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

Eider Berganza,Miriam Jaafar,Agustina Asenjo,Oksana Chubykalo-Fesenko,Jose Angel Fernandez-Roldan,Konstantin Guslienko

doi:10.1038/s41598-022-07407-w

Abstract

Magnetic skyrmions are widely attracting researchers due to fascinating physics and novel applications related to their non-trivial topology. Néel skyrmions have been extensively investigated in magnetic systems with Dzyaloshinskii–Moriya interaction (DMI) and/or perpendicular magnetic anisotropy. Here, by means of micromagnetic simulations and analytical calculations, we show that 3D quasi-skyrmions of Néel type, with topological charge close to 1, can exist as metastable states in soft magnetic nanostructures with no DMI, such as in Permalloy thick cylindrical and dome-shaped nanodots. The key factor responsible for the stabilization of DMI-free is the interplay of the exchange and magnetostatic energies in the nanodots. The range of geometrical parameters where the skyrmions are found is wider in magnetic dome-shape nanodots than in their cylindrical counterparts. Our results open the door for a new research line related to the nucleation and stabilization of magnetic skyrmions in a broad class of nanostructured soft magnetic materials.

Highlights

Magnetic skyrmions are topologically non-trivial magnetization configurations which typically appear in systems with strong Dzyaloshinskii-Moriya interactions (DMI) and broken inversion symmetry
We present the state diagram for 3D quasi-skyrmions in soft magnetic dome-shape nanodots and nanopillars made of Permalloy in terms of the dot geometry
Micromagnetic simulations were conducted in 3D soft magnetic dots with cylindrical or curved geometry with neither perpendicular magnetic anisotropy (PMA) nor DMI, nor external magnetic fields

Summary

Introduction

Magnetic skyrmions are topologically non-trivial magnetization configurations which typically appear in systems with strong Dzyaloshinskii-Moriya interactions (DMI) and broken inversion symmetry. PMA together with DMI ensure either Bloch or Néel (or mixed) skyrmions stabilization, typically as metastable states at zero bias magnetic field[5,6] Both multilayered films[7–9] as well as B20 single crystals[10] can be appealing to controllably nucleate and drive skyrmions using external stimuli. For the existence of chiral Néel skyrmions, DMI has been considered as a necessary ingredient When it comes to real applications, skyrmions may need to be confined in nanostructured geometries, such as for instance magnetic stripes or dots. The occurrence of the vortex state and Bloch points is widely reported in nanodisks and s pheres[19–21,28] Apart from these magnetization configurations, we obtained a 3D quasi-skyrmion, (a spin texture having a radial configuration and a topological charge close to one in the basal plane), as a metastable state in dome-shaped nanodots and we have compared it to that in thick cylindrical dots. We have calculated 2D topological charges displaying strong dependence on the sample geometry in both types of the patterned nanostructures

Methods

Results

Conclusion