Generation of Spin Wave Envelope Solitons in Magnetic Film Systems

Mingzhong Wu,¹ Boris A. Kalinikos,^1,2 and Carl E. Patton¹

¹Department of Physics, Colorado State University, Fort Collins, Colorado 80523, USA

²St. Petersburg Electrotechnical University, 197376, St. Petersburg, Russia

Solitons are localized large-amplitude waves that travel without a change in shape and survive collisions. One can excite solitons in a variety of nonlinear dispersive media such as water, plasma, optical fibers, and magnetic thin films. This presentation will review two aspects of spin wave envelope (SWE) solitons in magnetic thin film systems, (1) the generation of SWE solitons through modulational instability in magnetic films and (2) the self-generation of SWE solitons in magnetic film active feedback rings.

It is well known that the nonlinear Schrödinger equation yields solitons through modulational instability only for an attractive nonlinearity. Experimentally, one finds that modulational instability processes can produce solitons for both attractive and repulsive nonlinearity conditions. This is done by taking advantage of the dipole gaps in the spin wave spectrum of a magnetic thin film with pinned surface spins. Through a simple change in frequency from one side of the dipole gap to the other, one moves from an attractive to a repulsive nonlinearity condition and thereby obtains both bright and dark SWE solitons in one and the same configuration. This realization of solitons for a repulsive nonlinearity is not yet resolved theoretically.

If one connects the amplified output signal from a magnetic film back to the input and forms a magnetic film based active feedback ring system, one can produce circulating SWE solitons in the ring with no external input. At a threshold ring gain, a cw spin wave signal is spontaneously generated. With an increase in the gain, the cw signal breaks up into either bright or dark solitons depending on the magnetic film/field configuration. These solitons circulate in the ring with constant amplitudes. With increasing the gain further, however, the amplitude of the circulating solitons breathes in a fractal pattern.

This work was supported in part by the National Science Foundation, Grant No. DMR-0108797, the U. S. Army Research Office, Grant Nos. DAAD19-02-1-0197 and W911NF-04-1-0247, the U. S. Office of Naval Research, Grant No. N00014-03-1-0070, and the Russian Foundation for Basic Research, Grant 05-02-17714.