Spin torque devices driven by tailored spin currents

自旋电子学通过为存储、处理和传输信息提供高能效的磁性设备，有可能彻底改变信息技术。许多现有的和提出的器件依赖于自旋力矩来控制磁化动力学和操纵纳米级器件的磁态。突出的例子是磁开关和自旋转矩振荡器。自旋力矩振荡器可用于产生局部微波场，以辅助硬盘中的磁写入。此外，它们可以通过向磁波导发射自旋波来传输信息。这种振荡器表现出丰富的非线性现象，使它们在新兴的神经形态计算范式中成为特别有吸引力的器件候选者。自旋力矩装置设计和实现的核心前提是高效地产生定制自旋力矩。自旋力矩是由注入磁性器件元件的自旋电流施加的。目前，下一代器件发展的主要瓶颈是纯自旋电流极化方向的限制和欧姆加热。拟议的研究解决了这些挑战，旨在推进现有的和激发新的设备概念。目标是克服纯自旋电流的极化限制，并利用热效应来产生可定制的自旋扭矩。在这项研究的过程中，研究生和本科生将接受设备制造，材料表征和磁谱学的最先进实验技能的培训。该提案包含一个面向当地学校教师的外联部分，这些教师将接受电磁学和自旋电子学概念方面的培训。此外，还将为当地的科学和艺术活动制定一个外展计划，并向学生展示。该方法利用金属铁磁体中的自旋轨道力矩（如反常霍尔效应和平面霍尔效应），进一步研究了双铁磁体耦合系统中通过自旋塞贝克效应的热自旋注入。计划由绝缘铁磁体和金属铁磁体组成的双层结构制造纳米线器件，其中金属铁磁体用作自旋注入器。利用铁磁共振测量来评估这些耦合自旋系统的自旋动力学，并研究自旋轨道效应和热效应引起的自旋力矩。此外，垂直和倾斜自旋极化的自旋注入器将被设计并应用于新的自旋电子应用，如垂直自旋扭矩振荡器、自旋超流体输送机和反铁磁平面开关。该研究将产生自旋电荷和自旋热换能器的工程概念，并刺激新型磁电子器件的发展。此外，它将为进一步发展自旋轨道电子学和自旋热电子学领域的基本概念提供有激励意义的实验数据。在拟议的研究过程中开发的设备将用于概念验证和原型目的。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。

Spin electronics has the potential to revolutionize information technologies by providing energy-efficient magnetic devices for storage, processing, and transmission of information. Many of the existing and proposed devices rely on spin torques which are used to control magnetization dynamics and to manipulate magnetic states of nanoscale devices. The prominent examples are magnetic switching and spin torque oscillators. Spin torque oscillators can be used to create local microwave fields assisting the magnetic writing in hard drives. Furthermore, they can transmit information by emitting spin waves into a magnonic waveguide. Such oscillators exhibit a rich palette of nonlinear phenomena that makes them particularly attractive device candidates within the emerging paradigm of neuromorphic computing. The central prerequisite for the design and realization of spin torque devices is the energy-efficient generation of customized spin torques. Spin torques are exerted by spin currents injected into a magnetic device element. Currently, the major bottlenecks for the development of next generation devices are limitations to the polarization direction of pure spin currents and ohmic heating. The proposed research addresses these challenges, aiming to advance existing and to spark novel device concepts. The objective is to overcome the polarization constraints for pure spin currents and to utilize thermal effects for the generation of customizable spin torques. In the course of this research, graduate and undergraduate students will be trained in state-of-the-art experimental skills of device fabrications, material characterization, and magnetic spectroscopy. The proposal contains an outreach component that targets local school teachers who will receive training in electromagnetism and spintronics concepts. Moreover, an outreach program for a local science and arts event will be developed and presented to the students.The proposed approach utilizes spin-orbit torques in metallic ferromagnets (such as anomalous Hall effect and planar Hall effect) and furthermore investigates thermal spin injection via spin Seebeck effect in coupled two-ferromagnet systems. It is planned to fabricate nanowire devices from bilayers consisting of an insulating ferrimagnet and a metallic ferromagnet, where the latter serves as spin injector. Spin torque ferromagnetic resonance measurements will be carried out to assess spin dynamics in these coupled spin systems and to investigate the spin torques due to the spin-orbit and thermal effects. Furthermore, spin injectors with perpendicular and oblique spin polarizations will be engineered and implemented in novel spin-electronic applications, such as perpendicular spin torque oscillators, spin superfluid conveyors, and antiferromagnetic planar switches. The research will result in engineering concepts for spin-charge and spin-heat transducers and stimulate the development of novel magneto-electronic devices. It will, furthermore, provide incentive experimental data for further development of fundamental concepts in the areas of spin-orbitronics and spin-caloritronics. The devices developed in the course of the proposed research will serve the proof-of-concept and prototypical purposes.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.