Dynamics of bubble propagation in contiguous disk devices

Abstract

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 magnetooptic 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. The combined effects of pattern geometry and drive layer anisotropy are found to be responsible for very irregular bubble motion which is strongly influenced by the orientation of the propagation track with respect to the anisotropy axes. Velocity variations range from 5:1 for the so-called "bad" track to 2 : 1 for the "super" track; the "good" tracks, oriented parallel to a stripout direction, exhibit velocity variations of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\sim3.5:1</tex> . In general, the results show that the quality of a particular track orientation, in terms of its margin and minimum drive field, is directly related to the uniformity of bubble motion on that track. The measured values of maximum instantaneous velocity on the good tracks indicate an upper frequency limit of ∼600 kHz due to velocity saturation effects.