Ideal memristor based on the spin liquid state in magnetic heterostructures

用数字表示信息和布尔逻辑的计算机使科学和技术发生了革命性的变化。然而，由于它们无法适应和处理大量不准确的信息，它们仍然远远不如人脑。这些能力可以通过神经形态计算来实现，通过使用忆阻器-其电阻取决于其电气历史的电子设备-可以在硬件水平上有效地实现。现有的忆阻器大多像开/关开关一样工作，缺乏响应神经形态应用所需的电刺激而连续改变电阻的能力。这些设备通常依赖原子的物理运动，因此缺乏耐用性和重复性。该项目将基于铁磁/反铁磁双层膜的特殊磁性开发一类新的忆阻器。所提出的器件的工作将依赖于铁磁和反铁磁体之间的界面处的磁阻，这是由于两种材料的不相容的磁有序导致的，这将导致在反铁磁体中形成粘性自旋液体状态。该项目将探索最合适的材料和几何结构、使设备能够运行的电子机制，以及纳米级的设备功能。拟议的研究将通过开发一个全面的本科生材料和工程物理课程，将与STEM教育相结合，其中将包括一个动手的新生研讨会和一个面向本科生的最先进的研究培训课程。该计划还计划在当地小学组织一个科学俱乐部。理论上设想的理想忆阻器是一种电子设备，其电阻与通过它的总电荷成正比，比例系数被称为记忆力。该项目将利用双层低各向异性铁磁体(如坡莫合金)和反铁磁体薄膜(如NiO、CoO或Fe50Mn50)，在实验上实现理想的忆阻器纳米器件。由于与磁界面处的随机交换相互作用相关的磁受挫，预计在反铁磁体中将形成自旋液体状态。拟议的项目将结合材料和异质结构工程、纳米制造、时域磁动力学和横向交流磁化率的测量，来解决与器件操作的物理机制和器件设计相关的问题。这项拟议的研究将探索设计受挫的薄膜磁性异质结构的可能性，这种异质结构具有定义良好且可调的自旋液体状态，从而产生理想的记忆功能和可控的记忆功能。此外，该项目将确定和表征磁电子机制，这些机制可以促进基于粘性自旋液体的记忆器件的写入、读取和重置。将建立记忆特性的相关长度标尺，以确定所提议的设备是否可扩展到技术上相关的纳米尺度。通过解决这些问题，拟议的项目将为记忆器件的研究和开发提供革命性的贡献，该器件具有高耐用性、可扩展性和可调的记忆特性，将促进高效神经形态网络的实施。该奖项反映了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。

Computers operating with digital representation of information and Boolean logic have revolutionized science and technology. However, they remain far inferior to human brain due to their inability to adapt and to process massive amounts of imprecise information. These capabilities can be accomplished with neuromorphic computing, which can be efficiently implemented at the hardware level by utilizing memristors - electronic devices whose resistance depends on their electrical history. The existing memristors operate mostly like on/off switches, lacking the ability to continuously vary the resistance in response to electric stimuli required for neuromorphic applications. These devices commonly rely on the physical motion of atoms, and as a result lack durability and reproducibility. The proposed project will develop a new class of memristors based on the special magnetic properties of ferromagnet/antiferromagnet bilayers. The operation of the proposed devices will rely on the magnetic frustration at the interfaces between ferromagnets and antiferromagnets, resulting from the incompatible magnetic ordering of the two materials, which will lead to the formation of a viscous spin liquid state in the antiferromagnets. The project will explore the most suitable materials and geometries, electronic mechanisms enabling device operation, and device functionality at nanoscale. The proposed research will be integrated with STEM education through the development of a comprehensive undergraduate Materials and Engineering Physics program, which will include a hands-on freshman seminar and a state-of-art research training course for undergraduate students. The plan is also to organize a Science club at the local elementary school.A theoretically envisioned ideal memristor is an electronic device whose resistance is proportional to the total charge that passes through it, with the coefficient of proportionality known as memristance. The proposed project will experimentally realize ideal memristor nanodevices, by utilizing bilayers of low-anisotropy ferromagnets, such as Permalloy, and thin films of antiferromagnets such as NiO, CoO, or Fe50Mn50. A spin liquid state is expected to be formed in the antiferromagnets, due to the magnetic frustration associated with the random exchange interaction at the magnetic interface. The proposed project will utilize a combination of material and heterostructure engineering, nanofabrication, measurements of time-domain magnetic dynamics and transverse ac susceptibility, to address questions related to physical mechanisms of device operation, and device design. The proposed research will explore the possibility to engineer frustrated thin-film magnetic heterostructures that exhibit a spin liquid state with a well-defined and tunable viscosity, resulting in ideal memristive functionality with controlled memristance. Additionally, the project will identify and characterize the magnetoelectronic mechanisms that can facilitate writing, reading, and resetting of the memristive devices based on viscous spin liquids. The relevant length scales for the memristive properties will be established, to determine whether the proposed devices are scalable to the technologically relevant nanoscale dimensions. By addressing these questions, the proposed project will provide a transformative contribution to the research and development of memristive devices characterized by high-endurance, scalability, and tunable memristive properties, which will facilitate the implementation of efficient neuromorphic networks.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.