No description available.

Although it is known that gold (Au) is diamagnetic in bulk form, it has been reported that Au displays magnetic properties when reduced to the nano-scale. Researchers found magnetism in Au nanoparticles (NPs) in a size range from 2 to 10 nanometers. Moreover, the Au nanoparticles are usually coated by thiol-containing organic caps, which are believed to be responsible for the magnetism. However, others suggest that organic capping is not necessary to observe magnetism in Au NPs, and magnetism may be an intrinsic property for nano-structured gold. For this investigation, we used pulsed laser deposition to prepare nano-structured gold of different sizes and concentrations to investigate the magnetic properties. Our experiment results confirmed that for the samples in which Au is in the metallic state as nanoparticles with ~5 nm diameter, as well as inthe alloy form, bonded with indium, the samples show ferromagnetism when embedded in an Al2O3 matrix without any thiol-containing organic capping. Our results suggest that ferromagnetism is an intrinsic property of Au nano-structures, which means that it is not necessary to incorporate Au-S bonds with organic coatings in order to observe this phenomenon. We believe due to the significant broken symmetry at the surface of the nanoparticles, holes are generated in d bands of the surface Au atoms. These holes are most possibly responsible for ferromagnetism in Au nanoparticles. The realization of magnetism in Au coupled with the lack of clear understanding of its origin makes the investigation of magnetism of diamagnetic metals ripe for further inquiry. / Ph. D.

Ferroelectric and ferromagnetic alloy clusters are produced and studied in molecular beams. Nb clusters doped with 1-3 impurity atoms are ferroelectric with low transition temperatures. The alloy clusters with an even number of valence electrons have larger dipole moments than those with odd number of valence electrons. The ferroelectricity is suppressed by magnetic impurities or thermal excitations, and is enhanced by Au and Al doping. The observations strongly suggest that electron-pairing interactions exist in Nb clusters, which indicates Cooper pairing in clusters. The magnetic moments of Co clusters doped with small fraction of Mn,V and Al are studied and compared with those of the bulk alloys. CoMn alloy clusters have enhanced average magnetic moments with Mn doping, which is opposite to the behavior of bulk CoMn. CoV and CoAl alloy clusters behave similarly to their bulk counterparts. We explain the experimental results using the virtual-bound-state model. Finally, the magnetic properties of BiMn clusters are studied in molecular beams. The Mn local moments are found to couple ferromagnetically or ferrimagnetically depending on the composition of the clusters.

Thesis (PhD)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: We consider the ferromagnetic phase in pure neutron matter as well as charge neutral, betaequilibrated nuclear matter. We employ Quantum Hadrodynamics, a relativistic field theory description of nuclear matter with meson degrees of freedom, and include couplings between the baryon (proton and neutron) magnetic dipole moment as well as between their charge and the magnetic field in the Lagrangian density describing such a system. We vary the strength of the baryon magnetic dipole moment till a non-zero value of the magnetic field, for which the total energy density of the magnetised system is at a minimum, is found. The system is then assumed to be in the ferromagnetic state. The ferromagnetic equation of state is employed to study matter in the neutron star interior. We find that as the density increases the ferromagnetic field does not increase continuously, but exhibit sudden rapid increases. These sudden increases in the magnetic field correspond to shifts between different configurations of the charged particle’s Landau levels and can have significant observational consequences for neutron stars. We also found that although the ferromagnetic phase softens the neutron star equation of state it does not significantly alter the star’s massradius relationship. The properties of magnetised symmetric nuclear matter were also studied. We confirm that magnetised matter tends to be more proton-rich but become more weakly bound for stronger magnetic fields. We show that the behaviour of the compressibility of nuclear matter is influenced by the Landau quantisation and tends to have an oscillatory character as it increases with the magnetic field. The symmetry energy also exhibits similar behaviour. / AFRIKAANSE OPSOMMING: In hierdie studie het ons die ferromagnetiese fase in suiwer neutronmaterie, sowel as in ladingsneutrale, beta-ge¨ekwilibreerde neutronstermaterie, ondersoek. Vir die doeleindes het ons die Kwantum Hadrodinamika-model van kernmaterie gebruik. Dit is ’n relatiwistiese, veldteoretiese model wat mesone inspan om die interaksies tussen die protone en neutrone te bemiddel. Om die impak van die magneetveld te bestudeer, sluit ons ’n koppeling tussen die barioonlading en die magneetveld, asook barioondipoolmoment en die magneetveld, in by die Lagrange digtheid wat ons sisteem beskryf. Om die ferromagnetiese fase te ondersoek, varieer ons die sterkte van die barioondipoolmoment om ’n nie-nul waarde van die magneetveld wat energie digtheid sal minimeer te vind. Die ferromagnetiese toestandsvergelyking word toegepas op materie aan die binnekant van die neutronster en die impak hiervan op die waarneembare eienskappe van die ster word ondersoek. Ons vind dat die ferromagnetiese magneetveld nie kontinu toeneem soos die digtheid verhoog nie. Die skielike toenames in die magneetveld is die gevolg van die sisteem wat die konfigurasie van die gelaaide deeltjies se Landau-vlakke skielik verander en dit kan beduidende waarneembare gevolge vir die ster inhou. Ons vind ook dat die ferromagnetiese fase die toestandsvergelyking versag, maar dat die versagting die massa-radius verhouding van die ster nie grootliks beïnvloed nie. Die eienskappe van gemagnetiseerde kernmaterie word ook ondersoek. Ons bevestig dat gemagnetiseerde materie meer proton-ryk, maar minder sterk gebind word. Ons wys dat die saampersbaarheid van kernmaterie deur die teenwoordigheid van Landau-vlakke beïnvloed word en ossilerend saam met die magneetveld toeneem. Die simmetrie-energie manifesteer ook soortgelyke gedrag.

