Analysis of chaotic bright spin-wave soliton trains in magnetic films

Abstract

Abstract.We have experimentally studied a chaotic dynamics of bright spin-wave soliton trains. Thin yttrium iron garnet films having pinned surface spins were used for the experiments providing propagation of highly dispersive dipole-exchange spin waves. Chaotic soliton trains were excited in the frequency band around low-frequency part of dipole gap of spin wave spectrum. Analysis of fractal dimension, embedding dimension, and Lyapunov exponents was carried out based on measured time profiles of chaotic soliton sequences. We find that the fractal dimension and Lyapunov exponents are weak function of carrier frequency around dipole gap whereas embedding dimension is almost constant. IntroductionEnvelope solitons are formed in the nonlinear dispersive waveguiding media with pulsed excitation if the dispersion spreading of a nonlinear wave packet is compensated by the media nonlinearity. Solitons are also formed with a monochromatic wave excitation through development of the spontaneous modulation instability (SMI) [1,2].Among other media, high-quality magnetic films, such as single-crystal yttrium iron garnet (YIG) films, were proven to be excellent objects for experiments on nonlinear wave phenomena with microwave spin waves. We underline, that it was the YIG films where a formation of the stationary soliton trains from a monochromatic spin wave (SW) through development of the spontaneous modulation instability (SMI) has been discovered and studied [3][4][5].Theoretically, the soliton as a stationary solution of the nonlinear Schrodinger (NLS) equation happens to be stable. Experimentally, the soliton is also usually considered as a stable excitation which preserves its shape and speed during propagation. At the same time, using an optical modelocked laser, Bolton and Acton [6] have demonstrated in 2000 year a chaotic behavior of solitons which represented pulsations in amplitude of optical pulses circulating in the optical cavity. After that considerable amount of theoretical work was devoted to study of possible chaotic behavior of solitons in the different physical systems [7][8][9][10][11][12][13]. The concept of "dissipative solitons" [14,15] resolves the contradiction.At present, studies on chaotic wave excitations in waveguiding media and auto-oscillators are of great interest both for basic research and for their possible applications in advanced optical and microwave communication technology [16][17][18]. Recently, the chaotic behavior of solitons have been observed experimentally for spin waves propagating in magnetic films [19]. It is resulted in a new wave of interest for both theoretical and experimental studies of chaotic dynamics of solitons [20][21][22][23][24][25][26][27][28][29][30][31][32][33].

High-density spin-wave soliton train

“…One promising technique to overcome this problem is the utilization of the spin-wave soliton train. [17][18][19][20][21] As shown by pioneering research, the spin-wave envelope soliton-train enables high-intensity and high-density signal transmission on a millimeter scale yttrium-ion-garnet (YIG) device without losing the packet shape and power. 19) Based on the electric ring structure (feedback ring), the soliton train was generated by multiple excitations of spin-wave soliton.…”