All-Optical Magnonic Spin Torque Devices

智力优势：本提案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振子。据预测，这种热驱动的自旋扭矩可以导致量子成品率的提高，比目前最先进的电流驱动自旋扭矩装置高出近两个数量级。在其他条件不变的情况下，提高可用自旋扭矩将对自旋扭矩器件技术产生重大影响。鉴于其巨大的潜力，磁振子自旋扭矩器件将采用薄膜沉积和纳米光刻技术的结合来制造。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：超快泵浦探针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。这些装置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。飞秒激光脉冲将在磁性氧化层（如尖晶石铁磁体）中产生磁振子。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）湮灭，但它们的自旋动量将被转移到正常金属中的传导电子。因此，自旋极化电子的时间依赖性积累将在正常金属中产生。这种自旋积累的时间导数在金属铁磁体上产生扭矩，这强调了使用超快光学的重要性。器件性能将通过材料选择、创建和表征适合自旋转移的界面以及研究相关的长度尺度来优化。更广泛的影响：磁振子自旋扭矩器件的实验实现，其量子产率比目前的最先进技术提高了近两个数量级，将产生变革性的影响，从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目前运行所需的高电流密度，因为这会引起明显的加热，并通过不可避免的奥斯特场在自由层中形成涡核。磁振子自旋扭矩将解决这些问题，从而显著提高器件性能、制造要求和可靠性。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，将学生的教学和培训结合起来，从而使他们具备成为学术界和工业界下一代领导者所必需的多学科人才。国际合作将强调全球合作对现代研究的重要性。ppi将继续通过各种方式扩大代表性不足群体的参与，包括：指导南加州大学的学生？佛罗里达-乔治亚州路易斯·斯托克斯少数族裔参与联盟通往博士项目的桥梁；教育社区了解某些招生政策对代表性不足的群体的不成比例的过滤；与佛罗里达先进技术教育中心（FLATE）合作，为少数民族服务的中学组织夏令营，FLATE是NSF-ATE的区域卓越技术教育中心。通过与FLATE和希尔斯伯勒县学区的合作，还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.