Thesis (MSc)--Stellenbosch University, 2011. / ENGLISH ABSTRACT: Two problems in the field of materials-based condensed matter physics, specifically in the field of superconductivity, are studied theoretically. In both problems, where each is of current exper- imental interest, an extension of Ginzburg-Landau theory is used to describe a physical system, with focus on the energy associated to the interface(s) occurring in the respective systems. The first physical system under consideration is that of a two-band superconductor. Using Ginzburg-Landau theory for two-band superconductors, the interface energy ¾s between normal and superconducting states coexisting at the thermodynamic critical magnetic field is determined. From the theoretical and numerical analysis of the interface energy, it is found that close to the transition temperature, where the Ginzburg-Landau theory is applicable, the two-band problem maps onto an effective single band problem. This finding puts into question the possibility of intermediate, so called type-1.5 superconductivity, in the regime where the Ginzburg-Landau theory applies. The second physical system is that of a system with competing superconductivity and anti- ferromagnetism. From Ginzburg-Landau theory for such competing systems in a thermodynamic critical magnetic field, it is shown that two possible interfaces can occur: an interface between a pure anti-ferromagnetic state and a pure superconducting state; and an interface between a state with coexisting superconductivity and anti-ferromagnetism and a pure anti-ferromagnetic state. The energy associated to both these interfaces is analysed theoretically and numerically from which the boundary between type-I and type-II superconductivity is obtained for certain specific cases. / AFRIKAANSE OPSOMMING: Twee probleme in die veld van materiaal-gebaseerde gekondenseerde materie fisika, spesifiek in die veld van supergeleiding, word teoreties bestudeer. In beide probleme, albei tans van eksper- imentele belang, word ’n fisiese sisteem beskryf deur ’n uitbreiding van enkel-band Ginzburg- Landau teorie, met fokus op die energie geassosieer met die koppelvlak(ke) wat in die onderskeie sisteme aangetref word. Die eerste fisiese sisteem wat beskou word is die van ’n twee-band supergeleier. Deur van Ginzburg-Landau teorie vir twee-band supergeleiers gebruik te maak, word die koppelvlak energie ¾s tussen die gelyktydig bestaande normaal- en supergeleidende toestand in die termodinamiese kritieke magneetveld bepaal. Deur beide teoretiese en numeriese analieses word bepaal dat na aan die oorgangstemperatuur, waar Ginzburg-Landau teorie geldig is, die twee-band probleem op ’n effektiewe een-band probleem afbeeld. Hierdie bevinding bevraagteken dus die moontlikheid van onkonvensionele, of sogenaamde tipe-1.5 supergeleiding, vir gevalle waar Ginzburg-Landau teorie geldig is. Die tweede fisiese siteem wat beskou word is ’n sisteem met kompeterende supergeleiding en anti-ferromagnetisme. Met behulp van Ginzburg-Landau teorie vir sulke sisteme in ’n termod- inamiese kritiese magneetveld word gewys dat daar twee moontlike koppelvlakke kan ontstaan: ’n koppelvlak tussen ’n uitsluitlik anti-ferromagnetiese toestand en ’n uitsluitlik supergeleidende toestand; sowel as ’n koppelvlak tussen ’n uitsluitlik anti-ferromagnetiese toestand en ’n toes- tand van beide supergeleiding en anti-ferromagnetisme. Die energie geassosieer met beide hierdie koppelvlakke word teoreties en numeries geanaliseer wat lei tot ’n beskrywing van die grenslyn tussen tipe-I en tipe-II supergeleiding in sekere spesifieke gevalle.

