The research area of magnetic field effects (MFE) on organic systems has been intensively studied during the last decade. It has been revealed that there are processes that are subject to low fields (< 50 mT) and processes that are subject to high fields (> 50 mT). While the low field processes are widely accepted to be a result of the suppression of the spin mixing caused by random hyperfine fields and spin-orbit coupling within the devices, the origin of the high field processes is still not clear. Although several mechanisms, like triplet-charge carrier interaction (TCI) and triplet-triplet annihilation (TTA), were proposed to explain the high field MFEs, how these processes are affected by a magnetic field is not well understood. This thesis presents a study of the role of excitons on MFEs using aluminium tris(8-hydroxyquinolinate) (Alq3) based diodes, focusing on the behaviour of high field effects on electroluminescence (MEL). In order to investigate the role of excitons on high field MEL, devices with different structures were designed to modify the population of exciton and excess charge carriers in the devices via controlling the injection of charge carriers. In this way, the exciton population dependent TTA and TCI processes can be studied further and even distinguished, since the TTA depends mainly on the population of triplets while the TCI depends on the exciton to charge carrier ratio. Steady state MFE measurements were performed, and results show that significant high field MEL decay can be seen in a device with extremely low triplet concentration. This indicates that TTA cannot be the underlying mechanism of high field MEL decay. The gradual trend of high field MEL, changing from a moderate increase to significant decays upon adjusting the hole and electron injection from balanced to severely hole dominated, suggests that this high field decay is exciton-hole interaction dependent. To decompose the role of singlets and triplets on high MELs, transient MFE measurements were performed on the Alq3 based standard devices. Since in Alq3 layer singlets feature a lifetime of ~ns and triplets feature a lifetime of ~ms, the behaviour of MEL at the rising edge and the falling edge of a pulse can provide a useful tool. Results show that an extra component occurs in the transient MEL at large current density and high fields. This indicates that the high field MEL is related to triplet-charge carrier interaction.

Nesta disserta&ccedil;&atilde;o de mestrado se monitorou in situ e ex situ a corros&atilde;o de corpos de prova de cobre met&aacute;lico por resson&acirc;ncia magn&eacute;tica nuclear no dom&iacute;nio do tempo (RMN-DT). A rea&ccedil;&atilde;o ocorreu em solu&ccedil;&atilde;o aquosa de HCl 1 mol L-1 fornecendo &iacute;ons de cobre Cu2+ como produtos da corros&atilde;o. A corros&atilde;o foi monitorada com um espectr&ocirc;metro RMN de bancada, atrav&eacute;s da correla&ccedil;&atilde;o entre os tempos de relaxa&ccedil;&atilde;o transversal (T2) adquiridos por meio da sequ&ecirc;ncia de pulso CPMG e a concentra&ccedil;&atilde;o de Cu2+ na solu&ccedil;&atilde;o. As rea&ccedil;&otilde;es foram estudadas usando como corpos de prova placas e cilindros de cobre, na presen&ccedil;a e aus&ecirc;ncia de campo magn&eacute;tico e na presen&ccedil;a e aus&ecirc;ncia de potencial el&eacute;trico aplicado. Esses experimentos foram realizados para estudar o efeito das for&ccedil;as magn&eacute;ticas que podem afetar as rea&ccedil;&otilde;es. Os experimentos de RMN-DT-eletroqu&iacute;mica (RMN-DT-EQ) foram executados usando o corpo de prova em formato de placa de cobre como eletrodo de trabalho, fio espiral de platina como contra eletrodo