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In the present work, the thermodynamic activites of ironoxide, denoted as "FeO" in the slag systems Al2O3-"FeO", CaO-"FeO", "FeO"-SiO2, Al2O3-"FeO"-SiO2, CaO-"FeO"-SiO2and "FeO"-MgO-SiO2were investigated by employing the gasequilibration technique at steelmaking temperatures. Thestrategy was to expose the molten slag mixtures kept inplatinum crucibles for an oxygen potential, determined by aCO/CO2-ratio. A part of the iron reduced from the "FeO"in the slag phase was dissolved into the Pt crucible. In order to obtain the activites of "FeO", chemical analysisof the quenched slag samples together with thermodynamicinformation of the binary metallic system Fe-Pt is required.Careful experimental work was carried out by employing asolid-state galvanic cell technique as well as calorimetricmeasurements in the temperature ranges of 1073-1273 K and300-1988 K respectively. The outcome of these experiments wasincorporated along with previous studies into a CALPHAD-type ofthermodynamic assessment performed with the Thermo-Calc™software. The proposed equilibrium diagram enabledextrapolation to higher temperatures. The experimentally obtained activites of "FeO" in thepresent work, along with earlier investigations were assessedwith the KTH slag model, THERMOSLAG©. New binaryparameters were evolved and incorporated in THERMOSLAG©.The present model calculations are compared with othercommercially available software such as F*A*C*T™andThermo-Calc™. The validity of the modified model wasinvestigated by measurements carried out in case of Al2O3-"FeO"-SiO2, CaO-"FeO"-SiO2and "FeO"-MgO-SiO2ternary slags. The potential of the model tocompute the activities in the case of multicomponent slags wasdemonstrated. A correlation between the activity of a metallic oxide in aternary slag system and the sulphide capacity of the slag wasinvestigated by using the solubility of sulphur in the binarysystems CaO-SiO2and Al2O3-CaO along with the sulphide capacity of the Al2O3-CaO-SiO2system. The estimated values of the activitieswere found to be in good agreement with the measured values.This correlation also gives the possibility to elucidate theapplicability of Henry's law to the activity of a metallicsulphide and to determine the order in the affinity of a cationto sulphur between two metallic oxides in a slag. Model calculations were performed with THERMOSLAG©, by using plant data from the ladle refiningprocess at OVAKO Steel, Hofors, Sweden. It was found thatoxygen estimations in the metal from the "FeO" analyses ofslags, obtained by conventional sampling and analysis methodwere less reliable. Reliable estimation of the oxygen levelsutilising the sulphur partition between the slag and the metalwere carried out using THERMOSLAG© software. <b>Keywords:</b>Thermodynamics, Activity, Galvanic cell,Calorimetry, Gas equilibration technique, Iron-platinum alloys,FeO, Slags, Modelling, Ladle

<p>In the present work, the thermodynamic activites of ironoxide, denoted as "FeO" in the slag systems Al₂O₃-"FeO", CaO-"FeO", "FeO"-SiO₂, Al₂O₃-"FeO"-SiO₂, CaO-"FeO"-SiO₂and "FeO"-MgO-SiO₂were investigated by employing the gasequilibration technique at steelmaking temperatures. Thestrategy was to expose the molten slag mixtures kept inplatinum crucibles for an oxygen potential, determined by aCO/CO₂-ratio. A part of the iron reduced from the "FeO"in the slag phase was dissolved into the Pt crucible.</p><p>In order to obtain the activites of "FeO", chemical analysisof the quenched slag samples together with thermodynamicinformation of the binary metallic system Fe-Pt is required.Careful experimental work was carried out by employing asolid-state galvanic cell technique as well as calorimetricmeasurements in the temperature ranges of 1073-1273 K and300-1988 K respectively. The outcome of these experiments wasincorporated along with previous studies into a CALPHAD-type ofthermodynamic assessment performed with the Thermo-Calc™software. The proposed equilibrium diagram enabledextrapolation to higher temperatures.</p><p>The experimentally obtained activites of "FeO" in thepresent work, along with earlier investigations were assessedwith the KTH slag model, THERMOSLAG©. New binaryparameters were evolved and incorporated in THERMOSLAG©.The present model calculations are compared with othercommercially available software such as F*A*C*T™andThermo-Calc™. The validity of the modified model wasinvestigated by measurements carried out in case of Al₂O₃-"FeO"-SiO₂, CaO-"FeO"-SiO₂and "FeO"-MgO-SiO₂ternary slags. The potential of the model tocompute the activities in the case of multicomponent slags wasdemonstrated.