HORIZONTAL BLOCH LINES AND ANISOTROPIC-DARK-FIELD OBSERVATIONS

Anisotropic-dark-field optical imaging is shown to reveal the presence of horizontal Bloch lines (HBL's) in the moving walls of bubble garne ts. It relies on the deformation of the wall shape under dynamic condi tions due to the presence of a HBL. The wall tilt is detected because it affects the intensity of the wall images much in the same way as lo calized wall tilts reveal the location of vertical Bloch lines (VBL's) in static conditions. Quantitative time-resolved measurements of wall intensity are presented and shown to compare very favorably with nume rical computations. These use a simplified spin dynamics equation (Slo nczewski's equations) describing the wall position and wall-core magne tization in-plane angle, as a function of position across the thicknes s, and time. Dynamic reversals of VBL's contrast have also been observ ed. The fact that they occur for one half of the possible configuratio ns is puzzling. They are tentatively explained on the basis of a dynam ically induced charge distribution at VBL location, which arises from a wall wave developing around the moving VBL.