Signatures of higher order skyrmionic textures revealed by magnetic force microscopy

Abstract: Higher-order skyrmions and antiskyrmions are topologically protected spin textures with an integer topological charge other than $\pm 1$ and nucleate from topological point defects in regular Bloch walls, known as vertical Bloch lines. So far, they have only been observed using Lorentz transmission electron microscopy. In this work, we show that higher-order spin textures coexisting in Co/Ni multilayers at room temperature can be visualized by high-resolution magnetic force microscopy (MFM). The experimental results are supported by micromagnetic simulations confirming that different spin objects give rise to distinct MFM contrast in full agreement to our observations.