It is increasingly important to identify the nature of the interfacial water in biology in order to explain how biological functions and systems work. It is not simply a matter of which biomolecules are present in a cell, but also of how these biomolecules interact with one another. This body of work uses neutron scattering techniques to explain the nature of the vibrational dynamics of water interacting with biomolecules and systems that mimic the biological molecular crowding environment of a cell. Recent work in science has seen the synthesis of periodic mesoporous organosilicas with organic groups attached. In the first paper in this thesis, the use of one of these materials is highlighted to look at confined water, equivalent to the water found in a crowded cellular environment. Here it is shown that the properties of the water within the pores and water molecules around the surface were shown to be different and then identified as interfacial and bulk water respectively. In order to develop the investigation of interfacial water with biological matter, it seemed appropriate to start with the most basic molecules, amino acids. The second paper presents a complete survey of the 20 biologically important amino acids using one of the world's highest resolution neutron scattering spectrometer (TOSCA at ISIS, Rutherford Appleton Laboratory). Computer simulation of the experimental work through molecular dynamics, allows many vibrational modes to be assigned for the first time and correlated with the broader vibrational peaks previously observed for proteins. Comparison of the dry states with the hydrated states of amino acids, gives some insight into the sites within the amino acid side chains where water molecules are likely to bind. For serine this is the hydroxyl group in the side chain. The third paper focuses on IINS data of serine in more detail and discusses several low energy vibrational modes that have been assigned and for the first time, shows how the presence of water molecules changes the dynamic behaviour of librational and torsional modes differently. The combination of these studies allows a clearer picture of how water in biology interacts with biomolecules and of the importance of water to our existence.

A collection of studies are reported that focus on the examination of exchange interactions in complexes containing paramagnetic ions with a large magnetic anisotropy. A number of complementary techniques are used to analyse the complicated systems that arise, including high-field high-frequency electron paramagnetic resonance, inelastic neutron scattering, SQUID magnetometry, and ab initio calculations. The nuclearity of the complexes ranges from dimetallic, to trimetallic, to octametallic. A family of five water- and carboxylate-bridged nickel(II) dimetallics are the focus of a magneto-structural correlation study that succeeds in measuring the magnitude of the exchange interaction despite dominating effects from large zero-field splitting effects. Similar work is reported for four cobalt(II) analogues of these compounds, with the relationship between exchange interactions and geometry also being probed by pressure INS. Charge density studies that combine high resolution X-ray and neutron diffraction studies are reported on cobalt and nickel analogues from the same family of dimetallics, revealing strong evidence for non-direct exchange. A family of four trimetallic triangle complexes containing two nickel(II) ions and one chromium(III) ion bridged by a central fluoride and a total of six carboxylates are reported, and the exchange interactions are elucidated from a global model that accounts for the low-field magnetic, heat capacity, and EPR data. Two new octametallic vanadium(III) wheels—where each pair of adjacent metals are bridged by a fluoride and two carboxylates—are reported along with preliminary results from magnetic measurements and solid state proton NMR spectra, which reveal significant field-dependent effects arising from level crossings at high fields.

Title: Magnetic excitations in cerium compounds Author: Kristina Vlášková Department: Department of Condensed Matter Physic Supervisor: doc. Mgr Pavel Javorský, Dr., Department of Condensed Matter Physics Abstract: Thanks to presence of only one electron in 4f shell of cerium ion, Ce based compounds reveal wide range of exceptional magnetic properties like valence fluctuations, magnetic ordering or spin glass behavior. In present thesis we mainly focus on tetragonal CeCuxAl4-x system and its magnetic behavior. Former results of inelastic neutron experiments opened discussion about energy levels of cerium ions in CeCuAl3. Except two crystal field excitations also one additional energy level was present, phenomenon of vibron quasi-bound state was proposed to explain observed energy structure. Measurement and analysis of specific heat and neutron inelastic scattering on compounds with various Cu content should help to understand phenomenon of vibron state and also its development with Cu/Al concentration. Another two types of cerium compounds will be investigated in means of specific heat and resistivity measurement, polycrystalline sample of CePt4Al and single crystal of Ce3Ru4Al12. Preparation, characterization and measurement of low temperature properties are subjects of this work. Results will be discussed...

The document is the PhD thesis of Stanislav Nikitin. It summarizes results of the comprehensive investigation of the magnetic fluctuations in several quantum magnets by means of elastic and inelastic neutron scattering.

