  Magnetic skyrmions are intriguing topological spin textures that promise
future high-density spintronic devices. The creation of magnetic skyrmions has
been understood based on the energetics of skyrmions, but the detailed dynamic
process of the skyrmion creation remains unclear. Here topological evolution in
conversion from uneven domains to N\'eel-skyrmions is investigated using
micromagnetic simulations. We find that, rather than the overall topological
charge, annihilation of novel topological defects, i.e., recently suggested
domain wall skyrmions, dominantly govern the skyrmion creation process. Also,
the topological charge evolution is interpreted in terms of the number and the
combination of such topological defects.
