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| Home > Publications database > Advanced methods for atomic scale spin simulations and application to localized magnetic states |
| Home > Publications database > Advanced methods for atomic scale spin simulations and application to localized magnetic states |
| Book/Dissertation / PhD Thesis | FZJ-2019-05414 |
2019
Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag
Jülich
ISBN: 978-3-95806-432-4
Please use a persistent id in citations: http://hdl.handle.net/2128/23565
Abstract: An active field of research in magnetism today involves studies of solitons – localised magnetic textures possessing particle-like properties. They are considered promising for various applications but are also intriguing from a fundamental point of view. Most of the effects related to magnetic solitons, including in particular skyrmions, can be described in classical spin-lattice models. In this context, effective tools for materials and device design are needed in order to calculate properties, such as thermal stability, lifetime, critical velocity, characteristic dynamical modes and much more. This thesis is devoted to the development of new methodology and the implementation and verification of a new software framework for the simulation of atomistic spin systems. Going beyond the widely known approaches of Monte Carlo and Landau-Lifshitz- Gilbert (LLG) dynamics, this thesis describes the recently developed geodesic nudged elastic band (GNEB) method and harmonic transition state theory in a consistent mathematical framework. The minimum mode following (MMF) method, which can be used to seek out first order saddle points in the energy landscape, is formulated for magnetic systems. Such saddle point searches are an essential part in identifying possible transition processes between magnetic configurations and therefore in estimating the rates of transitions between magnetic states, which determine the states’ lifetimes. Using the MMF method, a mitosis-like skyrmion duplication – or inversely a merger – transition was found and could be reproduced in LLG dynamics simulations using an external magnetic field pulse. The entire set of methods discussed in this thesis has been implemented into a novel, open source software framework. Using scripting and graphical user interfaces, including powerful real-time visualisation features, the methods can now be used easily in conjunction with and complementary to one another. The implementation, including high performance parallelisation schemes, is described and a key set of its features are demonstrated. The software framework is applied to a variety of challenging problems in twoand three-dimensional systems. In two dimensions, complex higher-order skyrmionic textures are studied using the GNEB method and mitosis-like transitions identified. Three-dimensional systems are shown to host a large variety of complex spin textures, including a novel three-dimensionally localised state – the magnetic globule. This state is composed of two coupled quasi-monopoles, also known as Bloch points, and may form stable spin textures in a wide range of parameters and in various situations. The software framework presented here brings simulations of atomic scale magnetic systems to a higher level and represents a significant step in the modernisation of computational tools in magnetism. It brings benefits in productivity and ease of use and improves accessibility of recent and novel methodology.
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