The thesis is dealing with the investigation of charge and orbital order and their behaviour under external pressure. Therefore, a new pressure cell has been developed which allows the observation of superlattice reflections corresponding to the order phenomena under pressure using scattering of high-energy synchrotron radiation. The maximum pressure that can be reached is 1.25 GPa. Until today there has been no possibility to conduct such studies of charge and orbital order superlattice reflections under pressure using x-ray scattering. The intensities of the reflections of the single crystalline samples are quite weak compared to fundamental peaks. Therefore the measurements are strongly affected by the absorption of the radiation in the pressure cell itself. Further difficulties result from the facts that low temperatures are needed and the sample has to be oriented in reciprocal space after being mounted into the cell. Therefore, the design of a compact clamp-type piston pressure cell was chosen here. The cell is made from a copper-beryllium alloy with the wall thickness reduced in the height of the sample volume. This allows the usage inside a closed-cycle cryostat mounted on a three-axis-diffractometer. Absorption effects are minimized due to the combination of reduced wall thickness and the usage of high energy synchrotron radiation (E = 100 keV at the beamline BW5 at HASYLAB/DESY). The new experimental technique was established and used for a study of two representatives of the transition metal oxide compounds, i.e. doped cuprates and manganites, which belong to the class of strongly correlated electron systems. The 1/8-doped cuprate La_{2-x}Ba_{x}CuO_{4} reveals an ordered state at low temperatures. Inside the CuO_{2} planes a combined order of charge stripes and antiferromagnetic spin stripes is observed. The ordering results from the interaction between charge, spin and lattice degrees of freedom. Here the lattice degrees of freedom play a major role. Particularly, a structural transition from an orthorhombic to a tetragonal symmetry is prerequisite for the observation of the ordered state. The cell constructed in this work allows a more exact analysis of the coupling between the crystal lattice and the formation of the charge and spin ordered phase. The manganite system Pr_{0.7}(Ca_{0.9}Sr_{0.1})_{0.3}MnO_{3} shows a strong magnetoresistive effect, called colossal magnetoresistance (CMR). In this system, several ordered phases can be found, which exhibit charge, spin and - since the orbital degree of freedom is also present in the manganites - additionally orbital ordering phenomena. In particular, an antiferromagnetically spin ordered insulating phase, which is connected to a charge- and orbital ordered state competes with a ferromagnetic metallic phase. This competition leads to a phase separation, which determines the properties of the sample. Both phases are strongly coupled to the lattice degrees of freedom, so that application of external pressure drastically affects the interplay between the different phases and allows a detailed study of the relation between the charge and orbital ordered phase and the crystal structure. / Die vorliegende Arbeit befaßt sich mit dem Studium der Ordnungszustände von Ladungen und Orbitalen und deren Beeinflußung durch externen Druck. Als experimentelle Neuentwicklung wurde dafür eine Druckzelle entworfen, mit deren Hilfe die Beobachtung der jeweiligen Ordnungsphänomene unter Druck mittels der Streuung hochenergetischer Synchtrotronstrahlung möglich ist. Die Zelle erlaubt die Messung der orbitalen und Ladungsüberstrukturreflexe, welche aus den geordneten Zuständen resultieren, in einem Druckbereich bis 1.25 GPa. Die experimentelle Herausforderung ergibt sich hierbei aus der Tatsache, dass die Überstrukturreflexe im Vergleich zu den fundamentalen Reflexen der einkristallinen Proben sehr schwach sind und zusätzlich durch die Absorption im Mantelmaterial der Druckzelle stark beeinträchtigt werden. Darüber hinaus soll die Zelle bei tiefen Temperaturen einsetzbar und die Probe auch innerhalb der Zelle im reziproken Raum orientierbar sein. Bei dem hier realisierten Ansatz wurde für das Design daher der Typ einer kompakten Klemmdruckzelle aus einer Kupfer-Beryllium-Legierung gewählt, deren Zellwände im Bereich des Probenvolumens reduziert wurden. Dadurch ist der Einsatz der Zelle im Inneren eines Closed-Cycle-Kryostaten auf einem Einkristall-Diffraktometer möglich. Aufgrund der geringen Wandstärke der Zelle und der Nutzung von hochenergetischer Röntgenstrahlung (E = 100 keV am Messplatz BW5 des HASYLAB/DESY) werden Absorptionseffekte minimiert. Die neue Messmethode wurde im Rahmen der Arbeit etabliert und zur Untersuchung zweier wichtiger Übergangsmetalloxidverbindungen (dotierte Kuprate, Manganate), die zur Klasse der stark korrelierten Elektronensysteme gehören, eingesetzt. Das 1/8-dotierte Kupratsystem La_{2-x}Ba_{x}CuO_{4}, weist bei tiefen Temperaturen einen statisch geordneten Zustand auf. Innerhalb der CuO_{2}-Schichten des Kristalls ergibt sich eine Ordnung, bei der sich Streifen lokalisierter Löcher und antiferromagnetische Bereiche abwechseln. Ursache dieses Zustands ist das Wechselspiel von Ladungen, Spins und strukturellen Freiheitsgraden. Dabei spielen letztere eine herausgehobene Rolle. So ist insbesondere ein struktureller Übergang von einer orthorhombischen zu einer tetragonalen Phase Voraussetzung für die Beobachtung der Ordnung. Die in dieser Arbeit aufgebaute Druckzelle erlaubt eine genauere Analyse des Zusammenhangs zwischen Struktur des Kristalls und der Ausbildung der ladungs- und spingeordneten Phase. Das Manganatsystem Pr_{0.7}(Ca_{0.9}Sr_{0.1})_{0.3}MnO_{3}, zeichnet sich durch einen sehr starken magnetoresistiven Effekt aus, der auch als kolossaler Magnetowiderstand (CMR) bezeichnet wird. Auch hier kann bei tiefen Temperaturen eine geordnete Phase beobachtet werden. Allerdings spielt in diesem System zusätzlich der orbitale Freiheitsgrad der Elektronen eine entscheidende Rolle, so dass sich eine kombinierte Ladungs- und Orbitalordnung ergibt. Diese Phase, die isolierend und zusätzlich antiferromagnetisch geordnet ist, steht im direkten Wettbewerb zu einer ferromagnetischen Phase. Aus dieser Konkurrenz ergibt sich eine Tendenz zur Phasenseparation, deren Effekte die Eigenschaften des Kristalls dominieren. Da beide Phasen stark an die strukturellen Freiheitsgrade gekoppelt sind, läßt sich das Gleichgewicht zwischen ihnen durch externen Druck beeinflussen und die Abhängigkeit der ladungs- und orbitalgeordneten Phase von den strukturellen Eigenschaften des Kristalls im Detail untersuchen.