e um eletrodo de refer&ecirc;ncia de Ag/AgCl (KCl 3 mol L-1). Os experimentos sem potencial aplicado foram realizados usando-se somente os corpos de prova de cobre na solu&ccedil;&atilde;o de HCl. Os resultados mostraram que o campo magn&eacute;tico n&atilde;o alterou o efeito da corros&atilde;o quando se aplicou um potencial de 1V. No entanto a rea&ccedil;&atilde;o foi inibida na corros&atilde;o sem potencial el&eacute;trico aplicado. Esses resultados levaram a hip&oacute;tese de que, na rea&ccedil;&atilde;o com potencial aplicado, a for&ccedil;a de Lorentz foi minimizada pelas for&ccedil;as de gradiente de campo magn&eacute;tico e for&ccedil;a de gradiente da concentra&ccedil;&atilde;o de esp&eacute;cies paramagn&eacute;tica. No caso da corros&atilde;o sem potencial el&eacute;trico aplicado, a hip&oacute;tese para a inibi&ccedil;&atilde;o da corros&atilde;o foi que as for&ccedil;as de gradiente mantiveram os &iacute;ons de cobre na interface corpo de prova/solu&ccedil;&atilde;o, o que dificultou a rea&ccedil;&atilde;o. O efeito do campo magn&eacute;tico sobre a superf&iacute;cie do cilindro de cobre ao final do processo de corros&atilde;o tamb&eacute;m foram analisados pelas t&eacute;cnicas de microscopia eletr&ocirc;nica de varredura e microscopia de for&ccedil;a at&ocirc;mica enquanto que a solu&ccedil;&atilde;o resultante do processo de corros&atilde;o teve os valores da concentra&ccedil;&atilde;o de &iacute;ons Cu2+ quantificados pelas espectroscopias de absor&ccedil;&atilde;o no ultravioleta e vis&iacute;vel e de absor&ccedil;&atilde;o at&ocirc;mica com chama. / In this Masters dissertation the corrosion of metallic copper samples was monitored in situ and ex situ by time domain nuclear magnetic resonance (TD-NMR). The reaction was performed in an aqueous solution containing HCl (1 mol L-1), where Cu2+ ions were the corrosion products. A benchtop NMR spectrometer was used to monitor the reaction through the correlation between the transverse relaxation times (T2), acquired with the CPMG pulse sequence, and the concentration of Cu2+ in the solution. The reactions were studied using copper plaques and cylinders in the presence and absence of a magnetic field and in the presence and absence of an applied potential. These experiments were performed to study the effect of the magnetic forces which affect reactions with and without an applied potential. The coupling experiments between TD-NMR and electrochemistry (EC-NMR) were performed using a copper plaque as a working electrode, a platinum wire in a spiral shape as a counter electrode and a Ag/AgCl KCl 3 mol L-1 reference electrode. Experiments in which no potential was applied were performed by inserting the copper sample in an HCl aqueous solution. Results showed that the magnetic field didn&rsquo;t alter the corrosion process when a 1V potential was applied but it did inhibit the corrosion of copper when no potential was applied. These results lead to the hypothesis that, in the reaction with an applied potential, the Lorentz force was minimized by the forces created by the magnetic field and the concentration gradient of the paramagnetic species (Cu2+). In the case of corrosion experiments without an applied potential a possibility is that the forces created by the concentration gradient force copper ions to stay on the interface copper/solution, which hinders the reaction. The effect of the magnetic field on the surface of the copper cylinder at the end of the corrosion process was also analysed by scanning electron microscopy and atomic force microscopy while the concentration of Cu2+ in the solution was measured by UV-vis spectroscopy and flame atomic absorption spectrometry.

