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

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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.