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Abstract: Gas-phase Fe nanoparticles with a diameter ~ 2nm, have been used in all the nanostructured material in this thesis. In pure Fe nanoparticle systems with different thicknesses, two important parameters the exchange interaction (Hex) and random anisotropy (Hr) were investigated using the Random Anisotropy Model (RAM). This reveals that for the same particle size Hex remains almost constant for varying Fe thicknesses; whereas Hr increases with the increase of Fe film thickness. This is ascribed to increasing strain imposed at the nanoparticle level. The observed high values of Hr are related to an oxide on the cluster surface in these films, whose effect is also observed in low temperature magnetometry data. This shows the appearance of exchange bias in the films. The RAM approach when applied to Fe clusters in Co matrices, reveals much lower values of Hr than found in pure Fe nanoparticles and both Hr and Hex show an increase with the Volume Fraction (VF) of Fe in Co. The increase in Hex is ascribed to the increasing spin moment with Fe volume fraction. The nature of Fe clusters in very thick layers produce a high frequency Ferromagnetic Resonance response in the radio frequency range, which is an important finding for many applications. The EXAFS study of Fe nanoparticles in Cr matrices show no structural modification relative to the bulk bcc structure of both elements. The magnetometry results suggest that in dilute Fe concentration films, the observed decrease in the overall magnetization is due to the development of a nonmagnetic shell at the interface between Fe and Cr at each cluster boundary. This is reinforced by the lack of any evidence of EB. With increasing VF at about 10% of Fe there is strong evidence of the formation of a super-spin-glass (SSG) that shows the characteristic memory effect. Increasing the Fe nanoparticles VF to 20% Fe in Cr, the magnetization exceeds that expected for Fe indicating that the interaction induces some of the Cr to order ferromagnetically. Core-shell nanoparticle systems have been synthesised by a method that allows a complete control over the morphology of these assemblies. Atomic investigations in Fe@Cu CS nanoparticles reveal that Fe nanoparticles adopt the fcc structure with a 20 monolayer Cu shell thickness and stay in the bcc structure for 1-2 monolayer thick Cu shells. No alteration in the Fe atomic structure has been reported for different Au shell thicknesses in Fe@Au. The magnetic data show a reduced magnetization of the FM-AFM Fe@Cr CS nanoparticles as compared to the bulk value which is also ascribed to the formation of a non-magnetic Fe shell at the interface.

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Abstract: Zircon (ZrSiO4) is a durable mineral found in most igneous rocks; it is highly retentive of the trace element concentrations it acquires at crystallisation, and its high initial concentrations of U and Th relative to Pb make it the most important mineral for radiometric dating. Therefore, it is a valuable archive of magmatic processes, particularly with regard to those occurring on the early Earth. Based on crystal chemistry, anomalous Ce and Eu concentrations in zircon relative to other rare earth elements (REE) seem likely to reflect the oxidation state of the magma. Zircons were grown experimentally under controlled conditions of oxygen fugacity (fO2) and the crystals and coexisting glass were analysed by SIMS and LA-ICP-MS to examine the covariation of the partition coefficients of Ce and Eu, as well as those of other trace elements. This revealed that with increasing fO2, Ce becomes more compatible and Eu and U become less compatible. There is a narrow window of fO2s in which a Ce and a Eu anomaly coexist. Literature data allow the partitioning data obtained for the heavy REE in this study to be extrapolated to other temperatures. To allow extrapolation of the partitioning experiments, Ce- and Eu-doped glasses of various melt compositions were prepared at a range of fO2s and temperatures. X-ray absorption near edge structure (XANES) spectroscopy of these glasses was carried out at the LIII-edge of these elements to determine their oxidation state ratios. Because of beam damage effects for the Eu-bearing glasses, a limited number of XANES spectra were recorded in situ at 1400 °C, and some samples were analysed by electron paramagnetic resonance spectroscopy. The results obtained were compared to trace element concentrations in zircons from some natural samples, and suggestions for future work made.