Nesta disserta&ccedil;&atilde;o de mestrado se monitorou in situ e ex situ a corros&atilde;o de corpos de prova de cobre met&aacute;lico por resson&acirc;ncia magn&eacute;tica nuclear no dom&iacute;nio do tempo (RMN-DT). A rea&ccedil;&atilde;o ocorreu em solu&ccedil;&atilde;o aquosa de HCl 1 mol L-1 fornecendo &iacute;ons de cobre Cu2+ como produtos da corros&atilde;o. A corros&atilde;o foi monitorada com um espectr&ocirc;metro RMN de bancada, atrav&eacute;s da correla&ccedil;&atilde;o entre os tempos de relaxa&ccedil;&atilde;o transversal (T2) adquiridos por meio da sequ&ecirc;ncia de pulso CPMG e a concentra&ccedil;&atilde;o de Cu2+ na solu&ccedil;&atilde;o. As rea&ccedil;&otilde;es foram estudadas usando como corpos de prova placas e cilindros de cobre, na presen&ccedil;a e aus&ecirc;ncia de campo magn&eacute;tico e na presen&ccedil;a e aus&ecirc;ncia de potencial el&eacute;trico aplicado. Esses experimentos foram realizados para estudar o efeito das for&ccedil;as magn&eacute;ticas que podem afetar as rea&ccedil;&otilde;es. Os experimentos de RMN-DT-eletroqu&iacute;mica (RMN-DT-EQ) foram executados usando o corpo de prova em formato de placa de cobre como eletrodo de trabalho, fio espiral de platina como contra eletrodo e um eletrodo de refer&ecirc;ncia de Ag/AgCl (KCl 3 mol L-1). Os experimentos sem potencial aplicado foram realizados usando-se somente os corpos de prova de cobre na solu&ccedil;&atilde;o de HCl. Os resultados mostraram que o campo magn&eacute;tico n&atilde;o alterou o efeito da corros&atilde;o quando se aplicou um potencial de 1V. No entanto a rea&ccedil;&atilde;o foi inibida na corros&atilde;o sem potencial el&eacute;trico aplicado. Esses resultados levaram a hip&oacute;tese de que, na rea&ccedil;&atilde;o com potencial aplicado, a for&ccedil;a de Lorentz foi minimizada pelas for&ccedil;as de gradiente de campo magn&eacute;tico e for&ccedil;a de gradiente da concentra&ccedil;&atilde;o de esp&eacute;cies paramagn&eacute;tica. No caso da corros&atilde;o sem potencial el&eacute;trico aplicado, a hip&oacute;tese para a inibi&ccedil;&atilde;o da corros&atilde;o foi que as for&ccedil;as de gradiente mantiveram os &iacute;ons de cobre na interface corpo de prova/solu&ccedil;&atilde;o, o que dificultou a rea&ccedil;&atilde;o. O efeito do campo magn&eacute;tico sobre a superf&iacute;cie do cilindro de cobre ao final do processo de corros&atilde;o tamb&eacute;m foram analisados pelas t&eacute;cnicas de microscopia eletr&ocirc;nica de varredura e microscopia de for&ccedil;a at&ocirc;mica enquanto que a solu&ccedil;&atilde;o resultante do processo de corros&atilde;o teve os valores da concentra&ccedil;&atilde;o de &iacute;ons Cu2+ quantificados pelas espectroscopias de absor&ccedil;&atilde;o no ultravioleta e vis&iacute;vel e de absor&ccedil;&atilde;o at&ocirc;mica com chama. / In this Masters dissertation the corrosion of metallic copper samples was monitored in situ and ex situ by time domain nuclear magnetic resonance (TD-NMR). The reaction was performed in an aqueous solution containing HCl (1 mol L-1), where Cu2+ ions were the corrosion products. A benchtop NMR spectrometer was used to monitor the reaction through the correlation between the transverse relaxation times (T2), acquired with the CPMG pulse sequence, and the concentration of Cu2+ in the solution. The reactions were studied using copper plaques and cylinders in the presence and absence of a magnetic field and in the presence and absence of an applied potential. These experiments were performed to study the effect of the magnetic forces which affect reactions with and without an applied potential. The coupling experiments between TD-NMR and electrochemistry (EC-NMR) were performed using a copper plaque as a working electrode, a platinum wire in a spiral shape as a counter electrode and a Ag/AgCl KCl 3 mol L-1 reference electrode. Experiments in which no potential was applied were performed by inserting the copper sample in an HCl aqueous solution. Results showed that the magnetic field didn&rsquo;t alter the corrosion process when a 1V potential was applied but it did inhibit the corrosion of copper when no potential was applied. These results lead to the hypothesis that, in the reaction with an applied potential, the Lorentz force was minimized by the forces created by the magnetic field and the concentration gradient of the paramagnetic species (Cu2+). In the case of corrosion experiments without an applied potential a possibility is that the forces created by the concentration gradient force copper ions to stay on the interface copper/solution, which hinders the reaction. The effect of the magnetic field on the surface of the copper cylinder at the end of the corrosion process was also analysed by scanning electron microscopy and atomic force microscopy while the concentration of Cu2+ in the solution was measured by UV-vis spectroscopy and flame atomic absorption spectrometry.

