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Exploiting two-photon direct laser writing for fabrication of 3D magnetic nanowires

Askey, Joseph 2023. Exploiting two-photon direct laser writing for fabrication of 3D magnetic nanowires. PhD Thesis, Cardiff University.
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This thesis presents new and novel fabrication routines, by exploiting direct laser writing optical lithography and combining with other processing techniques and optical modifications in order to realise magnetic nanostructures. Direct laser writing is coupled with standard lithography, electrodeposition and processing to realise cylindrical magnetic nanowires, which are characterised experimentally using physical and magnetic imaging methods; and further modelled using finite- difference micromagnetic simulations. Direct laser writing with a 405 nm wavelength laser is demonstrated, and the expected feature sizes in both the lateral and axial directions are characterised experimentally and modelled through simulation of the point spread function in a high numerical aperture imaging environment. 405 nm direct laser writing is coupled with the use of annular apertures to investigate the effects of the reduced kz bandwidth on the shape and size of the printing element, the voxel. Furthermore, a novel 405 nm retro-reflecting and auto-regulating 4π direct laser writing scheme is demonstrated and benchmark nanostructures are fabricated and characterised with atomic force and scanning electron microscopy, allowing the experimental realisation of polymer nanostructures with aspect ratios (ratio of axial to lateral features) as low as 0.8. Finally, 405 nm DLW is used to realise three-dimensional magnetic nanowires with sub-100 nm feature sizes, with longitudinal and cross-sectional curvature. Expected domain wall structures are modelled using finite-element micromagnetics, and the domain wall pinning is characterised using magnetic force microscopy imaging in applied fields. The domain wall pinning probabilities along the nanowires are characterised, and a simple model of depinning fields is used to elucidate the behaviour when the total field experienced along the nanowire local tangents are considered.

Item Type: Thesis (PhD)
Date Type: Completion
Status: Unpublished
Schools: Physics and Astronomy
Subjects: Q Science > QC Physics
Uncontrolled Keywords: three-dimensional nanomagnetism, two-photon lithography, direct laser writing, two-photon absorption, multi-photon absorption, bloch points, domain walls, magnetic force microscopy, scanning electron microscopy, atomic force microscopy, cylindrical magnetic nanowires, annular apertures, 4Pi, 405nm, micromagnetic simulations, thermal evaporation, electrodeposition
Date of First Compliant Deposit: 28 June 2023
Last Modified: 28 Jun 2024 01:30

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