Intrinsic DMI-free skyrmion formation and robust dynamic behaviors in magnetic hemispherical shells

Abstract

We performed finite-element micromagnetic simulations to examine the formation of skyrmions without intrinsic Dzyaloshinskii–Moriya interaction (DMI) in magnetic hemispherical shells. We found that curvature-induced DM-like interaction allows for further stabilization of skyrmions without the DMI in curved-geometry hemispherical shells for a specific range of uniaxial perpendicular magnetic anisotropy (PMA) constant Ku. The larger the curvature of the shell, the higher the Ku value required for the formation of the skyrmions. With well-stabilized skyrmions, we also found in-plane gyration modes and azimuthal spin-wave modes as well as an out-of-plane breathing mode, similarly to previously found modes for planar geometries. Furthermore, additional higher-frequency hybrid modes were observed due to coupling between the gyration and azimuthal modes. This work provides further physical insight into the static and dynamic properties of intrinsic DMI-free skyrmions formed in curved-geometry systems.

The impacts of molecular adsorption on antiferromagnetic MnPS3 monolayers: enhanced magnetic anisotropy and intralayer Dzyaloshinskii–Moriya interaction

“…Furthermore, the successful synthesis of 2D magnets provides a promising platform to study the Dzyaloshinskii-Moriya interaction (DMI) [13][14][15] . DMI, an antisymmetric exchange interaction between two magnetic atoms within one surface layer 16,17 , originates from spin-orbit coupling (SOC) and competes with the perpendicular magnetic anisotropy and the Heisenberg exchange coupling to generate the chiral magnetic structures like the chiral domain walls, helical spins, and skyrmions [18][19][20] . These chiral magnetic structure possess great application potential in next-generation memory devices 21 .…”

3D quasi-skyrmions in thick cylindrical and dome-shape soft nanodots

“…Indeed, the other two possible core polarity–chirality combinations have not been obtained in micromagnetic simulations under the same conditions. We have found that they can be stabilized by, for example, introducing additional radial 27 or perpendicular 26 magnetic anisotropy (see Sect. 2 of the “ Supplementary Information ”, where a magnetization configuration with P*C = − 1 is presented).…”

“…The article 20 reports the formation of skyrmion states in soft hemi-ellipsoidal particles, but at non-zero applied magnetic fields, while Refs. 26 , 27 report them in hemispheres at zero field but with an additional magnetic anisotropy. Here we demonstrate the possibility to observe 3D quasi-skyrmions in both cylindrical and dome-shaped thick nanodots with no need of special magnetic material, i.e., with no DMI and no out-of-plane anisotropy, in particular, in ultra soft Permalloy nanostructures with radius ca.…”

“…Our group has recently reported the observation of half-hedgehog spin textures, nucleated and further stabilized by the MFM probe stray field 27 . Recent numerical simulations 26 , 27 also demonstrated the existence of skyrmions in hemispherical nanoparticles with no DMI but with PMA. However, up to our knowledge, Néel skyrmions have not been reported in systems with no DMI nor any magnetic anisotropy.…”

“…First, in cylindrical nanopillars (with large aspect ratio height-to-diameter) the effect of the magnetostatic interactions leads to an effective out-of-plane anisotropy. Secondly, in ultra-thin magnetic caps with curved geometry, a part of the exchange integral on the curvilinear surface was shown to have functional form similar to DMI 24 – 26 . In this sense, the curved geometry itself may produce similar effects to that of DMI systems, with no need of real DMI of the relativistic origin and therefore leading to less constraints in the choice of materials.…”