be used to measure the magnetostriction of these films and the optimal deposition parameters will be used in the subsequent goals. The second goal is to make a non-contact torque sensor as a test device to study the device physics of Galfenol films. The torque sensors will be evaluated in an existing rotating shaft torque test stand. The third goal involves high-risk, high-payoff measurements of magnetostriction in nanoscale devices (10-100nm diameter Galfenol nanowires). Wires with the right composition, crystal structure, and even necessary segmentation have been previously made, but measuring magnetostriction at this scale is difficult due to unknown strains, very small magnetic fields (from single wires), and general size constraints. Here, measurements of giant magnetoresistance (GMR) in individual nanowires will be used to determine the effect of applied tensile and compressive strains. In addition, magnetic force microscopy will be used to observe magnetization rotation in bent nanowires to verify GMR results. The fourth and last goal will involve making high-resolution tactile sensors using Galfenol nanowires to learn more about their behavior and integration into devices. This research will have impact in a broad variety of fields including spintronics (FeGa on GaAs), vibration sensors, energy harvesters as cantilevers and/or nanowires, and a wide range of sensors and actuators using non-contact mechano-magneto coupling (e.g. conformal non-contact torque sensors and structural health monitoring sensors). This research will impact the education of undergraduates via REU programs at both universities, and especially underrepresented students via faculty mentoring programs. Graduate students will benefit from course development that will include the research results from this project and from interactions with industry via industrial centers with annual reviews, journal clubs, and seminars. Finally, the PIs' will train students in outreach to k-12 students to continue the broad impact in the next generation.