Dissertations / Theses: 'Crystal field'

1

吳潔貞 and Kit-ching Betty Ng. "Correlation effects in crystal field splitting." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1986. http://hub.hku.hk/bib/B31230714.

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Ng, Kit-ching Betty. "Correlation effects in crystal field splitting /." [Hong Kong : University of Hong Kong], 1986. http://sunzi.lib.hku.hk/hkuto/record.jsp?B12323342.

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3

Lee, Michael James. "Crystal field matrix reduction and polarisation interference calculations." Thesis, University of Canterbury. Physics and Astronomy, 1999. http://hdl.handle.net/10092/8169.

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The theory of one-electron crystal field parametrisation for optical spectra of rare-earth doped crystalline lattices dates back over forty years. The effect of the crystal host material is to split the free-ion degeneracy of the rare-earth multiplets. Some of these multiplets have structure which defies explanation in terms of crystal field theory and new developments have emerged within the last five years to address the problem. One of these methods takes the set of crystal field operators and appends two-electron correlation operators. Another adjusts the crystal field operators to include excited state configuration effects. A direct comparison of fitted parameters is meaningless, the corresponding operators being defined on different spaces. Here the techniques of matrix reduction, as developed in effective operator theory, are applied to larger configuration Hamiltonians to model their effects in correlation space. Correlation operators are then fitted to the reduced configuration matrices to establish a connection between the two approaches. Transition intensity parametrisation has a similar lengthy history and formulation. Geometric effects first brought to light fifteen years ago suggest the possibility of polarisation dependent interference between the transition moments of different Cartesian axes. This would manifest itself in the directional dependence of fluorescence intensity for low symmetry crystal hosted rare-earth centres. To date there have been no experimental tests of these predictions and here a case is made for certain transitions of hydrogenated praseodymium doped fluorite. There are certain practical difficulties which must be overcome and these are also addressed.

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盧德成 and Tak-shing Lo. "Two-body operators and correlation crystal field models." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1993. http://hub.hku.hk/bib/B31210922.

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Praetorius, Simon. "Efficient Solvers for the Phase-Field Crystal Equation." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-195532.

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A preconditioner to improve the convergence properties of Krylov subspace solvers is derived and analyzed in this work. This method is adapted to linear systems arising from a finite-element discretization of a phase-field crystal equation.

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Lo, Tak-shing. "Two-body operators and correlation crystal field models /." [Hong Kong : University of Hong Kong], 1993. http://sunzi.lib.hku.hk/hkuto/record.jsp?B13437549.

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7

Yeung, Yau-yuen. "Alternative parametrization schemes in lanthanide crystal field theory /." [Hong Kong : University of Hong Kong], 1986. http://sunzi.lib.hku.hk/hkuto/record.jsp?B12324863.

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8

Matias, Jean de Souza. "Crystal electric field efect in non-conventional structures." reponame:Repositório Institucional da UFABC, 2017.

