Probing magnetic singularities during magnetization process in FePd films

We report the use of Lorentz microscopy to observe the domain wall structure during the magnetization process in iron-palladium thin foils. We have focused on the magnetic structure of domain walls of bubble-shaped magnetic domains near saturation. Regions are found along the domain walls where the magnetization abruptly reverses. Multiresolution magnetic simulations showed that these regions are vertical Bloch lines (VBL) and that the different bubble shapes observed are related to the inner structure of the VBL. Combining these two complementary methods, we were thus able to probe the presence of magnetic singularities as small as Bloch points in the inner magnetization of the domain walls.