Detection of stored momentum in magnetic bubbles by a bias jump effect

Abstract

A pulse of uniform bias field is applied to an isolated ∼5-μm bubble in a garnet film. The bubble (S=0) was previously propagated by a strong gradient-field pulse. The bubble is observed to jump forward in the same direction as the previous gradient propagation, irrespective of the sign of the bias-field pulse. Subsequent bias pulses may cause further "bias jumps" of this type until a maximum displacement is reached, which can be many μm in typical cases. Dependence of the bias jumps on the strength and length of the bias-field pulses and also of the previous gradient-field pulses is reported. The shape of the bubbles, observed by high-speed photography during the bias pulse, is elliptical, indicating lower mobility on the sides of the bubble perpendicular to the over-all direction of motion. These results provide evidence for the existence of unwinding Bloch-line pairs which remain in the bubble wall at the end of a gradient propagation. These Bloch lines are shown to be tantamount to a stored bubble momentum, which is released when the bias pulses are applied.