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Orientadora: Profa. Dra. Raquel de Almeida Ribeiro
Dissertação (mestrado) - Universidade Federal do ABC, Programa de Pós-Graduação em Física, 2017.
Em Física da Matéria Condesada, as terras raras apresentam um papel importante em várias aplicações tecnológicas. Suas camadas 4f incompletas possuem enumeras con- gurações diferentes possibilitando o desenvolvimento e melhoramento de propriedades interessantes. Materiais supercondutores, lasers de estado sólido, radares e ímãs permanentes são bons exemplos de dispositivos que utilizam materiais desenvolvidos com terras raras. Quando terras raras são colocadas em um material matriz, as interações entre esses elementos ou entre a matriz e as terras raras fazem com que os seus estados eletrônicos mudem. Estruturas cristalinas apresentam campo elétrico cristalino, cuja teoria desenvolvida no século passado foi amplamente estudada e aplicada à vários grupos de simetria em cristais bulk. Até o momento, porém, muito pouco tem sido estudado a respeito de como o campo elétrico de estruturas não convencionais, como quasicristias e nanocristais, afeta os autoestados das terras raras. Portanto, o objetivo desse projeto foi analizar o efeito de campo elétrico cristalino em dois tipos de materiais: Nanopartículas cúbicas com tamanho de 8 nm e quasicristais icosaédricos, bem como seu aproximante. Para isso, nanopartículas de NaY1..xRExF4 (RE = Yb, Er, Dy, Gd) foram sintetizadas pelo método de termo-decomposição e quasicristais de Au-Al-Yb foram crescidos em forno a arco. Para a determinação parâmetros de campo elétrico cristalino Bm n , foram feitos ajustes das curvas de magnetização dependentes da temperatura e do campo magnético aplicado. Além disso, para os quasicristais foi encontrado um grupo de simetria pontual equivalente e seus parâmetros de campo elétrico cristalino foram comparados com os de seus aproximantes. Com isso, observou-se que somente parâmetros de segunda ordem apresentaram uma diferença signicativa quando comparados entre essas duas estruturas; B0 2 é 20 vezes maior para a estrutura quasicristalina. Para as nanopartículas cúbicas, uma Hamiltoniana total foi proposta e com isso foi feita um simulação para determinar a separação total dos níveis de energia da camada incompleta 4f das terras raras. Além disso, o espectro de Up conversion foi medido e comparado com a simulação teórica. A largura de linha do espectro teórico, 470 20 K, para a transição 4S3=2 ! 4I15=2 , é comparável aos resultados empíricos, 650 50 K. O estado fundamental dos sistemas foi conrmado pela técnica de Ressonância Eletrônica de Spin. Dessa forma, foi estabelecida uma realação de como a separação total dos multipletos-J afeta a emissão de Up conversion destas NP's.
In Condensed Matter Physics, rare earth elements play an important role in several technological applications. Their complex 4f unfullled shell presents numerous dierent congurations, making possible to engineer or tune interesting properties. Superconductors, solid state lasers, radars and permanent magnets are some examples of cutting edge devices using materials developed with rare earth elements. When a rare earth ion is placed in a host material, their interactions with each other or with the host lattice are responsible for the arrangement of their electronic state. Crystalline structures exhibit the crystal eld eect, whose theory developed in the last century has been largely applied and studied to various point group symmetries in bulk crystals. However, there is a lack of researches in how the electric eld of non-conventional host lattices, such as quasicrystals and nanocrystals, aect rare earth's eigenstates. Therefore, the aim of this project was to analyze the crystal eld eect in two dierent kind of materials: Cubic nanoparticles with 8 nm in size and icosahedral bulk quasicristals, as well as their crystal approximant. For that, NaY1..xRExF4 (RE = Yb, Er, Dy, Gd) nanoparticles were synthesized by temperature decomposition and Au-Al- Yb quasicrystals were grown by arc-melting. Fittings of the thermal and eld dependent magnetization were used to determine the crystal electric eld parameters Bmn . In the quasicrystal material case, an equivalent point group symmetry was obtained and their crystal electric eld parameters were compared with the ones of their approximant. Only parameters of second order substantially diered between both structures, B02 was found out to be around 20 times larger than that for the approximant. Moreover, in the cubic nanostructures case, the overall splitting of the 4f unfullled shell of the RE elements was determined diagonalizing a proposed total Hamiltonian, whose terms include the Crystal Electric Field parameters. In addition, the up-conversion light emission signal was acquired and compared with a theoretical simulation. The theoretical up-conversion light emission line-width found out as 471 20 K, for the transition 4S3=2 ! 4I15=2 , is comparable to empirical results, 650 50 K. The ground state of the systems was conrmed by Electron Spin Resonance analysis. In this case, a relation with how the overall energy splitting of the J-multiplets aect the UC conversion light emission of theses NP's was established.

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9

Zeis, Roswitha. "Single crystal field-effect transistors based on layered semiconductors." [S.l.] : [s.n.], 2005. http://deposit.ddb.de/cgi-bin/dokserv?idn=975775405.

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10

Hashim, K. I. "A study of crystal growth by field emission microscopy." Thesis, Bangor University, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.380230.

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11

Han, Zong-Pei. "Exchange and crystal-field effects in rare-earth compounds." Thesis, University of Manchester, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.488004.

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Aleksandrova, Svetlana. "Buoyant convection in cavities in a strong magnetic field." Thesis, Coventry University, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.364613.

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13

楊友源 and Yau-yuen Yeung. "Alternative parametrization schemes in lanthanide crystal fieldtheory." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1986. http://hub.hku.hk/bib/B31231044.

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14

Swift, Michael Joseph Robert. "Aspects of single crystal and thin film high field electroluminescence." Thesis, University of Hull, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.304437.

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15

Babateen, Muhammed Omar. "An investigation of magnetic properties of some rare earth Heusler alloys." Thesis, Loughborough University, 1994. https://dspace.lboro.ac.uk/2134/27053.

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The magnetic properties of some rare earth based Heusler alloys have been investigated. Rare earth Heusler alloys of the form Pd2Reln exhibit magnetic behaviour characterised by magnetic moments localised on the rare earth atoms. X-ray and neutron diffraction investigation show that all alloys crystallise in the cubic L21 Heusler structure with space group Fm3m.