Spin interactions play a key role in the function of molecular materials from naturally occurring biological complexes to synthetic materials for light-harvesting and light-emission. This thesis investigates the spin interactions of spin-1 triplet excitons formed by singlet fission. Singlet fission produces two triplet excitons from one light-induced singlet state and holds promise to enable solar energy generation beyond traditional efficiency limits. As the lifetime of triplet pairs depends sensitively on their spin degree of freedom, in this thesis we deploy spin-sensitive techniques to understand the interactions and evolution of triplet pairs. After introducing the relevant theoretical and experimental background underlying singlet fission and the role of spin, we describe the first observation of strongly exchange coupled, high-spin triplet-pair states ($S=2$) in a solid-state organic semiconductor and show that the singlet fission process allows for the formation of long-lived, strongly coupled spin-two states. We then describe the development and use of photoluminescence-detected avoided level-crossings in applied magnetic fields to quantify the strength of exchange coupling and identify specific optical signatures of exchange-coupled triplet pairs. Using high magnetic fields ($\leq\mbox{60 T}$) we isolate and measure the exchange coupling and optical signatures of multiple distinct triplet pairs in the same material. Finally, we probe the mechanisms of formation and decay of spin polarization from triplet pair states using pulsed spin resonance. The measured dynamics are consistent with polarization driven by fluctuations in exchange coupling between pairs and spin-orbit mediated decay of triplet excitons to the ground state. The combined measurements of the spin parameters and polarization dynamics of triplet pairs from ns to ms timescales provides a quantitative picture of the spin states generated by singlet fission.

It has been found that a small magnetic field (<300 mT) can substantial change the electroluminescence, photoluminescence, photocurrent, electrical injection current in nonmagnetic organic semiconductors. It is generally believed that these magnetic field effects (MFE) are related to the spin dependent processes in organic semiconductor. However, the origin of MFE is still not well understood. In this dissertation, we investigate the underlying mechanism for magnetic field effects on electroluminescence (MFEEL) and magnetoresistance (MR) and demonstrate the complete tuning of MFEEL and MR based on our theoretical understanding. We consider MFE arising from magnetic field sensitive intersystem crossing (ISC) and triplet charge reaction. Magnetic field can increase the singlet ratios through ISC, accounting for positive MFEEL. Magnetic field modulated ISC strongly depends on the electron-hole pair separation distance. MFE can be enhanced by increasing the electron hole pair distance through material mixing and interplaying the electric dipole-dipole interaction. Meanwhile, two possible mechanisms corresponding for negative MFEEL: triplet-triplet annihilation and triplet charge reaction are also discussed. The negative MFEEL is achieved through adjusting triplet density charge confinement and exciton/charge ratio, which indicates that triplet charge reaction is a dominate process accountable for negative MFEEL. Significant MR and MFEEL are observed in strong spin orbital coupling iridium complex based OLED device after introducing the non-magnetic insulating blocking PVA layer. A possible mechanism for this new interface induced MR and MFEEL is proposed based on magnetic field perturbed spin-spin interaction at short capture distance of inter-charge carriers. The comparative study of two strong spin orbital coupling materials Ir(ppy)3 and Ir(ppy)2(acac) with different electrical dipole moments indicate the electric dipole-dipole interaction can change MR and MFEEL from short distance capture based regime to long distance intersystem-crossing regime. At last, we demonstrate the fully tuning sign of magnetic field effect on the fluorescence (MFEFEL) and phosphorescence (MFEPEL) by using the ISC, energy transfer and spin-spin interaction. In addition, we demonstrate a giant MFEEL (400%) in electrochemical cells and attribute this giant MFEEL to Lorentz force driven ion transport and Lorentz force dependent diffusion layer thickness through convection.

