Controlled Topological Transitions by Manipulating Monopole Injection in Fe/Gd Multilayers

Topological spin textures in magnetic materials have garnered significant interest due to their unique physical behaviors associated with the skyrmion number (Q). A non-zero skyrmion number provides enhanced stability compared to topologically trivial spin textures with Q=0 [1, 2]. Owing to their high stability, the topological spin textures are promising candidates for next-generation spin-based electronic devices. To stably form such topological spin textures, it is essential to induce transitions that change the skyrmion number (ΔQ≠0) called topological transition. Achieving these topological transitions requires the controlled injection of magnetic singularities, particularly magnetic monopoles or Bloch points [3, 4].

Here, we show controlled topological transitions between stripe domains, topologically trivial bubbles, and magnetic skyrmions in Fe/Gd multilayers by manipulating monopole injection by tuning in-plane magnetic fields using magnetic transmission x-ray microscopy combined with micromagnetic simulations. Additionally, we show that in-plane magnetic fields increase the local exchange energy density at the top and bottom surfaces, thereby triggering monopole injection. Our work offers a promising pathway for developing spin-based memory and logic devices, with the controlled injection of magnetic monopoles serving as a key mechanism for topological transitions.