</p><p>A correlation between the activity of a metallic oxide in aternary slag system and the sulphide capacity of the slag wasinvestigated by using the solubility of sulphur in the binarysystems CaO-SiO₂and Al₂O₃-CaO along with the sulphide capacity of the Al₂O₃-CaO-SiO₂system. The estimated values of the activitieswere found to be in good agreement with the measured values.This correlation also gives the possibility to elucidate theapplicability of Henry's law to the activity of a metallicsulphide and to determine the order in the affinity of a cationto sulphur between two metallic oxides in a slag.</p><p>Model calculations were performed with THERMOSLAG^©, by using plant data from the ladle refiningprocess at OVAKO Steel, Hofors, Sweden. It was found thatoxygen estimations in the metal from the "FeO" analyses ofslags, obtained by conventional sampling and analysis methodwere less reliable. Reliable estimation of the oxygen levelsutilising the sulphur partition between the slag and the metalwere carried out using THERMOSLAG© software.</p><p><b>Keywords:</b>Thermodynamics, Activity, Galvanic cell,Calorimetry, Gas equilibration technique, Iron-platinum alloys,FeO, Slags, Modelling, Ladle</p>

Silicon nanowires, silicon nanorods, and magnetic nanocrystals have shown interesting size, shape, mechanical, electronic, and/or magnetic properties and many have proposed their use in exciting applications. However, before these materials can be applied, it is critical to fully understand their properties and how to synthesize them economically and reproducibly. Silicon nanowires were synthesized in high boiling point ambient pressure solvents using gold and bismuth nanocrystals seeds and trisilane as the silicon precursor. Reactions temperatures as low as 410°C were used to promote the solution-liquid-solid (SLS) growth of silicon nanowires. The silicon nanowires synthesis was optimized to produce 5 mg of silicon nanowires with average diameters of 30 nm and lengths exceeding 2 [mu]m by adjusting the silicon to gold ratio in the injection mixture and reaction temperature. Silicon nanorods were synthesized using a solution-based arrested-SLS growth approach where gold seeds, trisilane, and a dodecylamine were vital to the success. Dodecylamine was found to prevent gold seed coalescence at high temperatures -- creating small diameter rods -- and bond to the crystalline silicon surface -- preventing silicon nanorod aggregation. Furthermore, an etching strategy was developed using an emulsion of aqua regia and chloroform to remove the gold seeds from the silicon nanorods tip. A thin silicon shell surrounding the gold seed of the silicon nanorod was subsequently observed. Multifunctional colloidal core-shell nanoparticles of iron platinum or iron oxide encapsulated in fluorescent dye doped silica shells were also synthesized. The as-prepared magnetic nanocrystals are initially hydrophobic and were coated with a uniform silica shell using a microemulsion approach. These colloidal heterostructures have the potential to be used as dual-purpose tags, exhibiting a fluorescent signal that could be combined with enhanced magnetic resonance imaging contrast. Compositionally-ordered, single domain, antiferromagnetic L1₂ FePt₃ and ferromagnetic L1₀ FePt nanocrystals were synthesized by coating colloidally-grown Pt-rich or stoichiometricly equal Fe-Pt nanocrystals with thermally-stable SiO₂ and annealing at high temperature. Without the silica coating, the nanocrystals transform predominately into the L1₀ FePt phase due to interparticle diffusion of Fe and Pt atoms. Magnetization measurements of the L1₂ FePt₃ nanocrystals revealed two antiferromagnetic transitions near the bulk Neél temperatures of 100K and 160K. Combining L1₂ FePt₃ nanocrystals with L1₀ FePt nanocrystals was found to produce a constriction in field-dependent magnetization loops that has previously been observed near zero applied field in ensemble measurements of single domain silica-coated L1₀ FePt nanocrystals. Dipole interactions between FePt@SiO₂ nanoparticles with varying SiO₂ shell thickness was also explored. / text

