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The magnetic properties of ultrathin cobalt films grown epitaxially on copper (001) and (110) substrates have been investigated <I>in-situ</I> using the magneto-optical Kerr effect. The evolution of the magnetic properties of Co/Cu(110) during growth have been studied in the few monolayer (ML) regime, and strong differences in the magnetic behaviour of films grown at 80 K and 300 K are seen. For Co growth at 80 K, a magnetic signal is first recorded at ≈3 ML thickness. In the range 2.7 - 4.1 ML, a variation in the <I>M-H</I> loop squareness <I>S</I> is seen - this is attributed to a morphology-driven oscillation in the surface anisotropy of the sample. For Co growth at 300 K, a magnetic response characteristic of superparamagnetic islands is detectable at 5.2±0.6 ML. At 5.65±0.15 ML, a dynamic evolution of the <I>M-H</I> loop is observed at constant Co thickness, from a linear response to a ferromagnetic response characteristic of reversal along an easy axis. This is attributed to lateral diffusion processes in the Co film linking the islands and producing a continuous ferromagnetic film. The effects of a Cu overlayer on the Co/Cu(001) system are reported for Co films with a range of thicknesses. Strong variations in the magnetic properties are observed for submonolayer Cu coverages- in particular, at 0.2 ML a maximum in <I>S</I>, a peak in the <I>M-H</I> loop amplitude and a minimum in the coercivity are seen. The data is attributed to the presence of steps on the substrate inducing a uniaxial contribution to the magnetic anisotropy. A model to describe the behaviour is developed in which the Cu adsorbs preferentially at the steps, compensating the uniaxial anisotropy and simultaneously enhancing the magneto-optical response. The temperature dependence of the magnetisation and the coercive field of a Co/Cu(001) film is reported, for a sample in which the Curie temperature is below 300 K. It is shown that the phase transition is compatible with the 2D Ising model, within errors. The decrease of the magnetisation with increasing temperature is compared to a spin-wave model.

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The report of the presence of LaC₂ and YC₂ encapsulated in carbon shell layers found in a carbonaceous deposit grown on a cathode surface of a carbon arc has attracted particularly great interest because encapsulating materials in the hollow core of carbon nanostructures (nanocapsules/nanotubes) had changed the physical properties of the encapsulated materials. Not only does the process offer an opportunity to investigate dimensionally confined systems, but also the encapsulated materials are likely to be immune to environmental effects or degradation, because of the protective carbon sheets around them. The formation of carbon encapsulated ferromagnetic nanoparticles and nanowires has been the goal of this research. Three novel techniques for the formation of carbon encapsulated ferromagnetic nanoparticles are introduced in this thesis: Carbon Arc in Localized Gas Pressure (CA), Water Arc Discharge (WA) and Pulsed Laser Deposition (PLD). In addition, a new technique of producing encapsulated ferromagnetic nanowires by nanotube-assisted oriented attachment is also introduced. The resultant materials have had their structural and magnetic properties assessed by High Resolution Transmission Electron Microscopy (HRTEM), X-Ray Diffraction (XRD) and Vibrating Sample Magnetometer (VSM) respectively. A carbon arc technique has been modified by creating a N₂ gas jet through the office of the anode, which resulted in a localized gas pressure in the arc region. The second technique successfully implemented has been that of the electric arc submerged in deionised water inside a 2.5 litre breaker. The third technique that has been explored is PLD. In our experiments, a KrF 248 nm Lambda Physique excimer laser was used to ablate two composite targets composed of Co + C (80 wt% Co) and Ni + C (80 wt% Ni) under the pressure of N₂ gas jet respectively. Pulsed laser respectively. Pulsed laser deposition coupled with the addition of N₂ gas jet has successfully been employed to grow carbon encapsulated Co and Ni nanoparticles with small means particle sizes of 12.4 and 15.5 nm respectively. Finally, a new technique in growing ferromagnetic nanowires encapsulated in carbon tubules through oriented attachment is presented. The process is based on the evaporation of fluorocarbon capsule (PCTFE in this case) over ferromagnetic particles dissolved in toluene onto lacey carbon TEM grids at 375°C for 72 hours.

A new type of magnetic microscopy is described: Real-Time Scanning Kerr Microscopy (RTSKM) uses high bandwidth detectors to study single-shot magnetisation reversal events without averaging or stroboscopic techniques. The advantages of RTSKM are localised measurements of magnetisation, compatibility with high applied fields and ability to extract statistical details of reversal. These advantages are constructed with current dynamic magnetic microscopies. The details of the development of the equipment are presented: 100 MHz brandwidth photodetectors of sufficient sensitivity, swept field source capable of providing 3 . 10⁶ Oes^-1 and data representations to cope with the large volume of data. A fitting procedure is described that extracts parameters from single-shot RTSKM measurements that characterise the reversal. Distributions of these parameters gives valuable information on the stochastic nature of reversal. Measurements made of continuous Fe (15 nm)/GaAs films for slow field sweep rates are presented. A measurement of the domain wall velocity is calculated from a transit time measurement and compared with the values obtained directly from the dynamic MOKE data. Other domain wall phenomena are observed and discussed. The measurements show the need for statistical measurements on domain wall motion. Results are also presented of Fe(15nm)/GaAs film that was patterned into 50 mm circular dots. This sample was also studied at low field sweep rates. An inhomogeneous switching mechanism is found which is not fully explained. The switching mechanism proceeds via three stages, each of which is associated with a different region of the dot. The different regions are analysed separately and different domain wall dynamics are found.

