Magnetic imaging of 3D artificial spin-ice structures

Harding, Edward 2023. Magnetic imaging of 3D artificial spin-ice structures. PhD Thesis, Cardiff University. Item availability restricted.

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Abstract

This thesis is a meticulous journey into the realm of three-dimensional Artificial Spin Ices (ASI), pushing the boundaries of exploration beyond the familiar territories of two dimensions. Employing methodologies like two-photon lithography and thermal evaporation, it navigates the intricate landscape of diamond-bond lattice geometries, unveiling emergent behaviours such as monopole propagation. Section 3 meticulously charts the ASI structure's three-dimensional phase diagram, comparing predictive Monte Carlo simulations with experimental observations. The diversity of predicted phases, from double-charged monopole crystals to conventional spin ice, is scrutinized through magnetic force microscopy (MFM), revealing new vertex types and providing data for comparisons with simulations. Discrepancies between anticipated and observed ground states are attributed to an effective chemical potential (μ^*) and limitations in the deterministic demagnetisation protocol. Ferromagnetic dominance on the upper surface layer and a higher μ^* for monopole formation impede the anticipated double-charged crystal, except in localized disorder regions. Recommendations for modifying the topography of the surface layer are proposed to realize this state. Delving deeper into the system, x-ray magnetic circular dichroism (XMCD) is suggested to probe layers with a 1-unit cell thickness, expanding comprehension. Future plans involve transforming the 3D ASI into a thermally dynamic system, challenging for measurement techniques like MFM due to state perturbation and extended times. Section 4 delves into synchrotron-based techniques, notably transmission X-ray microscopy with XMCD, affirming permalloy nanowire structures' crescent-shaped cross-section. Refinements in fabrication methods, despite revealing oxidization of the magnetic coating, offer nuanced insights into magnetic behaviours within the 3D ASI. XMCD measurements hint at weak signals, particularly in SL2, suggesting the need for further fabrication refinements and envisioning polymer-free magnetic nanowire-based 3D ASI designs for future exploration. In a meticulous journey through ASI's three-dimensional landscapes, this thesis unearths complexities, proposes modifications, and sets the stage for deeper explorations into emergent phenomena.

Item Type:	Thesis (PhD)
Date Type:	Completion
Status:	Unpublished
Schools:	Physics and Astronomy
Subjects:	Q Science > QC Physics
Uncontrolled Keywords:	Artificial Spin Ice (ASI) 3D ASI Monopoles Magnetism Diamond-bond lattice Two-photon lithography Thermal evaporation Monte Carlo simulations Magnetic force microscopy (MFM) Phase diagram Spin ice Effective chemical potential X-ray magnetic circular dichroism (XMCD) Transmission X-ray microscopy Permalloy nanowires Synchrotron techniques Magnetic nanowire structures
Funders:	EPSRC
Date of First Compliant Deposit:	13 August 2024
Last Modified:	13 Aug 2024 15:41
URI:	https://orca.cardiff.ac.uk/id/eprint/171358

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