Interest into the effects of weak static magnetic fields on chemical reactions involving spin correlated radical pairs has increased over the last few decades, particularly as scientists have become more curious about the mechanisms by which animals can sense and respond to small variations in the Earth's weak (50 µT) magnetic field. The magnetosensitivity of radical pairs, as dictated by the radical pair mechanism, lies at the heart of the most heavily supported hypothesis of this magnetoreception phenomenon. This thesis is concerned with the spectroscopic investigations of isotropic and anisotropic magnetic field effects in fluorescent systems. First of all, an introduction to spin chemistry and magnetoreception is presented. In chapter 3, the effects of weak radiofrequency oscillating fields when applied in combination with weak static fields are explored in isotropic solutions. The validity of the high-field model, typically used to describe spin dynamics in magnetic resonance, is tested and the effects of orientation and field strength on magnetic field effects are discussed in detail. In Chapter 4, a range of exciplex systems are studied by fluorescence methods and their energetics are explored. The factors which determine the formation of an exciplex, i.e. the complex equilibrium between the exciplex and the spin-correlated radical pair,are considered and used to assess the existence and magnitude of MFEs. Radical pair systems investigated, using MARY spectroscopy, with respect to their potential to act as model chemical compasses are introduced in chapter 5. Solid-state media are used to align the exciplex systems to detect any magnetic field direction dependence. Finally, in chapter 6, AMELIA, an experiment which can directly measure the anisotropic magnetic field response of a system, is presented and applied successfully to systems to detect directly the anisotropic field response of a photoexcited anthracene crystal.

Magnetoreception is the ability of some animals to use the weak magnetic field of the Earth for navigation over long-distance migrations. It is a well-known phenomenon, but its underlying biophysical mechanisms remain poorly understood. One proposal involves light-induced, magnetically sensitive chemical reactions occurring within cryptochrome proteins, rationalised via the radical pair mechanism (Chapter 1). The absence of evidence in support of this hypothesis is in part due to the lack of sufficiently sensitive techniques to measure magnetic field effects (MFEs) in biological samples. Cavity-enhanced detection, most commonly in the form of cavity ring-down spectroscopy (CRDS) or cavity-enhanced absorption spectroscopy (CEAS), is widely used in the gas phase to provide significant sensitivity gains over traditional single-pass measurements (Chapter 2). However, successful studies in the condensed phase are less prevalent due to the additional background losses inherent to the sample. This thesis reports on the application of broadband (i.e. monitoring > 100nm) variants of CRDS and CEAS to the study of MFEs on the radical recombination reactions of flavin-based systems in solution. The broadband CRDS (BBCRDS) instrument employed in Chapter 4 is able to monitor the spectral changes induced by magnetic fields with submicrosecond time resolution. However, the need to scan both the probe wavelength and time delay to construct time-resolved spectra leads to prohibitively long acquisition times, and hence exposure of sensitive samples to high numbers of photons. The broadband CEAS (BBCEAS) studies reported in Chapter 5 combine the high irradiance and spectral coverage of a supercontinuum radiation (SCR) source with a CCD detector to simultaneously acquire absorption spectra across the visible region (480–700nm). The CW nature of this technique precludes the possibility of following radical pair kinetics in real time. In an effort to combine the respective advantages of these two instruments, which individually have represented powerful advances in capability, a new cavity-enhanced technique is reported for the first time (Chapter 6). The result, optical cavity-enhanced transient absorption spectroscopy (OCTAS), is able to simultaneously monitor spectral evolution and associated MFEs on the microsecond timescale, with comparable sensitivity to the existing techniques. Magnetic responses in animal cryptochrome proteins have successfully been recorded using all three techniques, lending considerable weight to the hypothesis that these molecules are at the heart of the magnetic sense in animals.