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Abstract: The variation in geographical distribution of selenium (Se) in environmental settings and the food chain can cause serious human health deficiencies, or poisoning and fatal death. Although Se toxicity is usually inferred as caused by local geology or human activities, the current food trade practices raise Se concerns to a global level, as the Se contained in agricultural products is often unknown. In most natural settings, the prime -. source of Se are shale rocks. Yet, Se weathering pathways and release mechanisms are poorly understood because the locus and the distribution of Se in shales are unknown. Therefore, this thesis assessed the geochemical environment surrounding Se in shales and identified the main inorganic and organic host phases and elucidated the Se speciation and the way this may affect the Se mobilization pathways. This was done by combining simple and complex geochemical, mineralogical and spectroscopic techniques -that were statistically validated to analyse shale samples from the UK, Colombia and China that were representative for typical (1 - 10 ug/g) and extreme (>1 %) Se concentrations. The first important result was the identification of pyrite and organic matter as the two main Se host phases. Additionally, the data showed that in typical shales (e.g. with <6% organic C and 1-2% reduced inorganic S) Se was preferentially associated to pyrite, while in low pyrite shales the association between Se and organic matter was favoured. Interestingly, the data also revealed that depending on the formation pathways pyrite morphology also differentially bound Se with euhedrals concentrating more Se than framboids. Finally, the spectroscopic data showed that Se was not substituting S in pyrite, instead Se was present as an independent FeSex species in close association with both euhedral and framboidal pyrite. Conversely, in the organic matrix, nanosized elemental Se and organo-Se species (Se=C, Se-Se and Se-C bonds) were the main Se carriers.

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Abstract: We present recent experimental results on the structural, electrical, magnetic, and magneto-optical properties of Mn-implanted Si and Co-doped TiO2?? magnetic oxides. Si wafers, both n- and p-type, with high and low resistivity, were used as the starting materials for implantation with Mn ions at the fluencies up to 5 × 1016 cm?2. The saturation magnetization was found to show the lack of any regular dependence on the Si conductivity type, type of impurity and the short post-implantation annealing. According to XMCD Mn impurity in Si does not bear any appreciable magnetic moment at room temperature. The obtained results indicate that above room temperature ferromagnetism in Mn-implanted Si originates not from Mn impurity but rather from structural defects in Si. The TiO2?? :Co thin films were deposited on LaAIO3 (001) substrates by magnetron sputtering in the argon–oxygen atmosphere at oxygen partial pressure of 2·10?6–2·10?4 Torr. The obtained transverse Kerr effect spectra at the visible and XMCD spectra indicate on intrinsic room temperature ferromagnetism in TiO2?? :Co thin films at low (< 1%) volume fraction of Co.

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Abstract: Although at 1 atm pressure the oxidation state of W in silicate melts is 6 + at oxygen fugacities from air down to several logfO2 units below Fe-FeO (IW) equilibrium, Cottrell et al. (2009) suggested that, at pressures above 6 GPa, W becomes predominantly 4 + in this oxygen fugacity range. Wade and Wood (2005), using a similar, but expanded metal-silicate partitioning dataset found, however, no evidence for an oxidation state change. In order to resolve the issue we collected tungsten L3 edge XANES spectra of a series of synthetic tungsten- bearing glass standards and of silicates from a range of high-pressure (1.5 to 25 GPa) metal/silicate partitioning experiments. Glass standards were made at 1 atm pressure and equilibrated at oxygen fugacities spanning a range from approximately 5.5 log units below the Fe-FeO buffer (IW-5.5) to Air. Metal-silicate partitioning experiments were performed at oxygen fugacities between IW-6.2 and IW-1 and at pressures between 1.5 and 25 GPa. At low pressures and oxygen fugacities above IW-3.5, W exists in the silicate melt almost exclusively as W6 + (identical L3-edge energy to WO3) with the progressive reduction to W4 + completed by about IW-6. The XANES spectra of W from experiments at 6, 7 and 25 GPa are completely consistent with those from 1 atm and 1.5 GPa experiments and with that of WO3. We conclude that there is no change of oxidation state with increasing pressure to 25 GPa and that modelling of the oxygen-fugacity dependence of core formation requires use of a + 6 oxidation state of W.