Controlled generation of stable winding and unwinding vertical Bloch lines in

Generation of pairs of Bloch loops (BL) and vertical Bloch lines (VBL) occurs when the bubble translational velocity is monotonically increased. A magnetic bubble is translated continuously in a circular trajectory by means of the Rotating Gradient Experiment (RGE) and changes in the values of the winding number (S) and the dimensionless momentum (P) are observed. The specific transitions of the bubble wall structure are always found to be repeatable under the same experimental conditions. Increases in S are generally seen for the clockwise (CW) circulation, while decreases in S occur for the CCW sense of circulation. In addition to finding S with the RGE, the Rocking Experiment (RE) is used to independently determine the value of S from the deflection angle of the bubble trajectory. In all cases, the values of S determined from the RGE and from the RE have been found to be the same. Particular cases of transitions of S and P are reviewed for three samples having different compositions and material parameters. Changes in the value of S are caused by the annihilation of pairs of VBL's during a bubble state transition. Any two +π (or -π) VBL's are found to stay together both for moving and stationary bubbles.