In dieser Arbeit wurde die durch Bestrahlung mit schnellen Neutronen bedingte Materialalterung von Reaktordruckbehälterstählen untersucht. Das Probenmaterial umfasste unbestrahlte, bestrahlte und ausgeheilte RDB-Stähle russischer und westlicher Reaktoren sowie Eisenbasis-Modelllegierungen. Mittels Neutronen-Kleinwinkelstreuung ließen sich bestrahlungsinduzierte Leerstellen/Fremdatom-Cluster unterschiedlicher Zusammensetzung mit mittlerem Radius um 1.0 nm nachweisen. Ihr Volumenanteil steigt mit der Strahlenbelastung monoton, aber im allgemeinen nicht linear an. Der Einfluss der Elemente Cu, Ni und P auf den Prozess der Clusterbildung konnte herausgearbeitet werden. Eine Wärmebehandlung oberhalb der Bestrahlungstemperatur reduziert den Anteil der Strahlendefekte bis hin zu deren vollständiger Auflösung. Die Änderungen der mechanischen Eigenschaften der Werkstoffe lassen sich eindeutig auf die beobachteten Gefügemodifikationen zurückführen. Die abgeleiteten Korrelationen können als Hilfsmittel zur Vorhersage des Materialverhaltens bei fortgeschrittener Betriebsdauer von Leistungsreaktoren mit herangezogen werden.

Cette thèse a pour motivation l'étude de l'ordre magnétique à q=0 dans les cuprates supraconducteurs à haute température critique. Cet ordre a déjà été reporté dans quatre familles de cuprates grâce à la diffusion de neutrons polarisés. Il est établi, sur une large gamme de dopage en trous, que cet ordre se développe à partir d'une température Tmag comparable à la température d'apparition de la phase de pseudo-gap T*. Ces observations sont compatibles avec un modèle de boucles de courant, qui induisent des moments magnétiques orbitaux. Les symétries mises en jeu sont la brisure par renversement du temps et l'invariance par translation. D'un point de vue expérimental, il s'agit non seulement de vérifier systématiquement l'existence de cet ordre magnétique, mais également de saisir sa nature. Nous nous sommes particulièrement intéressés à l'étude de deux systèmes bicouches, YBa2Cu3O6+x et Bi2Sr2CaCu2O8+x. Dans un premier temps, nous avons montré la persistance de l'ordre magnétique à q=0 pour une valeur de Tmag relativement élevée, dans des échantillons proches du dopage optimal. Toutefois, l'intensité magnétique associée est fortement réduite. Nous avons montré que ceci était en fait dû à la présence de domaines de taille finie, l'ordre est à courte portée. Aussi, nous avons déterminé le facteur de structure le long de l'axe c, il présente une décroissance rapide unique. Dans le cadre des boucles de courant, une possible modélisation consisterait en une résultante de deux anapoles pointant le long de b* au sein de la bicouche. D'autre part, nous avons confirmé l'existence d'un moment magnétique incliné sous Tmag. Nous avons cependant mis en évidence un caractère Ising le long de l'axe c à haute température. Enfin, nous avons prouvé que le signal associé à l'ordre magnétique à q=0 continue d'augmenter dans l'état supraconducteur. / This work is motivated by the study of the intra-unit-cell magnetic order in cuprate high temperature superconductors. It has been already reported in four cuprate families by using polarized neutron scattering, and it is well documented in a wide hole doping range. This order develops below Tmag, which matches the pseudo-gap temperature T*. This magnetic phase could be induced by the staggered orbital magnetism within the unit cell as proposed in the loop current model. This intra-unit-cell magnetic order indicates that time reversal symmetry is broken, but translation invariance is preserved. Experimentally, the goal is not only to systematically verify the existence of this intra-unit-cell magnetic order, but also to seize its nature. We particularly focused on two bilayer systems, YBa2Cu3O6+x and Bi2Sr2CaCu2O8+x. First, we revealed the persistence of the intra-unit-cell magnetic order at relatively high Tmag, near optimal doping. Compared to samples with a lower hole doping level, the magnetic intensity is strongly reduced. We demonstrated that this is due to finite magnetic correlation lengths. Moreover, we determined the associated magnetic structure factor along c, which displays a unique sharp decreasing. It is consistent with a model in which the sum of two anapoles within the bilayer is pointing along b*. Besides, below Tmag, we confirmed the existence of a tilt of the magnetic moment. However, we showed that at high temperature an Ising-like response along the c-axis is recovered. Finally, we proved that the magnetic signal associated to the intra-unit-cell magnetic order is still increasing in the superconducting state.

