Manipulating the Topology of Nanoscale Skyrmion Bubbles by Spatially Geometric Confinement.

The discovery of magnetic skyrmion bubbles in centrosymmetric magnets has been receiving increasing interest from the research community, due to the fascinating physics of topological spin textures and its possible applications to spintronics. However, key challenges remain, such as how to manipulate the nucleation of skyrmion bubbles to exclude the trivial bubbles or metastable skyrmion bubbles that usually coexist with skyrmion bubbles in the centrosymmetric magnets. Here, we report having performed this task by applying spatially geometric confinement to a centrosymmetric frustrated FeSn magnet. We demonstrate that the spatially geometric confinement can indeed stabilize the skyrmion bubbles by effectively suppressing the formation of trivial bubbles and metastable skyrmion bubbles. We also show that the critical magnetic field for the nucleation of the skyrmion bubbles in the confined FeSn nanostripes is drastically less, by an order of magnitude, than that required in the thin plate without geometrical confinement. By analyzing how the width and thickness of the nanostripes affect the spin textures of skyrmion bubbles, we infer that the topological transition of skyrmion bubbles is closely related to the dipole-dipole interaction, which we find is consistent with theoretical simulations. The results presented here bring us closer to achieving the fabrication of skyrmion-based racetrack memory devices.