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16

Kelly, Martin. "The role of lattice vibrations in the zero field splitting of Gd'3'+ in an ethylsulphate host lattice." Thesis, University of Warwick, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.357631.

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17

Culverhouse, Stephen Richard. "Neutron spectroscopy of rare earth intermetallics and high temperature superconductors." Thesis, University of Southampton, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.255651.

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18

Kabro, Pierre. "Optical spectroscopy, crystal field analysis, upconversion and energy transfer studies of Er³§+ doped yttrium vanadate single crystals." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/nq25909.pdf.

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19

Miyashita, Satoru, Yukio Saito, and Makio Uwaha. "Fractal Aggregation Growth and the Surrounding Diffusion Field." Elsevier, 2005. http://hdl.handle.net/2237/7318.

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20

Barnes, Nicholas Roland. "Electric field effects in side chain liquid crystal ploymers and elastomers." Thesis, University of Reading, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.316362.

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21

Gimenez, Pinto Vianney Karina. "MODELING LIQUID CRYSTAL POLYMERIC DEVICES." Kent State University / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=kent1398039813.

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22

Cheng, Hui-Chuan. "Vertical Field Switching Blue Phase Liquid Crystals for Field Sequential Color Displays." Doctoral diss., University of Central Florida, 2012. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/5161.

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Low power consumption is a critical requirement for all liquid crystal display (LCD) devices. A field sequential color (FSC) LCD was proposed by using red (R), green (G) and blue (B) LEDs and removing the lossy component of color filters which only transmits ~30% of the incoming white light. Without color filters, FSC LCDs exhibit a ~3X higher optical efficiency and 3X higher resolution density as compared to the conventional color filters-based LCDs. However, color breakup (CBU) is a most disturbing defect that degrades the image quality in FSC displays. CBU can be observed in stationary or moving images. It manifests in FSC LCDs when there is a relative speed between the images and observers* eyes, and the observer will see the color splitting patterns or rainbow effect at the boundary between two different colors. In Chapter 2, we introduce a five-primary display by adding additional yellow(Y) and cyan(C) colors. From the analysis and simulations, five primaries can provide wide color gamut and meanwhile the white brightness is increased, as compared to the three-primary. Based on the five-primary theorem, we propose a method to reduce CBU of FSC LCDs by using RGBYC LEDs instead of RGB LEDs in the second section. Without increasing the sub-frame rate as three-primary LCDs, we can reduce the CBU by utilizing proper color sequence and weighting ratios. In addition, the color gamut achieves 140% NTSC and the white brightness increases by more than 13%, as compared to the three-primary FSC LCDs. Another strategy to suppress CBU is using higher field frequency, such as 540 Hz or even up to 1000 Hz. However, this approach needs liquid crystals with a very fast response time (<1 ms). Recently, the polymer-stabilized blue-phase liquid crystal (PS-BPLC) draws great attentions because of improved temperature range which enables the applications for photonic devices and displays. PS-BPLC is a good candidate for FSC LCDs because of its submillisecond gray-to-gray response time, no need for alignment layer, and isotropic dark state. So far, almost all the BPLC devices utilize planar or protruded in-plane switching (IPS) electrode configuration. The structure of planar IPS is relatively simple, but the operating voltage is too high for thin-film transistor (TFT) addressing. Moreover, high voltage causes deformation of polymer network and induces a noticeable hysteresis. Protruded IPS is helpful for lowering the operating voltage, but the manufacturing process becomes more sophisticated. In Chapter 3, we propose a vertical field switching (VFS) mode for blue phase LCDs. The simple structure of VFS cell generates uniform vertical fields on the BPLC materials. From our experimental results, the operation voltage can be reduced to ~10Vrms while eliminating the hysteresis. We also defined a critical field below which hysteresis does not occur. Above critical field, lattice distortion and other irreversible phase transition processes would occur. As a result, the associated response time would be slower. Therefore, VFS mode also shows faster response time than IPS mode. The operating voltage can be further reduced by choosing an optimized cell gap and a larger oblique incident angle in VFS blue phase LCDs. In Chapter 4, we propose several compensation mechanisms to improve the viewing angle of VFS blue-phase LCDs. The compensation principles are analyzed and simulation results evaluated. Because VFS blue-phase LCD processes several advantages over IPS blue-phase LCD and conventional LCDs, it could become a strong contender for next-generation display technology.
Ph.D.
Doctorate
Optics and Photonics
Optics and Photonics
Optics

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23

Berry, Andrew John. "Optical spectroscopy of terbium elpasolites." Thesis, University of Oxford, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.320164.

