Magnetic bubble dynamics in asymmetric half-disk propagator

The dynamics of bubbles propagating in a 14-μm period, 1.8-μm gap, asymmetric half-disk field-access device operated at 148 kHz was studied using a high-speed optical sampling technique. The nonuniform character of the bubble propagation along the asymmetric half-disk is primarily evidenced by large variations in velocity. The peak velocity (around 13 m/s), occurring at the gap traversal, is more than 3 times greater than the average (4.2 m/s) value. The path followed by the leading edge (apex) is shorter than that followed by the trailing edge, resulting in a 12 percent difference in their time average velocities. The phase lag between the bubble position and drive field orientation varies with bias and drive field magnitude, but is not more than 16°. In general the bubble shape is oval, with small distortions which change with its position along the half-disk. The size reaches its two peaks when the bubble lies along the narrow half-disk leg and at the gap traversal. The variations in shape and size are most pronounced during the propagation in a low bias and a high drive field.