Two-Dimensional Magnets in Spintronic Devices: Roles of Spin Fluctuations

在磁性材料中，存在一种叫做磁振子的有趣的准粒子。就像电子的自旋一样，磁振子具有角动量但不带电荷。与通过焦耳加热产生能量损失的电子电流不同，磁振子的流动，称为磁振子电流，提供了显着更高的能量效率。本项目对基于二维磁性材料的磁振子器件进行了全面的理论研究。主要目的是阐明在现实的二维结构中产生、传播和检测磁振子电流的机制。具体来说，该项目致力于确定能够产生与传统电子自旋电流相当甚至超过传统电子自旋电流的磁振子电流的材料参数。从这项研究中获得的见解为开发以大幅降低功耗为特征的磁振子电流驱动器件带来了希望。此外，该提案的教育成分是广泛的，旨在积极地让学生参与动手研究，提供培训机会，促进参观工业实验室，并加强自旋电子学课程。利用首席研究员二十多年来在自旋电子学教学方面的丰富经验，该项目旨在通过让学生沉浸在前沿研究工作中来丰富教育景观。与三维系统不同，二维材料表现出显著的量子涨落，严重影响平衡和非平衡磁特性。现有的半经典模型忽略了这些量子涨落，往往不能适用于二维系统。目前的项目旨在为基于二维材料的自旋电子器件创建新颖的建模工具。目的是评估自旋波动对自旋输运性质的影响，使用实验观察到的材料作为基准。具体的重点是放在一个整体的理论方法解决磁振子电导，自旋泵，磁振子阻力和自旋电荷转换在二维异质结构的设置。冒险进入这些材料的颗粒自旋模型，提出的理论模型是为了阐明自旋波动在成型自旋电子器件中的内在作用。此外，目标扩展到利用这些创新的理论模型来仔细分析实验结果，并预测新的自旋电子现象的出现，这些现象是明显的量子自旋涨落所固有的。该研究将阐明二维和三维器件对自旋电流和外部磁场响应的区别。彻底掌握热和量子涨落影响——从磁性拓扑状态、自旋霍尔和自旋电流，到自旋力矩和磁化反转——可以催化在二维磁性材料上的自旋电子器件的进步，并为低维物理提供实质性的见解。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。

In magnetic materials, intriguing quasi-particles called magnons exist. Much like the spin of an electron, magnons possess angular momentum but lack electric charge. Unlike electron currents, which incur energy losses through Joule heating, the flow of magnons, known as magnon current, offers significantly higher energy efficiency. This project undertakes a comprehensive theoretical investigation of magnon devices built upon two-dimensional (2D) magnetic materials. The primary objective is to elucidate the mechanisms underlying the generation, propagation, and detection of magnon currents within realistic 2D structures. Specifically, the project endeavors to identify material parameters capable of engendering a magnon current comparable to, or even surpassing, conventional electron spin currents. The insights gleaned from this research hold promise for the development of magnon current-driven devices characterized by substantially reduced power consumption. Additionally, the educational component of this proposal is extensive, aiming to actively involve students in hands-on research, provide training opportunities, facilitate visits to industry labs, and enhance the spintronics course curriculum. Leveraging the Principal Investigator's extensive experience spanning over two decades in teaching spintronics, this project seeks to enrich the educational landscape by immersing students in cutting-edge research endeavors.Distinctly from three-dimensional systems, two-dimensional materials demonstrate significant quantum fluctuations, critically influencing both equilibrium and non-equilibrium magnetic characteristics. Existing semiclassical models that overlook these quantum fluctuations often fall short for two-dimensional systems. The present project sets out to create novel modeling tools tailored for two-dimensional material-based spintronic devices. The objective is to assess the repercussions of spin fluctuations on spin transport properties, using experimentally observed materials as a benchmark. The specific focus is placed on a holistic theoretical approach addressing magnon conductance, spin pumping, magnon drag, and spin-charge conversion in the setting of two-dimensional heterostructures. Venturing into the granular spin models of these materials, the proposed theoretical model is to elucidate the intrinsic role of spin fluctuations in molding spintronic devices. Furthermore, the goal extends to utilizing these innovative theoretical models to meticulously analyze experimental outcomes and projecting the emergence of novel spintronic phenomena intrinsic to the pronounced quantum spin fluctuations. The research will shed light on the distinctions in two- and three-dimensional device responses to spin current and external magnetic fields. A thorough grasp of thermal and quantum fluctuation impacts – from magnetic topological states, spin Hall, and spin currents, to spin torques and magnetization reversals – can catalyze advancements in spintronic devices hinging on two-dimensional magnetic materials and provide substantial insights into low-dimensional physics.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.