The transport of cosmic rays in the heliosphere is studied by making use of a newly developed modulation model. This model employes stochastic differential equations to numerically solve the relevant transport equation, making use of this approach’s numerical advantages as well as the opportunity to extract additional information regarding cosmic ray transport and the processes responsible for it. The propagation times and energy losses of galactic electrons and protons are calculated for different drift cycles. It is confirmed that protons and electrons lose the same amount of rigidity when they experience the same transport processes. These particles spend more time in the heliosphere, and also lose more energy, in the drift cycle where they drift towards Earth mainly along the heliospheric current sheet. The propagation times of galactic protons from the heliopause to Earth are calculated for increasing heliospheric tilt angles and it is found that current sheet drift becomes less effective with increasing solar activity. Comparing calculated propagation times of Jovian electrons with observations, the transport parameters are constrained to find that 50% of 6 MeV electrons measured at Earth are of Jovian origin. Charge-sign dependent modulation is modelled by simulating the proton to anti-proton ratio at Earth and comparing the results to recent PAMELA observations. A hybrid cosmic ray modulation model is constructed by coupling the numerical modulation model to the heliospheric environment as simulated by a magneto-hydrodynamic model. Using this model, it is shown that cosmic ray modulation persists beyond the heliopause. The level of modulation in this region is found to exhibit solar cycle related changes and, more importantly, is independent of the magnitude of the individual diffusion coefficients, but is rather determined by the ratio of parallel to perpendicular diffusion. / PhD (Space Physics), North-West University, Potchefstroom Campus, 2013

The transport of cosmic rays in the heliosphere is studied by making use of a newly developed modulation model. This model employes stochastic differential equations to numerically solve the relevant transport equation, making use of this approach’s numerical advantages as well as the opportunity to extract additional information regarding cosmic ray transport and the processes responsible for it. The propagation times and energy losses of galactic electrons and protons are calculated for different drift cycles. It is confirmed that protons and electrons lose the same amount of rigidity when they experience the same transport processes. These particles spend more time in the heliosphere, and also lose more energy, in the drift cycle where they drift towards Earth mainly along the heliospheric current sheet. The propagation times of galactic protons from the heliopause to Earth are calculated for increasing heliospheric tilt angles and it is found that current sheet drift becomes less effective with increasing solar activity. Comparing calculated propagation times of Jovian electrons with observations, the transport parameters are constrained to find that 50% of 6 MeV electrons measured at Earth are of Jovian origin. Charge-sign dependent modulation is modelled by simulating the proton to anti-proton ratio at Earth and comparing the results to recent PAMELA observations. A hybrid cosmic ray modulation model is constructed by coupling the numerical modulation model to the heliospheric environment as simulated by a magneto-hydrodynamic model. Using this model, it is shown that cosmic ray modulation persists beyond the heliopause. The level of modulation in this region is found to exhibit solar cycle related changes and, more importantly, is independent of the magnitude of the individual diffusion coefficients, but is rather determined by the ratio of parallel to perpendicular diffusion. / PhD (Space Physics), North-West University, Potchefstroom Campus, 2013

Les Alliages à Mémoire de Forme Magnétiques (AMFM) sont des matériaux actifs qui présentent des comportements inhabituels par rapport aux matériaux " classiques ". Ils peuvent par exemple présenter de larges déformations réversibles sous l'action d'un champ magnétique ou sous une action mécanique. Ce sont des candidats potentiels pour des applications dans des domaines de pointe (automobile, aéronautique, spatial, etc.). Les AMFM présentent par ailleurs un avantage indéniable par rapport aux matériaux à mémoire de forme " thermique " en raison de leur réponse dynamique à haute fréquence. Il est bien connu que ces comportements sont dus à un couplage magnéto-mécanique et à un phénomène physique lié à l'orientation des variantes de martensite. L'objectif de cette thèse est d'analyser les comportements magnéto-mécaniques des AMFM. Pour ce faire, nous étudions expérimentalement et théoriquement, la réorientation martensitique dans les AMFM. Tout d'abord, une analyse énergétique en 2D/3D est proposée et intégrée dans des diagrammes d'état pour une étude systématique de la réorientation martensitique dans les AMFM sous chargements tridimensionnels quelconques. Ainsi, des critères de large déformation réversible sous des chargements cycliques sont obtenus. L'analyse énergétique montre que les AMFM, sollicités sous chargement multiaxiaux présentent plus d'avantages que ceux sollicités en 1D ; en particulier, on montre que l'état multiaxial permet d'augmenter (d'améliorer) la contrainte fonctionnelle, ce qui augmente