自旋流磁纳米器件中非平庸拓扑磁结构的稳定性和动力学研究

Memory is one of the most important components used in every computer system, storage solution and mobile devices. Unlike the charge-based memories, magnetic random access memory (MRAM) uses magnetic states to store information and has many advantages compared with charge-based memories such non-volatile, radiation hard and high speed. In addition, the low power consumption and high density advantages also will emerge if its size can scale well below 10 nm. Therefore, spin-transfer torque (STT) MRAM is well suited for many mainstream applications. In recent years, the topologically non-trivial magnetic structures, such as magnetic skyrmions, found in ultrathin magnetic heterostructures with broken inversion asymmetry not only exhibit many new chiral and topological magnetic effects, but also have the advantages of nanometer-size and very low driving current. They are considered to be promising candidates for future high-density, low-power magnetic data storage solutions. Based on our previous accumulated techniques and preliminary work on spin-polarized current generation and manipulation, nanofabrication and detection techniques of magnetic nano-devices (spin Hall devices, spin-valve, magnetic tunnel junction), as well as dynamical skyrmion in spin current auto-oscillator, in this project we will symmetrically study the dynamics and static stability of non-trivial magnetic structures through high precision electrical microwave detection of these nano-structures based spin current nano-oscillators and spin-transfer torque nano-devices (spin-valve and MTJ). We will also perform micromagnetic simulations and numerical calculation and analysis to understand exotic topological phenomena emerged in these non-trivial magnetic nano-devices, meanwhile try to find some topological quantum effects related to their particular chiralities and topologies which may help to develop new quantum devices.

存储器是计算机、移动设备和存储器件中最重要部件之一。与半导体中电荷型存储器不同，磁随机存储器是用磁畴微粒的不同磁态来存储信息，具有非易失性、抗辐射和高速等优点。如果由热涨落所限制的磁畴微粒的极限尺寸被突破，磁随机存储器的低功耗和高容量优势也将显现出来。近年来，在金属薄膜中发现稳定的非平庸拓扑磁结构不仅体现出许多新奇的磁手性和拓扑效应，而且具有纳米尺寸和极小的电流驱动等优点，使其被视为下一代磁存储器件中的最佳信息存储载体。本项目将在自旋极化和操控，拓扑自旋结构的多场调控及纳米磁器件制备和测试技术的积累和前期工作的基础上，系统地开展以非平庸磁结构为基的自旋电流和自旋转移矩纳米器件的设计和磁电特性的研究。我们将通过磁电阻效应和微波检测及微磁学模拟，以期获得此类拓扑纳米自旋结构具有哪些奇特的磁电性能、拓扑量子效应以及其稳定性的信息，进一步加速其在纳米磁存储器和磁微波器件领域的应用和发展。

基于自旋极化和操控，拓扑自旋结构的多场调控及纳米磁器件制备和测试技术，开展以非平庸磁结构为基的自旋电流和自旋转移矩纳米器件的设计和磁电特性的研究，揭示其丰富的非线性磁电效应，探索其在纳米磁存储器和磁微波器件领域的应用前景。具体对不同自旋极化材料和磁性异质结体系构建的相关纳米自旋电子器件进行了自旋轨道力矩、高频微波、磁场驱动磁矩进动和翻转的实验测量和动力学研究。研究内容包括1）器件制备的各项工艺条件对自旋纳米电子器件稳定性的影响；2）微磁模拟和COMSOL多物理模块对实验设计的器件进行数值模拟和数值估算，指导和优化器件的空间结构和材料参数选择；3）技术上完善已有的器件的设计和微加工工艺，测量装置和测量控制与数据采集系统；4）基于原型器件的实验数据，分析其非线性磁动力学行为，探讨其背后的物理机制以及潜在的应用。取得的重要研究成果有：在Pt/[Co/Ni]n垂直磁化体系纳米自旋振荡器中实现了零外磁场纯直流电流激发和调控自旋波；发现纳米自旋霍尔振荡器中的自旋波存在共存和非线性耦合导致自旋动力学混沌行为；在具有垂直磁各向异性Pt/[Co/Ni]体系中设计了一种垂直点接触的纳米自旋振荡器；基于自旋电子器件的非线性和短时记忆效应构建了物理蓄水池模型的神经形态计算网络等。最后，对“对三角”结构的纳米间隙型、“蝴蝶结”型、纳米线型、垂直纳米点接触型以及阵列等具有各类器件结构的自旋霍尔纳米振荡器所体现出来的丰富非线性动力学特性进行了详细讨论与归纳，其在新型低能耗量子磁振子自旋器件和非冯诺依曼架构的自旋型人工神经网络计算方面具有潜在应用前景。