Stimulated nucleation of skyrmions in a geometrically asymmetric structure*

Understanding the dynamics of skyrmion nucleation and manipulation is important for applications in spintronic devices. Here, we have investigated the magnetic texture transformation using Lorentz transmission electron microscopy (LTEM) in a centrosymmetric magnet Fe₃Sn₂ with an engineered geometrical asymmetry in the form of a thickness gradient. Using sample tilting and tunable magnetic field strength in the LTEM we developed a new approach for skyrmion nucleation at magnetic domain boundaries. This approach enables nucleation of isolated skyrmions in Fe₃Sn₂ using in-plane fields (< 5 mT) that are two orders of magnitude lower than the previously reported critical magnetic field (~800 mT). Micromagnetic simulations combined with LTEM experiments reveal that the rotatable anisotropy and thickness dependence of the response to the external in-plane field are the critical factors for the skyrmion formation. These results suggest that magnetic materials with rotatable anisotropy are potential skyrmionic systems and provide a novel approach for the manipulation of skyrmions in spintronic devices.