The III-V ferromagnetic semiconductor Gallium Manganese Arsenide ((Ga,Mn)As) is one of the most interesting and well studied materials in spintronics research area. The first chapter is a brief introduction to spintronics, the properties of (Ga,Mn)As and the growth technique molecular beam epitaxy (MBE). Then the thesis presents a detailed study of the effect on the Curie temperature (TC) of varying the growth conditions and post-growth annealing procedures for epitaxially grown (Ga,Mn)As materials. The results indicate that it is necessary to optimize the growth parameters and post-growth annealing procedure to obtain the highest TC. From detailed magnetotransport studies, the carrier densities of high TC (Ga,Mn)As and H-doped (Ga,Mn)As have been achieved. It is found that the anomalous Hall resistance is the dominant contribution even at room temperature for these samples, which means it is incorrect to obtain carrier densities directly from Hall slope at high temperature. The results also show that the as-grown and lightly annealed H-doped (Ga,Mn)As samples have relatively high Curie temperatures down to low carrier density which make them good candidates for showing strong gate control of ferromagnetism. Besides (Ga,Mn)As, this thesis also discusses the studies of III-V ferromagnetic semiconductors (Ga,Mn)(As,P), (Al,Ga,Mn)As and some heterostructures based on these materials. The experimental investigation shows that a (Ga,Mn)(As,P) single layer grown on GaAs substrate has perpendicular anisotropy easy axis after annealing. It also demonstrates a method to suppress the diffusion of interstitial Mn ions during low temperature annealing from specific layers in (Al,Ga,Mn)As based heterostructures. The magnetometry study shows that the individual layers in the heterostructure have tailored magnetic properties, which makes this material useful for the further investigation of tunnelling magnetoresistance and spin transfer torque phenomena.

Quantum dots offer a number of advantages over standard fluorescent dyes for monitoring biological systems including high luminescence, stability against photobleaching, and a wide range of fluorescence wavelengths from blue to infrared depending on the particle size. In this work, we investigated in using the protein cage apoferritin as a template for the synthesis of colloidal quantum dots. We obtained apoferritin after reductive dissolution of the ferritin iron core and showed that the protein structure was left intact during this process. We further studied the solubility of ferritin, apoferritin and cationized ferritin in organic and fluorinated solvents by hydrophobic ion pairing methodology in order to expand the possibility of using an apoferritin template for the synthesis of quantum dots in organic media. We then focused on the synthesis and fluorescence properties of PbS quantum dots in aqueous solution. PbS dots are thermally stable and emit in the range 1,100 to 1,300 nm depending on their size. We demonstrated the encapsulation of these PbS quantum dots within the cavity of the iron storage protein apoferritin using two routes: 1) the disassembly/reassembly of apoferritin subunits trapping previously synthesised PbS quantum dots; and 2) use of the channels present in the protein shell to allow the entrance of Pb2+ and S2- ions leading to formation of quantum dots in the apoferritin cavity. We show that PbS-apoferritin composites emit in the near infrared region which make them promising labels for biological applications. Furthermore, we demonstrated that PbS QDs can be excited via a bioluminescence resonance energy transfer (BRET) using luciferin from Luciola mingrelica which could be developed into a self-illuminating labelling system. Finally, in order to make PbS-apoferritin composites selectively attachable to biomolecules during labelling experiments, the apoferritin was modified by the incorporation of analogues of methionine introducing azido groups absent in the proteins. The azido groups can then be selectively modified in complex mixtures e.g. cell lysates using `bio-orthogonal' reactions such as the Cu(I) catalysed Staudinger ligation and Huisgen cycloaddition. This would allow highly selective addition of receptor targeting or cellular permeation of peptides to the outer surface of the apoferritin shell.