Iron platinum (FePt) has attracted growing interest because of its high Curie temperature, magneto-crystalline anisotropy and chemical stability. Nanoparticles (NPs) made of this alloy are promising candidates for a wide range of biomedical applications including magnetic separation, magnetic targeted drug delivery, hyperthermia for cancer therapy and also as magnetic resonance imaging (MRI) contrast agents. This thesis presents the synthesis, functionalization and characterization of FePt NPs along with a toxicity study and an investigation into their application as MRI contrast agents. Regarding their synthesis, different approaches have been explored including the co-reduction of Fe and Pt precursors in an aqueous media, the thermal decomposition in a conventional high-boiling solvent such as benzyl ether, and in low-melting organic salts (ionic liquids). The data revealed an inhomogeneous composition distribution of Fe and Pt between particles obtained in aqueous media, due to the iron salts hydrolysis, and a mismatch in the co-reduction kinetic of the two metal precursors. While the iron content in the NPs could be increased by using more hydrolytically stable iron precursors or stronger reducing agents, there are remaining limiting parameters which prevent further Fe content increase in NPs. In contrast, by excluding the water from the reaction system and using a Fe²⁻ iron precursor, homogenous 1:1 Fe to Pt ratio NPs can be obtained through a modified thermal decomposition pathway in benzyl ether. Based on the study of synthesis in this conventional chemical, the potential of ionic liquids (ILs) to be used as novel solvents for FePt NPs synthesis was further explored. It was then demonstrated that ionic liquids (ILs) can not only be used as a solvent for synthesis of FePt NPs, but also can provide an exciting alternative pathway to direct synthesis fct-FePt NPs. In the context of the bioapplication of FePt NPs, a family of FePt NPs was specifically designed to enhance their MRI contrast agents properties. In contrast with previous reports, this thesis demonstrates that FePt NPs can be made non-toxic and provides the first data on their cellular uptake mechanisms. A six times increase in the FePt based T₂ contrast properties compared to clinical iron oxide NPs is reported. The relationship between the MRI contrast properties and the NPs architecture is explored and rationalised as the basis for the design of NPs as enhanced MRI contrast agents. Finally, the first observations of cellular and in vivo MR imaging with FePt NPs is also reported. This study opens the way for several applications of FePt NPs such as regenerative medicine and stem cell therapy, thus providing a bio-platform to develop novel diagnostic and therapeutic agents.

La fabrication d’aimants permanents nano-structurés est l’une des solutions envisagées pour remplacer les aimants actuels à base de terres rares, pour lesquelles se posent des problèmes géopolitiques et environnementaux. Dans le but d’élaborer de tels matériaux, nous avons suivi une approche bottom-up utilisant des méthodes chimiques.Nos travaux ont visé dans un premier temps à synthétiser des nanoparticules (NPs) magnétiques dures qui peuvent servir de briques élémentaires dans la fabrication d’aimants nano-structurés. Notre étude systématique sur des nanobâtonnets de cobalt (NBs Co) synthétisés par voie polyol, a montré que leur champ coercitif augmente de 3 à 7 kOe avec la diminution du diamètre et l’augmentation du rapport d’aspect structural. Des simulations micro-magnétiques ont montré qu’un mécanisme de retournement d’aimantation par nucléation-propagation de parois rendait compte des résultats expérimentaux. Des NPs bi-métalliques FePt et tri-métalliques FePtX (X = Ag, Cu, Sn, Sb) de structure CFC ont été obtenues par l’adaptation d’une synthèse organométallique ou par la réduction d’acétylacétonates métalliques. Les recuits à haute température (650°C pour FePt, 400°C pour FePtX) ont conduit à la transition de phase FePt CFC L10 et à des champs coercitifs élevés (>12 kOe). La maîtrise d’un procédé multi-étapes, impliquant la protection des NPs FePt CFC par une coquille MgO et un recuit à 850°C, a permis d’obtenir des NPs FePt L10 de taille moyenne 10 nm présentant des champs coercitifs jusqu’à 27 kOe.La seconde partie de nos travaux a porté sur l’assemblage de NPs présentant des anisotropies différentes. Deux systèmes ont été étudiés : FePt CFC+FeCo CC, FePt L10+NBs Co HCP. Dans les deux cas, le contact entre les deux types de NPs a été favorisé par l’utilisation d’un ligand bi-fonctionnel suivi d’un traitement thermique. Dans le système FePt+FeCo, le recuit à haute température (650°C), nécessaire pour obtenir la phase FePt L10, a entraîné l’inter-diffusion des phases et la quasi-disparition de la phase FeCo CC. Dans le second système FePt+Co, un comportement de spring magnet a clairement été identifié, les deux phases étant efficacement