Ground state search, hysteretic behaviour and reversal mechanism of skyrmionic textures in confined helimagnetic nanostructures
Marijan Beg1, Rebecca Carey1, Weiwei Wang1, David Cortés-Ortuño1, Mark Vousden1, Marc-Antonio Bisotti1, Maximilian Albert1, Dmitri Chernyshenko1, Ondrej Hovorka1, Robert L. Stamps2, and Hans Fangohr1
1 Faculty of Engineering and the Environment, University of Southampton, Southampton SO17 1BJ, United Kingdom
2 SUPA School of Physics and Astronomy, University of Glasgow, G12 8QQ, Glasgow, United Kingdom
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Magnetic skyrmions have the potential to provide solutions for low-power, high-density data storage and processing. One of the major challenges in developing skyrmion-based devices is the skyrmions’ magnetic stability in confined helimagnetic nanostructures. Through a systematic study of equilibrium states, using a full three-dimensional micromagnetic model including demagnetisation effects, we demonstrate that skyrmionic textures are the lowest energy states in helimagnetic thin film nanostructures at zero external magnetic field and in absence of magnetocrystalline anisotropy. We also report the regions of metastability for non-ground state equilibrium configurations. We show that bistable skyrmionic textures undergo hysteretic behaviour between two energetically equivalent skyrmionic states with different core orientation, even in absence of both magnetocrystalline and demagnetisation-based shape anisotropies, suggesting the existence of Dzyaloshinskii-Moriya-based shape anisotropy. Finally, we show that the skyrmionic texture core reversal dynamics is facilitated by the Bloch point occurrence and propagation.
This repository provides Ubermag simulation code to reproduce results from Beg et al. Ground state search, hysteretic behaviour and reversal mechanism of skyrmionic textures in confined helimagnetic nanostructures. Scientific Reports, 5, 17137 (2015). All notebooks hosted in this repository can be run in the cloud (see next section on Binder), and thus the results reproduced by anybody.
The key statement of the paper is that skyrmions are stable confirmations in confined geometries such as flat cylinders, even without crystal anisotropy and without applied fields. A central result of the work is figure 2 which shows for which applied field and which cylinder diametre a skyrmion is obtained as the lowest energy configuration and for which fields.
The production of figure 2 required to run many simulations, starting from different initial configurations for the magnetisation, minimising the system energy for each configuration, identify the resulting configuration with the lowest energy, and putting together a phase diagram that classifies the final configuration.
The following notebook demonstrates how this calculation can be done for 2 points in the phase plane.
- figure-02-ground-state.ipynb (nbviewer rendering) (github rendering)
- figure-02-ground-state-more-details.ipynb, includes meta-stable states,(nbviewer rendering) (github rendering)
- Interactively execute the notebooks using Binder
Licensed under the BSD 3-Clause "New" or "Revised" License. For details, please refer to the LICENSE file.
Please cite paper as:
Developed as a part of OpenDreamKit – Horizon 2020 European Research Infrastructure project (676541). This work was financially supported by the EPSRC’s Doctoral Training Centre (DTC) grant EP/ G03690X/1. R.L.S. acknowledges the EPSRC’s EP/M024423/1 grant support. D.C.-O. acknowledges the financial support from CONICYT Chilean scholarship programme Becas Chile (72140061). We acknowledge the use of the IRIDIS High Performance Computing Facility and associated support services at the University of Southampton, in the completion of this work. We also thank Karin Everschor-Sitte for helpful discussions.