This thesis consists of three main studies: magnetic field effects in thermally activated delayed fluorescent (TADF) organic light emitting diodes (OLEDs), magnetic field effects in bipolar and unipolar polythiophene (P3HT) devices and a study of hybrid organic/inorganic perovskite devices. Spin-dependent transport and recombination processes of spin-pair species have been detected by magnetic field effect (MFE) technique in carbon-based semi- conductor devices. Magneto-electroluminescence (MEL) and magneto-conductivity have been measured as a function of the applied magnetic field, B, in light emitting diodes. TADF materials have been used instead of simple fluorescent materials in OLEDs. We have observed very large magnetic response with TADF materials. The second study is magnetic field effects of regio-regular P3HT based OLED devices. P3HT is a well known semiconducting polymer, and its electrical properties such as magneto-conductance can be affected by an applied magnetic field. P3HT was chosen because it exhibits a sign change in magnetoresistance (MR) as the bias is increased. Unipolar and bipolar devices have been fabricated with different electrode materials to understand which model can be best to explain organic magnetoresistance effect, possibly depending on the operating regime of the device. Transport and luminescence spectroscopies were studied to isolate the different mechanisms and identify their fingerprints. The third study is on hybrid organic-inorganic perovskite devices. With the potential of achieving very high efficiencies and the very low production costs, perovskite solar cells have become commercially attractive. Scanning electron microscopy (SEM) images and absorption spectrum of the films were compared in single-step solution, two-step solution and solution-assisted vapor deposition techniques. Grain size, morphology and thickness parameters of perovskite films were studied within these techniques. Perovskite solar cells were fabricated and their efficiencies were measured.

There is an increasing interest in nanostructured and nanocomposite surface finishings for automotive and aerospace applications. The widespread applicability of these novel materials is based on their unique mechanical, physical, and chemical properties. An advantageous production method is the electrocodeposition (ECD) process from metal plating baths containing dispersed nanoparticles. By using this technique, a broad range of substrate sizes and shapes can be coated cost-effectively. However, the prediction of the amount as well the distribution of nanoparticles within the metal film fails frequently. There is no complete understanding of the particle incorporation mechanism. The goal of this research was to improve the fundamental understanding of the ECD mechanism. In order to identify the forces affecting the codeposition behavior of nanoparticles in a metal matrix, the effects of a variety of interrelated process parameters on the composite film formation have been investigated systematically. Nanocomposites containing metal and metal oxide nanoparticles in a nickel matrix have been prepared by means of ECD from two different types of nickel plating baths, an acidic sulfamate (pH 4.3) and an alkaline pyrophosphate bath (pH 9.5). The effect of deposition conditions on the ECD process was investigated utilizing two electrode configurations, viz. a parallel plate electrode (PPE) and impinging jet electrode (IJE) and different deposition techniques, viz. direct current (DC) deposition, both pulse plating (PP) and pulse-reverse plating (PRP). The surface charge and sedimentation behavior of the nanoparticles in these electrolytes were characterized by zeta potential and stability measurements. The surface charge, hydrodynamic diameter and colloidal stability of the nanoparticles in the nickel electrolytes were mainly affected by the composition and pH of the bath. The particles tend to form agglomerates in both nickel baths. Smaller agglomerates and an improved colloidal stability occurred in the case of the alkaline bath. Composites with a maximum particle content of either ~3.6 vol-% of 13 nm Al2O3 or ~10.4 vol-% of 21 nm TiO2 were obtained using a parallel plate electrode and DC deposition conditions. Both jet plating as well as pulse plating resulted in a distinct increase of the particle codeposition. A maximum incorporation of ~12 vol-% of 50 nm Al2O3 particles in a nickel matrix was achieved using an unsubmerged IJE system, while PP and PRP resulted in composites with particle contents up to 11 vol-% of 13 nm Al2O3. The particle incorporation increased with the particle content of the electrolyte for all deposition conditions studied. A beneficial effect on the amount of codeposited particles was found with decreasing average current density. The Al2O3 and TiO2 particles were found to be negatively charged in the alkaline pyrophosphate bath, and positively charged in the acidic sulfamate bath. It could be shown that