Experimental realization of metastable target skyrmion states in continuous films

TL;DR

This study demonstrates the experimental stabilization of metastable target skyrmion states in continuous magnetic films at near-room temperatures, revealing their robustness and potential for technological applications in spintronics.

Contribution

We experimentally realize and stabilize multiple target skyrmion states in continuous films, supported by micromagnetic simulations, advancing understanding of topological spin textures in practical materials.

Findings

Target skyrmions are stable at zero field and near room temperature.

Skyrmions collapse under applied magnetic fields but resist higher fields due to topological protection.

Simulations show a 30% probability of skyrmion nucleation at 300 K.

Abstract

Target skyrmions (TSks) are topological spin textures where the out-of-plane component of the magnetization twists an integer number of $m$-$\pi$ rotations. Based on a magnetic multilayer stack in the form of $n\times$[CoFeB/MgO/Ta], engineered to host topological spin textures via dipole and DMI energies, we have successfully 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 ($\approx$ 2 $\times$ TSk annihilation field), as the core is topologically protected. Micromagnetic simulations support our experimental findings, showing no TSk nucleation at 0 K, but a $\approx$ 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, creating a platform transferable to technological applications where the dynamics of the topological textures can be exploited beyond geometrical confinements.