Hyperpolarised gas Magnetic Resonance Imaging (MRI) is a non-invasive method developed to provide images of the void spaces of the lungs, and evaluate the distal airways via diffusion weighted techniques. The work in this thesis covers the use of both hyperpolarised 3He and hyperpolarised 129Xe gas MRI, for both diffusion measurement studies and ventilation imaging, on healthy, asthmatic and cystic fibrosis volunteers. The first study covered in this thesis aimed to determine the nature of the acinar airway involvement in asthma sufferers via the use of Computed Tomography densitometry and hyperpolarised 3He diffusion MRI at multiple timescales alongside standard lung function tests such as spirometry and multiple breath washout (MBW). It was hypothesised that Asthma patients with an elevated MBW parameter 'Sacin' would manifest altered long-range diffusion, as suggestive of intra-acinar airway disease. It was found that there appeared to be an association between the MBW 'Sacin' parameter and subtle alterations in diffusion within the acinar airways for participants with asthma, suggesting a structural abnormality in the pulmonary acinus. However, further longitudinal studies are required before the long-term prognostic significance of acinar airway disease in asthma can be determined. The second study aimed to determine if a relationship exists between measurements from standard lung function test, spirometry and body plethysmography, and the measurements of hyperpolarised 3He diffusion MRI. 18 Cystic Fibrosis patients were recruited, alongside 27 age-matched healthy subjects. It was found that the short timescale diffusion values were lower in patients with Cystic Fibrosis, although not substantial enough to use an indicator to distinguish between a healthy volunteer and a Cystic Fibrosis patient. No strong correlations were found between the lung function measurements and the hyperpolarised 3He diffusion MRI measurements. The final section of this thesis looks at the preliminary results of a pilot study to develop scan sequences, protocols and gas delivery of hyperpolarised 129Xe MRI, in preparation for future clinical studies at the University of Nottingham. The main focus was on the development of in vivo ventilation images of the human lungs, to a high standard of quality and repeatability. Good progress was demonstrated, with lung images achieved down to 2.5 cm thick slices, with initial images of both dynamic ventilation and dissolved-phase 129Xe lung images. However the pilot study was not yet complete, and more development on the techniques discussed was still required.

Over the past years there has been great progression in the field of micro- and nanomechanics with devices with higher and higher Q factors being created. This has been made possible thanks to a combination of advances in fabrication techniques and an increase in understanding as to what causes dissipation in nanometre scale structures. This understanding of dissipation mechanisms is still incomplete however. While lots of work has been done investigating mechanisms such as thermoelastic dissipation and dissipation due to two level systems (TLS) within the standard tunnelling model (STM) a full understanding has not been forthcoming. The increase in the quality of nanomechanical systems has allowed them to be coupled to optical or microwave cavities allowing the position of the mechanical system to be measured with near quantum limited accuracy. This thesis looks at both these streams of research within nanomechanics. It looks at the fabrication of silicon nitride torsional resonators that can have either their flexural or torsional modes preferentially actuated via a piezoelectric drive. It was found for a single paddle resonator that the room temperature Q factor of the flexural mode was 2870±70 and for the torsional mode was 5050±220. It was shown that while thermoelastic damping was reduced in the torsional mode it was still present meaning that we could not use the model for a simple beam to describe thermoelastic damping for a paddle resonator. The properties of an nanomechanical beam fabricated from a single crystal of aluminium were also investigated. It was found that at 1.5 K it had an unloaded Q factor of 36900 which is at least 2 times larger then any other group has reported. We also used our knowledge of high stress silicon nitride membranes to design a system that could couple an aluminium on silicon nitride membrane to a LCR circuit. Calculations show that this would have a coupling constant, g, of over 1000 putting it well within the regime where ground state cooling and quantum limited measurements are possible.

