Experimental realization of metastable target skyrmion states in continuous films

Target skyrmions (TSks) are topological spin textures where the out-of-plane component of the magnetization twists an integer number of k- $π$ rotations. Based on a magnetic multilayer stack in the form of $n ×$[CoFeB/MgO/Ta], engineered to host topological spin textures via dipole and DMI energies, we have stabilized 1  $π$⁠, 2  $π$⁠, and 3  $π$ target skyrmions by tuning material properties and thermal-excitations close to room temperature. The nucleated textures, imaged via Kerr and Magnetic Force Microscopies, are stable at zero magnetic field and robust within a range of temperatures (tens of Kelvin) close to room temperature (RT = 292 K) and over long time scales (months). Under applied field (mT), the TSks collapse into the central skyrmion core, which resists against higher magnetic fields (⁠ $≈$ 2  $×$ TSk annihilation field), as the core is topologically protected. Micromagnetic simulations support our experimental findings, showing no TSk nucleation at 0 K, but a $≈$ 30  $%$ probability at 300 K for the experimental sample parameters. Our work provides a simple method to tailor spin textures in continuous films, enabling free movement in 2D space and creating a platform transferable to technological applications where the dynamics of the topological textures can be exploited beyond geometrical confinements.