Dark soiitons of magnetostatic surface waves in magnetic films have been observed for the first time. The experiments were conducted at 5.19 GHz on 7.2 /im single-crystal yttrium iron garnet films. The dark soiitons were excited by 15 ns wide **off" pulses in a high power cw microwave signal applied to the film. The characteristic soliton narrowing effect in the output pulses was observed as the input power was increased above the 0.5-1 W threshold levels. The shape of the ''dark" pulse agrees with the |tanh| functional dependence predicted from theory. Direct measurements of the carrier signal showed a phase shift of close to 180° at the center of the dark soliton, also in agreement with theory.PACS numbers: 75.30.Ds, 76.50.+g, 85.70.Ge Envelope soiitons are nonlinear wave packets which preserve their shape without dispersive spreading. In recent years, soliton excitations have been realized in many physical systems [1-3]. One well-known example is the optical-envelope soliton in optical fiibers [4,5]. Envelope soiitons for spin waves at microwave frequencies have been observed in yttrium iron garnet (YIG) thin films for various magnetic field and propagation combinations, including forward-volume wave [6,7], surface wave [8], and backward-volume wave [9] configurations.The envelope of nonlinear spin wave packets propagating in ferromagnetic thin films has been found to be best described by the nonlinear Schrodinger (NLS) equation [10,11]. It is well known that the NLS equation has two different types of solutions which correspond to bright and dark soiitons, depending on the relative signs of the dispersion coeflficient and the nonlinearity coeflficient in the equation [12,13]. Bright soliton solutions exist when the product of these two coefficients is negative, while dark soliton solutions exist when the product is positive. All of the magnetic experiments to date have been for bright soiitons, that is, for normal propagating wave packets.This Letter reports the first observation of microwave magnetic-envelope dark soiitons and the first experimental verification of the 180° phase shift in the carrier signal at the center of the pulse for any category of NLS dark soliton. The experiments were done at 5.19 GHz on in-plane magnetized single-crystal YIG films. Both the output signal envelope and the actual carrier signal output were measured. For input power levels above a certain threshold in the range of 0.5-1 W, the output signal pulses showed a narrowing which is characteristic of dark soiitons and the carrier showed at 180° phase shift over the central minimum region, also characteristic of dark soiitons. These results are in quantitative agreement with the theoretical dark soliton solutions for the NLS equation [13].The propagating spin waves were excited in the magnetic thin film by applying cw microwave power to a magnetostatic wave (MSW) delay line structure using a microstrip transducer [14]. The width of the dark pulse was controlled by chopping the cw signal with a fast microwave switch. The cw si...

Microwave-magnetic-envelope (MME) solitons generated from nonlinear magnetostatic-backwardvolume wave packets have been observed in magnetic thin films. The MME signals were excited by 5-50-ns wide microwave pulses at 5.8 6Hz in a 15-mm-long by 2.5-mm-wide, 7.2-pm-thick single-crystal yttrium iron garnet {YIG) film strip magnetized in plane and parallel to the long side of the strip. The wave packets were propagated parallel to the static field. The wave packets were launched and the propagating MME pulse signals were detected with planar microstrip transducers 4 mm apart. Envelope soliton behavior was evident from the time-resolved wave forms observed for various input power and pulse width combinations. At low power levels, one sees a relatively broad output pulse which scales with the width of the input pulse and a peak power which increases linearly with the input power. As the input power is increased above some threshold in the 0.5-1-% range, output pulses show a narrowing and steepening which is characteristic of microwave-magnetic-envelope solitons. Further increases in input power produce multiple-peak profiles, characteristic of multiple soliton generation. The experimental results are consistent with the various characteristic times for linear and nonlinear MME pulse propagation and soliton formation. However, numerical modeling based on the magnetic form of the nonlinear Schrodinger equation with initial conditions and parameters which match the experiments yields calculated profiles which show soliton effects but do not quantitatively match the experimental results.

The end edge reflection and collision of backward volume wave bright microwave magnetic envelope solitons in long and narrow yttrium iron garnet single-crystal films has been studied experimentally. The experiments were done on 5.1-m-thick, 1-mm-wide films. The bright solitons were excited by single or double 8-36-ns-wide microwave pulses with a nominal carrier frequency of 5.8 GHz. The experiments utilized a movable transducer structure to make measurements for a range of transducer separations from 2 to 15 mm and for pulses before and after reflection. The soliton character was established from single-pulse decay versus time and distance measurements. Three decay regions were observed, a slow decay region before soliton formation, a fast decay region characteristic of solitons, and a second slow decay for linear pulses. The soliton region included both incident and reflected pulses. The exponential decay rate for the soliton regime was greater than for the linear. The soliton pulses retained the same shape and speed after edge reflection. An observed drop in pulse amplitude after passing under the pickup transducer provided a way to measure the actual power and amplitude of the soliton signal. The measured amplitudes and widths were in fair agreement with predictions for a simple sech-type order one soliton pulse. For properly timed double-pulse experiments in which a reflected lead pulse collides with the follow-on pulse before detection, the effects of soliton collisions could be examined. In the single soliton power regime, the pulses were found to retain their shape and speed after collision. At higher powers, shapes were not retained. In addition, a wake effect was observed in which the lead pulse causes a change in the detected signal for the follow-on pulse, even without collision.

A new method for the analysis of microwave magnetic envelope (MME) solitons has been developed. This method is based on the determination and analysis of output microwave pulse phase profiles. Simple analytical results based on the nonlinear Schrödinger equation show that MME soliton phase profiles contain the necessary and sufficient information needed to define a particular pulse as a linear dispersive pulse or a fully formed soliton. The effects are demonstrated both theoretically and experimentally for magnetostatic backward volume wave and magnetostatic surface wave pulse signals. Theoretical phase profiles are considered for Gaussian, hyperbolic secant, and rectangular pulse shapes. Experimental profiles are obtained for rectangular input pulses. The measured phase profiles compare favorably with the numerical results. Both the data and the theory show that a constant phase profile across the pulse provides a consistent and quantitative criterion for an MME soliton.

No abstract