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Ahmad, Noor Atinah. "Phase-field model of rapid solidification of a binary alloy." Thesis, University of Southampton, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.242477.

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Christodoulos, F. "Crystal fields for Er'3'+ in gold and zero-field splittings for Gd'3'+ in lanthanum ethylsulphate." Thesis, University of Warwick, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.383344.

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Golin, Sarah M. "Studies of Crystal Structure Using Multiphoton Transitions in GaAs." Thèse, Université d'Ottawa / University of Ottawa, 2012. http://hdl.handle.net/10393/23369.

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We demonstrate experimentally that the multiphoton ionization rate in gallium arsenide depends on the alignment of the laser polarization with respect to the crystal axis. We show real-time modulation of 1900nm laser ionization rate, through viewing transmission, which mimics the symmetry of the semiconductor crystal. We propose that the modulation in the ionization rate arises because the varying reduced effective carrier mass, as predicted by Keldysh theory. We show direct comparison of the experimental transmission modulation depth with that predicted by Keldysh theory. This opens up a novel method for real-time non-invasive crystallography of crystalline materials.

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Eastop, A. D. "Ultrasonic investigations of magnetic field induced textural changes in superfluid '3He-A." Thesis, University of Manchester, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.376592.

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Wang, Billie. "Integrated Computational Microstructure Engineering for Single-Crystal Nickel-base Superalloys." The Ohio State University, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=osu1228147112.

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Wang, Wei. "Computational Spectroscopic Analysis of Orbital Hybridization and Crystal Field Interaction for Trivalent Uranium Ion in Crystals of Hexagonal Symmetry." University of Cincinnati / OhioLINK, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1258479110.

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30

Mellenthin, Jesper. "Modélisation de la croissance de matériaux polycristallins par la méthode du champ de phase." Phd thesis, Ecole Polytechnique X, 2007. http://pastel.archives-ouvertes.fr/pastel-00003136.

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La méthode d'élimination sur le terrain est devenu ces dernières années la méthode de choix pour modéliser la formation des motifs de la microstructure lors de la solidification. Pour monocristaux, accord quantitatif avec des expériences et des solutions analytiques ont été obtenues. La modélisation des polycristaux, qui sont composées de nombreux grains d'une même phase thermodynamique, mais différentes orientations du réseau cristallin, est beaucoup moins avancée. Deux types de modèles ont été proposés: les modèles multi-phase-champ d'utiliser un champ de phase pour chaque grain, et les modèles d'orientation-champ d'utiliser un petit nombre de domaines, mais ont des termes non analytiques dans leur énergie libre fonctionnel. Ce travail examine les divers aspects de la phase de modélisation du champ de polycristaux et est divisé en trois parties. Dans la première, une nouvelle possibilité de décrire l'orientation locale est explorée, en utilisant un paramètre d'ordre tensoriel qui représente automatiquement la symétrie locale du système. Cette approche est testée en phase de développement d'un modèle de champ pour la transition de phase nématique-isotrope dans les cristaux liquides. Le modèle est appliqué pour simuler la solidification directionnelle''''d'un cristal liquide. L'effet du couplage entre l'orientation et la forme nématique interface est étudiée. Les résultats de simulation pour la stabilité d'une interface plane en bon accord avec une analyse de stabilité généralisée, qui tient compte d'une condition nouvelle d'ancrage à l'interface: l'orientation à l'interface nématique est le résultat de l'interaction entre la déformation en vrac et l'anisotropie d'interface. La forme et la stabilité des cellules bien développé est également influencée par cet effet. Numériquement, l'utilisation d'un paramètre d'ordre tensoriel simplifie le traitement des symétries dans le système de manière significative, tandis que les équations de mouvements deviennent beaucoup plus compliquées. Dans la deuxième partie, les joints de grains sont étudiés sur une échelle plus petite longueur, en utilisant un modèle de cristal phase de terrain, où les propriétés élastiques et des dislocations apparaissent naturellement. Avec ce modèle, l'ordre local dans les interfaces est examiné et la stabilité des films liquides entre deux grains solides est étudiée ci-dessous le point de fusion. Cette situation peut être décrite par un potentiel d'interaction entre les deux interfaces solide-liquide, qui est extraite numériquement. Les résultats sont comparés avec un modèle phénoménologique qui se trouve à tenir pour les joints de grains à forte inclinaison, où les dislocations se chevauchent. Pour les joints de grains à faible angle, autour de préfusion dislocation ainsi qu'une brisure de symétrie (paires de dislocations forme) est observée. En conséquence, le potentiel d'interaction devient nonmonotonous, et se compose d'une attraction à longue portée et une répulsion à courte portée. Dans la troisième partie, un nouveau modèle de phase sur le terrain est développé en utilisant une variable d'angle pour décrire l'orientation cristalline. Contrairement aux modèles déjà existants, l'énergie libre est construit sans un terme proportionnel au module du gradient du champ de l'orientation. Au lieu de cela, le gradient de la norme au carré est utilisé, mais il est couplé à la phase du champ avec une fonction de couplage singulier. Diverses simulations référence sont réalisés afin de tester le modèle. Il se trouve qu'elle présente plusieurs artefacts tels que la rotation et le mouvement du grain parasite interface, mais ces effets sont extrêmement petites, telles que le modèle donne des résultats satisfaisants que si la surfusion est très faible. Enfin, les problèmes observés sont analysés et des moyens d'obtenir une meilleure description de la dynamique de l'angle de champ sont discutées.

