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Magnetic structures and proximity effects in rare-earth / transition metal ferromagnetic and superconductor systems 10.17863/CAM.27483 Higgs, Thomas David Charles Robinson, Jason The antiferromagnetic coupling between a rare-earth (RE) and a tran- sition metal (TM) ferromagnet can be exploited to engineer normal state and superconducting functional devices. RE/TM ferromagnetic multi- layers were previously used as spin-mixers to generate spin-triplet su- percurrents. This was possible due to magnetic inhomogeneity present in the devices, however the precise nature of the inhomogeneity was not understood. Here we present a comprehensive study of the Ni/Gd/Ni system using a powerful element-specific measurement technique: x-ray magnetic circular dichroism. In order to analyse the experimental results we present a novel model based on the Stoner-Wohlfarth model, which shows that significant inhomogeneity exists at the Ni/Gd interfaces due to the competition between the exchange energies within the system and the Zeeman energy of the applied magnetic field. The experiment and model together provide a complete overview of the Ni/Gd/Ni system due to the breadth of temperatures and thicknesses studied. The knowledge gained from this work is then applied to designing and test- ing new spin valves based on the intrinsic inhomogeneity at the RE/TM interface, and both Ni/Gd- and Gd/Ho-based devices show reversible magnetic switching behaviour which alters the superconducting critical temperature. University of Cambridge 2018-10-20 Thesis Doctoral Doctor of Philosophy (PhD) en EPSRC https://www.repository.cam.ac.uk/handle/1810/280118 https://apollo8-f-pro.lib.cam.ac.uk/bitstreams/8e84f1f5-ef62-44ff-ba49-08c7dff296ce/download 439ddeb4b9a071cc263961d92b5397a1 https://apollo8-f-pro.lib.cam.ac.uk/bitstreams/4df5e294-5a7f-4b03-959d-c3b6f3bad2bb/download 87eda9de84448d1f82354d60eee3eb5f https://creativecommons.org/licenses/by-nc-sa/4.0/ magnetism superconductivity thin-film xmcd proximity effect ferromagnet antiferromagnet python rare-earth transition metal holium gadolinium nickel niobium exchange bias