le champ d'application des ces matériaux. Ensuite, afin de valider les prédictions de l'analyse énergétique, des expériences bi-axiales ont été effectuées sur des éprouvettes en AMFM. Les résultats révèlent que la dissipation intrinsèque et la déformation de transformation dues à la réorientation martensitique sont constantes dans tous les états de contraintes. De plus, les résultats ont permis de valider nos prédictions théoriques quant à l'augmentation de la contrainte fonctionnelle. Enfin, afin de prédire les comportements magnéto-mécaniques des AMFM sous des chargements multiaxiaux, un modèle tridimensionnel est développé dans le cadre de la thermodynamique des processus irréversibles avec liaison interne. Toutes les variantes de martensite ont été considérées et l'effet de température a également été pris en compte. Les simulations numériques montrent un très bon accord (rejoignent/confirment les résultats) avec les résultats expérimentaux existant dans la littérature. Le modèle a ensuite été programmé dans un code de calcul par éléments finis afin d'étudier les comportements non linéaires de flexion des poutres en AMFM. L'effet géométrique et l'effet d'anisotropie du matériau ont été systématiquement pris en compte.

The issue of prosthetic infection leading to implant failure due to the formation of bacterial biofilms on biomaterial surfaces has been widely recognized as a major issue, often leading to revision surgery. The growing number of patients requiring synthetic biomaterials as implants is on the rise and so is the risk of infection arising from pre/peri-/post-operative surgical procedures. Traditional antibiotic treatment has led to the emergence of bacterial drug resistance. Therefore, the development of novel bactericidal methods to combat drug resistant microbial pathogens is the need of the hour. The first part of the thesis is an attempt to address prosthetic infection by the development of novel ultrasmall gold nanoparticles (AuNPs) which are cytocompatible and present a therapeutic dosage window for eliciting antimicrobial property. Towards this end, ultrasmall AuNPs with 0.8 nm and 1.4 nm gold core sizes, stabilized by monosulphonated triphenylphosphine ligand shells were synthesized. Such intricately designed AuNPs with ultrasmall gold cores and phosphine-based ligand chemistry were demonstrated to be highly potent bactericidal agents against staphylococci, the most common human pathogen causing biomaterial associated infection. The antibacterial efficacy of these AuNPs was significant even in mature staphylococcal biofilms. In another study, the application of high strength pulse magnetic fields (1-4 Tesla) was examined for bacterial growth inactivation in vitro. A magnetic field strength dependent decrease in bacterial viability with a concomitant increase in the production of reactive oxygen species (ROS) and longer doubling times were recorded. The mechanism of action was explained through an analytical model which involves ion-transport interference of essential ions like Ca2+ and Mg2+ and disruption of FeS clusters leading to inactivation of bacterial redox enzymes. On the contrary, such high magnetic fields did not pose any detrimental effects to eukaryotic cells under similar exposure. Additionally, the potency of low intensity direct current electric field (DC EF: 1V/cm) against biofilm formation by methicillin resistant Staphylococcus aureus (MRSA) was explored on antimicrobial surfaces of hydroxyapatite and Zinc oxide (HA-xZnO; x = 0, 5, 7.5 and 10 wt%). An EF exposure time dependent decline in the viability and stability of MRSA biofilms were noted. Further, EF treatment resulted in bacterial membrane depolarization and reduced biofilm formation on HA-ZnO composites, independent of the substrate composition. In summary, the above three studies were cases of the developmental methods to address prothetic infection. The second part of the thesis is focused on the development of magneto-responsive biomaterials as implants for orthopaedic applications. Under this category, the sintering/ hot pressing of hydroxyapatite-magnetite (HA-xFe3O4; x = 0, 5, 10, 20 and 40 wt%) powders in oxidizing and inert atmospheres was carried out and the resulting phases and microstructure were characterized. A detailed analysis of the phase assemblage by Rietveld refinement of the X-ray diffraction (XRD) data and Mössbauer spectroscopy revealed the major retention of Fe3O4 along with wustite (FeO) formation under reducing conditions while hematite (α-Fe2O3) was the oxidized product of conventional sintering in ambient atmosphere. A good correlation between the unit cell volume increases in HA observed from Rietveld refinements and Fe incorporation into the apatite lattice from Mössbauer spectral parameters was evident. Further, the Mössbauer data analysis indicated a preferential occupancy of Fe at the Ca(1) site under oxidizing conditions and Ca(2) site in inert atmosphere. The above phase analyses were further confirmed by X-ray photoelectron spectroscopy (XPS), Infrared spectroscopy (FT-IR) and CHN analysis. The microstructure of the hot-pressed samples observed under transmission electron microscope (TEM) divulged similar phases as deduced from XRD as well as the formation of translational Moire fringe patterns due to inference of overlapping crystal planes of HA and Fe3O4 in the HA-40 wt% composite. Such translational Moire fringes suggest a preferred arrangement and orientation of the crystallites