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Autoren: Schönke, Daniel
Hauptberichter: Kläui, Mathias
Titel: Static and Dynamic Magnetic Imaging of Diffent Magnetic Materials Using Scanning Electron Microscopy with Polarization Analysis
Online-Publikationsdatum: 4-Mär-2021
Erscheinungsdatum: 2021
Sprache des Dokuments: Englisch
Zusammenfassung/Abstract: In the field of spintronics the statics and dynamics of magnetic states in various materials and geometries are of high interest for finding new physics and mechanisms that could be employed in devices. Highly reliable states and switching pathways are required to encode information, as well as efficient switching mechanisms. Experimental research in this area uses different methods, including electrical transport measurements and magnetic imaging. The research progress strongly depends on the improvement of the instruments that are used for the sample fabrication and investigation. The ongoing trend of device miniaturization and high speed requirements ask for experimental techniques with high spatial and temporal resolution. I improved a scanning electron microscopy with polarization analysis (SEMPA) to enable dynamic magnetic imaging with high spatial resolution. In addition to the novel time-resolved imaging mode, I employed a phase-sensitive detection (PSD) approach to detect small periodic magnetization changes. I determined the temporal resolution to be less than 2 ns and demonstrated a fivefold signal-to-noise ratio enhancement using PSD. SEMPA with PSD was employed to probe current-induced surface spin accumulation in heavy metals (Pt, Ta) that can be used to switch efficiently magnetic states. SEMPA is especially suited for these experiments because it has a very high surface sensitivity. However, the unambiguous detection of spin accumulation was hindered by artefacts induced by an inhomogeneous sample potential if a current was applied. Next I employed time-resolved SEMPA to investigate the magnetic switching and its reliability in two geometries: First, I demonstrated in a Ni80Fe20 half ring pair the ability to detect irregularities in the magnetization switching with a very small probability of 10^(-6) by a novel data analysis scheme. Further, the magnetic field-induced nucleation of vortex domain walls in curved wires proved to be one method to reliably generate vortex domain walls with a fixed chirality. Second, I demonstrated an angular dependence in the field-induced switching behaviour in asymmetric full rings. Depending on the field orientation with respect to the ring symmetry axis, either onion-to-onion state or vortex-to-onion-to-vortex state switching takes place. Thermal assistance was found to alter the probability of domain wall nucleation in the switching process. Finally I studied new promising material classes with properties ranging from ferro- to antiferromagnetic. In general, SEMPA can not image antiferromagnets directly. However, I showed with three examples that for certain systems based on multilayers or ferrimagnets, SEMPA is a well-suited imaging technique. I demonstrated the dependence of the biquadratic coupling on the buffer layer and the smoothness of the films in a heterostructure. I further imaged skyrmion bubble domain walls in GdFeCo and Mn2Au domains indirectly via an exchange-coupled Fe layer. Overall, I show in this thesis different promising geometries and material systems that could be beneficial for the development of reliable and fast spintronic devices. At the same time I demonstrate the enhanced versatility of the newly developed time-resolved SEMPA imaging technique and discuss analysis approaches that provide additional information about the reliability of the observed dynamics.
DDC-Sachgruppe: 530 Physik
530 Physics
Veröffentlichende Institution: Johannes Gutenberg-Universität Mainz
Organisationseinheit: FB 08 Physik, Mathematik u. Informatik
Veröffentlichungsort: Mainz
URN: urn:nbn:de:hebis:77-openscience-5a36ef77-13a2-4992-8ac6-dbd67bbaf8063
Version: Original work
Publikationstyp: Dissertation
Nutzungsrechte: CC BY
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Umfang: 214 Seiten
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