Figure 3. Skyrmionic magnetic structures.

(a) Hexagonal unit cell for the tight-binding model, containing 961 magnetic sites. It is 8.4 nm wide, using the lattice constant of the Pd/Fe/Ir(111) system. The cones show the orientation of the spin moments and are coloured by their polar angle. The skyrmion radius, R_sk, is defined by θ(R_sk)=90°. (b–e) Top view of structures with different skyrmion numbers, N_sk=−2, −1, +1, +2, respectively (equation 2; here γ=0). The chiral skyrmions in Pd/Fe/Ir(111) correspond to N_sk=−1. Achiral skyrmions have N_sk=+1.