  It is well established that the spin-orbit interaction in heavy
metal/ferromagnet heterostructures leads to a significant interfacial
Dzyaloshinskii-Moriya Interaction (DMI) that modifies the internal structure of
magnetic domain walls (DWs) to favor N\'{e}el over Bloch type configurations.
However, the impact of such a transition on the structure and stability of
internal DW defects (e.g., vertical Bloch lines) has not yet been explored. We
present a combination of analytical and micromagnetic calculations to describe
a new type of topological excitation called a DW Skyrmion characterized by a
$360^\circ$ rotation of the internal magnetization in a Dzyaloshinskii DW. We
further propose a method to identify DW Skyrmions experimentally using Fresnel
mode Lorentz TEM; simulated images of DW Skyrmions using this technique are
presented based on the micromagnetic results.