The thesis is dealing with the investigation of charge and orbital order and their behaviour under external pressure. Therefore, a new pressure cell has been developed which allows the observation of superlattice reflections corresponding to the order phenomena under pressure using scattering of high-energy synchrotron radiation. The maximum pressure that can be reached is 1.25 GPa. Until today there has been no possibility to conduct such studies of charge and orbital order superlattice reflections under pressure using x-ray scattering. The intensities of the reflections of the single crystalline samples are quite weak compared to fundamental peaks. Therefore the measurements are strongly affected by the absorption of the radiation in the pressure cell itself. Further difficulties result from the facts that low temperatures are needed and the sample has to be oriented in reciprocal space after being mounted into the cell. Therefore, the design of a compact clamp-type piston pressure cell was chosen here. The cell is made from a copper-beryllium alloy with the wall thickness reduced in the height of the sample volume. This allows the usage inside a closed-cycle cryostat mounted on a three-axis-diffractometer. Absorption effects are minimized due to the combination of reduced wall thickness and the usage of high energy synchrotron radiation (E = 100 keV at the beamline BW5 at HASYLAB/DESY). The new experimental technique was established and used for a study of two representatives of the transition metal oxide compounds, i.e. doped cuprates and manganites, which belong to the class of strongly correlated electron systems. The 1/8-doped cuprate La_{2-x}Ba_{x}CuO_{4} reveals an ordered state at low temperatures. Inside the CuO_{2} planes a combined order of charge stripes and antiferromagnetic spin stripes is observed. The ordering results from the interaction between charge, spin and lattice degrees of freedom. Here the lattice degrees of freedom play a major role. Particularly, a structural transition from an orthorhombic to a tetragonal symmetry is prerequisite for the observation of the ordered state. The cell constructed in this work allows a more exact analysis of the coupling between the crystal lattice and the formation of the charge and spin ordered phase. The manganite system Pr_{0.7}(Ca_{0.9}Sr_{0.1})_{0.3}MnO_{3} shows a strong magnetoresistive effect, called colossal magnetoresistance (CMR). In this system, several ordered phases can be found, which exhibit charge, spin and - since the orbital degree of freedom is also present in the manganites - additionally orbital ordering phenomena. In particular, an antiferromagnetically spin ordered insulating phase, which is connected to a charge- and orbital ordered state competes with a ferromagnetic metallic phase. This competition leads to a phase separation, which determines the properties of the sample. Both phases are strongly coupled to the lattice degrees of freedom, so that application of external pressure drastically affects the interplay between the different phases and allows a detailed study of the relation between the charge and orbital ordered phase and the crystal structure. / Die vorliegende Arbeit befaßt sich mit dem Studium der Ordnungszustände von Ladungen und Orbitalen und deren Beeinflußung durch externen Druck. Als experimentelle Neuentwicklung wurde dafür eine Druckzelle entworfen, mit deren Hilfe die Beobachtung der jeweiligen Ordnungsphänomene unter Druck mittels der Streuung hochenergetischer Synchtrotronstrahlung möglich ist. Die Zelle erlaubt die Messung der orbitalen und Ladungsüberstrukturreflexe, welche aus den geordneten Zuständen resultieren, in einem Druckbereich bis 1.25 GPa. Die experimentelle Herausforderung ergibt sich hierbei aus der Tatsache, dass die Überstrukturreflexe im Vergleich zu den fundamentalen Reflexen der einkristallinen Proben sehr schwach sind und zusätzlich durch die Absorption im Mantelmaterial der Druckzelle stark beeinträchtigt werden. Darüber hinaus soll die Zelle bei tiefen Temperaturen einsetzbar und die Probe auch innerhalb der Zelle im reziproken Raum orientierbar sein. Bei dem hier realisierten Ansatz wurde für das Design daher der Typ einer kompakten Klemmdruckzelle aus einer Kupfer-Beryllium-Legierung gewählt, deren Zellwände im Bereich des Probenvolumens reduziert wurden. Dadurch ist der Einsatz der Zelle im Inneren eines Closed-Cycle-Kryostaten auf einem Einkristall-Diffraktometer möglich. Aufgrund der geringen Wandstärke der Zelle und der Nutzung von hochenergetischer Röntgenstrahlung (E = 100 keV am Messplatz BW5 des HASYLAB/DESY) werden Absorptionseffekte minimiert. Die neue Messmethode wurde im Rahmen der Arbeit etabliert und zur Untersuchung zweier wichtiger Übergangsmetalloxidverbindungen (dotierte Kuprate, Manganate), die zur Klasse der stark korrelierten Elektronensysteme gehören, eingesetzt. Das 1/8-dotierte Kupratsystem La_{2-x}Ba_{x}CuO_{4}, weist bei tiefen Temperaturen einen statisch geordneten Zustand auf. Innerhalb der CuO_{2}-Schichten des Kristalls ergibt sich eine Ordnung, bei der sich Streifen lokalisierter Löcher und antiferromagnetische Bereiche abwechseln. Ursache dieses Zustands ist das Wechselspiel von Ladungen, Spins und strukturellen Freiheitsgraden. Dabei spielen letztere eine herausgehobene Rolle. So ist insbesondere ein struktureller Übergang von einer orthorhombischen zu einer tetragonalen Phase Voraussetzung für die Beobachtung der Ordnung. Die in dieser Arbeit aufgebaute Druckzelle erlaubt eine genauere Analyse des Zusammenhangs zwischen Struktur des Kristalls und der Ausbildung der ladungs- und spingeordneten Phase. Das Manganatsystem Pr_{0.7}(Ca_{0.9}Sr_{0.1})_{0.3}MnO_{3}, zeichnet sich durch einen sehr starken magnetoresistiven Effekt aus, der auch als kolossaler Magnetowiderstand (CMR) bezeichnet wird. Auch hier kann bei tiefen Temperaturen eine geordnete Phase beobachtet werden. Allerdings spielt in diesem System zusätzlich der orbitale Freiheitsgrad der Elektronen eine entscheidende Rolle, so dass sich eine kombinierte Ladungs- und Orbitalordnung ergibt. Diese Phase, die isolierend und zusätzlich antiferromagnetisch geordnet ist, steht im direkten Wettbewerb zu einer ferromagnetischen Phase. Aus dieser Konkurrenz ergibt sich eine Tendenz zur Phasenseparation, deren Effekte die Eigenschaften des Kristalls dominieren. Da beide Phasen stark an die strukturellen Freiheitsgrade gekoppelt sind, läßt sich das Gleichgewicht zwischen ihnen durch externen Druck beeinflussen und die Abhängigkeit der ladungs- und orbitalgeordneten Phase von den strukturellen Eigenschaften des Kristalls im Detail untersuchen.

