Computational simulations of complex chiral magnetic structures

Abstract

Since the last century there has been significant progress in the research of novel magnetic materials, which has been stimulated by the development of magnetic based technologies such as information recording. In recent years, advances in imaging and microscopy techniques have allowed the experimental observation of chiral magnetic orderings in a range of materials where Dzyaloshinskii-Moriya interactions (DMI) are present. In particular, a whirling structure known as a magnetic skyrmion has become popular since it can be as small as a few nanometres in size, and its non-trivial topology provides this configuration with an extra stability and particle-like features. It has been demonstrated that these properties make a skyrmion an important candidate for a variety of potential applications, especially for storing information bits. In general, the thermal stability of magnetic structures is an engineering problem that is crucial for any real life application of a magnetic technology. Hence, recently the stability of skyrmions has started to be addressed. In this thesis we investigate, through computer simulations, chiral magnetic structures, with special emphasis on skyrmions, in different materials with DMIs. In addition, we implement a numeric algorithm called the Nudged Elastic Band Method (NEBM) to calculate transition paths and energy barriers between equilibrium states of ferromagnetic systems. The barrier scan be used to estimate the average lifetime of these states. We apply the NEBM to analyse the destruction mechanisms of a skyrmion in a thin film and we find that the lowest energy barrier is associated to the skyrmion annihilation through the boundary of the sample. Furthermore, we study hexagonally shaped ferromagnetic islands to find parameter regions, such as applied field or sample size, where different chiral configurations can be stabilised, combining energy and NEBM calculations. Our results are obtained using computer software developed at our research group in a collaborative manner and we discuss the importance of good coding and data sharing practices for computational based scientific research.

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Identifiers

ORCID for David Ignacio Cortes: orcid.org/0000-0003-3799-3141

ORCID for Hans Fangohr: orcid.org/0000-0001-5494-7193

ORCID for Ondrej Hovorka: orcid.org/0000-0002-6707-4325

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