  The domain structure in in-plane magnetized Fe/Ni/W(110) films is
investigated using spin-polarized low-energy electron microscopy. A novel
transition of the domain wall shape from a zigzag-like pattern to straight is
observed as a function of the film thickness, which is triggered by the
transition of the domain wall type from out-of-plane chiral wall to in-plane
N\'eel wall. The contribution of the Dzyaloshinskii-Moriya interaction to the
wall energy is proposed to explain the transition of the domain wall shape,
which is supported by Monte-Carlo simulations.