Ce projet illustre cinq études, mettant l'emphase sur le développement d'une nouvelle approche diagnostique cardiovasculaire afin d'évaluer le niveau d’oxygène contenu dans le myocarde ainsi que sa fonction microvasculaire. En combinant une séquence de résonance magnétique cardiovasculaire (RMC) pouvant détecter le niveau d’oxygène (OS), des manœuvres respiratoires ainsi que des analyses de gaz artériels peuvent être utilisés comme procédure non invasive destinée à induire une réponse vasoactive afin d’évaluer la réserve d'oxygénation, une mesure clé de la fonction vasculaire. Le nombre de tests diagnostiques cardiaques prescrits ainsi que les interventions, sont en pleine expansion. L'imagerie et tests non invasifs sont souvent effectués avant l’utilisation de procédures invasives. L'imagerie cardiaque permet d’évaluer la présence ou absence de sténoses coronaires, un important facteur économique dans notre système de soins de santé. Les techniques d'imagerie non invasives fournissent de l’information précise afin d’identifier la présence et l’emplacement du déficit de perfusion chez les patients présentant des symptômes d'ischémie myocardique. Néanmoins, plusieurs techniques actuelles requièrent la nécessité de radiation, d’agents de contraste ou traceurs, sans oublier des protocoles de stress pharmacologiques ou physiques. L’imagerie RMC peut identifier une sténose coronaire significative sans radiation. De nouvelles tendances d’utilisation de RMC visent à développer des techniques diagnostiques qui ne requièrent aucun facteur de stress pharmacologiques ou d’agents de contraste. L'objectif principal de ce projet était de développer et tester une nouvelle technique diagnostique afin d’évaluer la fonction vasculaire coronarienne en utilisant l' OS-RMC, en combinaison avec des manœuvres respiratoires comme stimulus vasoactif. Ensuite, les objectifs, secondaires étaient d’utilisés l’OS-RMC pour évaluer l'oxygénation du myocarde et la réponse coronaire en présence de gaz artériels altérés. Suite aux manœuvres respiratoires la réponse vasculaire a été validée chez un modèle animal pour ensuite être utilisé chez deux volontaires sains et finalement dans une population de patients atteints de maladies cardiovasculaires. Chez le modèle animal, les manœuvres respiratoires ont pu induire un changement significatif, mesuré intrusivement par débit sanguin coronaire. Il a été démontré qu’en présence d'une sténose coronarienne hémodynamiquement significative, l’OS-RMC pouvait détecter un déficit en oxygène du myocarde. Chez l’homme sain, l'application de cette technique en comparaison avec l'adénosine (l’agent standard) pour induire une vasodilatation coronarienne et les manœuvres respiratoires ont pu induire une réponse plus significative en oxygénation dans un myocarde sain. Finalement, nous avons utilisé les manœuvres respiratoires parmi un groupe de patients atteint de maladies coronariennes. Leurs myocardes étant altérées par une sténose coronaire, en conséquence modifiant ainsi leur réponse en oxygénation. Par la suite nous avons évalué les effets des gaz artériels sanguins sur l'oxygénation du myocarde. Ils démontrent que la réponse coronarienne est atténuée au cours de l’hyperoxie, suite à un stimuli d’apnée. Ce phénomène provoque une réduction globale du débit sanguin coronaire et un déficit d'oxygénation dans le modèle animal ayant une sténose lorsqu’un supplément en oxygène est donné. En conclusion, ce travail a permis d'améliorer notre compréhension des nouvelles techniques diagnostiques en imagerie cardiovasculaire. Par ailleurs, nous avons démontré que la combinaison de manœuvres respiratoires et l’imagerie OS-RMC peut fournir une méthode non-invasive et rentable pour évaluer la fonction vasculaire coronarienne régionale et globale. / This project encompasses five studies, which focus on developing a new cardiovascular diagnostic approach for assessing myocardial oxygenation and microvascular function. In combination with oxygenation-sensitive cardiovascular magnetic resonance (OS-CMR) imaging, breathing maneuvers and altered arterial blood gases can be used as a non-invasive method for inducing a vasoactive response to test the oxygenation reserve, a key measurement in vascular function. The number of prescribed cardiac diagnostic tests and interventions is rapidly growing. In particular, imaging and other non-invasive tests are frequently performed prior to invasive procedures. One of the most common uses of cardiac imaging is for the diagnosis of significant coronary artery stenosis, a critical cost factor in today’s health care system. Non-invasive imaging techniques provide the most reliable information for the presence and location of perfusion or oxygenation deficits in patients with symptoms suggestive of myocardial ischemia, yet many current techniques suffer from the need for radiation, contrast agents or tracers, and pharmacological or physical stress protocols. CMR imaging can identify significant coronary artery stenosis without radiation and new trends in CMR research aim to develop diagnostic techniques that do not require any pharmacological stressors or contrast agents. For this project, the primary aim was to develop and test a new diagnostic technique to assess coronary vascular function using OS-CMR in combination with breathing maneuvers as the vasoactive stimulus. Secondary aims then used OS-CMR to assess myocardial oxygenation and the coronary response in the presence of altered arterial blood gases. An animal model was used to validate the vascular response to breathing maneuvers before translating the technique to human subjects into both healthy volunteers, and a patient population with cardiac disease. In the animal models, breathing maneuvers could induce a significant change in invasively measured coronary blood flow and it was demonstrated that in the presence of a haemodynamically significant coronary stenosis, OS-CMR could detect a myocardial oxygen deficit. This technique was then applied in a human model, with healthy participants. In a direct comparison to the infusion of the coronary vasodilator adenosine, which is considered a standard agent for inducing vasodilation in cardiac imaging, breathing maneuvers induced a stronger response in oxygenation of healthy myocardium. The final study then implemented the breathing maneuvers in a patient population with coronary artery disease; in which myocardium compromised by a coronary stenosis had a compromised oxygenation response. Furthermore, the observed effects of arterial blood gases on myocardial oxygenation were assessed. This demonstrated that the coronary response to breath-hold stimuli is attenuated during hyperoxia, and this causes an overall reduction in coronary blood flow, and consequently an oxygenation deficit in a coronary stenosis animal model when supplemental oxygen is provided. In conclusion, this work has improved our understanding of potential new diagnostic techniques for cardiovascular imaging. In particular, it demonstrated that combining breathing maneuvers with oxygenation-sensitive CMR can provide a non-invasive and cost-effective method for assessing global and regional coronary vascular function.

Studies have shown that creative mathematically founded reasoning (CMR) outperforms algorithmic reasoning (AR) in regards to retention and (re)construction of knowledge. This suggests that creativity should be encouraged in national high-school mathematics curricula. The aim of the present study is to compare how creativity is framed in different national high-school mathematics curricula, using the following definition: creativity is the characteristics of people, processes, and environments which lead to new and original products that are useful or otherwise attractive to an individual or a society. Utilizing content and discourse analysis, the present study thus contrasts how the high-school mathematics curricula of Singapore, Hong Kong, Sweden, and Norway handle and value creativity, and also examines which role creativity takes in each curricula. Findings suggest that Singapore’s curriculum emphasizes creativity the most, and frequently does so in relation to assessment. Hong Kong’s curriculum is found to emphasize creativity in diverse ways, often using words with connotations to playfulness. Analysis of Sweden’s curriculum indicates a relatively minute focus on creativity, tending to put it in a teacher-centered context. A feature of Norway’s curriculum is an increasing emphasis on creativity as courses approach tertiary education. This also suggests a rising value of creativity in its curriculum. A similar though not as pronounced trajectory is found also in Singapore’s curriculum. In the Asian and Norwegian curricula, creativity is expressed both as a means and an end, while in Sweden’s curriculum it is only seen as an end. The results are discussed in terms of potential reasons for the prominent national features, and the study also includes an evaluation of the aptness of the suggested definition of creativity, a review of the limitations of the study, as well as propositions for further research. Finally, two recommendations are given to the National Agency for Education in Sweden – Skolverket – based on the results of the study: 1) diversify the emphasis on creativity in the curriculum, and 2) ensure alignment between what teachers value and what Skolverket values with respect to creativity.

