Skyrmion-Bubble Bundles in an X-Type Sr₂Co₂Fe₂₈O₄₆ Hexaferrite above Room Temperature

Magnetic skyrmions are spin swirls that possess topological nontriviality and are considered particle-like entities. They are distinguished by an integer topological charge Q. The presence of skyrmion bundles provides an opportunity to explore the range of values for Q, which is crucial for the advancement of topological spintronic devices with multi-Q properties. In this study, a new material candidate, Sr2Co2Fe28O46 hexaferrite of the X-type, which hosts small dipolar skyrmions at room temperature and above is presented. By exploiting reversed magnetic fields from metastable skyrmion bubbles at zero fields, skyrmion-bubble bundles with different interior skyrmion/bubble numbers, topological charges, and morphologies at room temperature are incorporated. These experimental findings are consistently supported by micromagnetic simulations. These results highlight the versatility of topological spin textures in centrosymmetric uniaxial magnets, thereby paving the way for the development of room-temperature topological spintronic devices with multi-Q characteristics.