Hard disk drives (HDDs) have been the dominant secondary memory device in computing for over 50 years, while more recently magnetoresistive random access memory (MRAM) has emerged as a candidate for primary computing memory. Both HDDs and MRAM store information in the polarity of a magnetic layer, which is written and read by non relativistic mechanisms. There is now gathering interesting in using relativistic mechanisms whose origins lie with spin-orbit coupling (SOC) for MRAM writing because of potential benefits in terms of scalability, device design, and efficiency. This thesis investigates the fundamental physics of SOC phenomena that can write (spin-orbit torque (SOT), Neel order SOT) or read (anisotropic magnetoresistance (AMR), magnetic gating) the magnetic state by the application of electrical current. These phenomena are studied in ferromagnetic and antiferromagnetic semiconducting materials that offer a relevant electrical conductivity for integration into commercial electronic devices. Effective magnetic fields which parametrise the SOT phenomenon are measured in the diluted magnetic semiconductor (Ga,Mn)As using a technique based upon experimental planar Hall effect measurements and analytical fitting with a free energy equation for coherent magnetization rotation. It is found that effective magnetic fields which originate from Dresselhaus SOC increase in magnitude with increasing temperature, whereas those originating from Rashba SO have no significant temperature dependence within experimental uncertainty. The size of the measured effective fields per unit of current density, as well as the ratio of Dresselhaus to Rashba effective field magnitudes averaged over all temperatures are comparable to previous experimental measurements. Sb-based diluted magnetic semiconductors (Ga,Mn (As0.9,Sb0.1) and (Ga,Mn)Sb are characterised by magnetic and transport measurements. The Curie temperature (Tc) of (Ga,Mn)(As0.9,Sb0.1) increases from 28K to 55K upon sample annealing. The Tc of as-grown (Ga,Mn)Sb is found to be 34K, and in contrast to (Ga,Mn)(As0.9,Sb0.1) does not change upon annealing, indicating a lack of interstitial Mn in (Ga,Mn)Sb. Field rotation transport measurements for current along various crystalline directions reveal significant crystalline and non crystalline contributions to the AMR of both as-grown and annealed (Ga,Mn)(As0.9,Sb0.1). An anomalous temperature dependence of the AMR of the annealed (Ga,Mn (As0.9,Sb0.1) sample for current along the [110] crystalline direction is accounted for by considering the relative sizes of the individual AMR contributions as a function of temperature. Results are shown of an attempt to vary the current flow through a non-magnetic GaAs/AlGaAs 2D electron gas (2DEG) by changing the magnetization orientation of an electrically insulated Fe gate layer. Such magnetic gating of electrical current is based upon the principle that, as a result of SOC, the electrochemical potential of a ferromagnet is anisotropic with respect to its magnetization orientation. The magnetic gating experiment proved to be unsuccessful due to an AMR-like signal arising in field rotation measurements of 2DEG samples both with and without the gate layer. The origins of this AMR-like signal are unknown, and it cannot not be accounted for by fitting analysis.

This extended abstract describes the background to the 14 research papers that the author, as staff candidate, is submitting for the award of PhD by published works. The core part of this work refers to the development of volumetric biomarkers within the human digestive tract using magnetic resonance imaging (MRI) and their application to answer novel biomedical research questions. In particular the author’s work has focussed on applying these techniques within the human colon and the first two papers (which detail this work) were led and written by the author. This work was pioneering in its field, the first time that physiologically undisturbed colon volumes were measured in healthy human subjects and in patients suffering from irritable bowel syndrome (IBS) and provided novel insights into the post-prandial symptoms experienced. Subsequently the effect of an experimental stress on this post prandial response was evaluated in healthy subjects, also the first time such an effect had been measured. The third paper, also written by the author, describes her work on the first clinical application of similar volumetric techniques to assess the human nasal airways and their response to pharmacological intervention, in this case the efficacy of a nasal decongestant. This document seeks to set the gastro-intestinal papers within their scientific and physiological background and to show their original contribution to the current understanding of the physiological processes within the human gastro-intestinal tract. Between mouth and anus, a complex myriad of mechanical, chemical and biological procedures interact to liquefy and transport food; to break it down into increasingly simpler chemical forms; absorb nutrients and then eject what is no longer required. MRI provides a unique window into the functions and form of this environment at the macroscopic level; a non-invasive tool for detecting and measuring the structure and physical movements of the abdominal organs and their contents, monitoring fluid transport and providing insights into the biological processing therein. This can provide quantitative biomarkers to rigorously assess the normal undisturbed physiology in health and disease and the effect of pharmacological interventions. It is a hitherto relatively unexplored area and it is the development and application of such measurements that form the bulk of the author’s research contained within the presented publications.