Studies on perovskite rare earth manganites of general formula R1-xAxMnO3 (where R is a trivalent rare earth ion such as La3+, Pr3+ etc. and A is a divalent alkaline earth ion such as Ca2+, Sr2+, Ba2+, have been a very active research area in the last few years in condensed matter physics. Manganites have a distorted perovskite crystal structure with R and A ions situated at the cube corners, oxygen ions at the edge centers of the cube and Mn ions at the centres of the oxygen octahedra. In these manganites the Mn ions are found to be in mixed valence state i.e., in Mn3+ and Mn4+ states. In the octahedral crystal field of oxygen ions the single ion energy levels are split into t2g and eg levels. Mn3+ being a Jahn-Teller ion, the eg level is further split due to the Jahn-Teller effect. A strong Hund’s coupling between the spins in the t2g and eg levels renders the Mn3+ ions to be in the high spin state. The interplay of competing super exchange between Mn ions which determines the antiferromagnetism, orbital ordering and insulating behavior and double exchange between Mn ions which leads to ferromagnetism and metallicity gives rise to very complex phase diagrams of manganites as a function of composition, temperature and magnetic field. The strength of these interactions is determined by various factors such as the A-site cation radius and the Jahn-Teller distortion due to the presence of Mn3+ ions. The strongly coupled charge, spin, lattice and orbital degrees of freedom in manganites gives rise to complex phenomena such as colossal magnetoresistance (CMR), charge order (CO) and orbital order (OO) and phase separation (PS) etc. The properties of these materials are sensitive functions of external stimuli such as the doping, temperature and pressure [1-5] and have been extensively studied both experimentally and theoretically in single crystal, bulk polycrystalline and thin film forms of the samples [6-9]. Charge ordering is one of the fascinating properties exhibited by manganites. Charge ordering has historically been viewed as a precursor to the complex ordering of the Mn 3d orbitals, which in turn determine the magnetic interactions and these magnetic interactions are the driving force for charge localization and orbital order. This ordering of Mn3+ / Mn4+ charges can be destabilized by many methods. An external magnetic field can destabilize the charge ordered phase and drive the phase transition to the ferromagnetic metallic state [10-11]. Other than magnetic field, charge ordering can also be ‘melted’ by a variety of perturbations like electric field [12, 13], hydrostatic and chemical pressure [14-16], irradiation by X-rays [17], substitution at the Mn -site [18 -21] and A-site [22]. Of these, A-site substitution with bigger cations like barium is particularly of great interest since it does not interrupt the conduction path in the “MnO3” frame work Recently attention has been drawn towards the properties of nanoscale manganites. The nanoscale materials are expected to behave quite differently from extended solids due to quantum confinement effects and high surface/volume ratio. Nanoscale CMR manganites have been fabricated using diverse methods in the form of particles, wires, tubes and various other forms by different groups. It has been shown that the properties of CMR manganites can be tuned by reducing the particle size down to nanometer range and by changing the morphology [23-27]. As mentioned above, charge order is an interesting phase of manganites and these CO mangnites in the form of nanowires and nanoparticles show drastic changes in their properties compared to bulk. In contrast to the studies on the CMR compounds, there are very few reports on charge ordering nano manganites except on nanowires of Pr0.5Ca0..5MnO3 [28] and nanoparticles of Nd0.5Ca0.5MnO3 [29] and Pr0.5Sr0..5MnO3 [30]. This thesis is an effort in understanding certain aspects of charge order destabilization by two different methods, namely, doping bigger size cation (barium) in A-site (external perturbation) and by reducing the particle size to nano scale ( intrinsic). For this purpose we have selected the charge ordering system Pr1-xCaxMnO3 (PCMO) with composition x = 0.43. The reason behind choosing this composition is the observation [31] that CO is particularly weak for this value of x. We have prepared bulk, nanoparticles and nanowires of Pr0.57Ca0.41Ba0.02MnO3 manganite and have carried out microstructure, magnetic, magneto transport and EMR measurements to understand the nature of CO destabilization and also to understand other aspects such as magneto transport and magnetic anisotropy . Apart from destabilization of the charge order in PCMO we have also studied the bismuth based manganite Bi0.5Ca0.5MnO3. The reason behind choosing this system is the robust charge order of Bi0.5Ca0.5MnO3 compared to rare earth based manganites. So far no attempt has been made in comparing the electron paramagnetic resonance properties of bismuth based manganites with those of the rare earth based manganites. We have studied the magnetic, transport and electron paramagnetic resonance properties of Bi0.5Ca0.5MnO3 prepared by solid state reaction method and compared the results with those of Pr0.5Ca0.5MnO3 . In the following we present a chapter wise summary of the thesis. Chapter 1 of the thesis contains a brief introduction to the general features of manganites describing various interesting phenomena exhibited by them and the underlying interactions . Chapter 2 contains a detailed review of EPR studies on manganites describing the current level of understanding in the area. In this chapter we have also described the different experimental methodology adopted in this thesis. Chapter 3 reports the effect of a small amount (2%) of barium doped in the charge ordered antiferromagnetic insulating manganite Pr0.57Ca0.43MnO3. The samples were prepared by solid state synthesis and charecterized by various techniques like XRD, EDXA. The results of magnetization, magnetotransport and EPR/EMR experiments on both Pr0.57Ca0.43MnO3 and Pr0.57Ca0.41Ba0.02MnO3 are compared. The magnetization studies show that barium doping induces ferromagnetic phase in place of the CO-antiferromagnetic phase of the pristine sample at low temperatures as reported earlier by Zhu et al.,[31]. The transport studies show insulator to metal transition. The EPR parameters viz line width, intensity and ‘g’ value of Pr0.57Ca0.43MnO3 and Pr0.57Ca0.41Ba0.02MnO3 are compared. The magnetization and EPR studies reveal that the CO transition temperature TCO has shifted to a slightly lower value accompanied by a small decrease in the strength of the charge order. Thus a small amount of barium affects the CO phase of Pr0.57Ca0.43MnO3 and it also induces a ferromagnetic metallic phase at low temperature. Another most important and unexpected result of EMR experiment is the observation of high field signals, i.e. two EMR signals are observed at low temperatures in the ferromagnetic phase of Pr0.57Ca0.41Ba0.02MnO3. The appearance of the high field signals are understood in terms of the effects of magneto crystalline anisotropy. Chapter 4, reports the microstructure, magnetization and EMR studies of Pr0.57Ca0.41Ba0.02MnO3 nanoparticles prepared by sol-gel method. We have mainly focused on the effect of size on the charge ordered phase. The samples were characterized by different techniques like XRD, EDXA and TEM. The obtained particle size of the samples are 30, 60 and 100 nm respectively. We have compared the magnetic, magneto transport and EMR results of these nano samples with the bulk properties. The 30 nm particles do not show the CO phase whereas the 60 and 100 nm particles show CO signatures in DC- magnetization measurements. The EPR intensity also shows a similar trend. These results confirm that charge ordering can also be destabilized by reducing the particle size to nano scale. But the EPR linewidth which reflects the spin dynamics shows a change in the slope near the CO temperature and there by indicates the presence of premonitory charge ordering fluctuations in smaller particles. We also observed that the EMR linewidth increases with the decrease of particle size. Another striking result is the disappearance of high field signals in all the nanosamples. This is understood in terms of a decrease in the magnetic anisotropy in nanoparticles. Part of the result of this chapter is published [32]. Chapter 5, reports the morphological, magnetic and electron paramagnetic resonance studies of Pr0.57Ca0.41Ba0.02MnO3 nanowires. Recently our group has studied the nanowires of Pr0.5Ca0..5MnO3 [28]. In the nanowire sample of Pr0.5Ca0..5MnO3 only a partial suppression of CO is observed. This raises the question about the incomplete suppression of the CO in the nanowires: is this a consequence of the material being microscopic in one dimension and is it necessary to have a 3-dimensional nano material to have full suppression of the charge order ? In the present work we attempt to provide an answer to this question. PCBM nanowires of diameter 80-90 nm and length of ∼ 3.5 μm were synthesized by a low reaction temperature hydrothermal method. We have confirmed the single phase nature of the sample by XRD experiments. Scanning electron microscopy (SEM) and trasmission electron microscopy (TEM) were used to characterize the morphology and microstructures of the nanowires. The surface of nanowires was composed of particles of different grain size and interestingly some particles were hexagonal in shape. The bulk PCBM manganite exhibits charge order at 230 K along with a ferromagnetic transition at 110 K. However, SQUID measurements on PCBM nano-wires show a complete melting of the charge ordering and a ferromagnetic transition at 115 K. The magnetization observed in the nanowires was less compared to that in the bulk. EPR intensity measurements also support this result. Characteristic differences were observed in linewidth and ‘g’ factor behaviors of nanowires when compared with those of the bulk. EPR linewidth which reflects the spin dynamics shows a slope change near the CO temperature (like in nanoparticles) possibly due to charge order fluctuations in nanowires. The high field signals were absent in nanowires as well. Part of the result of this chapter is published [33]. Chapter 6 deals with the magnetic and electron paramagnetic resonance studies on Pr0.5Ca0.5MnO3 and Bi0.5Ca0.5MnO3. These manganites are prepared by solid state reaction method and characterized by different techniques like XRD and EDXA. Further, we have compared the results of magnetization and electron paramagnetic resonance properties of Pr0.5Ca0.5MnO3 with those of Bi0.5Ca0.5MnO3 manganite in the temperature range of 10- 300 K. The two charge ordered manganites show significant differences in their behavior. The temperature dependence of the EPR parameters i.e. line width, central field and intensity of Bi0.5Ca0.5MnO3 are quite different from the rare earth based manganite i.e. Pr0.5Ca0.5MnO3. Linewidth of BCMO is large compared to PCMO manganite and interestingly the temperature dependence of the central fields (CF) of PCMO and BCMO show opposite behavior. The CF of PCMO decreases with decrease in temperature as found in a large number of other CO systems, whereas CF of BCMO increases with decrease in temperature. This unusual behavior of resonance field is attributed to the different magnetic structure of BCMO system at low temperatures. Chapter 7 sums up the results reported in the thesis. The insight gained from the present work in understanding the destabilization of charge order by chemical doping and size reduction is discussed as well as the differences in the properties of bismuth and rare earth manganites. Further, we have indicated possible future directions of research in this area.

