Este trabalho consistiu na implementação de um método de homogeneização de campo, denominado shimming passivo. Esse método é caracterizado pela inserção de pequenas peças ferromagnéticas no interior do magneto; a interação destas peças com o campo magnético principal produz campos locais capazes de corrigir inomogeneidades indesejadas, quando várias peças são estrategicamente combinadas. Embora esse método já tenha sido bem discutido, implementado e publicado por D.I.Hoult na década de 80, ele ainda não havia sido desenvolvido para um magneto resistivo com núcleo de ferro e peças polares, como é o caso do Artro-ToRM. Nosso objetivo era, através do Artro-ToRM, encontrar uma metodologia de modelagem e correção de campo que fosse útil para magnetos com a mesma geometria. Foram utilizados métodos computacionais de ajuste numérico que, a partir de mapas originais de campo, foram capazes de encontrar configurações de peças magnéticas que pudessem reduzir as inomogeneidades presentes. Um dos maiores desafios do trabalho, foi encontrarmos elementos passivos com comportamento previsível quando submetidos ao campo magnético principal, já que os programas de otimização presupunham que trabalhávamos com dipolos magnéticos, para efeitos de simplificação. Finalmente, considerando uma região cilíndrica com raio de 5 cm e comprimento de 10 cm, mostramos uma melhora de 390 ppm para 250 ppm na homogeneidade, após a correção passiva. / This work presents the implementation of a method for field correction, called passive shimming. The method is characterized by the insertion of small iron pieces in magnet bore; the interaction of these pieces with the main magnetic field produces local fields capable of correcting undesired inhomogenity, when some parts are strategically combined. Although this method has been already proposed by D.I.Hoult in the eighties, it still has not been developed for resistive magnets with polar pieces, such as the Artro-ToRM. Our objective were to find a method for field modeling and correction that could be useful for magnets with similar geometry. Computational methods of numerical adjustment were used from the original field maps, it was possible to find the optimal the configurations of magnetic parts for reducing the field inhomogenity. One of the biggest challenges of the work, was to find passive elements with previsible behavior when submitted to magnetic field main, since the optimization programs preassumed that we worked with magnetic dipoles, for the purpose of simplification. Finally, considering a cilindrical region, we show an improvement of 390 ppm to 250 ppm in the homogenity, after the passive correction.

Para discutir os efeitos magneto-óticos nos calcogenetos de Eu desenvolvemos uma expressão geral para a polarizabilidade de um sistema onde as transições eletrônicas importantes sao de orbitais localizados (orbitais 4f) para estados itinerantes (estados de Wannier 5dt2g). Tratamos em detalhe os elementos de matriz do operador dipolo elétri co levando em conta que o orbital 4f é um estado de muitas partículas. Incluimos explicitamente (numa aproximação simples) nos estados intermediários o potencial coulombiano criado pela lacuna no estado localizado 4f. Apresentamos um cálculo numérico da constante de Verdet e do deslocamento de fase Voigt (fases paramagnética e ferromagnética), dicro! smo circular e linear (fase ferromagnética)para o EuSe. Nosso resultado para a constante de Verdet concorda razoavelmente bem com os resultados experimentais e permite-nos estimar o valor da integral radial (4f|r|5d)~4x10-9cm. / To discuss the magneto-optical effects in the Eu chalcogenides we derive a general expression for the polarizability of a system in which the important electronic transitions are from localized to itinerant orbitals. This expression is applied to a model system in which the electronic transitions take place from a 4f orbital to a 5dt2g Hannier orbital centered at the same cell. We treat in detail the matrix elements of the electric dipole operator taking into account the many-body character of the 4f shell. The Coulow) potential of the intermediate state localized hole is included explici tely vli thin a simple approximation. We present a numerical calculation of the frequency dependent, Verdet constant and Voigt phase shift (paramagnetic and ferromagnetic phases), circular and linear dichroism (ferromagnetic phase) for the EuSe. The fittin~ of the Verdet constant to the experimental results is fairly good and allmv us to estimate the value of the integral (4flrl5d)~4x10-9cm.

