Titel: Atomic scale investigation of non-coplanar spin structures: Zero-field skyrmionic states and multi-Q textures
Sprache: Englisch
Autor*in: Spethmann, Jonas
Schlagwörter: Domain Wall; Rowwise antiferromagnet; 3Q state; Skyrmion lattice; Spin-polarized STM
GND-Schlagwörter: Magnetisches SkyrmionGND
Erscheinungsdatum: 2023-02-08
Tag der mündlichen Prüfung: 2023-02-07
Magnetic skyrmions are topologically protected whirls in the spin structure that are of great interest due to their stability and particle-like nature. However, skyrmions have certain characteristics, which can be detrimental to their usage in any type of spintronic application. For example, they typically require external magnetic fields to be stabilized and gain a transversal component under lateral movement (skyrmion Hall effect), which can lead to skyrmion annihilation at the edge of the skyrmion hosting material. One proposal to mitigate these problems is the creation of a potential well that allows higher skyrmion velocities by guiding the skyrmions along a desired pathway. Alternatively, there is also a push towards the development of spintronics devices with antiferromagnetic building blocks, e. g., antiferromagnetic skyrmions, which have a negligible stray field, do not show the skyrmion Hall effect and are expected to have generally faster dynamics.
In this thesis, the spin-polarized scanning tunneling microscopy (SP-STM) technique is utilized to investigate the properties of skyrmionic states and other non-collinear or non-coplanar spin structures, including antiferromagnetic single- and multi-Q states. In the first part, the island edges of a well established skyrmion model system—the atomic bilayer of Pd/Fe on Ir(111)—are decorated with a ferromagnetic rim. This rim prevents skyrmion annihilation at the film edge, stabilizes skyrmions and target states in zero field and also gives rise to edge-pinned skyrmions in applied magnetic fields. Following this, spin dynamics simulations are employed to investigate what types of attractive and repulsive skyrmion-edge interactions can explain the observed effects. In the second part, the antiferromagnetic Mn monolayer on Re(0001) is investigated, which leads to the discovery of the row-wise antiferromagnetic single- and the so-called triple-Q state. The former is a collinear spin state with a new type of non-collinear domain wall that is made up of a double-Q superposition state. The latter is a non-coplanar multi-Q state that is stabilized by higher-order exchange interactions. Both of these states exist in different stackings of the Mn monolayer. In the final part, the surface of the centrosymmetric GdRu2Si2 bulk crystal is investigated. GdRu2Si2 has been previously investigated using multiple techniques: The magnetic phase diagram of GdRu2Si2 consists of several multi-Q states including a skyrmion lattice in a perpendicular field of B = 2.5 T. Here, using SP-STM, evidence for the multi-Q nature of the different magnetic ground states is provided and details of the magnetic and electronic contrast mechanisms are discussed with support from theory. Finally, it is confirmed that the Gd-terminated surface shows additional magnetic phase transitions that are not observed for the Si-terminated surface or the GdRu2Si2 bulk crystal.
URL: https://ediss.sub.uni-hamburg.de/handle/ediss/10078
URN: urn:nbn:de:gbv:18-ediss-106806
Dokumenttyp: Dissertation
Betreuer*in: von Bergmann, Kirsten
Wiesendanger, Roland
Enthalten in den Sammlungen:Elektronische Dissertationen und Habilitationen

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