Phase conjugation of magnetostatic waves by a local longitudinal pump in yttrium iron garnet films is observed experimentally. Theoretical expressions are obtained which describe the experimental curves well.

Parametric interaction of a dipolar spin wave pulse with electromagnetic field of a localized nonstationary (pulsed) pumping is studied experimentally and theoretically in yttrium-iron garnet (YIG) films. This interaction leads to the effective amplification of the incident BVMSW pulse, and also to the formation of a phase-conjugated and amplified pulse propagating in the reverse direction. Numerical calculation of amplification and conjugation coefficients are in good quantitative agreement with experiment.

A solution is obtained for the general problem of the nonstationary interaction of backward volume magnetostatic waves in films of yttrium-iron garnet with local parametric pumping. In the case of a large pump region, l ≫ λ , where λ is the wavelength of the backward volume magnetostatic waves, the problem reduces to a system of truncated equations for two packets of counter propagating waves. In the opposite case, l < λ , the exact problem of parametric interactions of the eigenmodes of a ferrite film (both counterpropagating and in the same direction) is solved numerically. Both cases are studied experimentally and good qualitative and quantitative agreement is obtained with the theory. For the first time, the reversal of a wave front and the time reversal of the shape of backward volume magnetostatic wave pulses are observed and a change in the propagation time for the peak of the signal pulse and a reduction in its width owing to pumping are recorded. Two operating regimes are identified for a nonstationary parametric backward volume magnetostatic wave amplifier with local pumping, which differ in the ratio of the duration of the pump pulse to the transit time for the wave through the local pump region, and the effect of the parametric excitation of two-dimensional spin waves on the interaction of backward volume magnetostatic waves with a local nonstationary parametric pump is determined.

Envelope solitons propagating in a weakly dissipative medium broaden, and their amplitudes decrease twice as fast as the amplitude of a sinusoidal signal. In optics, these effects are compensated by erbium-doped fiber amplifiers inserted in a communication line.1 In our present paper, we report the observation of a parametric amplification of spin wave envelope solitons propagating in yttrium–iron–garnet (YIG) films. We used a conventional delay-line structure2 consisting of an input and output transducers (width 50 μm) separated by l=8 mm, and a third transducer placed in the middle. A tangentially magnetized (He=910 Oe) YIG film (thickness 6.4 μm, 2ΔH=0.5 Oe) was placed in the delay-line structure. Rectangular pulses of backward volume magnetostatic waves (duration T=30–40 ns, carrier frequency f=4.65 GHz) were launched at the input transducer. Parameters of the input pulses were chosen to guarantee a single-soliton regime of pulse propagation.2 To create an active region under the middle transducer, a microwave pumping of the frequency 2f=9.3 GHz and power 0.3–10 W was supplied to that transducer τ μs earlier than the input pulse was launched. We measured the gain coefficient for the propagating soliton (defined as the ratio of peak powers of the output pulses with and without pumping) as a function of the pumping power. The results are presented in Fig. 1 for τ=0.25 μs and τ=3.00 μs. When the time interval τ was smaller than the characteristic time of development of parametric instability of pumping field τp=2π/γΔH=1.43 μs, the propagating soliton was amplified (G>0). When τ>τp, the propagating soliton was attenuated (G<0) due to its interaction with parametric waves of the frequency f resulting from the parametric decay of the pumping field. We believe that by using a dielectric resonator instead of the middle transducer we will get considerably higher values of gain G for spin wave solitons in YIG films.

In the 3 cm band dependences of the epitaxial HTS film surface resistance on the magnitude of ac and dc magnetic fields have been measured. YBa2Cu3O7-delta films on sapphire were investigated. It was established that alternating magnetic field produces a stronger impact on the surface resistance than de field. To explain experimental results the assumption is made that a HTS film is not an ideal superconductor and consists of series-connected sections of various types: sections of an ideal superconductor, sections of low and large resistance intragranular Josephson junctions, shunted by the ideal superconductor, and finally, sections of intergranular Josephson functions few for epitaxial films. In these conditions the dependences of the surface resistance on de magnetic field are caused by Abrikosov's vortices moving in ideal superconductive sections, and dependences on the amplitude of ac magnetic field are caused by switching of large resistance junctions to a low resistance state.