Rare Earth Garnets for Spintronic Research

非技术摘要能够以低功耗执行存储器或逻辑运算的新设备正在紧张地开发中。“自旋电子”现象，即材料的磁性状态可以通过使用电信号来控制和检测，提供了通向此类设备家族的途径。该项目开发新材料，并研究它们的生长、结构和性能，以及如何控制它们的性能。这些材料是以石榴石为基础的，石榴石是一种自然生成的氧化物。石榴石的性质和行为可以在广泛的范围内操纵，这为自旋电子学的研究和应用带来了新的机会。这项工作的更广泛影响包括对研究生和本科生的培训，包括那些在科学和工程领域传统上代表性不足的学生，以及将有助于室温自旋电子器件的材料和知识的开发。通过剑桥科学节的纳米天文台活动，向公众介绍麻省理工学院的纳米制造和纳米技术，以及在免费在线课程中纳入自旋电子学模块，开展了公众宣传活动。技术摘要这项建议解决了材料和自旋物理中的关键问题，这将为室温自旋电子器件指明方向。自旋电子现象正受到密切的研究，因为它们有望实现低功耗的存储器或逻辑设备。铁磁绝缘体特别令人感兴趣，因为它们传递自旋电流而不带电荷电流，并显示出低阻尼和高温功能。这类体系中最突出的一类是铁石榴石，其中研究最多的是Y铁石榴石，但Y位上稀土离子的取代使磁性得到了特殊的控制。这项工作的智力价值在于发展了合成方法，并研究了具有垂直磁各向异性的铁榴石薄膜中自旋轨道扭矩驱动的磁畴壁运动。材料性能的设计是通过在石榴石结构中加入稀土元素来改变磁晶各向异性、磁弹性系数和晶格应变、阻尼和补偿温度，并通过稀释Fe亚晶格来改变净磁化强度。利用高的法拉第旋转角和磁光克尔效应的测量，甚至对于不适合磁测量的非常薄(几纳米)的薄膜，以及自旋霍尔磁阻的测量，在电流或场脉冲期间，在不同的温度下探测了石榴石中的磁畴壁的行为。这项工作的更广泛的影响包括对研究生和本科生的培训，以及一套材料的开发，以及对有助于室温自旋电子器件的异质结构的更多了解。通过剑桥科学节的纳米天文台活动，向公众介绍麻省理工学院的纳米制造和纳米技术，以及在免费在线课程中纳入自旋电子学模块，开展了公众宣传活动。考虑到国家劳动力的日益多样化，PI将积极主动地招收在科学和工程领域传统上代表性不足的学生。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势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.