Chan Yuk-Lin = 並行機上量子自旋模型的對角化 / 陳玉蓮. / Thesis submitted in: September 2004. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2005. / Includes bibliographical references (leaves 121-123). / Text in English; abstracts in English and Chinese. / Chan Yuk-Lin = Bing xing ji shang liang zi zi xuan mo xing de dui jiao hua / Chen Yulian. / Abstract --- p.i / 摘要 --- p.ii / Acknowledgement --- p.iii / Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- Motivation --- p.1 / Chapter 1.2 --- Development of Theory of Magnetism --- p.2 / Chapter 1.3 --- Heisenberg Model --- p.5 / Chapter 1.4 --- Thesis Organization --- p.9 / Chapter 2 --- Introduction to Parallel Computing --- p.11 / Chapter 2.1 --- Architecture of Parallel Computer --- p.12 / Chapter 2.2 --- Symmetric Multiprocessors and Clusters --- p.16 / Chapter 2.2.1 --- Symmetric Multiprocessors --- p.16 / Chapter 2.2.2 --- Cluster --- p.18 / Chapter 2.2.3 --- Clusters versus SMP --- p.19 / Chapter 2.3 --- Hybrid Architectures (Cluster of SMPs) --- p.20 / Chapter 2.4 --- Hardware Platform for Parallel Computing --- p.21 / Chapter 2.4.1 --- SGI Origin 2000 (Origin) --- p.21 / Chapter 2.4.2 --- IBM RS/6000 SP (Orbit) --- p.22 / Chapter 3 --- Parallelization --- p.23 / Chapter 3.1 --- Models of Parallel Programming --- p.24 / Chapter 3.2 --- Parallel Programming Paradigm --- p.26 / Chapter 3.2.1 --- Programming for Distributed Memory Systems: MPI --- p.26 / Chapter 3.2.2 --- Programming for Shared Memory Systems: OpenMP --- p.31 / Chapter 3.2.3 --- Programming for Hybrid Systems: MPI + OpenMP --- p.39 / Chapter 4 --- Performance --- p.42 / Chapter 4.1 --- Writing a Parallel Program --- p.42 / Chapter 4.2 --- Performance Analysis --- p.43 / Chapter 4.3 --- Synchronization and Communication --- p.47 / Chapter 4.3.1 --- Communication modes --- p.47 / Chapter 5 --- Exact Diagonalization --- p.50 / Chapter 5.1 --- Symmetry Invariance --- p.52 / Chapter 5.2 --- Lanczos Method --- p.53 / Chapter 5.2.1 --- Basic Lanczos Algorithm --- p.54 / Chapter 5.2.2 --- Modified Lanczos Method --- p.56 / Chapter 5.3 --- Dynamic Memory Allocation --- p.58 / Chapter 6 --- Parallelization of Exact Diagonalization --- p.62 / Chapter 6.1 --- Parallelization of Lanczos Method --- p.62 / Chapter 6.2 --- Hamiltonian Matrix Decomposition --- p.66 / Chapter 6.2.1 --- Row-Wise Block Decomposition --- p.67 / Chapter 6.2.2 --- Column-Wise Block Decomposition --- p.69 / Chapter 7 --- Results and Discussion --- p.71 / Chapter 7.1 --- Lattice structure --- p.71 / Chapter 7.2 --- Definition of Timing --- p.72 / Chapter 7.3 --- Rowwise vs Columnwise --- p.73 / Chapter 7.4 --- SGI Origin 2000(0rigin) --- p.77 / Chapter 7.4.1 --- Timing Results --- p.77 / Chapter 7.4.2 --- Performance --- p.79 / Chapter 7.5 --- IBM RS/6000 SP(Orbit) --- p.82 / Chapter 7.5.1 --- MPI vs Hybrid --- p.82 / Chapter 7.5.2 --- Timing and Performance --- p.84 / Chapter 7.6 --- Timing on Origin vs Orbit --- p.89 / Chapter 8 --- Conclusion --- p.91 / Chapter A --- Basic MPI Concepts --- p.95 / Chapter A.1 --- Message Passing Interface --- p.95 / Chapter A.2 --- MPI Routine Format --- p.96 / Chapter A.3 --- Start writing a MPI program --- p.96 / Chapter A.3.1 --- The First MPI Program --- p.97 / Chapter A.3.2 --- Sample MPI Program #1 --- p.100 / Chapter A.3.3 --- Sample MPI Program #2 --- p.106 / Chapter B --- Compiling and Running Parallel Jobs in IBM SP --- p.111 / Chapter B.1 --- Compilation --- p.111 / Chapter B.1.1 --- Compiler Options --- p.112 / Chapter B.2 --- Running Jobs --- p.114 / Chapter B.2.1 --- Loadleveler --- p.114 / Chapter B.2.2 --- Serial Job Script --- p.114 / Chapter B.2.3 --- Parallel Job Script : MPI Program --- p.115 / Chapter B.2.4 --- Parallel Job Script: OpenMP Program --- p.117 / Chapter B.2.5 --- Parallel Job Script: Hybrid MPI/OpenMP Program . . --- p.118 / Chapter B.2.6 --- LoadLeveler Commands --- p.120 / Bibliography --- p.123

