The University of Southampton
University of Southampton Institutional Repository

Magnetic skyrmion research using virtual simulation environments

Magnetic skyrmion research using virtual simulation environments
Magnetic skyrmion research using virtual simulation environments
Magnetic skyrmions are particle-like structures in the magnetic moment field of a helimagnetic material. Since skyrmions are of the order of nanometres in size, they are a promising replacement for the larger magnetic domain structures proposed for racetrack memory devices. Skyrmions also motivate the design of small logic gate devices. However, skyrmions are only stable in limited regions of the parameter space defined by the strength of an external magnetic field and the properties of the material.

To model the behaviour of skyrmions and the magnetic moment field in a real sample, this thesis contains multiple numerical investigations using the micromagnetic model. Finite-element and finite-difference approaches are used to solve different problems. Due to the complexity of micromagnetic modelling, a software platform is implemented to perform simulations within virtual machines and containers. This novel mechanism has been deployed for public use to improve the reproducibility and accessibility of micromagnetic simulations, and is used for all numerical simulations in this thesis.

This thesis demonstrates the potential for materials with an easy-plane magnetocrystalline anisotropy to support skyrmions. This investigation augments existing analytical approaches by considering demagnetising and thickness effects to more accurately model a real helimagnetic material. Skyrmions are found to exist in easyplane anisotropy systems, expanding the space of possible materials for skyrmionbased devices. The size of the skyrmion is also found to increase with the strength of the easy-plane anisotropy, which impacts negatively on the storage density of these devices.

In addition to investigating the effect of easy-plane anisotropy, the micromagnetic approach is adapted to model arbitrary polycrystalline grain structures. This adaption is used to understand how a polycrystalline grain structure affects the magnetic moment field of a helimagnet. Individual skyrmions are found to be repulsed by grain boundaries, though skyrmions in neighbouring grains attract each other. This finding suggests that an individual skyrmion could be used as the data structure in logic gate devices, where the polycrystalline structure could determine the logic.

These two investigations are combined to model a real bulk helimagnetic material with an arbitrary grain structure and easy-plane anisotropy, and to explain a large topological Hall resistivity observation, which is an indicator of skyrmion presence. The thickness of the material gives rise to two additional skyrmionic structures. This means sufficiently thick materials with both easy-plane anisotropy and an irregular grain structure can support skyrmion states.
University of Southampton
Vousden, Mark
d45312dd-a46f-4376-89f4-38b1ac8957c9
Vousden, Mark
d45312dd-a46f-4376-89f4-38b1ac8957c9
Fangohr, Hans
9b7cfab9-d5dc-45dc-947c-2eba5c81a160

Vousden, Mark (2017) Magnetic skyrmion research using virtual simulation environments. University of Southampton, Doctoral Thesis, 175pp.

Record type: Thesis (Doctoral)

Abstract

Magnetic skyrmions are particle-like structures in the magnetic moment field of a helimagnetic material. Since skyrmions are of the order of nanometres in size, they are a promising replacement for the larger magnetic domain structures proposed for racetrack memory devices. Skyrmions also motivate the design of small logic gate devices. However, skyrmions are only stable in limited regions of the parameter space defined by the strength of an external magnetic field and the properties of the material.

To model the behaviour of skyrmions and the magnetic moment field in a real sample, this thesis contains multiple numerical investigations using the micromagnetic model. Finite-element and finite-difference approaches are used to solve different problems. Due to the complexity of micromagnetic modelling, a software platform is implemented to perform simulations within virtual machines and containers. This novel mechanism has been deployed for public use to improve the reproducibility and accessibility of micromagnetic simulations, and is used for all numerical simulations in this thesis.

This thesis demonstrates the potential for materials with an easy-plane magnetocrystalline anisotropy to support skyrmions. This investigation augments existing analytical approaches by considering demagnetising and thickness effects to more accurately model a real helimagnetic material. Skyrmions are found to exist in easyplane anisotropy systems, expanding the space of possible materials for skyrmionbased devices. The size of the skyrmion is also found to increase with the strength of the easy-plane anisotropy, which impacts negatively on the storage density of these devices.

In addition to investigating the effect of easy-plane anisotropy, the micromagnetic approach is adapted to model arbitrary polycrystalline grain structures. This adaption is used to understand how a polycrystalline grain structure affects the magnetic moment field of a helimagnet. Individual skyrmions are found to be repulsed by grain boundaries, though skyrmions in neighbouring grains attract each other. This finding suggests that an individual skyrmion could be used as the data structure in logic gate devices, where the polycrystalline structure could determine the logic.

These two investigations are combined to model a real bulk helimagnetic material with an arbitrary grain structure and easy-plane anisotropy, and to explain a large topological Hall resistivity observation, which is an indicator of skyrmion presence. The thickness of the material gives rise to two additional skyrmionic structures. This means sufficiently thick materials with both easy-plane anisotropy and an irregular grain structure can support skyrmion states.

Text
mvousden_thesis_v1_1 - Version of Record
Available under License University of Southampton Thesis Licence.
Download (53MB)

More information

Published date: June 2017

Identifiers

Local EPrints ID: 418027
URI: http://eprints.soton.ac.uk/id/eprint/418027
PURE UUID: d5599e04-32d0-49f1-8be7-e8f186c28714
ORCID for Hans Fangohr: ORCID iD orcid.org/0000-0001-5494-7193

Catalogue record

Date deposited: 20 Feb 2018 17:34
Last modified: 21 Nov 2019 01:37

Export record

Download statistics

Downloads from ePrints over the past year. Other digital versions may also be available to download e.g. from the publisher's website.

View more statistics

Atom RSS 1.0 RSS 2.0

Contact ePrints Soton: eprints@soton.ac.uk

ePrints Soton supports OAI 2.0 with a base URL of http://eprints.soton.ac.uk/cgi/oai2

This repository has been built using EPrints software, developed at the University of Southampton, but available to everyone to use.

We use cookies to ensure that we give you the best experience on our website. If you continue without changing your settings, we will assume that you are happy to receive cookies on the University of Southampton website.

×