resulting from hot-pressing, which correlated well with the room temperature magnetic measurements made with the help of a vibrating sample magnetometer (VSM). The compositional similarity of Fe doping in HA to that of the tooth enamel and bone presents these HA-Fe3O4 composites as potent dental/ orthopaedic implant materials. In the conclusive study, the hot-pressed HA-xFe3O4 composites were tested for their efficacy in supporting the osteogenesis of human mesenchymal stem cells (hMSCs) assisted by intermittent static magnetic field exposure. The magneto-responsive substrates were applied as platforms for the culture of hMSCs and the effect of static magnetic field (SMF) exposure on the viability, proliferation and differentiation of hMSCs were elucidated. With a mild compromise in viability, SMF triggered the osteogenic differentiation of hMSCs mediated by proliferative arrest in the G0/G1 phase and elevated intracellular calcium levels. The early bone marker genes - Runx2, Col IA and ALP were significantly up regulated upon SMF exposure on pure HA and HA-Fe3O4 composites. Further, the late osteogenic markers – OCN and OPN were detected exclusively in the HA-xFe3O4 (x = 10 and 40 wt%) composites. Matrix mineralization was enhanced and CaP nodules were detected on similar SMF treated HA-Fe3O4 composites. A substrate magnetization and time dependent modulation of gene expression was recorded which corroborated well with the temporal trending of osteogenic genes during bone development. In conclusion, substrate magnetization can be applied as a tool to modulate the behavior of stem cells and direct them towards osteogenic lineage. Such a pertinent combination of substrate magnetization and external magnetic field stimulation can be applied synergistically for stem cell based bone tissue engineering applications.

The subject of this thesis is the study of coherent interaction of light with matter (atoms) to improve the precision measurements and techniques. Special attention is drawn to get the narrow subnatural electromagnetically induced transmission (EIT), electromagnetically induced absorption (EIA) and nonlinear magneto-optic rotation (NMOR) caused by alkali atoms contained in a vapor cell. Subnatural polarization rotation introduces by a strong circularly polarized light in the absence of any external magnetic field was also studied. A detailed theoretical treatment, given in this dissertation, allows to associate each of the features of the spectra with a special physical mechanism. Many quantum phenomena related to interferences, coherences, optical pumping etc. experiments are studied using home-built diode lasers. This thesis also describes laser cooling and trapping of rubidium atoms using two techniques. Deflection of cold atoms horizontally from MOT using pushing beams are discussed in close consideration for the improvements in the precision measurements. This thesis is organized as follows. In Chapter 1, an introduction to the importance of sub-natural narrow resonance and simplified technique in the precision measurement will be discussed. In Chapter 2, an introduction to EIT, EIA and NMOR resonance are discussed. This chapter will provide a basic theoretical background of atom-field interactions, especially for Λ-type and N -type systems and its steady state solution using density matrix analysis and experimental tools. The most important notion of laser cooling of atoms, ions or molecule i.e., exchange of momentum between light and atoms combining with the Doppler effect will be discussed. In Chapter 3, the observation of subnatural EIT and subnatural EIA in closed and open degenerate two-level system using room temperature vapor cell filled with Rb will be presented. Physical mechanisms that contribute to EIT and EIA, and the contrast of our results from the coherent population trapping (CPT)–type resonances are discussed in detail in appendix A.2 according to our experimental results. In Chapter 4, the narrowing of subnatural EIT and subnatural EIA linewidth in closed and open systems again in degenerate two level transition, using the “Laguerre-Gaussian” control beam instead of generally studied Gaussian beam, will be discussed in detail. In Chapter 5, the conversion between subnatural EIT to subnatural EIA in a degenerate Λ system will be discussed. The physical mechanism created by the introduction of a coherent counter propagating control laser to the co-propagating probe and the control laser are studied. The effect of polarization and axial velocity Doppler averaging will also be studied. In Chapter 6, we will discuss the sensitive technique for precise measurement of small magnetic fields using the NMOR, by chopping the resonant laser beam. We will study the sensitivity and the potential application of this technique in the measurement of an atomic electric-dipole moment. In Chapter 7, we will be studying about the induced optical rotation by a circularly polarized control laser on the linearly polarized probe laser. The effect of the intensity of the control laser beam on the higher order optical rotation will also be studied. In Chapter 8, we will be studying about the cooling and trapping of 87Rb in magneto-optic trap. We will be studying two techniques of trapping of atoms in MOT. The cold cloud of atoms from the MOT are deflected horizontally by using different configuration of pushing beam are studied. A brief summary and outlook of my thesis work will be discussed at Chapter 9.

