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

Colorado State University, Fort Collins CO

Investigators

Abstract

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.