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Influence of the magnetic substrate and of the Gaussian fluctuations of the molecular fields on the properties of the magnetic bilayer described by the Blume-Emery-Griffiths model

Wojciech Jaworski

Abstract

The main object of this PhD thesis is the classical spin model for the spin S = 1, known as the Blume-Emery-Griffiths model (BEG). It has been used to describe a ferromagnetic bilayer, being an example of ultrathin magnetic layers, which physicians are very interested in. In order to investigate the thermodynamic and magnetic properties of the BEG bilayer the methods of both analytic calculations and computer simulations have been used. First of them included the molecular field approximation (MFA) and its extension – the Gaussian fluctuations approximation (GFA). The effect of two types of fluctuations has been examined using the phase diagrams of the BEG model, which have been obtained within three variants of the GFA method. Variations in the occurrences of phase transition lines and critical points have been discussed and the results have been compared with the ones obtained within different methods (CVMPA, MC). Moreover, an emphasis has been put on phase transitions occurring between meta- and unstable phases, the existence regions of which have been broadened. What is more, the Metropolis type Monte Carlo simulations (MC) have been used to investigate the influence of the coupling to a ferromagnetic substrate on the properties of the BEG bilayer. The models of the substrate and its interaction with the bilayer have been proposed and the calculations were made with the help of the quantum thermodynamic formalism.
Record ID
UAM1d58d7cde73544b580677bb0420476ff
Diploma type
Doctor of Philosophy
Author
Wojciech Jaworski Wojciech Jaworski,, Undefined Affiliation
Title in Polish
Wpływ magnetycznego podłoża oraz gaussowskich fluktuacji pól molekularnych na własności dwuwarstwy magnetycznej opisywanej modelem Blume-Emery-Griffithsa
Title in English
Influence of the magnetic substrate and of the Gaussian fluctuations of the molecular fields on the properties of the magnetic bilayer described by the Blume-Emery-Griffiths model
Language
pl Polish
Certifying Unit
Faculty of Physics (SNŚ/WyF/FoP)
Discipline
physics / (physical sciences domain) / (physical sciences)
Scientific discipline (2.0)
6.6 physical sciences
Defense Date
16-04-2012
Title date
16-04-2012
Supervisor
URL
http://hdl.handle.net/10593/2418 opening in a new tab
Keywords in English
Magnetic bilayer, BEG model, Gaussian fluctuations, Molecular field, Quantum thermodynamics
Abstract in English
The main object of this PhD thesis is the classical spin model for the spin S = 1, known as the Blume-Emery-Griffiths model (BEG). It has been used to describe a ferromagnetic bilayer, being an example of ultrathin magnetic layers, which physicians are very interested in. In order to investigate the thermodynamic and magnetic properties of the BEG bilayer the methods of both analytic calculations and computer simulations have been used. First of them included the molecular field approximation (MFA) and its extension – the Gaussian fluctuations approximation (GFA). The effect of two types of fluctuations has been examined using the phase diagrams of the BEG model, which have been obtained within three variants of the GFA method. Variations in the occurrences of phase transition lines and critical points have been discussed and the results have been compared with the ones obtained within different methods (CVMPA, MC). Moreover, an emphasis has been put on phase transitions occurring between meta- and unstable phases, the existence regions of which have been broadened. What is more, the Metropolis type Monte Carlo simulations (MC) have been used to investigate the influence of the coupling to a ferromagnetic substrate on the properties of the BEG bilayer. The models of the substrate and its interaction with the bilayer have been proposed and the calculations were made with the help of the quantum thermodynamic formalism.

Uniform Resource Identifier
https://researchportal.amu.edu.pl/info/phd/UAM1d58d7cde73544b580677bb0420476ff/

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