Parametric generation of soliton-like spin wave pulses in ferromagnetic thin-film ring resonators
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AL, NONLINEAR, AND SOFT MATTER PHYSICS
Parametric Generation of Soliton-like Spin Wave Pulses in Ferromagnetic Thin-Film Ring Resonators A. A. Sergaa, M. P. Kostylevb, B. A. Kalinikosb, *, S. O. Demokritovc, B. Hillebrandsa, and H. Bennerd a
Physics Department, Kaiserslautern University of Technology, Kaiserslautern, D-67663 Germany b St. Petersburg State Electrotechnical University, St. Petersburg, 197376 Russia c University of Muenster, D-48149 Muenster, Germany d Darmstadt University of Technology, Darmstadt, D-64289 Germany *e-mail: [email protected], [email protected] Received August 22, 2005
Abstract—Intense soliton-like spin wave pulses were parametrically generated in ferromagnetic thin-film ring resonators under the action of periodic parallel magnetic pulse pumping. Various types of nonlinear pulse sequences were observed depending on the pump pulse repetition period and the position of the pulse carrier frequency with respect to the ring resonator frequency spectrum. A theoretical model is suggested and calculations are performed that give a detailed explanation of the observed phenomena. PACS numbers: 75.30.Ds, 75.70.–i, 85.70.Ge DOI: 10.1134/S1063776106030125
1. INTRODUCTION The excitation and propagation of envelope solitons of two types, bright and dark, is possible in nonlinear dispersive media (e.g., see [1, 2]). Comparatively recently, “active rings” manufactured from nonlinear dispersive waveguiding media have been suggested for the self-generation of envelope solitons. For instance, ferromagnetic thin-film rings have been used for selfgeneration of both bright and dark spin microwave solitons [3–6]. In such rings, an “external” microwave amplifier connected in series with a ferromagnetic film is used to compensate for spin wave and other losses. The ring, which is actually a ring resonator, may operate under ring compensation conditions in a multifrequency self-generation mode with a discrete spectrum of excited frequencies. Active rings are used to effect two different mechanisms of self-generation of spin wave solitons. These mechanisms are based on the time [3] and frequency [4–6] filtering of circulating signals. For time filtering [3], the ring is periodically closed and opened and the commutation period is set equal to the round-trip time of one soliton in the ring. The circulating signal, which is initially a noise signal within “time transparency windows,” then first narrows spectrally because of the “revival” of only those its frequency components that satisfy the phase relations of the resonant ring and are within the ring amplification band. Next, the spectrum becomes “cut” because of dispersion. In other words, part of the spectral constituents of the wave packet are ahead of the instant of the next ring closure because of dispersion. Conversely, the
other spectral constituents arrive into the feedback circuit after ring opening. This is what ensures time filtering. After the attainment of the four-wave nonlinear interaction threshold, the packet acquires stati
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