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Ferromagnetic dynamics in coupled systems



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Patchett, James 


In this work, ferromagnetic thin films coupled strongly to other physical subsystems (magnetic or otherwise) are studied, and the effect this coupling has on their static and dynamic properties is investigated in order to understand both the ferromagnets themselves, and the systems they are coupled to.

This work investigates recent claims that spin-triplet superconducting Cooper pairs can be generated at superconducting Nb-fullerene interfaces in thin-film heterostructures by looking for evidence of an increase in magnetic damping below the Nb transition temperature in an adjacent permalloy (Py) layer. From these measurements, it is proposed that the experimental evidence purported to show evidence of a spin-triplet population can instead be understood as a signal from the vortex population within a spin-singlet superconductor.

It is shown how it is possible to apply group theory to the dynamic modes of a ferromagnet, or multiple coupled ferromagnets, obeying the linearised Landau-Lifshitz-Gilbert (LLG) equation. From this, the effect of symmetry on the expected resonance spectrum of antiferromagnetically coupled magnetic moments is investigated. Features such as anticrossings and mode degeneracies are shown to be understandable from symmetry arguments, and this is demonstrated experimentally via measurements of the ferromagnetic resonance spectrum of two synthetic antiferromagnets: one bilayer with close to identical ferromagnetic layers, and another bilayer with layers with disparate properties.

Features of the magnetoresistance behaviour in CoFeB single-layers and synthetic antiferromagnetic CoFeB/Ru/CoFeB nanowires adjacent to heavy-metal Pt layers are reported. It is shown how symmetry arguments can be applied to understand features of the magnetoresistive signal and observe a current dependent uniaxial magnetoresistive signal at high current densities which is attributed to the onset of auto-oscillations within the exchange magnon population of the nanowires.





Ciccarelli, Chiara


FMR, Group theory, Magnetism, Spintronics, Superconductors, Superspintronics


Doctor of Philosophy (PhD)

Awarding Institution

University of Cambridge
EPSRC (2125947)