At the present time there is a recognized need for a better means of measuring soil moisture in situ. Soil moisture measurements are required in fundamental studies of soil moisture flow and soil-plant-water relationships as well as in practical studies in irrigation practices. Various phases of engineering also utilize soil moisture data, for example, soil moisture determinations are made during the consturction of earth dams, road cuts and fills, and under airfield runways. The desired method should be quick, reliable, and adaptable over the moisture range from oven dryness to saturation. Reserach in nuclear physics has revealed the neutron scattering phenomena which may be utilized as a means of determining soil moisture. It is known that hydrogen nuclei have a large influence on the scattering of neutrons and that most of the hydrogen nuclei in soils occur primarily in water. Using this information it should be possible to correlate the scattering of neutrons in the soil with moisture content. Measurement of soil water in this would be independent of its physical or chemical state in the soil. This would eliminate variables that are inherent in the present methods, such as temperature, soil texture, and salt concentrations. The obejct of this study is to adapt the neutron scattering phenomena to a method of soil moisture determination in situ. The problem is one of instrumentation and calibration. The emphasis will be toward developing an instrument to be used for soil moisture determination in experimental plots. Other diverse applications will also be considered. The prerequisites of the method require that it be more accurate and precise than the present methods without increasing the time and costs involved.

Inhalt der vorliegenden Dissertation ist die Untersuchung der elektronischen und magnetischen Eigenschaften der Schwerfermionensubstanz CeCu2. Dafür wurden makroskopische Messungen der Magnetisierung, der Suszeptibilität sowie der spezifischen Wärme aus der Literatur miteinander verglichen und eigenen Neutronenstreuexperimenten gegenübergestellt. Ein Teil der Arbeit widmet sich der Entwicklung des neuen Dreiachsenspektrometers PANDA am FRM2 München. Für dieses wurden umfangreiche Simulationen durchgeführt, um zukünftige Leistungsdaten zu spezifizieren. Mit dem Ray - Trace - Simulationspaket McStas wurde das Neutronenstreugerät modelliert und das Zusammenspiel der neutronenoptischen Bauelemente optimiert. Der zweite Teil der Arbeit beschäftigt sich mit Messungen und Rechnungen zum magnetischen Phasendiagramm von CeCu2. Dazu wurden eigene Messungen der Magnetisierung (VSM) und elastische Neutronenstreuexperimente (D23, ILL Grenoble) einer McPhase - Rechnung gegenübergestellt. Der nächste Abschnitt der Arbeit befasst sich mit elastischen und inelastischen Neutronenstreuexperimenten (IN12 & IN20, ILL Grenoble) an CeCu2 Einkristallen. Diese Messungen untersuchen die statischen (Struktur, Phasendiagramm) sowie dynamischen Eigenschaften (Anregungen) in dieser Substanz. Insbesondere beschäftigen sich diese Messungen mit den Dispersionsrelationen der Magnonen in hohen magnetischen Feldern bis zu mu0H = 12 Tesla. Für diese Experimente wurde eine neue Probenbox für den Einsatz in Hochfeldmagneten entwickelt, welche die Probe fixiert und in einer Schutzgasatmosphäre einschließt. In den Messungen wurde eine unerwartete, dispersionslose Anregung gefunden, welche mit dem derzeitigen Spinwellenmodell unverträglich ist. Bei Erhöhung des Magnetfeldes steigt die Anregungsenergie doppelt so schnell, wie von gewöhnlichen Magnonen erwartet wird. Zur Erklärung wird ein neutroneninduzierter pi/2 - Spinflop - Prozess vorgeschlagen. In einer anderen Messung wurde mit polarisierten Neutronen nach dem bisher indirekt nachgewiesenen, ersten angeregten Kristallfeldniveau bei 9 Millielektronenvolt gesucht. Bei wachsenden Temperaturen konnte kaum magnetische Streuintensität unterhalb 10 Millielektronenvolt gefunden werden. Jedoch wurde eine stark verbreiterte Intensität von 8 bis 15 Millielektronenvolt gemessen. Diese Energie korreliert mit dem Übergang zwischen den angeregten Kristallfeldniveaus. Als Ursache für die Verbreiterung wird eine Kristallfeld - Phonon - Wechselwirkung angegeben. Aus dem Vergleich der in verschiedenen Richtungen gemessenen magnetischen Streuintensitäten des 23 Millielectronvolt Kristallfeldüberganges können dessen Übergangsmatrixelemente abgeschätzt werden. Diese wurden den errechneten Werten der veröffentlichten Kristallfeldparametersätze gegenübergestellt. Es zeigte sich, dass die alten Parametersätze die neuen Messdaten nicht beschreiben können. Deshalb wurde ein neuer Satz aufgestellt, welcher erstmals sowohl die makroskopischen Messungen als auch die Neutronenstreuexperimente erklärt. / In this thesis, the electronic and magnetic properties of the heavy-fermion system CeCu2 are investigated. For that purpose, measurements of susceptibility, magnetisation and specific heat from literature are compared with each other and are compared with neutron-scattering experiments performed for the present work. One part of the thesis is addressed to the design of the new triple-axis spectrometer PANDA, which is situated at the research reactor FRM2 in Munich. Extensive simulations were performed with the ray - tracing simulation package McStas in order to model this neutron scattering instrument and to optimise its neutron optic elements. The second part of this work deals with measurements and calculations of the magnetic phase diagram of CeCu2. The experiments include the macroscopic magnetisation (VSM) and elastic neutron-scattering measurements (D23, ILL Grenoble). The McPhase calculations are in a good agreement with the experiments. The next part presents elastic and inelastic neutron-scattering experiments (IN12 & IN20, ILL Grenoble) at CeCu2 single crystals. These measurements investigate the static (phase diagram) as well as dynamic properties (excitations) of this compound. Especially, the experiments are concentrated on the investigation of the dispersion relation of magnons in magnetic fields up to mu0H = 12 tesla. For these measurements, a new sample holder suitable for use in high magnetic fields was designed, which fixes the sample in a hermetically sealed containment. In the experiments an unexpected dispersionless excitation was observed, which does not fit the standard magnon model. With increasing magnetic field the energy of this excitation increases with a slope of twice the value expected for regular magnons. A neutron - induced pi/2 spin - flop process is proposed to explain this excitation. In another measurement with polarised neutrons the first excited crystal - field level at 9 millielectronvolt, which has not been directly detected up to now, was investigated. With increasing temperature, only small magnetic scattering intensity occurs below 10 millielectronvolt. >From 8 to 15 millielectronvolt a broad signal was detected, which corresponds to the energy of the transition between the two excited levels. Due to a strong crystal field - phonon interaction, the width is unusually broadened. The transition matrix elements can be estimated from the comparison of the components of the magnetic scattering intensities of the 23 millielectronvolt crystal - field transition. These values were compared with the calculated values from published crystal-field parameter sets. The old sets cannot explain the new measurements. A new set was derived which accounts for the macroscopic measurements and for the neutron - scattering data, too.

