Probing the Pinning Strength of Magnetic Vortex Cores with sub-nm Resolution

Topological magnetic textures such as vortex cores or skyrmions are key candidates for non-volatile information processing. This exploits the texture movement by current pulses that is typically opposed by pinning. A detailed understanding of pinning is hence crucial with previous experiments being either limited in terms of controlled magnetic texture positioning or in terms of spatial resolution. Here, we use spin-polarized scanning tunneling microscopy to track a magnetic vortex core that is deliberately moved by a 3D magnetic field. The core covering about 10.000 Fe-atoms gets pinned by defects that are only a few nm apart. Reproducing the vortex path via parameter fit, we deduce the pinning potential of the defects as a mexican hat with short-range repulsive and long-range attractive part. By comparison with micromagnetic simulations, the attractive part is attributed to a local suppression of exchange interaction. The novel approach to deduce defect induced pinning potentials on the sub-nm scale is transferable to other non-collinear spin textures eventually enabling an atomic scale design of defect configurations, e.g., for reliable read-out in race-track type devices.