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31

Vo, Thanh Phong. "Optical near-field characterization of Slow-Bloch Mode based photonic crystal devices." Phd thesis, Ecole Centrale de Lyon, 2011. http://tel.archives-ouvertes.fr/tel-00758323.

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2D-Photonic crystal (PC) structures have enabled the fabrication of a wide variety of nanophotonic components. In perfect PCs, the exploitation of the enhanced local density of states at critical points of the band diagram has attracted considerable attention. Near these points, where the group velocity vanished, low curvature flat bands give rise to delocalized and stationary optical slow Bloch modes (or slow light modes). Properties of slow light make them good candidates to enhance Purcell or various non-linear effects or to design low-threshold lasers. Among these modes, slow Bloch modes (SBMs) emitting in the vertical direction, i.e. located at the Γ- point of the Brillouin zone are particularly interesting for integrating 2D PC architectures with free space optics. In particular, some SBMs proved to be suitable for achieving strong vertical emission with peculiar polarization properties. Other promising applications concern disorder: by introducing a controlled randomness into the PC structure, it is possible to induce a transition from slow Bloch mode (in ordered PC) to Anderson's localization (in disordered PC) as a function of disorder degree. In this PhD dissertation, Slow Bloch modes have been studied and characterized by the means of Near-field Scanning Optical microscopy (NSOM). We particularly focused on Slow Bloch laser mode at Γ- point of a honeycomb 2DPC. This NSOM technique enables to visualize the evanescent component of the mode with a spatial resolution below the diffraction limit. In this work, we showed that the far-field and the near-field image of the mode at the 2D-PC surface are different and that near-field results yield a better insight in the real mode structure inside the PC slab in agreement with theoretical prediction. The importance of the probe selection (bare silica, metallized tip and bow-tie aperture nanoantenna) for studying III-V photonic crystal structures was also demonstrated. Besides intensity measurement of the electromagnetic field, the polarization of the electric field has been measured at the nanoscale for the first time by using a bow-tie nano-antenna probe. These results enable the unambiguous identification of the modes with the 3D-FDTD simulations.In this work is also reported the first observation of two-dimensional localization of light in two types of 2D random photonic crystal lasers, where Slow Bloch Mode (SBM) is scattered by artificial structural randomness in triangular PCs. The structural randomness is introduced whether by nanometer displacements in the positions of lattice elements (air holes), whether by variation of the hole diameters. The direct near-field imaging of the lasing mode by use of NSOM for the first time, allowed us to observe the transition of the extended planar SBM to be Anderson localized.

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Pinto, Jason Christopher. "Field-effect transistors from discotic liquid crystal semiconductors and polymer brush dielectrics." Thesis, University of Cambridge, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.612816.

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33

Hempel, Ulrike. "Lateral field excited quartz crystal resonators from theoretical approach to sensor application." Aachen Shaker, 2008. http://d-nb.info/990485196/04.

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34

Gao, Wenzhu. "Hierarchically Controlled Helical Polyacetylenes Synthesized in Advanced Asymmetric Liquid Crystal Reaction Field." 京都大学 (Kyoto University), 2009. http://hdl.handle.net/2433/124552.

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35

Tanner, Peter. "Spectroscopy of rare earth compounds." Thesis, University of Surrey, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.320993.

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36

Saensunon, Banchachit Physical Environmental &amp Mathematical Sciences Australian Defence Force Academy UNSW. "A study of the crystal field interaction for two rare earth intermetallic series." Awarded by:University of New South Wales - Australian Defence Force Academy. Physical, Environmental & Mathematical Sciences, 2009. http://handle.unsw.edu.au/1959.4/44105.

