Figure 2.

Plots of (a) m_z and (b) the radius of skyrmions as the magnetic field is swept. The inversion happens at $\pm |{\mathbf{H}}_{\mathrm{P}}|$, and the collapse to the FM state happens at $\pm |{\mathbf{H}}_{\mathrm{A}\mathrm{P}}|$. (c–f) Contour plots of the skyrmion-lattice magnetization show (c,d) the growth of skyrmions in parallel sweep with the topological charge localized at each skyrmion; (e) the hexagonal state with the topological charge delocalized on the 2π domain-wall boundary; and (f) the inverted skyrmion lattice. The external magnetic field is indicated in the bottom right-hand corner of the plots and the positive direction of the field is defined as that of the skyrmion-core polarization in zero field.