Field nucleation of magnetic bubbles

Nucleation of magnetic bubbles in the fields of a pulsed hairpin conductor is investigated experimentally and theoretically. It might be supposed that the current required for nucleation produces a vertical field in excess of the anisotropy field throughout the bubble film. We have found evidence that the current required is reduced because a) intense fields are required only at a surface of the bubble film, b) the horizontal field contributes in the initial surface reversal, and c) the surface of proton-implanted films is more easily reversed than the rest of the film. Field nucleation has been used to seed bubble generators and to generate bubbles controllably at 100 kHz.