  We report the use of Lorentz microscopy to observe the domain wall structure
during the magnetization process in FePd 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. Multiscale magnetic simulations shown that these regions are
vertical Bloch lines (VBL) and the different bubble shapes observed are then
related to the inner structure of the VBLs. We were thus able to probe the
presence of magnetic singularities as small as Bloch points in the inner
magnetization of the domain walls.