Physically assembled gels are widely applicable in the food industry, biomedical devices, drug delivery, and soft robotics due to their tunable mechanical properties and thermoreversibility. The mechanical responses of these gels originate from their microstructure. Therefore, factors affecting the gel microstructure like polymer molecular weight, solvent quality, and polymer concentration play a significant role in determining their mechanical behavior. Gel microstructure also changes during the deformations resulting in a deviation from the structure-property relationship established for the low deformations. During large deformations, other factors like stress relaxation, poroelasticity, and polymer chain entanglement contribute significantly to the gel response. This complexity extends to the understanding of their failure behavior that occurs at large deformations. The low strain mechanical behavior of gels is governed by load-bearing chain density. They are often represented with non-linear elastic models, which ignore the contribution from viscous dissipation, polymer entanglements, surface tension, and bond dissociation. In addition, the available theoretical models cannot capture the experimental conditions like boundary confinement, therefore, numerical simulations are useful to test the developed model by comparing with experimental observations. With this objective, the present dissertation is focused on understanding the failure of physically assembled gels that consists of an ABA-type triblock copolymer dissolved in a B-block (midblock) selective solvent. Here, gelation occurs as a result of relative difference in the solubility of A-blocks (endblocks) and B-blocks (midblocks) with solvent. The thermo-mechanical characterization of these gels was performed using rheology, cavitation rheology, and DSC. A custom-built experimental set-up was developed to conduct large deformation experiments like tensile tests, creep failure experiments, and fracture experiments with a predefined crack. To characterize the gel microstructure, small-angle x-ray/neutron techniques were used. A change in the gel microstructure during deformation was also captured. The microstructure of gels was tuned by varying temperature, polymer volume fraction, midblock length, and by addition of midblock homopolymer. Finite element simulations have been used to understand the effect of boundary confinement, surface tension, and viscous dissipation. The present work provides a better understanding of failure behavior in physically assembled gels through the polymer dynamics at nano-scale level.

The neutron-neutron (n-n) scattering length is a fundamental parameter in nuclear physics; however, measurements are plagued with large uncertainties caused by neutron detector cross talk. Many experimentalists also rely upon computer code to calibrate their neutron detectors. Experiments give one of two different numbers but there is still no adequate explanation for this discrepancy. We have developed a new neutron detector expressly for the purpose of improving the n-n scattering length measurement. It offers two important advantages: 1) minimal cross talk and 2) high counting efficiency. We calibrated the detector from 1 MeV to 6 MeV at 1 MeV increments. We have shown that the computer code, MCNP, does not always give the correct detector efficiency, and that reliance upon this code for calibration could be a large factor for error in previous experiments. Preliminary tests show no cross talk between two like detectors and suggest that these detectors in a n-n scattering length measurement.