Transition metal compounds, especially the oxides, containing dn (0 ≤ n ≤ 10) electronic configuration, constitute the backbone of solid state/materials chemistry aimed at realization of novel materials properties of technological importance. Some of the significant materials properties of current interest are spin-polarized metallic ferromagnetism, negative thermal expansion, second harmonic nonlinear optical (NLO) susceptibility, fast ionic and mixed electronic/ionic conductivity for application in solid state batteries, and last but not the least, high-temperature superconductivity. Typical examples for each one of these properties could be found among transition metal oxides. Thus, alkaline-earth metal (A) substituted rare-earth (Ln) manganites, Lnı.xAxMnΟ3, are currently important examples for spin-polarized magnetotransport, ZrV2O7 and ZrW2O8 for negative thermal expansion coefficient, KTiOPO4 and LiNbO3 for second harmonic NLO susceptibility, (Li, La) TiO3 and LiMn2O4 for fast-ionic and mixed electronic/ionic conductivity respectively, and the whole host of cuprates typified by YBa2Cu3O7 for high Tc superconductivity. Solid state chemists constantly endeavour to obtain structure-property relations of solids so as to be able to design better materials towards desired properties. Synthesis coupled with characterization of structure and measurement of relevant properties is a common strategy that chemists adopt for this task. The work described in this thesis is based on such a broad-based chemists' approach towards understanding and realization of novel materials properties among the family of metal oxides. A search for metallic ferro/ferrimagnetism among the transition metal perovskite oxides, metallicity and possibility of superconductivity among transition-metal substituted cuprates and second order NLO susceptibility among metal oxides containing d° cations such as Ti(IV), V(V) and Nb(V) - constitute the main focus of the present thesis. New synthetic strategies that combine the conventional ceramic approach with the chemistry-based 'soft1 methods have been employed wherever possible to prepare the materials. The structures and electronic properties of the new materials have been probed by state-of-the art techniques that include powder X-ray diffraction (XRD) together with Rietveld refinement, electron diffraction, thermogravimetry, measurement of magnetic susceptibility (including magnetoresistance), Mossbauer spectroscopy and SHG response (towards 1064 nm laser radiation), besides conventional analytical techniques for determination of chemical compositions. Some of the highlights of the present thesis are: (i) synthesis of new mixed valent [Mn(III)/Mn(IV)] perovskite-type manganites, ALaMn2O6-y (A = K, Rb) and ALaBMn3O9_y (A = Na, K; B = Ca, Sr) that exhibit ferromagnetism and magnetoresistance; (ii) investigation of a variety of ferrimagnetic double-perovskites that include ALaMnRuO6 (A = Ca, Sr, Ba) and ALaFeVO6 (A = Ca, Sr) and A2FeReO6 (A = Ca, Sr, Ba) providing new insights into the occurrence of metallic and nonmetallic ferrimagnetic behaviour among this family of oxides; (iii) synthesis of new K2NiF4-type oxides, La2-2xSr2XCui.xMxO4 (M = Ti, Mn, Fe, Ru) and investigation of Cu-O-M interaction in two dimension and (iv) identification of the structural rnotif(s) that gives rise to efficient second order NLO optical (SHG) response among d° oxides containing Ti(IV), V(V), Nb(V) etc., and synthesis of a new SHG material, Ba2-xVOSi2O7 having the fresnoite structure. The thesis consists of five chapters and an appendix, describing the results of the investigations carried out by the candidate. A brief introduction to transition metaloxides, perovskite oxides in particular, is presented in Chapter 1. Attention is focused on the structure and properties of these materials. Chapter 2 describes the synthesis and investigation of two series of anion-deficient perovskite oxides, ALaMn2O6-y (A = K, Rb, Cs) and ALaBMn3O9_y (A = Na, K; B = Ca, Sr). ALaMn2O6-y (A = K, Rb, Cs) series of oxides adopt 2 ap x 2 ap superstructure for K and Rb phases and √2 av x √2 ap x 2 ap superstructure (ap = perovskite subcell) for the Cs phase. Among ALaBMn3O9-y phases, the A = Na members adopt a new kind of perovskite superstructure, ap x 3 ap, while the A = K phases do not reveal an obvious superstructure of the perovskite. All these oxides are ferromagnetic (Tc ~ 260-325 K) and metallic exhibiting a giant magnetoresistance behaviour similar to alkaline earth metal substituted lanthanum manganites, Lai_xAxMnO3. However, unlike the latter, the resistivity peak temperature Tp for all the anion-deficient manganites is significantly lower than Tc. In Chapter 3, we have investigated structure and electronic properties of double-perovskite oxides, A2FeReO6 (A = Ca, Sr and Ba). The A = Sr, Ba phases are cubic (Fm3m) and metallic, while the A = Ca phase is monoclinic (P2yn) and nonmetallic. All the three oxides are ferrimagnetic with Tcs 315-385 K as reported earlier. A = Sr, Ba phases show a negative magnetoresistance (MR) (10-25 % at 5 T), while the Ca member does not show an MR effect. 57Fe Mossbauer spectroscopy shows that iron is present in the high-spin Fe3+ (S = 5/2) state in Ca compound, while it occurs in an intermediate state between high-spin Fe2+ and Fe3+ in the Ba compound. Monoclinic distortion and high covalency of Ca-O bonds appear to freeze the oxidation states at Fe+3/Re5+ in Ca2FeRe O6, while the symmetric structure and ionic Ba-O bonds render the FeReO6 array highly covalent and Ba2FeReO6 metallic. Mossbauer data for Sr2FeReO6 shows that the valence state of iron in this compound is intermediate between that in Ba and Ca compounds. It is likely that Sr2FeReO6 which lies at the boundary between metallic and insulating states is metastable, phase-seperating into a percolating mixture of different electronic states at the microscopic level. In an effort to understand the occurrence of metallicity and ferrimagnetism among double perovskites, we have synthesized several new members : ALaMnFeO6 (A = Ca, Sr, Ba), ALaMnRuO6 (A = Ca, Sr, Ba) and ALaVFeO6 (A = Ca, Sr) (Chapter 3). Electron diffraction reveals an ordering of Mn and Ru in ALaMnRuO6 showing a doubling of the primitive cubic perovskite cell, while ALaVFeO6 do not show an ordering. ALaMnRuOs are ferrimagnetic (Tcs ~ 200-250 K) semiconductors, but ALaVFeO6 oxides do not show a long range magnetic ordering . The present work together with the previous work on double perovskites shows that only a very few of them exhibit both metallicity and ferrimagnetism, although several of them are ferrimagnetic. For example, among the series Ba2MReO6 (M = Mn, Fe, Co, Ni), only the M = Fe oxide is both metallic and ferrimagnetic, while M = Mn and Ni oxides are ferrimagnetic semiconductors. Similarly, A2CrMoO6 (A = Ca, Sr), A2CrRe06 (A = Ca, Sr), and ALaMnRuO6 (A = Ca, Sr, Ba) are all ferrimagnetic but not metallic. While ferrimagnetism of double perovskites arise from an antiferromagnetic coupling of B and B' spins through the B-O-B' bridges, the occurrence of metallicity seems to require precise matching of the energies of d-states of B and B' cations and a high covalency in the BB'O6 array that allows a facile electron-transfer between B and B', Bn++B’m+↔B(n+1)++B’(m-1)+ without an energy cost, just as occurs in ReO3 and other metallic ABO3 perovskites. In an effort to understand the Cu-O-M (M = Ti, Mn, Fe, Ru) electronic interaction in two dimension, we have investigated K2N1F4 oxides of the general formula La2-2xSr2XCui.xMxO4 (M = Ti, Mn, Fe or Ru). These investigations are described in Chapter 4. For M = Ti, only the x = 0.5 member could be prepared, while for M = Mn and Fe, the composition range is 0 < x < 1.0, and for M = Ru, the composition range is 0 < x ≤ 0.5. There is no evidence for ordering of Cu(II) and M(IV) in the x = 0.5 members. While the members of the M = Ti, Mn and Ru series are semiconducting/insulating, the members of the M = Fe series are metallic, showing a broad metal-semiconductor transition around 100 K for 0 < x ≤ 0.15 that is possibly related to a Cu(II)-O-Fe(IV) < > Cu(III)-O-Fe(III) valence degeneracy. Increasing the strontium content at the expense of lanthanum in La2-2xSr2XCui.xFexO4 for x ≤ 0.20 renders the samples metallic but not superconducting. In a search for inorganic oxide materials showing second order nonlinear optical (NLO) susceptibility, we have investigated several borates, silicates and phosphates containing /ram-connected MO6 octahedral chains or MO5 square-pyramids, where M = d°: Ti(IV), Nb(V) or Ta(V). Our investigations, which are described in Chapter 5, have identified two new NLO structures: batisite, Na2Ba(TiO)2Si4O12, containing trans-connectd TiO6 octahedral chains, and fresnoite, Ba2TiOSi2O7, containing square-pyramidal T1O5. Investigation of two other materials containing square-pyramidal TiO5, viz., Cs2TiOP2O7 and Na4Ti2Si8O22. 