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A combination of 169Tm-Mo??ssbauer spectroscopy and inelastic neutron scattering (INS) has been used to investigate the crystal field (CF) interaction at the rare earth site for the tetragonal series RT2Si2 (where R = rare earth) and the orthorhombic series RNiAl4. Single phase specimens were prepared in an argon arc furnace and characterised using x-ray powder diffraction, specific heat and magnetic measurements. For the RT2Si2 series previous investigations were extended to include T = Mn and Cr whose sub-lattices are antiferromagnetic well above room temperature. However, the rare earth sub-lattices were confirmed to order close to liquid helium temperature. With the assistance of the lattice electric field gradient (EFG) for isostructural GdCr2Si2 (determined elsewhere using 155Gd-Mo??ssbauer spectroscopy) and the within-rank CF parameter ratios for HoCr2Si2 (determined elsewhere using INS), the experimental 169Tm quadrupole interaction data were analysed to arrive at CF parameters for the Tm3+ site in TmCr2Si2. The final CF parameters match well with the trend observed for other members of the series RT2Si2 (T = Fe, Co, Ni, Cu). CF schemes were also determined for Tm3+ in TmMn2Si2 and Er3+ in both ErCr2Si2 and ErMn2Si2. For the RNiAl4 series, TmNiAl4 was determined to be antiferromagnetic below TN = 4.7 K with the 169Tm-Mo??ssbauer spectra retaining a magnetic appearance up to 80 K due to the effect of slow spin-lattice relaxation. The relaxation data are consistent with a well-isolated ground state doublet (or pseudo-doublet) whose eigenfunctions have high components of mJ = ??6 states and with the relaxation proceeding via an excited state at 350 K. Because of the relaxation effect, the 169Tm-Mo??ssbauer data could not be interpreted in terms of CF parameters in the usual way. Instead, the INS spectra recorded for ErNiAl4 were analysed using a novel semi-empirical approach that coupled rank 2 CF parameters converted from the EFG tensor for isostructural GdCr2Si2 (determined elsewhere using 155Gd-Mo??ssbauer spectroscopy) with simple point-charge model calculations of the rank 4 and 6 within-rank CF parameter ratios. The first full set of CF parameters for this series was then determined for the Er3+ site in ErNiAl4.

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37

Korber, Rainer Johannes. "Low field DC SQUID nuclear magnetic resonance on single crystal UPtÃƒ?Ã‚Â³." Thesis, Royal Holloway, University of London, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.429492.

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38

Shibahara, Aya. "Low field dc SQUID NMR on room temperature samples and single crystal UPt3." Thesis, Royal Holloway, University of London, 2010. http://repository.royalholloway.ac.uk/items/60ae93f1-93a4-8001-24e7-5b75961fa6c3/11/.

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This thesis is an account of two distinct experiments with a common theme, which is the technique of dc SQUID NMR. Firstly the application of the technique for broadband spectroscopy on room temperature samples is described. The motivation behind this work was to try to obtain SQUID NMR signals from liquid samples such as water and the amino acid glycine in order to demonstrate a few of the potential applications of this technique in the low field regime. These include increased frequency resolution, the possible detection of relatively small amounts of oil contamination in water samples and low field J-spectroscopy as a chemical bond detector. Measurements were performed on samples of water and oil-water mixtures on a dipper probe that provided a simple, compact shielding arrangement that uses a two-stage SQUID sensor as the front end amplier. With the introduction of a low frequency amplier and modications to the setup the SNR was increased by a factor of 4. However, the SNR became limited by flux trapping in the superconducting materials surrounding the sample, leading to the investigation of alternative materials and methods to maintain low field homogeneity at higher polarising fields. The second part describes SQUID NMR measurements on a single crystal of the heavy fermion superconductor UPt3. Despite serious experimental and theoretical efforts, the symmetry and nature of the unconventional superconducting order parameter has not been resolved due to contradicting experiments, in particular that of the Knight shift into the superconducting state. Measurements were performed on a dilution refrigerator. A two-stage SQUID was mounted onto the fridge, a 3He marker was implemented for accurate local field determination and an overlapping superconducting shield was made to decrease the spectrometer deadtime. NMR measurements are presented for the static field parallel to the c-axis of the crystal from 600 mK down to 400 mK in a static field of 71.5 mT. The Knight shift is measured to decrease from -1.7 % in the normal state to -1.35 % at 400 mK. Together with the results from a Knight shift experiment at 30 degrees to the c-axis, it is argued that these results may provide evidence for the E2u model. Strategies for future measurements are addressed.

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Ryabtseva, Elena. "Analysis of a Magnetic-Field-Induced Periodic Instability in a Liquid Crystal Film." Kent State University / OhioLINK, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=kent1248126599.

