  Magnetic skyrmions can be considered as topologically protected localized
vortex-like spin textures. Due to their stability, their small size, and the
possibility to move them by low electric currents they are promising candidates
for spintronic devices. Without violating topological protection, it is
possible to create skyrmion-antiskyrmion pairs, as long as the total charge
remains unchanged. We derive a skyrmion equation of motion which reveals how
spin-polarized charge currents create skyrmion-antiskyrmion pairs. It allows to
identify general prerequisites for the pair creation process. We corroborate
these general principles by numerical simulations. On a lattice, where
topological protection becomes imperfect, the antiskyrmion partner of the pairs
is annihilated and only the skyrmion survives. This eventually changes the
total skyrmion number and yields a new way of creating and controlling
skyrmions.