No description available.

by Cho, King-sum. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1999. / Includes bibliographical references (leaves 108-110). / Text in English; abstracts in English and Chinese. / by Cho, King-sum. / Abstract --- p.i / 摘要 --- p.iii / Acknowledgment --- p.iv / Contents --- p.v / List of figures --- p.x / Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- Review of non-destructive techniques --- p.2 / Chapter 1.1.1 --- Liquid penetration technique --- p.2 / Chapter 1.1.2 --- Eddy current inspection --- p.2 / Chapter 1.1.3 --- Ultrasonic testing --- p.3 / Chapter 1.1.4 --- Radiography --- p.3 / Chapter 1.1.5 --- Magnetic testing methods --- p.4 / Chapter 1.2 --- Barkhausen emission --- p.4 / Chapter 1.3 --- The development of Barkhausen Emission --- p.5 / Chapter 1.4 --- The advantages of using Barkhausen emission --- p.6 / Figures for chapter1 --- p.8 / Chapter 2 --- Iron-carbon System --- p.9 / Chapter 2.1 --- Iron-iron carbide phase diagram --- p.9 / Chapter 2.2 --- Invariant reactions in the Fe-Fe3C phase diagram --- p.11 / Chapter 2.3 --- Classification of carbon steels --- p.12 / Chapter 2.4 --- Effect of heat treatment on plain-carbon steels --- p.13 / Chapter 2.4.1 --- Annealing and normalizing --- p.14 / Chapter 2.4.2 --- Slow cooling --- p.15 / Chapter 2.5 --- Process of recovery and recrystallization --- p.15 / Chapter 2.5.1 --- Recovery --- p.16 / Chapter 2.5.2 --- Recrystallization --- p.16 / Chapter 2.5.3 --- Grain growth --- p.17 / Figures for chapter2 --- p.18 / Chapter 3 --- Background Theory --- p.23 / Chapter 3.1 --- Ferromagnetism --- p.23 / Chapter 3.1.1 --- Localized moment theory --- p.24 / Chapter 3.1.2 --- Band theory --- p.25 / Chapter 3.1.3 --- Hysteresis loop --- p.25 / Chapter 3.2 --- Domain theory --- p.26 / Chapter 3.2.1 --- Magnetic domain --- p.26 / Chapter 3.2.2 --- Structure of domain wall --- p.27 / Chapter 3.2.3 --- Domain wall motion --- p.29 / Chapter 3.2.4 --- Magnetostatic energy --- p.30 / Chapter 3.2.5 --- Magnetization process --- p.32 / Chapter 3.3 --- Effect of applied stress --- p.33 / Chapter 3.3.1 --- Stress --- p.33 / Chapter 3.3.2 --- Magnetostriction --- p.34 / Chapter 3.3.3 --- Effect of stress on magnetization --- p.34 / Figures for chapter 3 --- p.37 / Chapter 4 --- Instrumentation --- p.39 / Chapter 4.1 --- Introduction --- p.39 / Chapter 4.2 --- Experimental setup for Barkhausen emission --- p.39 / Chapter 4.2.1 --- Magnetizing unit --- p.40 / Chapter 4.2.2 --- Signal detection unit --- p.41 / Chapter 4.2.3 --- Signal processing unit --- p.42 / Chapter 4.3 --- The typical BE profile --- p.42 / Chapter 4.4 --- Specimen treatment --- p.43 / Chapter 4.4.1 --- Optical microscope --- p.43 / Chapter 4.4.2 --- Vickers´ة hardness tester --- p.44 / Chapter 4.4.3 --- Thermal resistance furnace --- p.45 / Chapter 4.4.4 --- Instron loading machine --- p.45 / Figures for chapter4 --- p.47 / Chapter 5 --- Experiments and Results: Evaluation of Carbon Content in Steel --- p.52 / Chapter 5.1 --- Introduction --- p.52 / Chapter 5.2 --- Experiments and results --- p.52 / Chapter 5.3 --- Discussions --- p.53 / Chapter 5.3.1 --- The magnetization process --- p.53 / Chapter 5.3.2 --- The BE profiles 、 --- p.54 / Chapter 5.3.3 --- Hardness --- p.57 / Chapter 5.4 --- Conclusions --- p.57 / Figures for chapter5 --- p.58 / Chapter 6 --- Experiments and Results: The Effects of annealing on Barkhausen Emission in Mild Steel Bars --- p.64 / Chapter 6.1 --- Introduction --- p.64 / Chapter 6.2 --- Experiments --- p.64 / Chapter 6.3 --- Results and discussions --- p.64 / Chapter 6.3.1 --- The mechanical properties --- p.65 / Chapter 6.3.2 --- Grain size --- p.65 / Chapter 6.3.3 --- BE profiles --- p.66 / Chapter 6.4 --- Conclusions --- p.67 / Figures for chapter6 --- p.68 / Chapter 7 --- Experiments and Results: The Effects of Dynamic and Residual Stresses on Barkhausen Emission in Annealed Mild Steel Bars --- p.76 / Chapter 7.1 --- Introduction --- p.76 / Chapter 7.2 --- Experiments --- p.76 / Chapter 7.2.1 --- Measurement of dynamic loading (with samples of Set A) --- p.77 / Chapter 7.2.2 --- Measurement of residual stress (with samples of Set B) --- p.77 / Chapter 7.2.3 --- Measurement of continuous tensile stress (with samples of Set C) --- p.77 / Chapter 7.3 --- Results and discussions --- p.78 / Chapter 7.3.1 --- Peak ratio of the BE profile --- p.78 / Chapter 7.3.2 --- The initial peak value under the effects of increasing tensile stress --- p.81 / Chapter 7.4 --- Conclusions --- p.82 / Figures for chapter7 --- p.83 / Chapter 8 --- Experiments and Results: The Recovery of Strained Steel Bars by Annealing --- p.94 / Chapter 8.1 --- Introduction --- p.94 / Chapter 8.2 --- Experiments --- p.94 / Chapter 8.2.1 --- Measurement of annealed sample (Set D) --- p.95 / Chapter 8.2.2 --- Results of the Set E samples --- p.95 / Chapter 8.3 --- Results and discussions --- p.95 / Chapter 8.3.1 --- Hardness --- p.96 / Chapter 8.3.2 --- Peak ratio of the BE profile --- p.97 / Chapter 8.3.3 --- BE profile for the samples of Set E --- p.98 / Chapter 8.4 --- Conclusions --- p.99 / Figures for chapter8 --- p.100 / Chapter 9 --- Conclusions and Suggestions for Further Studies --- p.104 / Bibliography --- p.108

Thesis. 1976. Ph.D.--Massachusetts Institute of Technology. Dept. of Mathematics. / Microfiche copy available in Archives and Science. / Bibliography: leaves 171-175. / Ph.D.

Thesis. 1978. Sc.D.--Massachusetts Institute of Technology. Dept. of Materials Science and Engineering. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND SCIENCE. / Vita. / Includes bibliographical references. / Sc.D.

Determinamos a tensão superficial de um defeito do tipo parede de domínio, utilizando a aproximação semiclássica no contexto da teoria de campos à temperatura finita para o modelo ? (?2)2 com interação invariante por simetria O(N), obtendo em seguida a temperatura crítica Tc de transição de fase e cálculo dos expoentes críticos ? e ?, aplicando então os resultados obtidos para a descrição de um modelo fenomenológico descrevendo o ferromagnetismo. / We determine the surface tension of a domain wall defect by using the semi classical approach in the context of field theory at finite temperature for the ? (?2)2 model with O(N) invariant interaction obtaining the critical temperature Tc of phase transition and the calculation of the critical exponents ? and ? applying then the obtained results to a description of a phenomenological model describing ferromagnetism.