Spin information propagation in metallic and insulating ferromagnet based devices

自1988年巨磁电阻效应被发现以来，自旋电子学在理论和实验方面都取得了巨大的进展。特别是，与自旋积累和自旋流的产生和检测有关的许多新的物理概念已经被提出和证实。随后，一系列看似合理的基于自旋的器件被提出。然而，除了基于自旋阀和磁隧道结的硬盘驱动器和随机存取存储器的巨大成功外，其他提出的自旋设备甚至没有丝毫的前景。从目前的理论和模拟的角度来看，无法将自旋霍尔电导、自旋泵浦和自旋电动势等新的自旋现象转移到有希望的器件应用中，是因为这些现象所固有的信号太小，并且在实际器件制造中太困难。智能优点：本提议旨在通过研究各种外部可控条件下的非平衡自旋波传播来促进自旋电子场的发展。在传统的描述磁化动力学的方法中，磁化矢量是在有电流和磁场的情况下用广义Landau-Lifshitz-Gilbert方程来处理的。这里提出的新概念和方程涉及传导电子和磁化的量子性质：电子和磁化的激发是服从非平衡量子分布方程的量子物体。具体地说，传导电子和自旋波都能够在磁性介质中传播自旋信息，尽管它们满足不同的量子统计。广义自旋流，包括电子的自旋流和自旋波的自旋流，将在各种材料和器件中被研究。中心目标是在经典磁化传播之外的量子自旋传播的基础上寻找可能的自旋装置。更广泛的影响：自旋电子学的研究从根本上提高了我们在经典磁化和量子电子传输之间的边界的知识。提出的研究将把传统的经典磁化模型带到一个全新的领域。自旋波的量子非平衡分布可以产生前所未有的有趣现象。可能的器件概念和拟议的原型器件结构风险很高，但有可能在基于自旋的高级器件方面取得潜在突破。该提案的教育部分包括研究生积极参与研究、培训，并为研究生和本科生访问工业研究实验室，以及让PI开发与该研究项目相关的自旋电子学课程和教科书。

Since the discovery of the giant magnetoresistive effect in 1988, tremendous advances in spintronics theory and experiment have been made. In particular, numerous novel physics concepts related to the generation and detection of spin accumulation and spin current have been proposed and confirmed. A wide range of plausible spin-based devices have subsequently been proposed. However, aside from the colossal success of hard disk drives and random access memories which are based on spin valves and magnetic tunnel junctions, other proposed spin devices have not been even remotely promising. From the view point of current theory and simulation, the inability to transfer new spin phenomena such as spin Hall conductance, spin pumping and spin electromotive force to promising device application is attributed to too small signals inherent in these phenomena and too difficulty in practical device fabrication.Intellectual merit:The present proposal aims to advance the spintronics field by investigating non-equilibrium spin-wave propagation in various externally controllable conditions. In the traditional approach of describing magnetization dynamics, the magnetization vector has been treated classically via generalized Landau-Lifshitz-Gilbert equations in the presence of the current and the magnetic field. The new concepts and equations proposed here involve quantum nature of the conduction electrons and magnetization: the excitations of electrons and of magnetization are quantum objects which obey the equation of the non-equilibrium quantum distributions. Specifically, both conduction electrons and spin waves enable to propagate spin information in magnetic media although they satisfy different quantum statistics. The generalized spin current, including the spin current of electrons and of spin waves, will be investigated in various materials and devices. The central goal is to find possible spin devices based on the quantum spin propagation beyond classical magnetization propagation.Broader impact: The spintronics research has fundamentally advanced our knowledge at the boundary between classical magnetization and quantum electron transport. The proposed research would take the traditional classical modeling for the magnetization to a fundamentally new region. The quantum non-equilibrium distribution for spin waves can generate unprecedented interesting phenomena. The possible device concepts and proposed prototype device structures are high risks but a potential breakthrough in superior spin-based devices is a possibility. The educational components of the proposal include strong graduate student participation in research, training, and visiting industrial research laboratories for the graduate and undergraduate students, as well as for PI to develop a spintronics course and textbook related to this research project.