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Optical magnetometry and micromagnetic simulations of three-dimensional magnetic nanostructures

Hunt, Matthew 2017. Optical magnetometry and micromagnetic simulations of three-dimensional magnetic nanostructures. PhD Thesis, Cardiff University.
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Abstract

This thesis describes the magnetic properties of three-dimensional (3D) magnetic nanostructures fabricated using two-photon lithography (TPL) and measured by the magneto-optical Kerr effect (MOKE), with supporting micromagnetic simulations. Simulations were performed on individual cylindrical nanowires composed of permalloy (Py) with diameter 50nm and length 1.5μm. Hysteresis loops were taken where the external field was applied at angles of 0o, 35.25o, 54.75o, 70.5o and 90o with respect to the wire axis. From investigating the visualisations of the magnetisation it was observed that Bloch point domain walls were propagated down the wire during the switching process. The resulting hysteresis loops were compared with those generated from simulations performed on tetrapod structures in the principle directions [100], [110] and [111]. It was found that the [100] and [110] loops were reproducible from the individual wire loops where the field angles matched. However, the [111] loop could not be reproduced due to domain wall propagation through the vertex. Angled 3D nanowires and 3D magnetic structures in tetrapod geometry made of cobalt (Co) were fabricated using two-photon lithography and electrodeposition. From SEM imaging, the nanowires in both structures were found to have an elliptical profile with feature sizes of 750±40nm lateral width, 910±30nm length perpendicular to the wire axis and approximately 8μm length for the individual nanowires, and feature sizes of 610±55nm lateral width, 900±75nm length perpendicular to the wire axis and approximately 6.5μm length for the nanowires comprising the tetrapods. MOKE measurements were performed on 300μmx300μm arrays of both, in the polar and longitudinal geometries. It was found that the polar MOKE loops were comparable between the two structures, whereas the longitudinal MOKE loops for tetrapods showcased unexpected transition events at higher fields and could not be reproduced from the measurements of the single wires.

Item Type: Thesis (PhD)
Status: Unpublished
Schools: Physics and Astronomy
Subjects: Q Science > QC Physics
Uncontrolled Keywords: two-photon lithography, magneto-optical Kerr effect, MOKE, spin-polarised scanning electron microscopy, spin-SEM, 3D magnetic nanostructures, 3D fabrication, micromagnetic simulations, Bloch point domain walls
Funders: School of Physics and Astronomy, Cardiff University
Date of First Compliant Deposit: 21 March 2018
Last Modified: 05 Jun 2018 10:06
URI: http://orca-mwe.cf.ac.uk/id/eprint/110072

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