Direct observation of skyrmions with arbitrary helicity in patterned Co/Pt multilayers

Co/Pt multilayers with perpendicular magnetic anisotropy were locally irradiated with a focused beam of $H{e}^{+}$ ions to change the magnetic properties of the sample in strictly defined regions. Irradiated regions of 100–400-nm diameter served as pinning centers for chiral magnetic textures, resulting in the formation of magnetic skyrmions of the same diameter. The magnetization topology of such skyrmions was studied by Lorentz transmission electron microscopy. It was found that the helicity of skyrmions depended on its diameter and the ion irradiation fluence. Both Bloch-type skyrmions and Néel-type skyrmions, as well as skyrmions of the intermediate type, were observed. We assume that this behavior is due to a change in the balance of the magnetostatic energy and the Dzyaloshinskii-Moriya energy, which is confirmed by micromagnetic simulations.