4H2O, revealed that isolated TiO5 square-pyramids alone do not cause a second harmonic generation (SHG) response; rather, the orientation of T1O5 units to produce -Ti-O-Ti-O- chains with alternating long and short Ti-0 distances in the fresnoite structure is most likely the origin of a strong SHG response in fresnoite. Indeed, we have been able to prepare a new fresnoite type oxide, Ba2.xVOSi2O7 (x ~ 0.5) that shows a strong SHG response, confirming this hypothesis. In the Appendix, we have described three synthetic strategies that enabled us to prepare magnetic and NLO materials. We have shown that the reaction CrO3 + 2 NH4X > CrO2 + 2 NH3 + H2O + X2 (X = Br, I), which occurs quantitatively at 120-150 °C, provides a convenient method for the synthesis of CrO2. Unlike conventional methods, the method described here does not require the use of high pressure for the synthesis of this technologically important material. For the synthesis of magnetic double perovskites, we have developed a method that involves reaction of basic alkali metal carbonates with the acidic oxides (e.g. Re2O7) first, followed by reaction of this precursor oxide with the required transition metal/transition metal oxide (e.g. Fe/Fe2O3). By this method we have successfully prepared single-phase perovskite oxides, A2FeReO6, ACrMoO6 and ALaFeVO6. We have prepared the new NLO material Ba2_xV0Si207 from Ba2VOSi2O7 by a soft chemical redox reaction involving the oxidation of V(IV) to V(V) using Br2 in CH3CN/CHCI3. Ba2V0Si207 + 1/2 Br2 > Bai.5V0Si207 + 1/2 BaBr2. The work presented in this thesis was carried out by the candidate as part of the Ph.D. training programme. He hopes that the studies reported here will constitute a worthwhile contribution to the solid state chemistry of transition metal oxides and related materials.

Perovskite rare-earth manganites of the form R1-xAxMnO3 (R – rare earth ion or Bi, A – Ca,Sr) have drawn an overwhelming research interest during the last few years owing to their extraordinary physical properties. Some of the interesting phenomena exhibited by the manganites are (a) colossal magneotresistance (CMR) (b) charge, orbital and spin ordering and (c) phase separation at nano and micron scale. The manganites are strongly correlated systems in which the charge, spin and orbital degrees of freedom are coupled. The properties of these materials are sensitive functions of external stimuli such as the doping, temperature and pressure [1-5] and have been extensively studied both experimentally and theoretically on single crystal, bulk polycrystalline and thin film forms of the samples [6-9]. Recently attention has been drawn towards the properties of nanoscale manganites. The nanoscale materials are expected to behave quite differently from extended solids due to quantum confinement effects and high surface/volume ratio. Nanoscale CMR manganites have been fabricated using diverse methods in the form of particles, wires, tubes and various other forms by different groups. It has been shown that the properties of CMR manganites can be tuned by reducing the particle size down to nanometer range and by changing the morphology [10-14]. The physical properties of antiferromagnetic insulating charge ordered manganites have been well investigated by using numerous experimental techniques on bulk solids. It is known that the charge ordered (CO) phase is ‘melted’ resulting in a ferromagnetic, metallic phase on application of high magnetic fields, electric fields, impurity ion doping, high energetic ion irradiation and by pressure [15-17]. However, no attempts have been made on the fabrication and the physical property investigations on nanoscale charge ordered manganites. Hence, we have undertaken to study the properties of charge ordered manganites prepared at nanoscale using various experimental probes. In this thesis we present the results on magnetization, magnetotransport and Electron Magnetic Resonance (EMR) (electron paramagnetic resonance in the paramagnetic phase and ferromagnetic resonance in the ferromagnetic phase) studies of the following nanoscale compounds and compare the properties with those of their bulk counterparts; (a) highly robust antiferromagnetic insulating CE –type charge ordered manganite Pr0.5Ca0.5MnO3 (PCMO) (b) highly robust antiferromagnetic insulating CE- type charge ordered manganite Nd0.5Ca0.5MnO3 (NCMO) (c) moderately robust A-type charge ordered manganite Pr0.5Sr0.5MnO3 (PSMO) (d) highly robust insulating anti-ferromagnetic charge ordered manganites Bi0.5Ca0.5MnO3 (BCMO) and Bi0.5Sr0.5MnO3 (BSMO) and (e) a CMR manganite Pr0.7Pb0.3MnO3 (PPMO). Chapter 1 of the thesis contains a brief introduction to the general features of manganites describing various interesting phenomena and the interactions underlying them. Further, we have written a detailed review on the properties of nanometric CMR manganites of various sizes and shapes. In this chapter, we have also described the experimental methodology and the analysis procedure adopted in this work Chapter 2 reports the fabrication of nanowires and nanoparticles of Pr0.5Ca0.5MnO3 (PCMO) and the results obtained from magnetization, magnetotransport and electron magnetic resonance measurements performed on nanoscale PCMO along with their comparison with those of the bulk sample. Here, the nanowires of PCMO were prepared by hydrothermal method and the nanoparticles of mean sizes 10, 20 and 40 nm were prepared by polymer assisted sol-gel method. Solid state reaction method was used to prepare the micron sized PCMO bulk material. Different techniques like XRD, TEM, EDAX and ICPAES have been used to characterize the samples. The novel result of the present investigation is the weakening of charge order and switch over from the anti-ferromagnetic phase to ferromagnetic phase in PCMO nanowires [18]. In addition, the charge order is seem to have completely suppressed in 10 nm PCMO nanoparticles as observed from the magnetization measurements. These results are particularly very significant as one needs magnetic fields of ~ 27 T to melt the charge ordered phase in PCMO. Size induced insulator-metal transition TM-I is observed in nanoscale PCMO at low temperatures accompanied by ferromagnetism. CMR of 99.7% is obtained at TM-I and at a field of 11 T. EMR studies have confirmed the presence of ferromagnetic phase at low temperatures. Temperature dependent EMR line width and intensity have shown the presence of CO phase in PCMO10 though static magnetization measurements have shown the absence of CO phase. It is found that the EMR linewidth increases with the decrease of particle size. Chapter 3 reports the fabrication of nanoparticles of Nd0.5Ca0.5MnO3 (NCMO) and the results obtained from magnetization, magnetotransport and electron magnetic resonance measurements performed on nanoscale NCMO along with their comparison with those of bulk NCMO. The nanoparticles of NCMO of mean sizes 5, 20 and 40 nm were prepared by polymer assisted sol-gel method. Solid state reaction method was used to prepare the