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Skyrmionic states in confined helimagnetic nanostructures

Skyrmionic states in confined helimagnetic nanostructures
Skyrmionic states in confined helimagnetic nanostructures
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, we demonstrate that skyrmionic states are the lowest energy states in confined helimagnetic nanostructures at zero external magnetic field and in absence of magnetocrystalline anisotropy. We show that bistable skyrmionic states undergo hysteretic behaviour between two energetically equivalent skyrmionic configurations with different core orientation, even in the absence of both magnetocrystalline and demagnetisation-based shape anisotropies, suggesting the existence of novel Dzyaloshinskii-Moriya-based shape anisotropy. We show that the skyrmionic state core reversal is facilitated by the Bloch point occurrence and propagation. In this work, we also study the dynamic properties (resonance frequencies and corresponding eigenmodes) of these skyrmionic states in confined helimagnetic nanostructures. The eigenvalue method allows us to identify all resonance frequencies and corresponding eigenmodes that can exist in the simulated system. However, using a particular experimentally feasible excitation can excite only a limited set of eigenmodes. Because of that, we perform and report ringdown simulations that resemble the experimental setup using both an in-plane and an out-of-plane excitations. In addition, we report the nonlinear dependence of resonance frequencies on the external magnetic bias field and disk sample diameter and report the possible reversal mode of skyrmionic states. Finally, we show that neglecting the demagnetisation energy contribution or ignoring the magnetisation variation in the out-of-film direction in either static or dynamic simulations is not always justified.
University of Southampton
Beg, Marijan
499a2633-2ab7-4ec3-ab2a-c6eae1874f83
Beg, Marijan
499a2633-2ab7-4ec3-ab2a-c6eae1874f83
Fangohr, Hans
9b7cfab9-d5dc-45dc-947c-2eba5c81a160

Beg, Marijan (2016) Skyrmionic states in confined helimagnetic nanostructures. University of Southampton, Faculty of Engineering and the Environment, Doctoral Thesis, 133pp.

Record type: Thesis (Doctoral)

Abstract

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, we demonstrate that skyrmionic states are the lowest energy states in confined helimagnetic nanostructures at zero external magnetic field and in absence of magnetocrystalline anisotropy. We show that bistable skyrmionic states undergo hysteretic behaviour between two energetically equivalent skyrmionic configurations with different core orientation, even in the absence of both magnetocrystalline and demagnetisation-based shape anisotropies, suggesting the existence of novel Dzyaloshinskii-Moriya-based shape anisotropy. We show that the skyrmionic state core reversal is facilitated by the Bloch point occurrence and propagation. In this work, we also study the dynamic properties (resonance frequencies and corresponding eigenmodes) of these skyrmionic states in confined helimagnetic nanostructures. The eigenvalue method allows us to identify all resonance frequencies and corresponding eigenmodes that can exist in the simulated system. However, using a particular experimentally feasible excitation can excite only a limited set of eigenmodes. Because of that, we perform and report ringdown simulations that resemble the experimental setup using both an in-plane and an out-of-plane excitations. In addition, we report the nonlinear dependence of resonance frequencies on the external magnetic bias field and disk sample diameter and report the possible reversal mode of skyrmionic states. Finally, we show that neglecting the demagnetisation energy contribution or ignoring the magnetisation variation in the out-of-film direction in either static or dynamic simulations is not always justified.

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More information

Published date: April 2016
Organisations: University of Southampton, Computational Engineering & Design Group

Identifiers

Local EPrints ID: 402969
URI: http://eprints.soton.ac.uk/id/eprint/402969
PURE UUID: 7315ced5-107f-4442-8b94-8199f94e7d0a
ORCID for Hans Fangohr: ORCID iD orcid.org/0000-0001-5494-7193

Catalogue record

Date deposited: 05 Dec 2016 11:20
Last modified: 21 Nov 2019 01:37

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Contributors

Author: Marijan Beg
Thesis advisor: Hans Fangohr ORCID iD

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