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Identifier

000443331

Title

Magnetic skyrmions and their dependence on system parameters

Alternative Title

Λύσεις χειρομορφών σκυρμιονιών

Author

Μπότση, Άννα

Thesis advisor

Κομηνέας, Σταύρος

Reviewer

Tomasello Riccardo

Abstract

In the first chapters of this thesis we will start by introducing the experimental obser¬vations that motivated the idea that there is a relation between the magnetic moment and the angular momentum and by the end of the chapter 2, we will have introduced the equation of motion for one spin. In chapter 3, we will consider the structure of a spin chain and we will describe the different types of interactions between them. With these known, we will proceed to the discussion of the dynamics for a spin chain, and in the end we will have modelled the continuum form of the equation of motion and also the case when there are dissipative effects, another parameter that we should consider when we talk about spin chain dynamics. In chapter 4 we mainly discuss the Landau-Lifshitz equation (later noted as LL Equation). We make some discussion about the basic ideas of this equation that origin on the Homotopy Theory. Later on this chapter we present the Landau-Lifshitz equation , the Laundau-Lifshitz-Gilbert Equation (later noted as LLG equation) and we solve them analytically in order to obtain the domain wall solution. With this chapter, the introductory part of the basic concepts and of the equations that will concern as on the next chapters, has ended. So with everything that were discussed before, we introduce Skyrmions. We present the experiment where they were first observed and their configuration. In the first part of this thesis, we introduced the different types of interaction between spins, on a spin chain. Here, we are most interested in the Dzyaloshinskii-Moriya interaction (later referred as DMI) and in which way it affects the configuration of a magnetic skyrmion. Because, skyrmions are solutions of the LL equation, and the DMI is an important interaction for the formation of this structure, we discuss the existence of the DMI term on the LL equation and we present its domain wall solution. Finally, we proceed with the micromagnetic simulations that were made for this thesis. We study the dependence of the skyrmion's diameter on different system parameters such as the DMI parameter, of the DMI energy, the anisotropy parameter K, of the anisotropy energy, the exchange parameter A, of the exchange energy, the external field parameter, of an external magnetic field that is being applied on the system. At last, we insert a dimensionless parameter on the problem, the parameter e that combines the DMI, the A and the K parameters studied before and we observe how it affects the diameter of the skyrmion. All this observations are being done by presenting graphs which we will discuss further on.

Language

English

Subject

Landau-Lifshitz

Σκυρμιόνια εξίσωση

Issue date

2021-11-26

Collection

School/Department--School of Sciences and Engineering--Department of Mathematics and Applied Mathematics--Post-graduate theses

Type of Work--Post-graduate theses

Permanent Link

https://elocus.lib.uoc.gr//dlib/f/e/a/metadata-dlib-1635940928-829758-30839.tkl