This Master’s thesis contains an overview of determining measurement uncertainties of direct and indirect measurements. It describes a way of creating a magnetic field with the help of Helmholtz coil and a more detailed description of some principles of magnetic field sensors. This thesis also contains a description of the experiments and the factors influencing them. The last part deals with the quantification of uncertainties from measured experiments and with the discussion of the results from these measurements.

La génération de seconde harmonique magnétique (mSHG pour magnetic Second Harmonic Generation) est un phénomène physique très sensible apparaissant grâce aux brisures de symétrie aux niveaux des surfaces et interfaces des structures métalliques magnétiques. Elle constitue donc un outil puissant pour explorer ce type d'interfaces et des nanostructures. Dans ce travail, nous nous intéressons aux couplages et interactions entre la mSHG et les ondes électromagnétiques pouvant se propager en surface des matériaux. Un intérêt spécifique est porté sur l’ excitation de (i) plasmon polaritons de surfaces (SPP) dans des films métalliques en structures multicouches, (ii) d'anomalies de diffraction (dîtes de Wood) dans des nanostructures métalliques périodiques. Pour étudier l'influence de l'excitation linéaire et non-linéaire des SPP sur la mSHG, l'intensité du signal réfléchi par génération de seconde harmonique (SH) et le contraste magnétique lié à ce signal ont été mesurés par la technique de l'effet Kerr magnéto-optique transverse (MOKE) en fonction de l'angle d'incidence. Via l'utilisation de sources lasers femtosecondes émettant dans le proche infrarouge, domaine spectral où les variations de la dispersion des SPP et du coefficient d'amortissement sont significatives, nous avons pu distinguer les différentes contributions linéaires et non-linéaires aux processus d'excitation. Ce travail de thèse a ainsi permis de montrer que l’accord de phase entre la mSHG et les ondes électromagnétiques de surface peuvent contribuer très efficacement à l'augmentation des signaux SH et de contraste magnétique associé. / Owing to surface and interface sensitivity, the magnetic Second Harmonic Generation (mSHG) represents a useful tool to probe magnetic interfaces and nanostructures. This work investigates the coupling and interaction of the mSHG with electromagnetic waves propagating along the surface. Two types of surface waves have been studied: (i) surface plasmon polaritons (SPP) at surfaces of metallic thin films and multilayers, and (ii) the diffraction anomaly at the surface of periodically arranged metallic nanostructures. To study influence of linear and nonlinear excitation of surface waves on the mSHG, the reflected second harmonic (SH) intensity and the magnetic SH contrast in the transverse magneto-optical geometry were measured as a function of the angle of incidence. The use of different femtosecond light sources in the near-infrared optical range, where the SPP dispersion and damping exhibit significant variations, made it possible to disentangle linear and nonlinear contributions to the excitation of surface waves. In this thesis, it is proven that phase-matching of the mSHG and surface electromagnetic waves can lead to the enhancement of both the SH yield and the nonlinear magneto-optical signal. These results are important for controlling of the nonlinear magneto-optical response and could impact the development of magnetic storage devices, label-free biosensors and nonlinear magneto-optical switches.

