Experimental realization of metastable target skyrmion states in continuous films
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Target skyrmions (TSks) are topological spin textures where the out-of-plane component of the magnetization twists an integer number of k- pi rotations. Based on a magnetic multilayer stack in the form of n x [CoFeB/MgO/Ta], engineered to host topological spin textures via dipole and DMI energies, we have stabilized 1 pi, 2 pi, and 3 pi 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 ( approximate to 2 x TSk annihilation field), as the core is topologically protected. Micromagnetic simulations support our experimental findings, showing no TSk nucleation at 0 K, but a approximate to 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.
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Applied physics letters, 125, American Inst. of Physics, Melville, NY, 2024, https://doi.org/10.1063/5.0236814