Xia, Daxue. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2011. / Includes bibliographical references. / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstract also in Chinese.

by Cheng Kai. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1997. / Includes bibliographical references. / by Cheng Kai. / Acknowledgments --- p.i / Abstract --- p.ii / Table of content --- p.iv / Chapter Chapter One --- Introduction / Chapter 1.1 --- Barkhausen emission --- p.1 / Chapter 1.2 --- Methods of measurements --- p.3 / Chapter 1.2.1 --- Magnetization of a sample --- p.4 / Chapter 1.2.2 --- Signal detection --- p.5 / Chapter 1.2.3 --- Signal processing --- p.5 / Chapter 1.3 --- Instrumentation --- p.6 / Chapter 1.3.1 --- Instron loading machine --- p.6 / Chapter 1.3.2 --- Optical microscopy --- p.7 / Chapter 1.3.3 --- Vicker's hardness tester --- p.7 / Chapter 1.3.4 --- Ceramic furnace --- p.8 / References --- p.9 / Chapter Chapter Two --- Domain Theory / Chapter 2.1 --- The postulate of domain --- p.16 / Chapter 2.2 --- Domain energy --- p.18 / Chapter 2.3 --- The magnetization process --- p.20 / Chapter 2.4 --- Effect of applied stress --- p.22 / Chapter 2.5 --- Hindrances to wall motion by inclusions --- p.23 / References --- p.24 / Chapter Chapter Three --- Steels / Chapter 3.1 --- The making of steel --- p.28 / Chapter 3.2 --- The iron-iron carbide phase diagram --- p.29 / Chapter 3.3 --- Heat treatment of plain-carbon steels --- p.29 / Chapter 3.3.1 --- Slow cooling of plain-carbon steels --- p.29 / Chapter 3.3.2 --- Rapid cooling of plain-carbon steels --- p.30 / Chapter 3.3.3 --- Annealing --- p.31 / References --- p.32 / Chapter Chapter Four --- Effects of carbon on Barkhausen emission in plain carbon steel / Chapter 4.1 --- introduction --- p.35 / Chapter 4.2 --- Experiments --- p.36 / Chapter 4.2.1 --- Samples --- p.36 / Chapter 4.3 --- Results and discussions --- p.37 / Chapter 4.4 --- Conclusions --- p.39 / References --- p.40 / Chapter Chapter Five --- Magnetization process in a steel plate/bar subjected to an increasing tensile load / Chapter 5.1 --- Introduction --- p.45 / Chapter 5.2 --- Experiments --- p.47 / Chapter 5.3 --- Results and discussions for the zinc-coated steel plate --- p.47 / Chapter 5.4 --- Results and discussions for mild steel --- p.50 / Chapter 5.5 --- A comparison between steel plate and steel bar --- p.52 / Chapter 5.6 --- Conclusions --- p.53 / References --- p.54 / Chapter Chapter Six --- Evaluation of residual stress in bent steel bars subjected to different heat treatment by Barkhausen emission / Chapter 6.1 --- Introduction --- p.60 / Chapter 6.2 --- Experiments --- p.60 / Chapter 6.3 --- Results and discussions --- p.61 / Chapter 6.4 --- Conclusions --- p.64 / References --- p.65 / Chapter Chapter Seven --- Effects of heat treatment on electrolytic zinc-coated steel plates by Barkhausen emission / Chapter 7.1 --- Introduction --- p.72 / Chapter 7.2 --- Experiments --- p.72 / Chapter 7.3 --- Results and discussions --- p.73 / Chapter 7.4 --- Conclusions --- p.75 / References --- p.76 / Chapter Chapter Eight --- Effects of demagnetizing and stray fields on Barkhausen emission / Chapter 8.1 --- Introduction --- p.80 / Chapter 8.2 --- Experiments --- p.80 / Chapter 8.3 --- Results and discussions --- p.81 / Chapter 8.4 --- Conclusions --- p.85 / References --- p.85 / Chapter Chapter Nine --- Conclusions and suggestions for further studies --- p.90

No description available.