Diese Dissertation stellt die erste Anwendung des magneto-optischen Kerr Effektes (MOKE) auf ferromagnetische Metall/Organische Heterostrukturen zur Aufklärung der optischen und chemischen Eigenschaften dar. Die MOKE-Untersuchungen wurden spektroskopisch in einem Energiebereich von 1.7 eV bis 5.5 eV durchgeführt. Heterostrukturen, wie sie hier untersucht werden, sind relevant für Anwendungen in der organischen Spintronik. Die Auswertung der Experimentellen Daten wird unterstützt durch numerische Simulationen eines Schichtmodells und ergänzende Untersuchung der strukturellen und magnetischen Eigenschaften unter Zuhilfenahme von AFM, TEM, SEM, STXM und SQUID-Magnetometrie. In der aktuellen Arbeit wurde Ni als Beispiel einer ferromagnetischen Schicht oberhalb oder unterhalb des organischen Films verwendet. Die organische Schicht besteht jeweils aus den diamagnetischen Molekülen Rubren, Pentacen und Fulleren, welche nur ein vernachlässigbares MOKE-Signal aufweisen. Zum Vergleich wurden das metallfreie Phtalocyanin H2Pc, welche ein nur eine bis zwei Größenordnungen schwächeres MOKE Signal als das genutzte Ni zeigen, betrachtet. Selbst Moleküle, welche kein intrinsisches MOKE-Signal zeigen, können über die optische Interferenz Einfluss auf das MOKE Signal von Ni nehmen. Daher kann die Dicke der organischen Schicht genutzt werden, um den Verlauf des MOKE Spektrum zu kontrollieren. Dies wird für Rubren und C60 gezeigt. Beim Vergleich des MOKE-Spektrums von Rubren/Ni- und Ni/Rubren-Doppelschichten war es möglich zu zeigen, dass die Metallablagerung an der Oberfläche einen Versiegelungseffekt hat, welcher die Oxidation der organischen Unterschicht verlangsamt. AFM und TEM Messungen zeigen, dass Ni die Morphologie der unteren Rubrenschicht annimmt. Die Proben, die mit einer geringen Wachstumsrate von Rubren hergestellt wurden, weisen bei einer nominellen Schichtdicke von 15 nm klar geformte Rubren-Inseln mit großen Abständen zwischen ihnen auf. In diesen Fällen zeigte die magnetische Hysteresemessung von MOKE bei Raumtemperatur eine unterschiedliche Gestalt in Abhängigkeit von der Photonenenergie. Die Hystereseschleifen wurden durch die Präsenz zweier magnetischer Phasen interpretiert. Die MOKE-Spektren dieser beiden Phasen wurden aus dem experimentellen Spektrum separiert. Die Gestalt des gemessenen Spektrums ändert sich mit der Stärke des angelegten Feldes aufgrund der unterschiedlichen Beiträge der zwei Phasen. An den ferromagnetischen Metall/organischen Schichten wurde TEM angewendet, um die Größe der Metallpartikel zu bestimmen, sowie STXM um die Orientierung der organischen Moleküle festzustellen. Die Schichtdicke, das Massenverhältnis sowie die Wechselwirkung zwischen Metall und organischen Material beeinflussen nachweislich das MOKE Signal.

