The effect of a second magnetic layer on hard bubbles

A new class of magnetic bubbles designated as hard (and intermediate) bubbles has been found to be a common feature in many bubble garnet films.1 These hard bubbles have been very disruptive to the operation of bubble circuits since they not only have a much lower mobility than normal bubbles, but also tend to move at an angle rather than parallel to the direction of the driving field gradient. Fortunately, it has recently been found that the presence of a second magnetic layer apparently eliminates these hard bubbles.2,3 This second layer can either be a growth layer with a sufficiently small moment so that its magnetization under a bias field is always oppositely directed to the magnetization within the bubble,2 or it can be a layer with magnetization perpendicular to the bubble magnetization. This latter layer might be produced by ion implantation to the point where a stress-induced uniaxial anisotropy in the plane of the film overcomes the previously existing anisotropy.3 We propose in this B.S.T.J. Brief that the apparent elimination of these hard bubbles is due to the presence of the domain wall between the bubble and this second layer.