Focused ion beam irradiation for generation of skyrmionic bubble like structures

Skyrmions provide high potential for low power magnetic computing. However, we are lacking methods for the controlled nucleation of skyrmions in magnetic thin films. We present a procedure for a controlled generation of skyrmionic bubble like structures (SBSs) at well-defined spots by focused ion beam (FIB) irradiation of magnetic multilayers. Series of Pt/Co/Ir and Pt/Co/W multilayers with interfacial Dzyaloshinskii-Moriya interaction (iDMI) were sputtered and optimized with respect to the domain structure and development under magnetic field. Applying an external magnetic field pulse of specific strength to a sample in both the demagnetized domain state and the uniform ferromagnetic state results in the condensation and nucleation of bubbles, respectively. In multilayer films, SBSs form randomly across the sample. To control the bubble nucleation, we irradiate the multilayer stacks with 50kVGa⁺ ions to alter the magnetic properties along a hexagonal grid. We observe nucleation and geometric confinement of bubbles within the center of the hexagons. The lowered anisotropy in irradiated regions forms potential barriers which stabilizes the bubbles at room temperature and zero field. FIB tuned magnetic thin films give an exciting platform to investigate the behavior of SBSs in a confined state and to study the possibilities of controlled field- and current-driven motion.