This thesis describes the growth and characterisation of four different III-V semiconductor materials. Growth was primarily performed by molecular beam epitaxy, while characterisation, which was largely structural, was carried out mainly using X-ray difraction and atomic force microscopy. Growth of low temperature(LT)GaAs was undertaken to investigate whether a phase transition accompanies the structural transition which occurs when GaAs is grown at temperatures below ~ 150C. It was found however, that LT GaAs remains zinc-blende, albeit with a signicant degree of disorder. Migration enhanced epitaxy was subsequently used to grow LT GaAs, resulting in single crystalline GaAs at growth temperatures down to 115C. The possibility of using AlN as a source for nitrogen, in the growth of GaAs based dilute nitrides was explored. No conclusive evidence has been presented to suggest that small amounts of nitrogen were incorporated into the GaAs lattice. The potential for ScN to be used as a buffer layer/interlayer to reduce the defect density in cubic GaN (c-GaN) was investigated. It was found that ScN grows on c-GaN(0 0 1)/GaAs(0 0 1) in a (1 1 1) orientation, leading to overgrowth of GaN occurring in the hexagonal phase. If the ScN interlayer was sufficiently thin (<3nm), then overgrowth of GaN was cubic, but no evidence of a reduction in stacking fault density was observed. Growth of ScN on GaAs(0 0 1) was also found to result mainly in a (1 1 1) orientation, but films were of poor quality. Growth of ScN on ScAs(0 0 1) was subsequently explored. ScN was found to grow in a (0 0 1) orientation, with both smoother surfaces and improved material quality than ScN(1 1 1). Growth of GaN atop ScN(0 0 1) was found to be c-GaN(0 0 1), but insuffcient studies have been carried out to determine the effect on material quality. During the growth of InGaN, it was found that unmounted substrates lead to large temperatures rises (>100C) for In rich compositions. Modelling heat absorption due to bandgap, phonon and plasmon absorption showed that this is due primarily to the large number of free carriers and not to the narrow bandgap (wrt substrate). The preliminary doping of In0.8Ga0.2N with Mn was investigated. The amount of Mn that can be incorporated without causing a signicant reduction in film quality was found to increase with decreasing growth temperature.

Phase images of the human brain acquired using gradient echo based Magnetic Resonance Imaging techniques show excellent contrast at 7T. This contrast is attributed to small variations in magnetic susceptibility that perturb the main magnetic field and thus yield a spatial variation of the NMR frequency. The work described in this thesis is primarily concerned with mapping the distribution of magnetic susceptibility within the human brain using these phase images. The main technical challenges of the project were first to extract accurate field maps based on phase data, and then to solve the ill-posed problem of inverting these field maps to reconstruct susceptibility (ϰ) maps. In initial work, simulations of field shifts based on known ϰ -distributions are compared to field maps acquired in vivo to highlight the non-local relationship between measured field offsets and the underlying susceptibility. These simulations were carried out using a recently derived Fourier method. The bulk of the thesis is then devoted to a detailed study of the process of inverting field maps generated from phase data using the Fourier relationship to yield quantitative 3D ϰ -maps. Unfortunately, the inversion problem is ill-posed and requires careful conditioning, either through rotation of the sample being imaged or through regularisation. A simple k-space threshold is introduced to condition the inversion and the preliminary results of applying this method to brain data from healthy subjects and patients with Parkinson's disease and multiple sclerosis are presented. The results suggest that susceptibility mapping is sensitive to iron deposition and could be a useful tool in investigating the progression of neurodegeneratived diseases. Iterative inversion algorithms, which deal with noise more robustly and allow more sophisticated filtering techniques to be employed, are then presented. These powerful regularisation methods are compared to previously described techniques, and are shown to yield high quality whole-brain ϰ -maps.

