Rare Earth Garnets for Spintronic Research

摘要低功耗的存储或逻辑运算的新器件正在得到大力发展。“自旋电子”现象，其中材料的磁性状态可以通过使用电信号来控制和检测，为这类设备的家族提供了一条途径。该项目开发新型材料，研究它们的生长、结构和性能，以及如何控制它们的性能。材料是基于石榴石，这是一种天然存在的氧化物。石榴石的性质和行为可以在很宽的范围内进行操纵，这为自旋电子学的研究和应用带来了新的机会。这项工作的广泛影响包括培养研究生和本科生，包括那些传统上在科学和工程领域代表性不足的学生，以及开发有助于室温自旋电子器件的材料和知识。在剑桥科学节上，通过纳米天文台的活动向公众介绍麻省理工学院的纳米制造和纳米技术，并在免费的在线课程中加入自旋电子学模块，开展了公众宣传。技术摘要：本提案解决了材料和自旋物理学中的关键问题，为室温自旋电子器件的研究指明了方向。自旋电子现象正受到密切的研究，因为它们有望使存储器或逻辑器件具有低功耗。铁磁绝缘体特别有趣，因为它们传递自旋电流而没有电荷电流，并且具有低阻尼和高温功能。这类体系中最突出的一类是铁石榴石，其中研究得最好的是钇铁石榴石，但在Y位上取代稀土离子可以对磁性进行特殊控制。本工作的智力价值在于研究了具有垂直磁各向异性的铁石榴石薄膜中自旋轨道转矩驱动的畴壁运动。通过在石榴石结构中加入铥等稀土元素来改变其磁晶各向异性、磁弹性系数、晶格应变、阻尼和补偿温度，并通过稀释铁亚晶格来改变其净磁化强度来设计材料性能。在电流或场脉冲过程中，在不同温度下探测了柘柘石畴壁的行为，利用高法拉第旋转和磁光克尔效应测量的优势，即使对于非常薄（几纳米）的薄膜，磁强计也不适合，并通过测量自旋霍尔磁电阻来补充。这项工作的广泛影响包括培养研究生和本科生，开发一系列材料，增加对异质结构的理解，这将有助于室温自旋电子器件。在剑桥科学节上，通过纳米天文台的活动向公众介绍麻省理工学院的纳米制造和纳米技术，并在免费的在线课程中加入自旋电子学模块，开展了公众宣传。鉴于全国劳动力日益多样化，PI将积极招收传统上在科学和工程领域代表性不足的学生。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Non-technical abstractNew devices that can carry out memory or logic operations with low power consumption are under intense development. "Spintronic" phenomena, in which the magnetic state of a material can be controlled and detected by using an electrical signal, provide a path towards a family of such devices. This program develops novel materials and investigates their growth, structure and properties, and how their properties can be controlled. The materials are based on garnet, which is a naturally occuring oxide. The properties and behavior of the garnet can be manipulated over a wide range, leading to new opportunities in spintronic research and applications. The broader impacts of this work include the training of graduate and undergraduate students, including those who have been traditionally underrepresented in science and engineering, and the development of materials and knowledge that will contribute to room temperature spintronic devices. Public outreach is carried out via the NanoObservatory event at the Cambridge Science Festival, where the public is introduced to nanofabrication and nanotechnology at MIT, and by incorporation of modules on spintronics in free online courses. Technical abstractThis proposal addresses key issues in materials and spin physics which will point the way towards room temperature spintronic devices. Spintronic phenomena are under intense investigation due to their promise in enabling memory or logic devices with low power consumption. Ferromagnetic insulators are particularly interesting because they convey spin currents without charge currents, and exhibit low damping and high temperature functionality. One of the most prominent classes of such systems is that of iron garnets, of which the best studied is yttrium iron garnet, but substitution of rare earth ions on the Y sites enables exceptional control over the magnetic properties. The intellectual merit of this work is to develop synthesis methods and examine spin orbit torque - driven domain wall motion in iron garnet films with perpendicular magnetic anisotropy. Materials properties are designed by substituting rare earths such as thulium into the garnet structure to alter the magnetocrystalline anisotropy, magnetoelastic coefficients and lattice strain, damping and compensation temperature, and by diluting the Fe sublattices to change the net magnetization. The behavior of domain walls in garnet is probed at various temperatures during current or field pulsing, taking advantage of the high Faraday rotation and magnetooptical Kerr effect measurements even for very thin (few-nm) films where magnetometry is unsuitable, and complemented by measurements of spin Hall magnetoresistance. The broader impacts of this work include the training of graduate and undergraduate students and the development of a set of materials and an increased understanding of heterostructures that will contribute to room temperature spintronic devices. Public outreach is carried out via the NanoObservatory event at the Cambridge Science Festival, where the public is introduced to nanofabrication and nanotechnology at MIT, and by incorporation of modules on spintronics in free online courses. Given the ever-increasing diversity in the national workforce, the PI will be proactive in recruiting students who have been traditionally underrepresented in science and engineering.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.