  We investigated magnetic textures in a Sc-doped hexaferrite film by means of
phase microscopy (PM) with a hole-free phase plate in a transmission electron
microscope. In a zero magnetic field, the stripe-shaped magnetic domains
coexist with magnetic bubbles. The magnetization in both magnetic domains was
oriented perpendicular to the film and the domain walls have an in-plane
magnetization. In the remnant state at 9.2 mT, several magnetic bubbles were
formed with the formation of stripe-shaped magnetic domains, and the
out-of-plane component in the stripe-shaped domains gradually appeared as the
film thickness increased. As the film thickness increases further, the magnetic
bubbles with clockwise or counter-clockwise spin helicities formed a triangular
lattice. These results in the remnant state suggest that the domain wall energy
in the magnetic bubble domains is lower in the thicker region.