This thesis describes the characterisation of GaMnAs, related compounds and heterostructures. GaMnAs and other (III,Mn)V compounds have provided many interesting insights into fundamental physics, and are of considerable potential interest commercially in the field of spintronics. This study examines a set of samples grown by molecular beam epitaxy and characterised using several techniques: primarily this study makes use of the x-ray absorption techniques, x-ray magnetic circular dichroism(XMCD) and x-ray absorption spectroscopy (XAS). In addition, x-ray diffraction (XRD), transport measurements and super conducting quantum interference device (SQUID) magnetometry were used as complimentary techniques. GaMnAs layers with epitaxial Fe grown on top, are shown to have a sub-nanometre interfacial layer which remains polarised above room temperature. A detailed understanding of these systems is obtained by applying the element specific nature of XMCD in combination with two different probing depths to explore separately the nature of the coupling of the bulk and interfacial region. The coupling between the interfacial layer and the Fe is shown to be strongly antiferromagnetic (AF). A weaker coupling is also shown to exist between the Fe and the bulk of the \gamnas layer below the Curie temperature (Tc). This coupling is also AF at low fields, leading to an exchange bias for the entire layer. Doping of GaMnAs with P is shown to have several effects on the magnetic properties of the GaMnAs layer. Changes in the layer strain are observed using high resolution XRD. This strain also manifests itself in the Mn L_2,3 XMCD spectra and the relationship between the two is shown to be linear. A pronounced effect on the magnetic anisotropy is observed using SQUID measurements, with the easy axis switching from in-plane, in the compressively strained GaMnAs, to out-of-plane in the higher doped GaMnAsP layers. A decrease in total magnetic moment per Mn atom and Tc are observed with increased doping. This is inferred not to be due to a direct effect of the P on the local surrounding of the Mn ions, owing to the striking similarity of the XMCD spectra. This is instead attributed to reduced participation of Mn ions in the magnetic ordering. Finally, K edge XMCD is used to reveal the element specific nature of unoccupied states near the Fermi level in a set of GaMnAs and (In,Ga,Mn)As samples with differing Mn doping levels . The character of the holes in low-doped samples is shown to be markedly different than for those in the highly doped metallic samples. A transfer of orbital magnetic moment from the Mn to the As sites is observed on crossing the metal-insulator transition, with the large XMCD on Mn sites in low doped samples interpreted as a sign of hole localisation around the Mn ion.

We have investigated the use of calix[4]arenes in 3d and 3d/4f chemistry which produced a family of 7 new complexes. These are: [MnIII2MnII2(OH)2(TBC4)2(DMF)6] (1) , the analogous version with C4 (2). [MnIII4GdIII4(OH)4(C4)4(NO3)2(DMF)6(H2O)6](OH)2 (3), [MnIII4TbIII4(OH)4(C4)4(NO3)2(DMF)6(H2O)6](OH)2 (4), [MnIII4DyIII4(OH)4(C4)4(NO3)2(DMF)6(H2O)6](OH)2 (5), [CuII9(OH)3(TBC4)3Cl2(DMSO)6](CuICl2)·DMSO (6·DMSO) (6) and [CuII9(OH)3(TBC4)3(NO3)2(DMSO)6](NO3)· DMSO (7·DMSO) (7). We continued with a series of Pseudo Metallocalix[6]arene planar disc complexes : [Ni7(OH)6(L1)6](NO3)2 (8), [Ni7(OH)6(L1)6](NO3)2.2MeOH (9), [Ni7(OH)6(L1)6](NO3)2.3MeNO2 (10), [Ni7(OH)6(L2)6](NO3)2.2MeCN (11), [Zn7(OH)6(L1)6](NO3)2.2MeOH.H2O (12) and [Zn7(OH)6(L1)6](NO3)2.3MeNO2 (13) and in the final part of this thesis we present a family of tetranuclear mixed valent Mn complexes using the tripodal ligand heedH2 : [MnII2MnIV2O2(heed)2(EtOH)6Br2]Br2 (14), [MnII2MnIV2O2(heed)2(H2O)2Cl4] (15), [MnII2MnIV2O2(heed)2(heedH2)2](ClO4)4 (16), [MnII2MnIV2O2(heed)2(MeCN)2(H2O)2(bpy)2](ClO4)4 (17), [MnII2MnIV2O2(heed)2(bpy)2Br4] (18); and the 2-D network of tetranuclear MnII/IV clusters {[MnII2MnIV2O2(heed)2(H2O)2(MeOH)2(dca)2]Br2}n (19). In total nineteen new complexes are reported. Studies of the magnetic properties show that 1 and 2 are SMM’s, whilst complex 3 is an excellent magnetic refrigerant for low-temperature applications and 4 and 5 behave as low-temperature molecular magnets.

