Direct visualization of nucleation intermediate state of magnetic skyrmion from helical stripes assisted by artificial surface pits

•Magnetic skyrmion is a particle-like spin texture promising for future novel spintronic devices.•We visualize the nucleation of skyrmion from helical stripes using DPC STEM technique.•We find the theoretically predicted antiskyrmion-like spin texture is actually created as the intermediate state during nucleation. Magnetic skyrmion is a particle-like spin texture promising for future novel spintronic devices. For such applications, microscopic mechanism of nucleation of skyrmion is essential to control the unique spin texture. Although real-space visualization techniques with high spatial resolution could be powerful to investigate the mechanism at the nanometer length scale, a direct visualization of skyrmion nucleation process from the helical stripe state is still technically challenging because not only a high spatial resolution but also a high temporal resolution is required to resolve the transient state. Furthermore, the location of the intermediate state is likely to move along the stripe, which hampers a successful visualization. Here, taking advantage of the high spatial resolution of aberration-corrected differential phase contrast scanning transmission electron microscopy, we observe the nucleation of skyrmion from helical stripes in a thin plate of FeGe1-xSix (x ~ 0.05). By slowing down the kinetics with a careful control of both magnetic field and temperature, while pinning the helical stripe by artificial surface pits fabricated on the surface of the thin plate specimen, we directly visualize the nucleation intermediate state of skyrmion. We find the theoretically predicted antiskyrmion-like spin texture is actually created as the intermediate state during nucleation.