From Solitons to Precessional Dynamics and Chaos - Nonlinear Spin Waves in Thin Films

本项目研究磁性薄膜对微波辐射的响应。微波可以在薄膜中产生新的响应，如磁包络(MME)孤子。该薄膜为研究高频非线性动力学和包络孤子的基本性质提供了一个强大而通用的“试验台”。这些结果与微波非线性波在磁性薄膜中的传播以及这些效应在微波和毫米波薄膜信号处理中的衍生应用有关。此外，多层膜中与磁通反转和自旋注入相关的动态非线性磁化过程也引起了人们的极大兴趣。新的计划将集中在：(1)直接测量与MME孤子相关或由MME孤子产生的自旋波；(2)使用新的时间和空间分辨探测技术来测量由纳秒或亚纳秒时间尺度上的这些脉冲组成的时空和波矢量；以及(3)与调制不稳定性和混沌、自由进动和自旋注入产生的自旋波有关的非线性磁化动力学。与该项目相关的研究生和博士后使用尖端的研究工具，接受技术磁性方面的出色培训。该项目研究磁性薄膜中相关磁偶极子(类似于微型指南针)的特性。在磁场中，偶极子旋转，或进动，很像自转的顶部由于引力场的进动。当进动角较大时，这将导致所谓的非线性效应。这种进动偶极子的链可以用来形成孤子形式的非线性脉冲。这种孤子脉冲非常健壮，可以在不扩散的情况下传播。进动还会导致薄膜整体磁矩方向的切换。孤子和开关都可以导致其他非线性效应，如产生新的脉冲和不同频率的进动自旋的附加波。这项工作的独特之处在于使用特殊的探测器来绘制纳秒时间尺度和亚毫米距离尺度上的进动动力学图。所得结果将有助于对非线性动力学的一般理解，并在微波信号处理和磁信息存储中有广泛的应用。与该项目相关的研究生和博士后使用尖端的研究工具，接受技术磁性方面的出色培训。他们做好了在学术界、工业界或政府工作的充分准备。

This project deals with response of thin magnetic films to microwave radiation. Microwaves can produce novel responses in the films, such as magnetic envelope (MME) solitons. The thin films provide a powerful and versatile "test bed" for the study of high frequency nonlinear dynamics and the fundamental properties of the envelope solitons. The results are relevant to microwave nonlinear wave propagation in magnetic films and spin-off applications of these effects in microwave and millimeter wave thin film signal processing. In addition, there is substantial interest in dynamical nonlinear magnetization processes associated with flux reversal and spin injection in multi-layer films. The new program will focus on: (1) direct measurement of the spin waves associated with or generated by MME solitons; (2) the use of new time and space resolved probe techniques to measure the spatio temporal and wave vector make up of these pulses on a nanosecond or subnanosecond time scale; and (3) the nonlinear magnetization dynamics associated with modulational instability and chaos, free precession, and spin wave generation by spin injection. Graduate students and post-docs associated with the project receive excellent training in technical magnetism, using cutting-edge research tools. They are well equipped for careers in academe, industry or government.%%%This project studies the properties of correlated magnetic dipoles (similar to tiny compass needles) in magnetic thin films. In magnetic field, the dipoles rotate, or precess, much like the precession of a spinning top due to gravitational field. This leads to so-called nonlinear effects when the precession angle is large. Chains of such precessing dipoles can be used to form nonlinear pulses in the form of solitons. Such soliton pulses are very robust and can propagate without spreading. The precession can also lead to a switching in the direction of the overall magnetic moment of a film. Both solitons and switching can lead to other nonlinear effects such as the generation of new pulses and additional waves of precessing spins at different frequencies. The unique feature of the work is in the use of special probes to map the precession dynamics on a nanosecond time scale and a sub-millimeter distance scale. The results will be useful for the understanding of nonlinear dynamics in general, with long range applications in microwave signal processing and magnetic information storage. Graduate students and post-docs associated with the project receive excellent training in technical magnetism, using cutting-edge research tools. They are well equipped for careers in academe, industry or government.