This work focuses on the development of a highly accurate energy-based hysteresismodel for the modeling of magnetic hysteresis phenomena. The model relies on anexplicit representation of the magnetic pinning effect as a dry friction-like force actingon the magnetic polarization. Unlike Preisach and Jiles-Atherton models, this modelis vectorial from the beginning and derives from thermodynamic first principles.Three approaches are considered: the first one, called vector play model, relies on asimplification that allows an explicit, and thus fast, update rule, while the two others,called the variational and the differential approaches, avoid this simplification,but require a non-linear equation to be solved iteratively. The vector play model andthe variational approach were already used by other researchers, whereas the differentialapproach introduced in this thesis, is a new, more efficient, exact implementation,which combines the efficiency of the vector play model with the accuracy of the variationalapproach. The three hysteresis implementations lead to the same result forpurely unidirectional or rotational excitation cases, and give a rather good approximationin all situations in-between, at least in isotropic material conditions.These hysteresis modeling approaches are incorporated into a finite-element code asa local constitutive relation with memory effect. The inclusion is investigated in detailfor two complementary finite-element formulations, magnetic field h or flux densityb conforming, the latter requiring the inversion of the vector hysteresis model,naturally driven by h, for which the Newton-Raphson method is used. Then, at thefinite-element level, once again, the Newton-Raphson technique is adopted to solvethe nonlinear finite-element equations, leading to the emergence of discontinuous differentialreluctivity and permeability tensors, requiring a relaxation technique in theNewton-Raphson scheme. To the best of the author’s knowledge, the inclusion of anenergy-based hysteresis model has never been successfully achieved in a b-conformfinite-element formulation before. / Doctorat en Sciences de l'ingénieur et technologie / info:eu-repo/semantics/nonPublished

Neste trabalho, utilizamos o método de primeiros princípios RS-LMTOASA (Real Space - Linear Muffin-Tin Orbital - Atomic Sphere Approximation), baseado na Teoria do Funcional da Densidade (DFT Density Functional Theory) e implementado para o cálculo de estruturas magnéticas não colineares, para investigar as propriedades magnéticas de nanoestruturas adsorvidas em superfícies metálicas. Primeiramente, devido ao aparecimento de estruturas magnéticas complexas, foram estudadas nanoestruturas magnéticas depositadas em substratos ferromagnéticos. Foram consideradas nanoestruturas de Mn tais como nanofios adsorvidos, pirâmides e aglomerados adsorvidos e embebidos, com o tamanho destas nanoestruturas variando de dois até nove átomos depositados em Fe(001) e Fe(110). Nossos cálculos indicam uma interação de troca magnética de longo alcance entre os átomos de Mn-Mn e Mn-Fe. Além disto, a presença de uma forte dependência destas interações de troca magnética com o meio local, frustrações magnéticas e o acoplamento spin-órbita forneceram a possibilidade da presença de estruturas magnéticas complexas tais como, por exemplo, spin espiral e half-skyrmion. Por fim, com o objetivo de estudar nanoestruturas que podem apresentar altos valores de momento magnético, foram investigados nanofios de FexCo1-x adsorvidos em uma superfície de Pt(111) . Nossos resultados indicam que os momentos magnéticos de spin dos átomos de Fe e Co são independentes da concentração de Fe e apresentam valores superiores quando comparados aos das ligas FeCo bcc, enquanto que o momento magnético médio de spin do nanofio FexCo1-x varia linearmente com a concentração de Fe, comportamento este que é diferente da curva de Slater-Pauling observada na liga FeCo bcc. O momento magnético orbital médio do nanofio de FexCo1-x é monotonicamente decrescente com a concentração de Fe que se apresenta bastante diferente a monocamada FexCo1-x sobre Pt(111). / We use the first principles RS-LMTO-ASA (Real Space - Linear Muffin- Tin Orbital - Atomic Sphere Approximation) method, in the framework of the Density Functional Theory and implemented to calculate noncollinear magnetic structures, to investigate the magnetic properties of nanostructures adsorbed on metallic surfaces. First, due to presence of the complex magnetic properties, we investigated magnetic nanostructures deposited on a ferromagnetic substrate. We have considered a variety of nanostructures such as adsorbed wires, pyramids, at and intermixed clusters with sizes varying from two to nine atoms deposited on Fe(001) and Fe(110). Our calculations reveal the long-range nature of exchange interactions between Mn-Mn and Mn-Fe atoms. Moreover, the presence of the strong dependence of these interactions on the local environment, the magnetic frustration, and the effect of spin-orbit coupling lead to the possibility of realizing complex noncollinear magnetic structures such as helical spin spiral and half-skyrmion. Finally, we also investigated FexCo1-x nanowires deposited on Pt(111) surface aiming to investigate materials with large local magnetic moment. Our results reveal that the Fe and Co spin magnetic moment are independent of the Fe concentration with the enhancement of the spin magnetic moment when compared with the FeCo bcc alloys, while the average spin magnetic moment is a linear function of the Fe concentration. This is in contrast to the Slater-Pauling model observed in the FeCo bcc alloys. The average orbital magnetic moment shows a linearly decreasing behavior with the Fe concentration which is in contrast to the behavior of FexCo1-x monolayer on Pt(111) surface.