couplées. L’inter-diffusion des phases a été limitée par la température modérée du recuit (400°C). Un champ coercitif de 10 kOe a été mesuré pour une teneur en Pt de seulement 25%at., malgré la perte de la forme anisotrope des NBs Co. / The production of nano-structured permanent magnets is a promising alternative to rare earth magnets, which induced geopolitical and environmental issues. In order to elaborate such materials, we followed a bottom-up approach based on chemical methods. A first objective consisted in synthesizing hard magnetic nanoparticles (NPs) as building blocks for nano-structured magnets. The properties of cobalt nanorods (Co NRs) synthesized by the polyol process have been systematically studied. Coercive fields could be raised from 3 to 7 kOe by decreasing the diameter and improving the structural aspect ratio. Micro-magnetic simulations showed that a magnetization reversal following a nucleation and domain-wall propagation process could explain the experimental results. Bi-metallic FePt and tri-metallic FePtX (X = Ag, Cu, Sn, Sb) exhibiting the FCC structure were synthesized following two routes based on the reduction of an organometallic Fe precursor or of metallic acetylacetonates. Annealing at high temperatures (650°C for FePt, 400°C for FePtX) allowed the phase transition FCC  L10 to occur, leading to high coercive fields (>12 kOe). A multi-steps process, involving the protection of FePt NPs with an MgO shell and an annealing at 850°C, was optimized to produce L10 FePt NPs with a mean size of 10 nm and a coercivity up to 27 kOe. In the second part of our study, we worked on assemblies of NPs with different magnetic anisotropies. Two systems were studied : FCC FePt+BCC FeCo, L10 FePt+HCP Co NRs. In both cases, the contact between the two types of NPs was favored by the presence of a bi-functional ligand followed by an annealing step. Concerning the FePt+FeCo system, the high temperature annealing (650°C), required to get the L10 FePt phase, led to the inter-diffusion of the phases and to the dissolution of the BCC FeCo phase. For the FePt+Co system, a spring magnet behavior has been clearly evidenced, the two phases being efficiently coupled The inter-diffusion of the phases was limited thanks to the fairly low annealing temperature (400°C). A coercive field of 10 kOe was measured for a Pt content as low as 25%at., eventhough the Co NRs anisotropic morphology was lost

Die polare magnetooptische Kerr-Effekt-Spektroskopie (MOKE) wird in dieser Arbeit zum ersten Mal zur Charakterisierung paramagnetischer Schichten eingesetzt. Die Schichten bestehen aus Phthalocyanin-Molekülen (H2Pc, VOPc, MnPc, CoPc und CuPc), die sich als Modellsystem zur Untersuchung des Einflusses des Molekülzentrums auf die elektronischen Zustände eignen. Die optischen Konstanten und die Dicken der Schichten werden mittels Ellipsometrie bestimmt. Mithilfe eines optischen Schichtmodells wird aus den Ellipsometrie- und MOKE-Daten die Voigt-Konstante, ein magnetooptischer Materialparameter, berechnet. Der Einfluss des Molekülzentrums auf die energetische Dispersion der Voigt-Konstante ist moderat. Vergleichsweise groß ist der Einfluss der Orientierung der Moleküle auf die Größe der Voigt-Konstante. Daher kann diese als Maß für den Aufstellwinkel des planaren CuPc herausgestellt werden. Darüber hinaus wird am Beispiel von CuPc gezeigt, dass sich die strukturelle Ordnung in molekularen Schichten mittels Reflexions-Anisotropie-Spektroskopie quantifizieren lässt. Die MOKE-Spektroskopie wird zusammmen mit MOKE-Magnetometrie auch zur Untersuchung von Eisen-Platin-Schichten mit Schichtdicken um 5 nm auf thermisch oxidiertem Silizium verwendet. Hier wird der Einfluss von eindiffundiertem Kupfer auf die magnetischen Eigenschaften Remanenz, Koerzitivität und magnetische Anisotropie der Schichten untersucht. Dabei wird neben der in Form einer Unterschicht bereitgestellten Kupfermenge die Temperatur variiert, bei der das Kupfer diffundiert. Die Magnetometrieuntersuchungen ergeben, dass Kupfer die magnetischen Eigenschaften der Eisen-Platin-Schichten verbessert, das Optimum des Kupfergehalts aber deutlich unter 20% liegt. Die optimale Mischtemperatur beträgt 600°C. Durch die Anwendung der MOKE-Spektroskopie wurde im Rahmen dieser Arbeit erstmals die Präsenz einer Feinstruktur der magnetooptischen Übergänge aus den 3d-Zuständen des Eisens entdeckt. Durch Vergleichsmessungen mit Schichten anderer Schichtdicke und auf anderen Substraten kann diese Feinstruktur mit mechanischen Verspannungen an der Grenzfläche zum Substrat in Verbindung gebracht werden.

