Experimental and micromagnetic study of
magnetisation behaviour in isolated
ferromagnetic nanowires
By
Musaab Salman Sultan
A thesis submitted in partial fulfilment of the requirements for the degree of
Doctor of Philosophy
University of Durham
2013
Abstract
A full understanding of the magnetism of isolated ferromagnetic nanowires is still an unresolved
issue and presents a research challenge for researchers. Understanding the intrinsic magnetic
properties of such nanowires is significant from a scientific point of view and will be an issue for
potential applications. Therefore, the aim of the work presented here is to investigate the
magnetic and magnetisation reversal behaviour of electrodeposited template released isolated
ferromagnetic nanowires complemented by detailed micromagnetic simulations.
To understand the fabrication techniques, characterisation systems and the materials used to
fabricate the nanowires, the elemental composition, surface topography and magnetic properties
of a range of electrodeposited thin films were investigated first.
In order to emphasis the reasons behind studying the magnetic behaviour of such isolated
nanowires, the statistical distribution of template pore size and spacing, nanowire dimension
distributions, and the morphology of such nanowires have been measured using high resolution
scanning electron microscope analysis. To determine the crystal structure and the crystallite sizes
within these nanowires, which might have a great influence on their magnetic properties, both the
template deposited and selected areas of individual nanowires have been studied using a
combination of X-ray diffraction and high resolution transmission electron microscopy
incorporating with electron diffraction, respectively.
To align the template released nanowires with respect to the prefabricated micromarkers and
electrical contact pads, magnetic field assisted alignment was developed. The effect of field
strength, nanowire composition and aspect ratio on the percentage of aligned nanowires have
been statistically analysed and the results explained.
The surface and bulk magnetisation reversal behaviour of isolated individual, small bundles and
clusters of nanowires is technically challenging but have been successfully measured here using
magneto-optical Kerr effect magnetometry and magnetoresistance, respectively. The
magnetic switching behaviour obtained from these techniques is compared with each other, the
literature and analytical models.
In addition, detailed micromagnetic simulations have been utilised to determine the magnetic
behaviour of two wire geometries: cylindrical and planar Ni81Fe19 nanowires with a range of
diameters and thicknesses, respectively. For both geometries, the effect of nanowire diameter and
thickness on the magnetic properties such as switching fields, remanent magnetisation and
magnetic
state before and during the switching behaviour, have been analysed and compared. The
switching field of the simulated nanowires are compared with their counterparts results obtained
from both MOKE and MR measurements. The magnetisation reversal behaviour of these wires
geometries was also investigated and compared with the classical analytical curling model of
magnetisation reversal.