Capturing of a Magnetic Skyrmion with a Hole
Jan Müller, M Sc (THP Universität Köln)

Magnetic whirls in chiral magnets, so-called skyrmions, can be manipulated by ultrasmall current densities. We study both analytically and numerically the interactions of a single skyrmion in two dimensions with a small hole in the magnetic layer. Results from micromagnetic simulations are in good agreement with effective equations of motion obtained from a generalization of the Thiele approach. Skyrmion-defect interactions are described by an effective potential with both repulsive and attractive components.For small current densities a previously pinned skyrmion stays pinned whereas an unpinned skyrmion moves around the impurities and never gets captured. For higher current densities, jc1 < j < jc2, however, single holes are able to capture moving skyrmions. The maximal cross section is proportional to the skyrmion radius and to the square root of the Gilbert damping. For j > jc2 all skyrmions are depinned. Small changes of the magnetic field strongly change the pinning properties, one can even reach a regime without pinning, jc2 = 0. We also show that a small density of holes can effectively accelerate the motion of the skyrmion and introduce a Hall effect for the skyrmion.