In the present work, the implications of ion irradiation on the magnetostatic and dynamic properties of soft magnetic Py/Ta (Py = Permalloy: Ni80Fe20) single and multilayer films have been investigated with the main objective of finding a way to determine their saturation magnetization. Both polar magneto-optical Kerr effect (MOKE) and vector network analyzer ferromagnetic resonance (VNA-FMR) measurements have proven to be suitable methods to determine µ0MS, circumventing the problem of the unknown effective magnetic volume that causes conventional techniques such as SQUID or VSM to fail. Provided there is no perpendicular anisotropy contribution in the samples, the saturation magnetization can be determined even in the case of strong interfacial mixing due to an inherently high number of Py/Ta interfaces and/or ion irradiation with high fluences. Another integral part of this work has been to construct a VNA-FMR spectrometer capable of performing both azimuthal and polar angle-dependent measurements using a magnet strong enough to saturate samples containing iron. Starting from scratch, this comprised numerous steps such as developing a suitable coplanar waveguide design, and writing the control, evaluation, and fitting software. With both increasing ion fluence and number of Py/Ta interfaces, a decrease of saturation magnetization has been observed. In the case of the 10×Py samples, an immediate decrease of µ0MS already sets in at small ion fluences. However, for the 1×Py and 5×Py samples, the saturation magnetization remains constant up to a certain ion fluence, but then starts to rapidly decrease. Ne ion irradiation causes a mixing and broadening of the interfaces. Thus, the Py/Ta stacks undergo a transition from being polycrystalline to amorphous at a critical fluence depending on the number of interfaces. The saturation magnetization is found to vanish at a Ta concentration of about 10–15 at.% in the Py layers. The samples possess a small uniaxial anisotropy, which remains virtually unaffected by the ion fluence, but slightly reduces with an increasing number of Py/Ta interfaces. In addition to magnetostatics, the dynamic properties of the samples have been investigated as well. The Gilbert damping parameter α increases with both increasing number of Py/Ta interfaces and higher ion fluences, with the former having a stronger influence. The inhomogeneous linewidth broadening ΔB0 increases as well with increasing number of Py/Ta interfaces, but slightly decreases for higher ion fluences. / In dieser Dissertation ist der Einfluss von Ionenbestrahlung auf die magnetostatischen und dynamischen Eigenschaften von weichmagnetischen Py/Ta-Einzel- und Multilagen (Py = Permalloy: Ni80Fe20) untersucht worden, wobei das Hauptziel gewesen ist, eine Methode zur Bestimmung der Sättigungsmagnetisierung zu finden. Sowohl polare magneto-optische Kerr-Effektmessungen (MOKE) als auch ferromagnetische Resonanzmessungen mittels eines Vektornetzwerkanalysators (VNA-FMR) haben sich als geeignet erwiesen, um µ0MS zu bestimmen, wobei das Problem des unbekannten effektiven magnetischen Volumens umgangen wird, welches bei der Verwendung von Techniken wie SQUID oder VSM auftreten würde. Unter der Voraussetzung, dass die Proben keinen senkrechten magnetischen Anisotropiebeitrag besitzen, kann die Sättigungsmagnetisierung selbst im Fall starker Grenzflächendurchmischung infolge einer großen Anzahl an Py/Ta-Grenzflächen und/oder Ionenbestrahlung mit hohen Fluenzen bestimmt werden. Ein weiterer wesentlicher Bestandteil dieser Arbeit ist die Konstruktion eines VNA-FMR-Spektrometers gewesen, welches vollautomatisiert ist, polare und azimutale Winkelabhängigkeiten messen kann und einen Magneten besitzt, der Proben, die Eisen beinhalten, sättigen kann. Von Grund auf beginnend umfasste dies zahlreiche Schritte wie z. B. die Entwicklung eines geeigneten koplanaren Wellenleiterdesigns sowie das Schreiben von Steuerungs-, Auswertungs- und Fitprogrammen. Mit steigender Fluenz und Zahl an Py/Ta-Grenzflächen ist eine Abnahme der Sättigungsmagnetisierung beobachtet worden. Im Fall der 10×Py-Proben findet diese bereits bei kleinen Fluenzen statt. Im Gegensatz dazu bleibt µ0MS der 1×Py- und 5×Py-Proben bis zu einer bestimmten Fluenz konstant, bevor sie sich dann umso schneller verringert. Die Bestrahlung mit Ne-Ionen verursacht eine Durchmischung und Verbreiterung der Grenzflächen. Infolgedessen erfahren die Py/Ta-Proben bei einer kritischen Fluenz, die von der Zahl der Grenzflächen abhängig ist, einen Phasenübergang von polykristallin zu amorph. Die Sättigungsmagnetisierung verschwindet ab einer Ta-Konzentration von etwa 10–15 Atom-% in den Py-Schichten. Die Proben besitzen eine kleine uniaxiale Anisotropie, die praktisch unbeeinflusst von der Fluenz ist, sich jedoch mit steigender Zahl an Py/Ta-Grenzflächen leicht verringert. Neben den statischen sind auch die dynamischen magnetischen Eigenschaften der Proben untersucht worden. Der Gilbert-Dämpfungsparameter α erhöht sich sowohl mit steigender Zahl an Py/Ta-Grenzflächen als auch mit höheren Fluenzen, wobei Erstere einen größeren Einfluss hat. Die inhomogene Linienverbreiterung ΔB0 nimmt ebenfalls mit steigender Zahl an Py/Ta-Grenzflächen zu, verringert sich jedoch bei größeren Fluenzen leicht.

