Magnetic structures and proximity effects in rare-earth / transition metal ferromagnetic and superconductor systems

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.

Name dc:type.qualificationname

Doctor of Philosophy (PhD)

Level dc:type.qualificationlevel

Doctoral

Grantor dc:publisher.institution

University of Cambridge

Year dc:date.issued

2018

Author dc:creator

• Higgs, Thomas David Charles

Advisor dc:contributor.advisor

• Robinson, Jason

• magnetism
• superconductivity
• thin-film
• xmcd
• proximity effect
• ferromagnet
• antiferromagnet
• python
• rare-earth
• transition metal
• holium
• gadolinium
• nickel
• niobium
• exchange bias

Licence

• https://apollo8-f-pro.lib.cam.ac.uk/bitstreams/4df5e294-5a7f-4b03-959d-c3b6f3bad2bb/download
• https://creativecommons.org/licenses/by-nc-sa/4.0/

Language dc:language

en

DOI dc:identifier.doi

https://doi.org/10.17863/CAM.27483

OAI identifier oai:identifier

oai:www.repository.cam.ac.uk:1810/280118