Dion, Troy; (2020) Study of High Frequency Magnetisation Dynamics in Artificial Nanomagnets Using Micromagnetic Simulation and Spin Wave Spectroscopy. Doctoral thesis (Ph.D), UCL (University College London).

Preview	Text Study of High Frequency Magnetisation Dynamics in Artificial Nanomagnets Using Micromagnetic Simulation and Spin Wave Spectroscopy - Troy Dion.pdf - Accepted Version Download (53MB) | Preview
	Video V1_Angle_of_Coincidence.mp4 - Supplemental Material Download (121kB)
	Video V2_ASI_Resonance.mp4 - Supplemental Material Download (2MB)
	Video V3_Minor_Loops.mp4 - Supplemental Material Download (3MB)
	Video V4_Kagome_Phase.mp4 - Supplemental Material Download (22MB)
	Video V5_Square_Phase.mp4 - Supplemental Material Download (26MB)
	Video V6_Kagome_Energy_Levels.mp4 - Supplemental Material Download (1MB)
	Video V7_Square_Energy_Levels.mp4 - Supplemental Material Download (1MB)
	Video V8_Square_Energy_Levels_Experimental.mp4 - Supplemental Material Download (2MB)
	Video V9_Spinwave_Gate_Comparison.mp4 - Supplemental Material Download (16MB)
	Video V10_Spinwave_Band_Structure_for_Gates.mp4 - Supplemental Material Download (9MB)
	Video V11_All_Best_On_Off_Ratios.mp4 - Supplemental Material Download (1MB)

Abstract

Artificial spin ice (ASI) is a metamaterial comprised of magnetic nanoislands arranged in a square or hexagonal lattice. ASI has been proposed as a reconfigurable magnonic crystal to be used in spin-wave based computing technologies. It also shares the necessary properties required for hardware-based neural networks, namely, nodes connected in a non-linear network via dipole-dipole interactions and memory capacity. In order to utilise these materials for future devices the collective magnetisation dynamics need to be explored. The frequency response can be tuned via shape anisotropy modification with differential patterning, microstate control or external magnetic field magnitude and orientation. Ferromagnetic resonance (FMR), spin-wave spectroscopy and micromagnetic simulations are used to investigate these systems. Control of the shape anisotropy by modifying the length and width of the elements in each sub-lattice of ASI can alter the magnetisation dynamics, suppress or allow modes and provide routes to microstates not practically feasible in homogeneous systems. Symmetry breaking in ASI via patterning causes degeneracy lifting and allows fingerprinting of underlying microstate using FMR which is relatively easier and quicker compared to other microstate reading techniques such as scanning probe or x-ray dichromism and can be integrated into future device designs. The effect of mode shifting due to changes in local field distributions is also discussed which is a sought after property in the field of magnonics. A one-dimensional reconfigurable magnonic crystal (1D-RMC) that can be placed in any desired microstate via topological magnetic defect injection is investigated. The system is prepared in various different microstates and spin-wave propagation is characterised. The spin-wave dispersion can be controlled by changing the pitch of reversed nanoislands. We also propose a spin-wave diode design based on these findings which may be an essential component in spin-wave based computing schemes.

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