Fe films have been grown epitaxially on Ag(001) and GaAs(001) substrates. Ultra high vacuum conditions were used to allow the evolution of structural and magnetic properties to be studied during film growth. Structural characterisation was by LEED and RHEED and in situ magnetic characterisation by longitudinal MOKE and BLS. These techniques were further used to study the effect of Ag and Cr overlayers on 6 and 14 <SUB>ML</SUB> Fe films. Some films were capped and further characterised ex situ by longitudinal and polar MOKE, and Kerr spectroscopy. Fe films deposited on Ag(001) were found to cover the substrate after approximately 4 <SUB>ML</SUB> had been deposited. Quantitative analysis of the LEED patterns enabled step separations to be estimated. It was found that there was a minimum average step separation at 3 <SUB>ML</SUB> Fe. The LEED patterns show pyramids, characteristic of growth dominated by Schwoebel barriers. In situ BLS and ex situ MOKE was used to study the evolution of the cubic and surface anisotropy constants <I>K<SUB>1</SUB> </I>and <I>K<SUB>s</SUB> </I>with thickness. For very low thicknesses <I>K<SUB>1</SUB> </I>becomes just negative. At low temperatures thin Fe films are magnetised normal to the plane of the film. At higher temperatures an apparent gap in the magnetisation at the out-of-plane transition is seen. At higher temperatures still no remanent perpendicular magnetisation is seen. The gap and loss of remanent magnetisation are found to be due to domain formation. Ag deposited on Fe was found to show very little interaction, and all magnetic effects were saturated within 3 ML<SUB>. </SUB>Cr deposition on Fe gave rise to changes in the surface anisotropy and magnetisation consistent with the antiferromagnetic nature of Cr with the first layer aligned antiparallel to the underlying Fe. This was seen on rougher Fe films.

This is an experimental thesis, intended to discover new features of the Fractional Quantum Hall Effect (FQHE), by the fabrication of lithographic microstructures. It begins with an exposition of the theory required to understand electrical transport in Gallium Arsenide high mobility semiconductor heterostructures at low temperatures, and high magnetic fields. It continues with the various theories which attempt to explain the origin of the FQHE, and some predictions that have been made. The role of fractionally-charged quasiparticles is discussed, particularly with reference to the Aharonov-Bohm effect (AB). Experimental measurements are presented of the Aharonov-Bohm effect in the FQHE, and analysis is presented as to their interpretation. Numerical models are shown to describe the energy dependence of the Aharonov-Bohm oscillations, and fitted to experiment. There is a discussion of how the Fermi liquid model of the edge states in the FQHE produces different predictions than the Luttinger liquid model, and the Fermi liquid model is shown to give a good fit to the experimental data. The edge of the sample in the FQHE is currently a subject of much discussion, so this thesis presents results about the equilibration of electronic edge states in the FQHE. An experimental device was developed which allows a continuous variation in the slope of the electrostatic potential at the edge, thus allowing the equilibration to be altered. Scattering coefficients between edge states, both in the integer and fractional Quantum Hall regimes are derived, and the implications discussed, as is the energy dependence of the scattering, for which a theory is developed. Novel oscillations in the scattering coefficients are also observed, and the system is used to experimentally refute the theoretical prediction that under certain circumstances quasiparticles propagate counter to the standard direction.

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The uniform magnetic susceptibility of La_2-xSr_xCu_1-yZn_yO₄ has been investigated over a wide range of impurity (Zn) concentration for different planar carrier (hole) content, p (º x, for this system), extending from underdoped to heavily overdoped regions. A doping dependent Zn-induced magnetic behaviour is observed for these compounds. The apparent Zn induced moment (expressed as p_eff²/Zn in units of m_B²) is larger in the underdoped side and, decreases quite sharply around p ~ 0.19,without much change for further overdoping. This indicates a possible role of the pseudogap on the Zn induced magnetic behaviour, as there are indications that the pseudogap is present only for p £ 0.19. It is shown that the data can also be interpreted in terms of a Zn-induced low energy quasiparticle resonance that depends on the presence of the pseudogap. The oxygen isotope exponents in superconducting transition temperature and superfluid density, a(T_c) and ap_s), respectively, have been studied as a function of hole (x) and impurity (y) contents in La_2-xSr_xCu_1-yZn_yO₄. The isotope exponents displayed a canonical relationship, except around the region of x ~ 1/8. The results are discussed in terms of the presence of the pseudogap and the stripe correlations. In-plane resistivity measurements under applied magnetic fields (up to 12 Tesla), p_ab(T,H), have been carried out on <i>c</i>-axis oriented thin films of Y_0.95Ca_0.05Ba₂(Cu_1-yZn_y)₃O_7-_dwith varying amount of in-plane disorder (Zn) and hole concentration. Following an earlier work on sintered compounds of the same system, we have obtained supplementary information about the characteristic pseudogap temperature, T*(p), from the analysis of the p_ab(T,H) data. Our thin film data support the earlier findings that T*(p) falls below T_c0(p) (º T_c(p) for pure compound) in the overdoped side and, extrapolates to zero at p ~ 0.19.