Boris A. Kalinikos

St.Petersburg Electrotechnical University, 197342, St.Petersburg, Russia

Investigations of spin wave (SW) envelope solitons in ferromagnetic films are of great interest for both fundamental and applied fields. During the last decade the processes of formation, propagation, collision, and amplification of microwave SW envelope solitons have been experimentally studied in yttrium iron garnet (YIG) films (see e.g. [1] and literature therein). Recent advances in SW envelope soliton excitation include the self-generation of both bright and dark SW envelope solitons in the absence of external microwave pulses [2-5]. The purpose of this paper is to review the investigations on spin wave soliton self-generation in ferromagnetic films with an emphasis on experimental work and applications. "Active rings" have been suggested to carry out experiments on SW soliton generation [2]. An "active ring" consists of a ferrite film delay line and a microwave amplifier connected in a re-circulation feedback loop. The function of the amplifier was to boost the microwave signal circulating in the ring. Its operating parameters were chosen in such a way that the dispersive and nonlinear properties of the active ring were determined solely by the ferrite film. To generate bright envelope solitons backward volume spin waves with positive dispersion coefficient D>0 and negative nonlinear response coefficient N<0 were used. To generate dark envelope solitons surface spin waves with negative dispersion coefficient D<0 and negative nonlinear coefficient N<0 were used. Spin wave soliton pulse self-generation was achieved slightly above the generation threshold, defined as the point in which the ring just break into harmonic oscillation. As was described in papers [2-5], the main features of active rings that made SW soliton self-generation possible, were: (i) the essentially discrete spectrum of spin wave eigen-modes and their resonant character, (ii) the nonlinear interaction between the eigen-modes which resulted in modulation instability, (iii) the possibility to change the number of the resonant modes involved in the modulation instability process. It has been demonstrated that two different operating regimes for soliton self-generation, synchronised time gating [2,3] and frequency filtering [4,5], were possible. The soliton character of the waveforms observed in experiments [2-5] was confirmed by measuring the corresponding power frequency spectra and phase-time profiles. In conclusion, we believe that the demonstrated active ring techniques are quite general and could be extended to generate soliton pulse sequences of various widths, frequencies, and peak powers by utilising different nonlinear dispersive systems.

Prof. N.G. Kovshikov, Prof. C.E. Patton, and Mr. M.M. Scott are gratefully acknowledged for cooperation in the investigations reported. This work was supported in part by the NATO Linkage Grant Program, Grant HTECH.LG 970538 and Russian Foundation for Basic Research, Grant 99-02-1630.

[1] C.E. Patton, P. Kabos, H. Xia, et al., J. Magn. Soc. Japan 23, 605 (1999).

[2] B.A. Kalinikos, N.G. Kovshikov, and C.E. Patton, Phys. Rev. Lett. 80, 4301 (1998).

[3] B.A. Kalinikos, N.G. Kovshikov, and C.E. Patton, JETP Lett. 68, 229 (1998).

[4] B.A. Kalinikos, M.M. Scott, and C.E. Patton, Phys. Rev. Lett. 84, 4697 (2000).

[5] M.M. Scott, B.A. Kalinikos, and C.E. Patton, Appl. Phys. Lett.78, 970 (2001).