The existence of magnetization signatures and landform modification antipodal to young lunar impact basins is investigated further by (a) producing more detailed regional crustal magnetic field maps at low altitudes using Lunar Prospector magnetometer data; and (b) examining Lunar Reconnaissance Orbiter Wide Angle Camera imagery. Of the eight youngest lunar basins, five are found to have concentrations of relatively strong magnetic anomalies centered within 10° of their antipodes. This includes the polar Schrödinger basin, which is one of the three youngest basins and has not previously been investigated in this context. Unusual terrain is also extensively present near the antipodes of the two largest basins (Orientale and Imbrium) while less pronounced manifestations of this terrain may be present near the antipodes of Serenitatis and Schrödinger. The area near the Imbrium antipode is characterized by enhanced surface thorium abundances, which may be a consequence of antipodal deposition of ejecta from Imbrium. The remaining three basins either have antipodal regions that have been heavily modified by later events (Hertzsprung and Bailly) or are not clearly recognized to be a true basin (Sikorsky-Rittenhouse). The most probable source of the Descartes anomaly, which is the strongest isolated magnetic anomaly, is the hilly and furrowed Descartes terrain near the Apollo 16 landing site, which has been inferred to consist of basin ejecta, probably from Imbrium according to one recent sample study. A model for the origin of both the modified landforms and the magnetization signatures near lunar basin antipodes involving shock effects of converging ejecta impacts is discussed.

This doctoral thesis presents density functionalcalculations applied in several domains of interest in solidstate physics and materials science. Non-collinear magnetismhas been studied both in an artificial multi-layer structure,which could have technological relevance as a magnetic sensordevice, and as excitations in 3d ferromagnets. The intricatebulk crystal structure of γ-alumina has been investigated.An improved embedded cluster method is developed and applied tostudy the geometric and electronic structures and opticalabsorption energies of neutral and positively charged oxygenvacancies in α-quartz. Ab initio total energycalculations, based on the EMTO theory, have been used todetermine the elastic properties of Al1-xLixrandom alloys in the face-centered cubiccrystallographic phase. The obtained overall good agreementwith experiment demonstrates the applicability of the quantummechanics formulated within the framework of the DensityFunctional Theory for mapping the structural and mechanicalproperties of random alloys against chemical composition.

Magnetic storage means storage of data using magnetised medium and is widespreadover the world today, especially in hard disk drives. Using this kind of storagerequires knowledge about these materials. A way to study thin magnetic materials isto use MOKE(magneto optical Kerr effect). A Moke-system is a setup to measure thinmagnetic films by shooting a laser and analyze the reflected beam.The purpose of this report is to document and if possible improve a MOKE-system,named HOMER. This includes temperature regulation, filters, amplifiers, opticalchopper, Helmholtz coils and a laser. HOMER was documented and some changeswere made. The PID-parameters were set successfully. A low pass filter wasremoved, which decreased the noise. Using an optical chopper and lock in amplifierhowever did not decrease the noise. A labview program was written to demagnetizethe samples in a certain time which seemed to work properly. The hall probe in thesystem was successfully calibrated.

The twofold purpose of this investigation was to design and construct an apparatus for direct magnetic susceptibility measurements as a function of temperature and to provide the complete susceptibility characterization of the free radical galvinoxyl in the room temperature-liquid nitrogen range.