Observation of Spin-Wave Soliton Fractals in Magnetic Film Active Feedback Rings

The manifestation of fractals in soliton dynamics has been observed for the first time. The experiment utilized self-generated spin-wave envelope solitons in a magnetic film based active feedback ring. At high ring gain, the soliton that circulates in the ring breathes in a fractal pattern. The corresponding power frequency spectrum shows a comb structure, with each peak in the comb having its own comb, and so on, to finer and finer scales.

Figure 1

Diagram of YIG-film-based active ring system. The magnetic field is parallel to the film strip. Microstrip transducers are used for spin-wave excitation and detection. The signal from the detection transducer is fed back to the excitation transducer through an attenuator and a microwave amplifier.

Figure 2

Schematic power frequency spectra that illustrate fractal development as the ring gain $G$ is increased from zero to some $G_1$, $G_2$, and $G_3$, in sequence.

Figure 3

Power frequency spectra for the magnetic film feedback ring structure at different ring gain $G$—values, as indicated. All vertical power scales are the same. In each panel, the larger diagram shows the full instrument-limited comb spectra, and the smaller $\times 100$ expanded frequency scale diagrams show the structure of the three main peaks.

Figure 4

Sequences of power versus time traces for the YIG film active ring structure at different ring gains, as indicated. From top to bottom, the data in the gray rectangle delineated intervals are shown in $\times 20$ expanded time windows as indicated.