Observation and characterisation of magnetisation ripple using Lorentz transmission electron microscopy

Cowan, Alison Anne (2021) Observation and characterisation of magnetisation ripple using Lorentz transmission electron microscopy. PhD thesis, University of Glasgow, Queen's University Belfast.

Due to Embargo and/or Third Party Copyright restrictions, this thesis is not available in this service.


Lorentz transmission electron microscopy (LTEM) has proved itself to be an invaluable technique when investigating in-situ micromagnetic behaviour of magnetic thin films. The nano-scale visualisation of the magnetic structure allows for not only the mapping of hysteresis behaviour, but quantitative characterisation of the materials micromagnetic properties. In this thesis, much of the previous work of experimental magnetisation ripple characterisation is reviewed. A newly developed methodology for characterisation of large sets of Fresnel images displaying magnetisation ripple properties is presented which is utilised throughout the rest of the body of work.

Ni45Fe55 has long been a high moment alternative for the more commonly used permalloy composition of Ni80Fe20 in hard disk (HDD) read-write head design. In this work a conventional TEM, and LTEM study was undertaken to investigate the effect of ultra-thin Ni79Fe21 seed layers on the physical and magnetic properties of Ni45Fe55. The dramatic effect of seed layer addition resulted in grain size and texture reduction, an increase in uniaxial anisotropy and a reduction in magnetisation ripple properties. This suggests that the film is a good candidate for controlling properties of Ni45Fe55 thin films, whilst maintaining a high magnetic moment density.

Micromagnetic modelling of magnetisation ripple using MuMax3 software has been presented using two different methods. Both models produced visually representative simulated Fresnel images, with work specifically focusing on magnetisation reversal processes and the quantitative analysis of magnetisation ripple properties. Models produced insights into the effect of parameters such as grain size, inter-granular exchange and magnetocrystalline anisotropy directionality.

Lastly, we can quantitatively assess the physical and magnetic variations between permalloy magnetostrictive samples with varying signs, without the need for external straining, to represent normal operating conditions in HDD devices. Analysis revealed near identical physical properties, with a subtle variation in bulk and magnetic ripple properties. However, it is not possible to determine if these variations are exclusively due to differences in magnetostrictive properties or if it is more likely due to compositional variations.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Keywords: Soft magnetic materials, polycrystalline, Lorentz microscopy, magnetisation ripple, anisotropy, hysteresis.
Subjects: Q Science > QC Physics
Colleges/Schools: College of Science and Engineering > School of Physics and Astronomy
Supervisor's Name: McVitie, Professor Stephen
Date of Award: 2021
Embargo Date: 31 July 2022
Depositing User: Dr Alison Cowan
Unique ID: glathesis:2021-82046
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 25 May 2022 07:57
Last Modified: 25 May 2022 07:58
Thesis DOI: 10.5525/gla.thesis.82046
URI: https://theses.gla.ac.uk/id/eprint/82046
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