All-Optical Magnonic Spin Torque Devices

智力优点：本计画的研究目标是设计一系列的自旋转移装置，其力矩来源于热产生的磁振子。据预测，这种热驱动的自旋扭矩可以导致量子产率的提高，比目前最先进的电流驱动自旋扭矩器件大近两个数量级。在其他条件不变的情况下增加可用的自旋扭矩将对自旋扭矩器件技术产生重大影响。鉴于巨大的潜力，磁振子自旋力矩器件将使用薄膜沉积和纳米光刻技术相结合。器件结构将包括磁性氧化物-正常金属-金属铁磁体自旋阀。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振子，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振子转移到自由铁磁层的磁化。磁振子将在磁性氧化物层中产生（例如，尖晶石铁磁体）。这些磁振子将在氧化物-正常金属界面（可能包含额外的磁性原子层）处湮灭，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自旋极化电子的时间依赖性积累。这种自旋积累的时间导数导致金属铁磁体上的扭矩，这强调了使用超快光学的重要性。器件性能将通过材料的选择，创建和表征接口服从自旋转移，并调查相关的长度scales.Broader影响：磁子自旋力矩器件的量子产率提高了近两个数量级的实验实现超出了目前的最先进的将有变革性的影响，基本上创建一个新的一类自旋力矩器件。自旋转移扭矩装置通常将受益于替换现在操作所需的高电流密度，因为这会引起明显的加热，并且通过不可避免的奥斯特场在自由层中形成涡旋成核。磁自旋矩将解决这些问题，允许在器件性能，制造要求和可靠性的显着改善。该计划将通过统一物理，电气工程，材料和光学科学的技术和思想来整合学生的教学和培训，从而使他们能够成为学术界和工业界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。PI将继续建立在他们的既定记录，扩大通过各种手段，包括参与代表性不足的群体：指导学生从USF？的佛罗里达州-佐治亚州路易斯斯托克斯少数民族参与联盟桥梁博士学位课程;教育社会对某些招生政策的不成比例的过滤代表性不足的群体;组织夏令营为少数民族服务的中学与佛罗里达先进技术教育中心（FLATE），卓越的NSF-ATE区域技术教育中心合作。在与FLATE和希尔斯伯勒县学区的合作中，额外的努力将有助于通过教师培训讲习班培养一支精通科学、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.