All-Optical Magnonic Spin Torque Devices

智力优势：这项提议的研究目标是设计一系列自旋转移装置，其扭矩来自热产生的磁子。据预测，这种热驱动的自旋扭矩可以使量子产额提高近两个数量级，比目前最先进的电流驱动自旋扭矩设备大两个数量级。在所有其他条件不变的情况下增加可用自转扭矩将对自旋扭矩设备技术产生重大影响。考虑到这种巨大的潜力，磁子自旋扭矩器件将使用薄膜沉积和纳米光刻技术相结合的方法来制造。器件结构将包括磁性氧化物-普通金属-金属铁磁自旋阀。器件性能的操作和表征将完全是光学的：超快泵浦-探测时间分辨磁光克尔效应首先激发氧化物中的磁子，然后观察金属铁磁体中产生的磁化动力学。这些器件的基本原理是将自旋动量从磁性氧化物中的磁子转移到自由铁磁层的磁化。磁子将通过飞秒激光脉冲在磁性氧化层(例如，尖晶石铁磁体)中产生。这些磁子将在氧化物-正常金属界面(可能包含额外的一层磁原子)上湮灭，但它们的自旋动量将转移到正常金属中的传导电子。因此，在正常金属中将产生与时间相关的自旋极化电子的积累。这种自旋积累的时间导数导致了金属铁磁体上的扭矩，这强调了使用超快光学的重要性。器件性能将通过选择材料、创建和表征可进行自旋转移的界面以及研究相关的长度尺度来优化。广泛的影响：磁子自旋扭矩器件的实验实现，其量子产额比目前最先进的设备提高了近两个数量级，将产生革命性的影响，本质上创造了一类新的自旋扭矩器件。一般来说，自旋转移扭矩装置将受益于取代现在运行所需的高电流密度，因为这会引起明显的加热，并通过不可避免的Oersted场在自由层中形成涡核。Magonic自旋扭矩将解决这些问题，使设备性能、制造要求和可靠性得到显著改善。该项目将通过统一物理、电气工程、材料和光学科学的技术和思想，将学生的教学和培训整合在一起，从而使他们拥有成为学术界和行业下一代领导者所需的多学科人才。国际合作将强调全球合作对现代研究的重要性。私人投资机构将继续以其通过各种方式扩大少数群体参与的既定记录为基础，包括：指导来自USF？S佛罗里达州-佐治亚州路易斯·斯托克斯少数群体参与联盟的学生进入博士学位计划；教育社区了解某些招生政策对少数群体的不成比例过滤；与佛罗里达州高级技术教育中心(FLAATE)合作为少数群体服务的中学组织夏令营，FATE是美国国家科学基金会下属的地区技术教育卓越中心。与Flate和Hillsborough县学区合作，将通过为教师举办培训讲习班，帮助培养一支精通科学、技术、工程和数学的劳动力队伍。

Intellectual merit: The research objectives of this proposal are to engineer a series of spin-transfer devices whose torque originates from thermally generated magnons. It has been predicted that such heat driven spin torque can lead to quantum yield improvements nearly two orders of magnitude greater than present state-of-the-art current-drive spin torque devices. Increasing the usable spin torque with all else constant will have a major impact on spin torque device technologies. Given the great potential, magnonic spin torque devices will be fabricated using a combination of thin film deposition and nanolithography techniques. Device structures will include magnetic oxide-normal metal-metallic ferromagnet spin valves. The operation and characterization of device performance will be entirely optical: ultrafast pump-probe time-resolved Magneto-Optical Kerr Effect to first excite magnons in the oxide, then observe the resulting magnetization dynamics in the metallic ferromagnet. The underlying principle of these devices is the transfer of spin momentum from magnons in a magnetic oxide to the magnetization of a free ferromagnetic layer. Magnons will be generated in the magnetic oxide layer (e.g., a spinel ferromagnet) by an femtosecond laser pulse. These magnons will annihilate at the oxide-normal metal interface (which may contain an additional layer of magnetic atoms), but their spin momentum will be transferred to conduction electrons in the normal metal. Thus, a time dependent accumulation of spin polarized electrons will be generated in the normal metal. The time derivative of this spin accumulation results in a torque on the metallic ferromagnet, which emphasizes the importance of using ultrafast optics. Device performance will be optimized through materials selection, creating and characterizing interfaces amenable to spin transfer, and investigating relevant length scales.Broader Impacts: The experimental realization of magnonic spin torque devices whose quantum yield is improved by nearly two orders of magnitude beyond the present state-of-the-art will have transformative impact by essentially creating a new class of spin torque devices. Spin-transfer torque devices in general would benefit from replacing the high current densities now necessary for operation, as this causes appreciable heating, and vortex nucleation in the free layer via the unavoidable Oersted field. Magnonic spin torque would address these issues, allowing significant improvements in device performance, fabrication requirements, and reliability. This program will integrate teaching and training of students by unifying techniques and ideas from physics, electrical engineering, and materials and optical sciences, thereby empowering them with the multidisciplinary talents necessary to become the next generation of leaders in academia and industry. An international collaboration will underscore the importance of global collaborations for modern research. The PIs will continue to build upon their established records of broadening the participation of underrepresented groups through a variety of means, including: mentoring students from USF?s Florida-Georgia Louis Stokes Alliance for Minority Participation Bridge to the Doctorate Program; educating the community about the disproportionate filtering of underrepresented groups by certain admissions policies; organizing summer camps for minority-serving middle schools in collaboration with the Florida Advanced Technological Education Center (FLATE), a NSF-ATE Regional Technological Education Center of Excellence. In collaboration with FLATE and the Hillsborough County School District, additional effort will help develop a science, technology, engineering, and math proficient workforce through training workshops for teachers.