Increased signal to noise ratio in high field magnetic resonance imaging (MRI) allows the acquisition of high resolution images and the development of the quantitative techniques for measuring tissue properties. This detailed information can provide a better understanding of the structure and function of the healthy brain but, more importantly, it can also provide methods for explaining pathological processes in neurodegenerative diseases. The work described in this thesis investigated iron and myelin content in the brain using 7T MRI. Multiple sclerosis (MS) is one of the most common demyelinating diseases. White matter (WM) lesions detected in MS with conventional MRI techniques show poor correlation with the disease progression. In this work investigation of degeneration of the WM as well as cortical and deep grey matter (GM) in MS and clinically isolated syndrome (CIS) suggestive of MS was performed using high resolution quantitative MRI techniques. Iron plays an important role in the physiological processes of the healthy brain, but its excessive accumulation in the particular brain structures accompanies neurodegeneration in Parkinson’s disease (PD). Studies analysing anatomy and quantitative properties of these structures, in vivo and post mortem, comparing PD patients with healthy controls are presented in this thesis. Investigation related to iron is supported by the simulations aimed at understand the effects of tissue microstructure related to iron on the MR signal. The presented analyses provide a better understanding of the complex dependencies of different MR contrasts on myelin and iron content.

This thesis is an experimental study of structural and magnetic properties, and hyperfine interactions in crystalline alloys Cu2GdIn, CrNiP, CrNiAs, EuCu2Si2, Cr2FeSe4 and icosahedral quasicrystals Al60Cr19.9Fe0.1Ge 20, Ag50In36Gd14, Zn77Fe 7Sc16. The Heusler alloy Cu2GdIn is shown to crystallize in the L21 crystal structure (space group Fm3¯ m) with a lattice constant of 6.6643(3) A. It is an antiferromagnet with the Neel temperature of 9.6(1) K, the effective magnetic moment of 7.98(4) muB per Gd atom, and the paramagnetic Curie temperature of --41.2(9) K. Its Debye temperature is 229(5) K. The alloys CrNiP and CrNiAs crystallize, respectively, in the Co 2P-type structure (space group Pnma) and the Fe 2P-type structure (space group P6¯2 m), with the lattice parameters a = 5.7965(1) A, b = 3.5337(1) A, c = 6.8123(2) A, and a = 6.1128(2) A, c = 3.6585(1) A. CrNiP is shown to be a three-dimensional Heisenberg ferromagnetic with the Curie temperature of 142.9(6) K, whereas CrNiAs is demonstrated to be a mean-field ferromagnet with the Curie temperature of 171.9(1) K. A long standing controversy concerning the Ni magnetic moment in these alloys is solved unequivocally: Ni atoms carry a magnetic moment of 0.14 muB in CrNiP and 0.15(3) mu B in CrNiAs. The Debye temperatures of CrNiP and CrNiAs are, respectively, 261(3) K and 221(1) K. EuCu2Si2 is one of the first Eu-based alloys in which intermediate valence behavior of Eu was observed. It is demonstrated here that there are no valence fluctuations of Eu in this alloy: Eu atoms are divalent in the temperature range 2-300 K. The Debye temperature of EuCu 2Si2 is shown to be 236(4) K. Cr2FeSe4 is found to have antiferromagnetism with weak ferrimagnetism due to the two different distortions of the octahedral Cr3+ and the octahedral Fe2+. A negative magnetization is found in a magnetic field of 5 De and below due to the coercive-field magnetization reversal. The magnetization reversal disappears in a magnetic field larger than 65 Oe. The icosahedral quasicrystals Al60Cr19.9Fe 0.1Ge20, Ag50In36Gd14, and Zn77Fe7Sc16 are shown to have a primitive six-dimensional Bravais lattice with a six-dimensional lattice constant of 6.558(2) A, 7.805(2) A, and 8.087(1) A, respectively. Al 60Cr19.9Fe0.1Ge20 is a paramagnet with the effective magnetic moment of 0.312(3) muB per Cr/Fe atom. Its Debye temperature is 463(15) K. The temperature dependence of the electrical conductivity of Al60Cr19.9Fe0.1Ge20 is well accounted for quantitatively by theories of quantum interference effects. Ag50In36Gd14 and Zn77Fe 7Sc16 are shown to be spin glasses with the spin freezing temperature of 4.25(5) K and 7.75(2) K, respectively. The hyperfine magnetic fields at 155Gd and 57Fe nuclei in g50 In36Gd14 and Zn77Fe7Sc 16 are shown to set in at temperatures larger than the corresponding freezing temperatures. The frequency dependence of the freezing temperature in Zn77Fe7Sc16 is shown to be equally well accounted for by the Vogel-Fulcher law and the power law. Analysis of the aging effects observed in Zn77Fe7Sc16 leads to a major finding that the nature of the spin-glass state in this quasicrystal is fundamentally different from that of a canonical spin glass. The Debye temperatures of Ag50In36Gd14 and Zn 77Fe7Sc16 are, respectively, 199(2) K and 443(8) K.

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