X-bar, a new propagation pattern for magnetic bubbles

It is possible to improve the margins of propagation in field-access bubble memories considerably by a new arrangement of the Permalloy bars which constitute the propagation path. More slender bars of equal length become possible if the bars form an X-shaped pattern and the bubbles propagate at an angle of 45° with respect to the bars. U-turns and bubble gates have been designed and tested successfully as well. By using a 50 μm platelet of Sm-Tb-orthoferrite and bars 20 μm in width, propagation speeds up to 600 kbit/s could be obtained. This represents an improvement by a factor of two as compared with the propagation along a conventional Y-bar pattern, also tested. Below the critical frequency of propagation the field margins are improved when using the X-bar pattern. Some details of the bar fabrication are given.