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Johnson, Louise. "Electric field-induced transitions and interlayer interactions in intermediate smectic liquid crystal phases." Thesis, University of Manchester, 2014. https://www.research.manchester.ac.uk/portal/en/theses/electric-fieldinduced-transitions-and-interlayer-interactions-in-intermediate-smectic-liquid-crystal-phases(64a81e3e-d148-48b4-8e94-4abd44117655).html.

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This thesis presents an investigation into the effects of an external electric field on the three- and four-layer intermediate smectic phases. Experiments were performed using electro-optic techniques; thresholds between phases were measured by studying changes in the effective optical tilt. A quantitative measure of the interlayer interaction constant was obtained from the analysis of field-temperature phase diagrams in several materials, which exhibited the intermediate smectic phases in various degrees of stability. Excellent agreement with theory was observed in the field-temperature phase diagrams of these materials. The effect of adding a chiral dopant to liquid crystal compounds was studied and it was found that the interlayer interaction strength is significantly lower in mixtures with a chiral dopant. These measurements provided quantitative information on the importance of the interlayer interaction, which is only indicated qualitatively by other measurements. Deviations from theory were reported in mixtures with increasing concentrations of chiral dopant, in particular in the nature of the transition from the four-layer phase to the three-layer phase. Interesting behaviour in the thresholds between phases was observed in several liquid crystal mixtures in temperature regions close to the triple point on the field- temperature phase diagrams. Measurements of the thresholds between the intermediate phases revealed an unexpected threshold. Further evidence of this unexpected threshold was presented in the form of results of the temperature dependence of effective optical tilt of the various phases; electric field dependence of the response time; and the transient current that flows upon the reversal of an electric field. These measurements revealed that the unexpected threshold was to a field-induced ferrielectric phase with a larger effective tilt than the three-layer phases. Finally, preliminary results are presented from an investigation into defects that form in the thin films in the antiferroelectric smectic phases, with the aim of studying how the elastic constants may affect the stability of the intermediate phases.

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Mori, Taizo. "Helical Polyacetylene Synthesized in Chiral Liquid Crystal Field-Morphology Control and Polymerizartion Mechanism." 京都大学 (Kyoto University), 2009. http://hdl.handle.net/2433/124549.

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42

Dharmatilleke, Medha. "INTERFEROMETRIC MEASUREMENT OF THE TEMPERATURE FIELD IN THE VICINITY OF AN EVOLVING DENDRITE CRYSTAL." University of Cincinnati / OhioLINK, 2001. http://rave.ohiolink.edu/etdc/view?acc_num=ucin997974236.

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Takeo, Hiroshi. "Copper electrodeposition in a magnetic field." PDXScholar, 1985. https://pdxscholar.library.pdx.edu/open_access_etds/3550.

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The effect of a magnetic field on copper electrodeposition was investigated. Copper was electrodeposited onto square copper cathodes 1 sq cm in area from an aqueous solution (0.5 M CuSO4, 0.5 M H2SO. A glass cell was placed between the pole pieces of an electromagnet, and the magnetic fields applied were in the range from 0 to 12.5 kG. The current density was in the range from 80 mA/sq cm to 880 mA/sq cm. In each of the experiments, cell current, cell voltage, and cell temperature were monitored with a microcomputer. The weight change, deposit surface and cross section morphology, and the hardness were also found. Anodes used in the experiments were studied to see the effect of various conditions on the surface finish. Copper was also electrodeposited onto copper grids in order to study how the uniformity of the deposit is affected by an applied magnetic field.

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Crispin, Katherine L. "Cation Diffusion in Periclase." Case Western Reserve University School of Graduate Studies / OhioLINK, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=case1309455282.

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45

Houshiar, Mahboubeh. "Kondo behaviour in Ce intermetallic compounds." Thesis, University of Southampton, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.242422.

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Wüest, Robert Andre. "Nanometer-scale technology and near-field characterization of InP-based planar photonic-crystal devices /." Zürich : ETH, 2007. http://e-collection.ethbib.ethz.ch/show?type=diss&nr=17146.

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47

Hempel, Ulrike [Verfasser]. "Lateral field excited quartz crystal resonators : From theoretical approach to sensor application / Ulrike Hempel." Aachen : Shaker, 2008. http://d-nb.info/1161303316/34.

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Alaimo, Francesco [Verfasser], Axel [Gutachter] Voigt, and Igor [Gutachter] Aronson. "Phase Field Crystal Modeling of Active Matter / Francesco Alaimo ; Gutachter: Axel Voigt, Igor Aronson." Dresden : Technische Universität Dresden, 2019. http://d-nb.info/1226900887/34.