The work presented in this thesis was broadly focussed on the investigation of the magnetic behaviour of different superconducting materials in the form of bulk (singe crystals and pellets) and thin films (nanomagnetic devices like superconducting spin valves etc). Neutrons and muons were extensively used to probe the structural and magnetic behaviour of these systems at the nanoscale along with bulk characterisation techniques like high-sensitive magnetic property measurements, scanning probe microscopy and magneto-transport measurements etc. The nanoscale interplay of Superconductivity and Ferromagnetism was studied in the thin film structures using a combination of Polarised Neutron Reflectivity (PNR) and Low Energy Muon Spin Rotation (LE-µSR) techniques while bulk Muon Spin Rotation (µSR) technique was used for microscopic magnetic investigation in the bulk materials. In the Fe/Pb heterostructure, evidence of the Proximity Effect was observed in the form of an enhancement of the superconducting penetration depth (λs) with an increase in the ferromagnetic layer thickness (dF) in both the bilayered and the trilayered structures. The existence of an Inverted Magnetic Region was also detected at the Ferromagnet-Superconductor (F/S) interface in the normal state possibly originating from the induced spin polarisation within the Pb layer in the presence of the neighbouring Fe layer(s). The spatial size (height and width) of the Inverted Magnetic Region did not change much while cooling the sample below the superconducting transition temperature(Tc)and it also stayed unaffected by an increase in the Fe layer thickness and by a change of the applied magnetic field. In the superconducting spin valve structure containing Permalloy (Py) as ferromagnetic layer and Nb as the superconducting layer, LE-µSR measurements revealed the evidence of the decay of magnetic flux density (as a function of thickness) within the Nb layer symmetrically from the Py/Nb interfaces towards the centre of the Nb layer in the normal state. The thickness dependent magnetisation decay occurred over two characteristic length scales in the normal state that stayed of similar values in the superconducting state also. In the superconducting state, an additional contribution towards the magnetisation was found in the vicinity of the Py/Nb interfaces possibly originating from the spin polarisation of the singlet Cooper pairs in these areas. The nanoscale magnetic investigation on a highly engineered F/S/F structure (where each of the F blocks made of multiple Co/Pd layers with magnetic moments aligned perpendicular to the plane of these layers and neighbouring magnetic blocks separated by Ru layers giving rise to antiferromagnetic alignment) using LE-µSR showed an antisymmetric thickness dependent magnetic flux density profile with two characteristic length scales. In the superconducting state, the magnetic flux density profile got modified within the superconducting Nb₆₇Ti₃₃ layer near the F/S interfaces in a way similar to that of observed in the case of Py/Nb system, most likely because of the spin polarisation of the superconducting electron pairs. The vortex magnetic phase diagram of Bi₂Sr₂Ca₂Cu₃O10-δ was studied using the Muon Spin Rotation (µSR) technique to explore the effects of vortex lattice melting and rearrangements for vortex transitions and crossover as a function of magnetic field and temperatures. At low magnetic fields, the flux vortices undergo a first order melting transition from a vortex lattice to a vortex liquid state with increasing temperature while another transition also occurred with increasing field at fixed temperature to a vortex glass phase at the lowest temperatures. Evidence of a frozen liquid phase was found in the intermediate field region at low temperature in the form of a lagoon in the superconducting vortex state which is in agreement with earlier observations made in BiSCCO-2212. The magnetic behaviour of the unconventional superconductor Sr₂RuO₄ was investigated using µSR to find the evidence of normal state magnetism and the nature of the vortex state. In the normal state, a weak hysteretic magnetic signal was detected over a wide temperature and field range believed to be supporting the evidence of a chiral order parameter. The nature of the vortex lattice structure was obtained in different parts of the magnetic phase diagram and the evidence of magnetic field driven transition in the lattice structure was detected from a Triangular→Square structure while the vortex lattice stayed Triangular over the entire temperature region below Tc at low fields with a disappearance of pinning at higher temperatures.