Composite magneto-dielectric materials have been investigated over the years because of their potential applications in RF and microwave devices as the dielectric constant and permeability can be individually changed in these materials. In the recent past, there is a renewed interest in systems classified as ferroelectromagnets or multiferroics, which possess simultaneous ferroelectric and magnetic ordering as well as interesting magnetoelastic phenomena. In all these ferrite-ferroelectric materials, the coupling between the permeability (μ) of the magnetically ordered phase and permittivity (e) of the ferroelectric phase make them attractive candidates for multifunctional applications. Ba0.5Sr0.5TiO3 (BSTO) is a ferroelectric with potential applications in tunable filters, antennas, and thin film capacitors. BaFe12O19 (BaF) is a hard ferromagnet with large in-plane anisotropy which makes it promising for use in microwave and RF devices that need permanent magnets for biasing requirements. We have used magnetron sputtering to deposit multilayer films of BSTO and BaF on Al2O3 and heated Si/SiO2. To our knowledge this is the first attempt at combining these technologically important materials in multilayer form. The as-deposited films were amorphous and post-annealing was optimized until distinct BSTO and BaF x-ray peaks could be identified. Surface and images were obtained by atomic force microscopy (AFM) and scanning electron microscopy (SEM). The multilayer structure and BSTO/BaF interfaces were identified using cross-sectional SEM. Magnetic properties of the multilayer films were measured using a Physical Properties Measurement System (PPMS) by Quantum Design at 10K and 300K over a range of magnetic field (0 < H < 7T). We have attempted to correlate some of the magnetic characteristics with the film microstructure. In addition, we have deposited layers of Fe3O4 nanoparticles onto both bare Si/SiO2 substrates and the surfaces of the multilayers using Langmuir-Blodgett technique. Preliminary images of monolayer Fe3O4 particles reveal some ordering present. We have also used the PPMS to look at the magnetic properties of the particles, both by themselves and deposited onto the multilayers to see what magnetic effects the particles have on ferrite-ferroelectric systems.

This thesis presents a study on core loss calculations in rotating electrical machines. The basic concepts concerning magnetic moments, ferromagnetism, magnetic domains and magnetic hysteresis are introduced. The three-term models for alternating and rotational core losses in electrical steel sheets are presented. Several core loss measurement techniques are reviewed and an experiment is carried out to measure the total core losses in an electrical sheet steel sample under alternating and rotational magnetic fields of various frequencies and amplitudes. The coefficients in the loss models for alternating and rotational core losses are obtained through curve fitting process. The theory of electromagnetic fields is presented through the Maxwell equations and field scalar equations. A detailed review on core loss models for rotating electrical machines is presented. A rotational core loss model is adopted to calculate the core losses in a PM motor. The total core loss in the PM motor is obtained by summing the element losses using a MATLAB program. An experiment is conducted to measure the total core loss in the PM motor. The calculated total core loss in the PM motor is compared with the experimental results. The calculated total core losses are about 19% lower than the tested results. Various possible causes for this discrepancy are discussed / Master of Engineering (Hons)

Spin-polarized first-principles electronic structure and total energy calculations have been performed to better understand the magnetic properties of Co doped ZnO (ZnO:Co) with vacancies and Ga co-dopants. The paramagnetic state of ZnO:Co, in which Co ions lose their magnetic moments, has been found to be unstable. The total energy results show that acceptor-like Zn vacancies and donor-like Ga co-dopants render the anti-ferromagnetic (AFM) and ferromagnetic (FM) states to be more favorable, respectively. With O vacancies, ZnO:Co has been found to be in the weak FM state. These magnetic properties can be understood by the calculated O- and Zn-vacancies and Ga-co-dopant induced changes of the electronic structure, which suggest that AFM and FM Co-Co couplings are mediated by O 2p-Co majority (¡ô)-spin 3d hybridized states in the valence band of ZnO and O-vacancy-derived p states or Ga sp states in the ZnO band gap, respectively. For ZnO:Co with Zn vacancies (Ga co-dopants) the AFM (FM) coupling outweighs the FM (AFM) coupling and results in the AFM (FM) state, while for ZnO:Co with O vacancies, both the FM and AFM couplings are enhanced by similar degrees and result in the weak FM state. This study reveals a competition between FM and AFM couplings in ZnO:Co with vacancies and Ga co-dopants, the detailed balancing between which determines the magnetic properties of these materials.

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