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Alaimo, Francesco. "Phase Field Crystal Modeling of Active Matter." 2018. https://tud.qucosa.de/id/qucosa%3A32687.

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Active matter describes systems that convert energy from their environment into directed motion. Therefore, these systems are in intrinsic nonequilibrium, unlike their passive counterparts. From a theoretical point of view, such active systems have been modeled by agent-based models, as well as hydrodynamic approaches, which allowed for the investigation of a wide range of observed collective phenomena characterizing active matter. In this thesis we develop a microscopic field-theoretical approach to describe generic properties of active systems. This description combines the phase field crystal model with a polar order parameter and a self-propulsion term. First, we validate this approach by reproducing results obtained with corresponding agent-based models, such as binary collisions, collective migration and vortex formation. We also perform a direct comparison between our model and a microscopic phase field description of active matter. Next, we use this continuum approach to simulate some larger active systems and to analyze the coarsening process in active crystals, as well as the mechanisms leading to mobile clusters. We show the generality of our approach by extending it to binary mixtures of interacting active and passive particles. Also in this case, we first validate the model by reproducing known results, such as enhanced crystallization via active doping and the suppression of collective migration in an active bath in the presence of fixed obstacles. Interestingly, for the regime of mobile passive particles in an active bath a laning state is found, which is characterized by an alignment of the active particles that is globally nematic, but polar within each lane. This state represents a theoretical prediction feasible to be validated experimentally. Finally, we explore the field of topological active matter. We develop an agent-based model to describe self-propelled particles on curved surfaces and study the complex spatiotemporal patterns that emerge.
Aktive Materie beschreibt Systeme, die Energie aus ihrer Umgebung in gerichtete bewegung umwandeln. Im Gegensatz zur passiven Materie befinden sich diese Systeme nie im physikalischen Gleichgewicht und offenbaren dadurch interessante physikalische Phänomene. Vom theoretischen Standpunkt her wurde aktive Materie bereits simuliert, typischerweise durch agenten-basierte Modelle oder hydrodynamische Ansätze, die es ermöglichen eine Vielzahl der auftretenden kollektiven Bewegungsprinzipien zu untersuchen. In dieser Doktorarbeit entwickeln wir einen mikroskopischen Kontinuumsansatz um die generischen Eigenschaften von aktiven Systemen zu untersuchen. Unsere Beschreibung kombiniert das Phasenfeld-Kristall Modell mit einem polaren Ordnungsparameter und einem Antriebsterm. Zuerst validieren wir den Ansatz durch Reproduktion bekannter Ergebnisse agenten-basierter Modelle, wie binäre Kollisionen, kollektive Bewegung und Wirbelformationen. Des Weiteren führen wir einen direkten Vergleich zwischen unserem Modell und einer mikroskopischen Phasenfeldbeschreibung aktiver Materie durch. Danach nutzen wir den kontinuierlichen Ansatz um große aktive Systeme zu simulieren und analysieren den Vergröberungsprozess in aktiven Kristallen und Mechanismen der mobilen Aggregatbildung. Wir illustrieren die Allgemeingültigkeit unseres Simulationsansatzes durch die Erweiterung auf binäre Systeme, in denen sowohl aktive als auch passive Partikel enthalten sind. Auch in diesem Fall validieren wir das Modell durch Vergleiche mit bekannten Resultaten, wie zum Beispiel die verstärkte Kristallisation durch aktives Doping oder die Unterdrückung kollektiver Bewegung durch die Einführung von Hindernissen in einem aktiven Bad. Interessanterweise finden wir bei der Präsenz mobiler passiver Partikel in einem aktiven Bad einen Fahrspur-Zustand, in welchem die aktiven Partikel nematische Fahrspuren bilden und sich nur jeweils innerhalb einer Fahrspur nematisch polar anordnen. Dieser bisher unbekannte Zustand stellt eine theoretische Vorhersage dar, die experimentell geprüft werden kann. Schließlich begeben wir uns auf das Gebiet der topologischen aktiven Materie. Wir entwickeln ein agenten-basiertes Modell um selbst-angetriebene Partikel auf gekrümmten Oberflächen zu beschreiben und untersuchen die dabei auftretenden zeitlich und räumlich komplexen Muster.%, die dabei auftreten.

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He, Meng Shu, and 何孟書. "Field emission and field ion microscope investigation of thermofield induced crystal growth." Thesis, 1994. http://ndltd.ncl.edu.tw/handle/15408297187762903993.

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Dissertations / Theses on the topic 'Crystal field'

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