Investigation of the magnetization process of domain walls in an iron-garnet film by direct optical observation of vertical Bloch lines

Vertical Bloch lines (VBL) were observed in a (YLuBi)₃(FeGa)₅O₁₂ magnetic garnet film from the light diffracted from the stripe domains. Experiments on the motion of the Bloch lines in response to magnetic fields perpendicular to and in the plane of the film were performed. For a bias-field pulse perpendicular to the film there was a nonlinear relationship between pulse amplitude and VBL displacement. The minimum static in-plane field for VBL displacement (VBL coercivity) was 1.3±0.4 Oe. Winding VBL pairs disappeared at an in-plane field. In a novel experiment, the amplitude of VBL displacement in response to a low-frequency AC in-plane field was measured. This experiment can be used to quantify the energy of the VBL in the vicinity of the pinning sites, which were found to occur regularly along the domain wall. A considerable variation in the strength and spacing of the pinning sites was found in the film studied