Generation of winding vertical Bloch lines and their effect on wall dynamics

Domain wall structure and its effect on wall mobility have been studied in a thin, single-crystal garnet film of (YBiLu)₃(FeGa)₅O₁₂. The magnetic bubble was maintained in continuous circular motion in a rotating gradient experiment, and the measured tangential and radial drive fields were used to deduce the mobility and structure of the wall. Large changes in bubble winding number, such as S=-9 to S=13, were observed in the experiments. A model was developed to show how the experimental conditions used would not permit the simple addition of an unwinding Bloch line pair. State changes were thus accompanied by Bloch point injection, resulting in the observed winding number changes. The large number of Bloch lines had little effect on the mobility of the bubble, indicating that the number of Bloch lines was less than that required for a hard bubble