micron sized NCMO bulk material. Different techniques like XRD, TEM, EDAX and ICPAES have been used to characterize the samples. A striking result of this particular investigation is the complete suppression of charge ordered phase in 5 and 20 nm NCMO nanoparticles as observed from the magnetization measurements [19]. Size induced insulator-metal transition TM-I is observed in nanoscale NCMO at low temperatures accompanied by ferromagnetism in accordance with Zener double exchange meachanism. CMR of 99.7% is obtained at TM-I and at a field of 11 T. EMR studies have confirmed the presence of ferromagnetic phase at low temperatures. Temperature dependent EMR line width and intensity have shown the presence of residual CO fluctuations in NCMO5 though the static magnetization measurements have shown the absence of CO phase. It is found that the EMR linewidth increases with the decrease of particle size. Low temperature X-ray diffraction measurements on NCMO20 indicate the absence of CO phase. But the preliminary results obtained from the optical spectroscopy measurements indicate the evidence for the presence of CO phase. In Chapter 4, we report the investigations on the nanoscale PSMO. PSMO nanoparticles of sizes 20, 40 and 60 nm are prepared by polymer precursor sol-gel method. PSMO nanowires of diameter 50 nm and lengths of a few microns have been prepared by hydrothermal method. The bulk polycrystalline PSMO is obtained by crushing the single crystal of the same prepared by float zone method. Various techniques like XRD, TEM, VSM, transport measurements and EMR spectroscopy have been employed to characterize and to study the size dependent magnetic, transport and electron magnetic resonance properties and to compare them with those of the bulk. Our results show that there is a disappearance of anti-ferromagnetic charge ordering phase and the appearance of a ferromagnetic phase at low temperatures in all PSMO nanoparticles and nanowires. Metal like behaviour is observed in the size induced ferromagnetic phase in nanoparticles. The EMR linewidth increases with the decrease of particle size. A comparison with the properties of the bulk material shows that the ferromagnetic transition at 265 K remains unaffected but the anti-ferromagnetic transition at TN = 150 K disappears in the nanoparticles. Further, the temperature dependence of magnetic anisotropy shows a complex behaviour, being higher in the nanoparticles at high temperatures, lower at lower temperatures in comparison with the bulk [20]. In Chapter 5, we present the fabrication, characterization and the results obtained from the magnetization and EMR measurements carried out on BCMO and BSMO nanoparticles and compare the results with those of the bulk. X-ray diffraction gives evidence for single phasic nature of the materials as well as their structures. Mono-dispersed to a large extent, isolated nanoparticles are seen in the transmission electron micrographs. High resolution electron microscopy shows the crystalline nature of the nanoparticles. Superconducting quantum interferometer based magnetic measurements from 10 K to 300 K show that these nanomanganites retain the charge ordering nature unlike the Pr and Nd based nanomanganites. The CO in Bi based manganites is thus found to be very robust consistent with the observation that magnetic fields of the order of 130 T are necessary to melt the CO in these compounds. These results are supported by electron magnetic resonance measurements [21]. In Chapter 6, we present our results on the effect of particle size on the magnetic properties of Pr0.7Pb0.3MnO3 (PPMO). PPMO nanoparticles of two different sizes (~5 nm and 30 nm) were prepared by the polymeric precursor sol-gel method. The samples are characterized by different techniques like XRD, TEM, SQUID magnetometry, EMR and optical spectroscopic measurements. It is found that the nanoparticles crystallize in the cubic perovskite structure. TEM measurements show that the 5 nm particles are uniform in size. They are also crystalline as seen by HREM and XRD measurements. SQUID magnetometry measurements have shown that the Curie temperature increases (from 220 K to 235 K) with the increase of particle size. Saturation magnetization is higher for the smaller particles studied. We have observed only one EMR signal down to 4 K in both the nanoparticles (5 and 30 nm) in contrast to the two EMR signal behaviour observed in bulk PPMO [22]. It is found that the EMR linewidth increases with the decrease of particle size in the paramagnetic phase. Temperature dependent optical spectroscopy measurements performed on 5 nm PPMO nanoparticles indicate that the insulator-metal transition temperature TM-I = 230 K, is not very different from TM-I = 235 K of the bulk sample [23] The thesis concludes with a brief writeup summarizing the results and pointing out possible future directions of research in the area.

The main focus of this thesis is in understanding the role of phase separation and microstructure in determining the physical properties of manganites. We also aim to be able to tune certain material properties using appropriate control mechanisms. For this, an understanding of the local electronic properties of manganites is essential. We thus set out to study the local electronic states in manganites using a highly sensitive probe: the scanning tunneling microscope (STM). The chapter 1 of the thesis gives an introduction to manganites, and of how manganites are susceptible to various perturbations due to closely lying ground states and an intricate interplay of their charge, spin and lattice degrees of freedom. Chapter 2 of this thesis gives a detailed account of various experimental methods used in the current investigation. In particular, we describe the design and fabrication of a variable temperature ultra-high vacuum scanning tunneling microscope (UHV-STM) which was used to carry out spatially resolved measurements on various manganite systems. This chapter also describes sample fabrication techniques by which strain and microstructure of thin films can be controlled. Other characterization techiniques, such as tranport and magnetotransport measurements, are also described in detail. Chapter 3 presents our investigation of the role of microstructure and phase separation on the DOS and local electronic properties of manganite thin films. We describe various spatially resolved STM/STS measurements carried out on La0.67Sr0.33MnO3 and La0.67Ca0.33MnO3 films having different micrsotructure and varying degrees of phase separation. We also present a theoretical model used in interpreting STS data to account for finite temperature effects and explain the existing data in this context. We use this model to gain insight into the behaviour of the DOS at EF near the MIT where thermal smearing can often give rise to misleading inferences. Chapter 4 presents our investigation on the density of states in a typical charge ordered manganite system, Pr1-xCaxMnO3. We describe STS measurements carried out on this system to study the occurrence and evolution of the charge ordering (CO) gap as a function if temperature as well as tunneling current. We report the observation of destabilization of the CO gap using tunnel current injection by an STM tip. Chapter 5 presents our investigation into the controlled and localized “nanoscale” phase separation in Pr1-xCaxMnO3 (PCMO) using an STM tip. The investigations were carried out on PCMO single crystal and PCMO epitaxial films. Our results raise the possibility of nano-fabrication of metallic nanoislands in a CO matrix using an STM tip. We demonstrate some examples of this and also raise the relevance of intrinsic phase separation in this context. We show that the “melting” of CO using tunnel current injection by an STM tip is analogous to the magnetic field-induced melting of CO on a microscopic scale. Chapter 6 summarizes the important results of this thesis work and suggests the scope for future experiments.

