An experimental investigation of potential wells and drive fields in bubble domain circuits

The effect of an in-plane field on the diameter of a bubble located under a permalloy element can be used to measure the potential wells and drive fields of a propagation circuit. The wells decrease in depth with increasing separation between the garnet film and permalloy element, but increase in depth with increasing in-plane fields. The wide variation in well depth with element geometry accounts for the previously observed uneven motion along propagation tracks. Changes in the operating margins for bubble propagation have been studied as a function of the silica spacing thickness, and can be qualitatively understood by reference to the potential well behaviour. A method is described for determining material mobilities of the garnet films from a knowledge of (a) the potential wells under stable locations, and (b) time-of-flight measurements between those positions.