negatively charged particles codeposited preferentially within the nickel matrix. The effect of PP and PRP conditions, e.g. pulse frequency, duty cycle and value of the peak current density, on the ECD of Ni-Al2O3 composites was studied using rectangular current pulses in the order of milliseconds. In general, low duty cycles and high pulse frequencies resulted in an enhanced particle codeposition. Using the unsubmerged IJE system, the effects of jet flow rate, particle loading and current density on the particle incorporation were studied. Referring to the experimental results from the ECD of 50 nm alumina with nickel using an IJE system, a kinetic model was developed. Therefore, the particle flux to the electrode was derived from an analysis of the total force acting on the particle in front of the electrode. The model took into account the convective diffusion of particles to the electrode surface, and the effect of gravitational and buoyancy forces on the particle flux. The gravitational force was found to be important for the ECD of 300 nm particles, but not for 50 nm particles. The effect of an external magnetic field on the ECD of Co or Fe3O4 nanoparticles in a nickel matrix has been studied for different current densities, particle contents of the electrolyte and magnetic flux density. The particle incorporation showed a distinct dependency on the orientation of an externally applied magnetic field. While the particle incorporation increased in a perpendicular field (perpendicular with regard to the electrode surface), it decreased in a parallel orientation. The influence of the magnetic field on the ECD of magnetic nanoparticles with nickel was explained by the interplay of Lorentz force and magnetophoretic force. The structure and the properties of the nickel matrix were significantly altered due to the codeposition of nanoparticles. The pure nickel deposits from the sulfamate bath exhibited a strong &amp;lt;100&amp;gt; texture, and those from the pyrophosphate bath a strong &amp;lt;110&amp;gt; preferred orientation. With increasing plating current density and particle incorporation, a variation in the crystallite size and a loss of texture was observed. High resolution TEM imaging proved a complete embedding of nanoparticles by the nickel matrix without any voids. In the case of both nickel baths, the Vickers microhardness showed a tendency to increase with the amount of particle incorporation. The enhanced hardness of the composite films was associated with modifications in the microstructure of the nickel matrix as well as with the nanoparticle incorporation. The wear resistance as examined by linear abrasion test increased with decreasing current density and due to the particle incorporation. Furthermore, the incorporation of magnetic nanoparticles resulted in a distinct increase of the magnetic hardness of the nickel matrix.

The outcome of chemical reactions proceeding via radical pair (RP) intermediates can be influenced by the magnitude and direction of applied magnetic fields, even for interaction strengths far smaller than the thermal energy. Sensitivity to Earth-strength magnetic fields has been suggested as a biophysical mechanism of animal magnetoreception and this thesis is concerned with simulations of the effects of such weak magnetic fields on RP reaction yields. State-space restriction techniques previously used in the simulation of NMR spectra are here applied to RPs. Methods for improving the efficiency of Liouville-space spin dynamics calculations are presented along with a procedure to form operators directly into a reduced state-space. These are implemented in the spin dynamics software Spinach. Entanglement is shown to be a crucial ingredient for the observation of a low field effect on RP reaction yields in some cases. It is also observed that many chemically plausible initial states possess an inherent directionality which may be a useful source of anisotropy in RP reactions. The nature of the radical species involved in magnetoreception is investigated theoretically. It has been shown that European Robins are disorientated by weak radio-frequency (RF) fields at the frequency corresponding to the Zeeman splitting of a free electron. The potential role of superoxide and dioxygen is investigated and the anisotropic reaction yield in the presence of a RF-field, without a static field, is calculated. Magnetic field effect data for Escherichia coli photolyase and Arabidopsis thaliana cryptochrome 1, both expected to be magnetically sensitive, are satisfactorily modelled only when singlet-triplet dephasing is included. With a view to increasing the reaction yield anisotropy of a RP magnetoreceptor, a brief study of the amplification of the magnetic field experienced by a RP from nearby magnetite particles is presented. Finally in a digression from RPs, Spinach is used to determine the states expected to be immune from relaxation and therefore long-lived in NMR experiments on multi-spin systems.