  Topological defects such as magnetic solitons, vortices, Bloch lines, and
skyrmions have started to play an important role in modern magnetism because of
their extraordinary stability, which can be exploited in the production of
memory devices. Recently, a novel type of antisymmetric exchange interaction,
namely the Dzyaloshinskii-Moriya interaction (DMI), has been uncovered and
found to influence the formation of topological defects. Exploring how the DMI
affects the dynamics of topological defects is therefore an important task.
Here we investigate the dynamic domain wall (DW) under a strong DMI and find
that the DMI induces an annihilation of topological vertical Bloch lines (VBLs)
by lifting the four-fold degeneracy of the VBL. As a result, velocity reduction
originating from the Walker breakdown is completely suppressed, leading to a
soliton-like constant velocity of the DW. Furthermore, the strength of the DMI,
which is the key factor for soliton-like DW motion, can be quantified without
any side effects possibly arising from current-induced torques or extrinsic
pinnings in magnetic films. Our results therefore shed light on the physics of
dynamic topological defects, which paves the way for future work in
topology-based memory applications.
