From Skyrmions to Skyrmion Bags: Steering Complex Spin Textures

Topologically non-trivial magnetic solitons—including skyrmions and their higher-order variants—are promising building blocks for next-generation spintronic and unconventional computing technologies. While deterministic creation of unit-charge skyrmions is now well established across multiple material platforms, the controlled formation of higher-order topological textures such as skyrmion bags has remained far less explored due to their demanding stability requirements.

Here, we demonstrate a generalizable pathway for generating, stabilizing, and tailoring both conventional skyrmions and higher-order skyrmion bags in ferromagnetic thin films. Using focused He⁺-ion irradiation, we create localized modifications of magnetic anisotropy that act as deterministic nucleation sites for complex spin textures. This approach enables the reproducible creation of skyrmionium, target skyrmion, and reconfigurable skyrmion bags under external magnetic fields or ultrafast laser pulses. We compare these activation pathways and find that optical excitation provides a highly efficient route for the conversion into higher-order topological states. Direct imaging via high-resolution x-ray microscopy confirms the robust stabilization of these textures, while micromagnetic simulations identify the key role of defect geometry and local magnetic energy landscapes in supporting closed-loop and multi-skyrmion configurations.

Our results establish a scalable and versatile scheme for deterministic, on-demand creation of higher-order skyrmion textures. Beyond static stabilization, the rich internal degrees of freedom of skyrmion bags—such as internal modes, shape variations, and topological charge programmability—open pathways toward energy-efficient neuromorphic elements, adaptive sensors, and other forms of dynamic information processing.