Dynamics of bubble propagation in contiguous disk structures

The dynamic response of 1 μm diameter bubbles propagating along 5 μm period, ion-implanted contiguous disk propagation tracks, fabricated on EuTmGaIG/GdYTmGaIG composites has been investigated using stroboscopic techniques. A pulsed laser magneto-optic system was used to determine the bubble position on the track as a function of the rotating field phase, and from this data velocity variations during the field cycle were obtained. Comparison of bubble motion at 155 KHz on the so-called super, good and bad tracks, as defined in (1) reveals very irregular bubble motion which is strongly influenced by the combined effects of pattern geometry and track orientation with respect to the crystal symmetry of the garnet drive layer. The nonuniformity in the instantaneous bubble velocity arises from instabilities in the position of the driving charged wall as a result of the tridirectional anisotropy in the implanted layer and is most pronounced on the bad track at low in-plane field and low bias field. The ratio of peak to average velocity, Vp/Vavranges from 3:1 for the bad track to 1:5:1 for the super track, at 60 Oe drive. For the good track the ratio Vp/Vavis 2:1 and is approximately constant over the frequency range 155-490 KHz. A saturation velocity of ∼ 35 m/s was found for these materials (2) and is consistent with the measured upper frequency limit of ∼ 600 KHz for propagation on good tracks.