Three-dimensional structure of magnetic skyrmions

Magnetic skyrmions (skyrmions hereafter) are magnetization configurations, whose topological robustness and nanoscale size have led to speculation that they could find use as a next-generation information carrier. Skyrmions have been observed in magnetic multilayer materials that are thin compared to the radius of a skyrmion, and chiral cubic single crystals that can be far larger than any characteristic skyrmion scale. In these single crystals, one would expect that skyrmions could exhibit interesting three-dimensional (3D) characteristics. Here, the symmetry of the micromagnetic free energy is investigated. This symmetry permits a complex 3D modulation of a skyrmion string, which we show to be a requirement of a skyrmion coexisting with the conical state. We discuss the implications of this modulation with respect to Thiele\u27s equation and interskyrmion interactions. Further to this internal modulation, we study theoretically and show experimentally that the strings themselves must contort towards the surfaces of their confining crystals

Field Driven Vortex Domain Wall Motion in Magnetic Nanostructures

This thesis deals with the research area of domain walls (DW). In particular, the dynamics of field-driven vortex domain walls (VDW) in ferromagnetic nano-stripes (Ni80Fe20 / Permalloy) is investigated experimentally as well as by means of analytical calculations and micromagnetic simulations (MUMAX3). The work focuses on the behaviour of VDWs in the special dynamic regime at fields exceeding the critical Walker field. Depending on the chirality of the VDW, a fast double reversal process of the vortex core (VC) polarity can occure. After providing a detailed presentation of the underlying theoretical background of DW dynamics (Landau-Lifshitz-Gilbert equation, Thiele equation, Collective Coordinate Approach), the resulting equation of motion are derived. Furthermore, the theoretical framework of the applied (Ferromagnetic Resonance, Magneto-Optical Kerr Effect) experimental techniques are given. In the consecutive chapter the thesis proves the reader an introduction to the experimental techniques (e.g. sample design based on a coplanar wave guide, Time-Resolved Kerr Microscopy, Full-Film Ferromagnetic Resonance, Wide-Field Kerr Microscopy) and methods of data evaluation which were used throughout this thesis in order to perform sample characterization and investigate domain motion (DWM). In the chapter dedicated to the experimental and simulational results, the outcome of the sample characterization (e.g. determination of the saturation magnetization Mₛ, magnetic damping parameter α, depinning probabilities, low field mobility) are presented. Based on experimental findings and micromagnetic simulations, four properties of the new found double reversal process (DRP) of the VC polarity are identified. They are explained by experimental results, micromagnetic simultaions and analytical calculations which is leading to a deep understanding of the DRP effect

Metamaterial

In-depth analysis of the theory, properties and description of the most potential technological applications of metamaterials for the realization of novel devices such as subwavelength lenses, invisibility cloaks, dipole and reflector antennas, high frequency telecommunications, new designs of bandpass filters, absorbers and concentrators of EM waves etc. In order to create a new devices it is necessary to know the main electrodynamical characteristics of metamaterial structures on the basis of which the device is supposed to be created. The electromagnetic wave scattering surfaces built with metamaterials are primarily based on the ability of metamaterials to control the surrounded electromagnetic fields by varying their permeability and permittivity characteristics. The book covers some solutions for microwave wavelength scales as well as exploitation of nanoscale EM wavelength such as visible specter using recent advances of nanotechnology, for instance in the field of nanowires, nanopolymers, carbon nanotubes and graphene. Metamaterial is suitable for scholars from extremely large scientific domain and therefore given to engineers, scientists, graduates and other interested professionals from photonics to nanoscience and from material science to antenna engineering as a comprehensive reference on this artificial materials of tomorrow