The goal of the thesis is to sum up the issues of the contract for the international carriage of goods by road and rail comprehensively, from the perspective of the Czech legal system, and to analyze the issues of the electronic consignment notes, to evaluate the advantages and disadvantages of their usage, or to asses the barriers for their usage if they are not widely used yet.

L'Imagerie par Résonance Magnétique pondérée en Diffusion (IRM-D) permet l'accès à l'information structurelle des tissus au travers de la lecture du mouvement brownien des molécules d'eau. Ses applications sont nombreuses en imagerie cérébrale, tant en milieu clinique qu'en recherche. Néanmoins le mouvement physiologique créé une perte de signal supplémentaire au cours de l'encodage de la diffusion. Cette perte de signal liée au mouvement limite les applications de l'IRM-D quant à l'imagerie cardiaque. L'utilisation de faibles valeurs de pondération (b) réduit cette sensibilité mais permet seulement l'imagerie du mouvement incohérent intra-voxel (IVIM) qui contient la circulation sanguine et la diffusion des molécules d'eau. L'imagerie IVIM possède pourtant de nombreuses applications en IRM de l'abdomen, depuis la caractérisation tissulaire à la quantification de la perfusion, mais reste inexplorée pour l'imagerie du coeur. Mon travail de thèse correspond à l'évaluation des conditions d'application de l'IRM-D à faibles valeurs de b pour le coeur humain, afin de proposer des contributions méthodologiques et d'appliquer les techniques développées expérimentalement. Nous avons identifié le mouvement cardiaque comme une des sources majeures de perte de signal. Bien que le mouvement global puisse être corrigé par un recalage non-rigide, la perte de signal induite par le mouvement perdure et empêche l'analyse précise par IRM-D du myocarde. L'étude de cette perte de signal chez un volontaire a fourni une fenêtre temporelle durable où le mouvement cardiaque est au minimum en diastole. Au sein de cette fenêtre optimale, la fluctuation de l'intensité atteste d'un mouvement variable résiduel. Une solution de répéter les acquisitions avec un déclenchement décalé dans le temps permet la capture des minimas du mouvement, c.-à-d. des maximas d'intensité en IRM-D. La projection du maximum d'intensité dans le temps (TMIP) permet ensuite de récupérer des images pondérées en diffusion avec un minimum de perte de signal lié au mouvement. Nous avons développé et évalué différentes séquences d'acquisition combinées avec TMIP : la séquence d'imagerie écho-planaire classique par écho de spin (SE-EPI) peut être adaptée mais souffre du repliement d'image ; une séquence Carr-Purcell-Meiboom-Gill combinée avec une préparation d'encodage de diffusion est plus robuste aux distorsions spatiales mais des artefacts de bandes noires empêchent son applicabilité ; finalement une séquence double-SE-EPI compensant les courants de Foucault et pleinement optimisée produit des images IRM-D moins artefactées. Avec cette séquence, l'IRM-D-TMIP permet la réduction significative de la perte de signal liée au mouvement pour l'imagerie cardiaque pondérée en diffusion. L'inconvénient avec TMIP vient de l'amplification du bruit positif d'intensité. Afin de compenser cette sensibilité du TMIP, nous séparons le bruit d'intensité des fluctuations lentes liées au mouvement grâce à une nouvelle approche basée sur l'analyse en composantes principales (PCA). La décomposition préserve les détails anatomiques tout en augmentant les rapports signal et contraste-à-bruit (SNR, CNR). Avec l'IRM-D-PCATMIP, nous augmentons à la fois l'intensité finale et la qualité d'image (SNR) en théorie et expérimentalement. Les bénéfices ont été quantifiés en simulation avant d'être validés sur des volontaires. De plus la technique a montré des résultats reproductibles sur des patients post-infarctus aigue du myocarde, avec un contraste cohérent avec la position et l'étendue de la zone pathologique. Contrairement à l'imagerie cérébrale, l'imagerie IRM-D par faibles valeurs de pondération in vivo doit être différentiée des analyses IRM-D ex-vivo. Ainsi l'IRM-D-PCATMIP offre une technique sans injection pour l'exploration du myocarde par imagerie IVIM. Les premiers résultats sont encourageants pour envisager l'application sur un modèle expérimental d'une maladie cardiovasculaire [etc...] / Diffusion weighted magnetic resonance imaging (DW-MRI, or DWI) enables the access to the structural information of body tissues through the reading of water molecules Brownian motion. Its applications are many in brain imaging, from clinical practice to research. However physiological motion induces an additional signal-loss when diffusion encoding is applied. This motion-induced signal-loss limits greatly its applications in cardiac imaging. Using low diffusion-weighting values (b) DWI reduces this sensitivity but permits only the imaging of intravoxel incoherent motion (IVIM), which combines both water diffusion and perfusion. IVIM imaging has many applications in body MRI, from tissue characterization to perfusion quantification but remains unexplored for the imaging of the heart. The purpose of this work was to evaluate the context of low b-values DWI imaging of the heart, propose methodological contributions and then apply the developed techniques experimentally. We identified cardiac motion as one of the major sources of motion-induced signal loss. Although bulk motion can be corrected with a non-rigid registration algorithm, additional signal-loss remains uncorrected for and prevents accurate DWI of the myocardium. The study of diffusion-weighted signal-loss induced by cardiac motion in a volunteer provided a time-window when motion is at minimum in diastole. Within this optimal time-window, fluctuation of intensity attests of variable remaining physiological motion. A solution to repeat acquisition with shifted trigger-times ease the capture of motion amplitude minima, i.e. DWI-intensity maxima. Temporal maximum intensity projection (TMIP) finally retrieves diffusion weighted images of minimal motion-induced signal-loss. We evaluated various attempts of sequence development with TMIP: usual spin-echo echo-planar imaging (se-EPI) sequence can be improved but suffers aliasing issues; a balanced steady-state free-precession (b-SSFP) combined with a diffusion preparation is more robust to spatial distortions but typical banding artifacts prevent its applicability; finally a state-of-the-art double-spin-echo EPI sequence produces less artifacted DWI results. With this sequence, TMIP-DWI proves to significantly reduce motion-induced signal-loss in the imaging of the myocardium. The drawback with TMIP comes from noise spikes that can easily be highlighted. To compensate for TMIP noise sensitivity, we separated noise spikes from smooth fluctuation of intensity using a novel approach based on localized principal component analysis (PCA). The decomposition was made so as to preserve anatomical features while increasing signal and contrast to noise ratios (SNR, CNR). With PCATMIP-DWI, both signal-intensity and SNR are increased theoretically and experimentally. Benefits were quantified in a simulation before being validated in volunteers. Additionally the technique showed reproducible results in a sample of acute myocardial infarction (AMI) patients, with a contrast matching the extent and location of the injured area. Contrarily to brain imaging, in vivo low b-values DWI should be differentiated from ex vivo DWI pure diffusion measurements. Thus PCATMIP-DWI might provide an injection-free technique for exploring cardiac IVIM imaging. Early results encourage the exploration of PCATMIP-DWI in an experimental model of cardiac diseases. Moreover the access to higher b values would permit the study of the full IVIM model for the human heart that retrieves and separates both perfusion and diffusion information