  We investigate the skyrmion formation process in nano-structured FeGe
Hall-bar devices by measurements of topological Hall effect, which extracts the
winding number of a spin texture as an emergent magnetic field. Step-wise
profiles of topological Hall resistivity are observed in the course of varying
the applied magnetic field, which arise from instantaneous changes in the
magnetic nano-structure such as creation, annihilation, and jittering motion of
skyrmions. The discrete changes in topological Hall resistivity demonstrate the
quantized nature of emergent magnetic flux inherent in each skyrmion, which had
been indistinguishable in many-skyrmion systems on a macroscopic scale.
