Real-space observation of individual skyrmions in helimagnetic nanostripes
Jin Chi-Minga),b),c), Du Hai-Feng†a),b)
       
Schematic ray diagram in a Fresnel image of a ferromagnetic specimen containing two 180° domain walls. (a) In-focus condition: the defected electron beams are focused in the final image plane so that no magnetic contrast appears. (b) and (c) Over- and under-defocus conditions: the defected electron beams lead to dark and bright contrasts, respectively. Image are taken from Ref. [ 26 ].