Vortices in thin ferromagnetic films and the skyrmion number
  We point out that a peculiar annihilation of a vortex-antovortex pair observed numerically by Hertel and Schneider [Phys. Rev. Lett. 97, 177202 (2006)] represents the formation and subsequent decay of a skyrmion. 
O. A. Tretiakov, O. Tchernyshyov