Die polare magnetooptische Kerr-Effekt-Spektroskopie (MOKE) wird in dieser Arbeit zum ersten Mal zur Charakterisierung paramagnetischer Schichten eingesetzt. Die Schichten bestehen aus Phthalocyanin-Molekülen (H2Pc, VOPc, MnPc, CoPc und CuPc), die sich als Modellsystem zur Untersuchung des Einflusses des Molekülzentrums auf die elektronischen Zustände eignen. Die optischen Konstanten und die Dicken der Schichten werden mittels Ellipsometrie bestimmt. Mithilfe eines optischen Schichtmodells wird aus den Ellipsometrie- und MOKE-Daten die Voigt-Konstante, ein magnetooptischer Materialparameter, berechnet. Der Einfluss des Molekülzentrums auf die energetische Dispersion der Voigt-Konstante ist moderat. Vergleichsweise groß ist der Einfluss der Orientierung der Moleküle auf die Größe der Voigt-Konstante. Daher kann diese als Maß für den Aufstellwinkel des planaren CuPc herausgestellt werden. Darüber hinaus wird am Beispiel von CuPc gezeigt, dass sich die strukturelle Ordnung in molekularen Schichten mittels Reflexions-Anisotropie-Spektroskopie quantifizieren lässt. Die MOKE-Spektroskopie wird zusammmen mit MOKE-Magnetometrie auch zur Untersuchung von Eisen-Platin-Schichten mit Schichtdicken um 5 nm auf thermisch oxidiertem Silizium verwendet. Hier wird der Einfluss von eindiffundiertem Kupfer auf die magnetischen Eigenschaften Remanenz, Koerzitivität und magnetische Anisotropie der Schichten untersucht. Dabei wird neben der in Form einer Unterschicht bereitgestellten Kupfermenge die Temperatur variiert, bei der das Kupfer diffundiert. Die Magnetometrieuntersuchungen ergeben, dass Kupfer die magnetischen Eigenschaften der Eisen-Platin-Schichten verbessert, das Optimum des Kupfergehalts aber deutlich unter 20% liegt. Die optimale Mischtemperatur beträgt 600°C. Durch die Anwendung der MOKE-Spektroskopie wurde im Rahmen dieser Arbeit erstmals die Präsenz einer Feinstruktur der magnetooptischen Übergänge aus den 3d-Zuständen des Eisens entdeckt. Durch Vergleichsmessungen mit Schichten anderer Schichtdicke und auf anderen Substraten kann diese Feinstruktur mit mechanischen Verspannungen an der Grenzfläche zum Substrat in Verbindung gebracht werden.

The increasing demand for nearline storage capacity in data centers calls for a continued enhancement in hard disk drive recording density far beyond one terabit per square inch. The thermal stability limit forces the drive manufacturers to develop new concepts in order to achieve this in the long term. Potential solutions are microwave-assisted magnetic recording (MAMR), heat-assisted magnetic recording (HAMR) and bit-patterned media (BPM). A simple example of BPM based on sputter-deposited Co/Pd multilayers and prepatterned substrates at hypothetical recording densities up to one terabit per square inch was studied by magnetic force microscopy (MFM). This system achieved promising results at lower densities, but an actual application for data storage, especially at one terabit per square inch and higher densities, requires elaborate optimizations. For some time now, FePt thin films have attracted much attention as prospective recording layers for high-density magnetic data storage due to their high magnetic anisotropy. The use of FePt films in HAMR is especially promising. This application has been tested successfully by Seagate and its key customers in recent years and is about to be introduced into the nearline hard disk drive market. It requires a tuning of the magnetic properties of FePt, especially of its Curie temperature. The addition of Cu proved to be effective in this regard and can also facilitate the formation of the crucial L10 structure and (001) texture during rapid thermal annealing of sputter-deposited thin films. Such films were prepared as bilayers of Cu and FePt on Si substrates, annealed for 30 s, and analyzed by X-ray diffraction (XRD) and SQUID vibrating sample magnetometry (SQUID-VSM). The influence of large Cu additions on important properties like lattice parameters, mosaicity, magnetic anisotropy and Curie temperature is discussed. The chemical long-range order was calculated from the XRD data, and a dedicated chapter of this thesis covers the most important factors to be considered in such calculations for textured thin films and other samples. The feasibility of creating patterned Fe-Cu-Pt films with perpendicular magnetic anisotropy, as needed for a combination of HAMR and BPM, by deposition through a PMMA mask, a lift-off process and subsequent annealing was investigated as well. The results indicate that the chosen approach might not lead to the required (001) texture when the nanostructures are small enough to compete with today's recording densities, so that either a continuous film might need to be etched after annealing or a seed layer might be required to induce the texture.:1. Motivation: Magnetic Data Storage 2. Experimental Techniques 3. Co/Pd Multilayers on Prepatterned Substrates 4. Fe-Pt and Fe-Cu-Pt Alloys 5. Rapid Thermal Annealing of FePt and FePt/Cu Films 6. Order Parameter Calculation 7. Summary