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@PHDTHESIS{Mller:767445,
author = {Müller, Gideon Philipp},
othercontributors = {Blügel, Stefan and Honerkamp, Carsten and Jonsson, Hannes},
title = {{A}dvanced methods for atomic scale spin simulations and
application to localized magnetic states},
school = {RWTH Aachen University},
type = {Dissertation},
address = {Aachen ; Reykjavik},
reportid = {RWTH-2019-08828},
pages = {xx, 194 Seiten : Illustrationen},
year = {2019},
note = {Cotutelle-Dissertation. - Veröffentlicht auf dem
Publikationsserver der RWTH Aachen University; Dissertation,
RWTH Aachen University, 2019. - Dissertation, University of
Iceland, 2019},
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 two- and
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.},
cin = {137510 / 130000},
ddc = {530},
cid = {$I:(DE-82)137510_20140620$ / $I:(DE-82)130000_20140620$},
typ = {PUB:(DE-HGF)11},
doi = {10.18154/RWTH-2019-08828},
url = {https://publications.rwth-aachen.de/record/767445},
}
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