Domain-wall vibrations

We report on a study of wall resonances of lattices of bubbles and parallel stripes in garnet films. An analytic theory applying to the main mode of any periodic domain lattice shows how long-range dipole-dipole interactions give rise to a finite isotropic slope of the frequency relation ν(k) at k=0. Quantitative support for two theories of ν(k) for a stripe lattice is provided by measurements of standing waves which are trapped between a pair of cracks in the film. Our results imply that wall vibrations in our garnet film specimen could transmit a broad wave packet with small spreading at a signal velocity of about 400 m/s. Extension of a flexed-mode theory takes simple account of the velocity limit due to incipient Bloch-line nucleation to predict an upper frequency-dependent limit on the amplitude of linear response. This limit is consistent with measured clipping of bubble-lattice response at low frequencies, which supports a predicted antiresonance. At higher frequencies, the experimental amplitude is limited to values consistent with the deLeeuw-Walker local saturation mechanism.