A central concern within the field of molecular magnetism has been the elucidation of magneto-structural correlations. This thesis describes a variety of systems and endeavours to study the relationship between structure and magnetic properties in these systems. The first body of work (chapters 2 and 3) studies CrIII dimers, with the metal centres displaying a dialkoxo bridging moiety and latterly an additional carboxylate bridge to direct the synthesis of ferromagnetic analogues. The second section of work (chapters 4‐6) moves forward to the study of larger, heterometallic 3d‐3d compounds, through the synthesis of a large family of Anderson type MIII 2MII 5 wheels and a subsequent family of (VIVO)2MII 5 wheels. Chapter 2 describes a series of di‐alkoxo bridged Cr(III) dimers, synthesised using the pyridine alcohol ligands 2‐pyridinemethanol (hmpH) and 2‐pyridineethanol (hepH) as well as 2‐picolinic acid (picH). The structures fall into four general categories and are of formula: [Cr2(OMe)2(pic)4], [Cr2(hmp)2(pic)2X2] (where X = Cl, Br), [Cr2(L)2Cl4(A)2] (where L = hmp, A = H2O; L = hmp, A = pyridine; L = hmp, A = 4‐picoline; L = hep, A = H2O), and [Cr(hmp)(hmpH)Cl2. Magnetic studies show relatively weak antiferromagnetic exchange interactions between the Cr(III) centres and DFT calculations are used to develop magneto‐structural correlations, showing that the magnitude and sign of the J value is strongly dependent upon the orientation of the dihedral angle formed between the bridging Cr2O2 plane and the O-R vector of the bridging group, and the Cr-O-Cr-O dihedral angle. Chapter 3 builds on the work from the previous chapter with discussion of a large family of chromium(III) dimers, synthesised using a combination of carboxylate and diethanolamine type ligands. The compounds have the general formula [Cr2(R1‐deaH)2(O2CR2)Cl2]Cl where R1 = Me and R2 = H, Me, CMe3, Ph, 3,5‐(Cl)2Ph, (Me)5Ph, R1 = Et and R2 = H, Ph. The compound [Cr2(Me‐deaH)2Cl4] was also synthesised in order to study the effect of removing/adding the carboxylate bridge to the observed magnetic behaviour. Magnetic studies reveal ferromagnetic exchange interactions between the Cr(III) centres in the carboxylate bridged family with coupling constants in the range +0.37 < J < +8.02 cm‐1. Removal of the carboxylate to produce the dialkoxide‐bridged compound results in antiferromagnetic exchange between the Cr(III) ions. DFT calculations to further develop the magneto-structural correlations reveal the ferromagnetic exchange is the result of an orbital counter-complementarity effect occurring upon introduction of the bridging carboxylate. Chapter 4 reports a family of heterometallic Anderson‐type 'wheels' of general formula [MIII 2MII 5(hmp)12](ClO4)4 (where MIII = Cr or Al and MII = Ni or Zn giving [Cr2Ni5], [Cr2Zn5], [Al2Ni5] and [Al2Zn5]; hmpH = 2‐pyridinemethanol) synthesised solvothermally. The metallic skeleton describes a centred hexagon with the MIII sites disordered around the outer wheel. The structural disorder is characterised via single crystal X‐ray crystallography, 1‐3D 1H and 13C solution‐state NMR spectroscopy of the diamagnetic analogue, and solid‐state 27Al MAS NMR spectroscopy of the Al containing analogues. Alongside ESI mass spectrometry, these techniques show that structure is retained in solution, and that the disorder is present in both the solution and solid‐state. Solid‐state dc susceptibility and magnetisation measurements on [Cr2Zn5] and [Al2Ni5] reveal the Cr‐Cr and Ni‐Ni exchange interactions to be JCr‐Cr = ‐1 cm‐1 and JNi‐Ni,r = ‐5 cm‐1, JNi‐Ni,c = 10 cm‐1. Fixing these values allows us to extract JCr‐Ni,r = ‐1.2 cm‐1, JCr‐Ni,c = 2.6 cm‐1, the exchange between adjacent Ni and Cr ions on the ring is antiferromagnetic and between Cr ions on the ring and the central Ni ion is ferromagnetic. Chapter 5 focusses on planar molecules, espanding the family of heterometallic Anderson‐type 'wheels' discussed in chapter 4 to include MIII = Cr, Al and MII = Co, Fe, Mn, Cu, affording five new species of formulae [Cr2Co5(hmp)12](ClO4)4, [Cr2Fe5(hmp)12](ClO4)4, [Cr2Mn5(hmp)12](ClO4)4, [Cr2Cu5(hmp)12](ClO4)2(NO3)2 and [Al2Co5(hmp)12](ClO4)4. As per previous family members, the two MIII sites are disordered around the outer wheel, with the exception of [Cr2Cu5] where the the CuII sites are localised. A structurally related, but enlarged planar disc possessing a [MIII 6MII] hexagon capped on each edge by a CuII ion is also reported, which is formed only when MIII = Al and MII = Cu. In [AlIII 6CuII 7(OH)12(hmp)12](ClO4)6(NO3)2 the Anderson moiety contains a central, (symmetry‐imposed) octahedral CuII ion surrounded by a wheel of AlIII ions. Solid‐state dc susceptibility and magnetisation measurements reveal the presence of competing exchange interactions in the Anderson wheels family, and weak antiferromagnetic exchange between the CuII ions in [Al6Cu7]. Chapter 6 describes two heterometallic wheels of formula [(VIVO)2MII 5(hmp)10Cl2](ClO4)2∙2MeOH (where MII = Ni or Co) displaying the same Anderson‐type structure as seen in chapters 4 and 5, however the use of the vanadyl moiety has the effect of removing the disorder, with the two vanadyl ions sitting on opposing sides of the ring. The magnetic properties of both show competing antiferroand ferromagnetic interactions.

The continued progress of modern information technology relies on understanding the influence of magnetic anisotropy on magnetic thin films. In this work, two sources of magnetic anisotropy are examined in two different soft ferromagnets: a uniaxial anisotropy induced during the fabrication of Ni80Fe20 and exchange anisotropy, or exchange bias, which occurs at the interface of Ni77Fe14Cu5Mo4/Fe50Mn50 bilayer. A home-built Magneto-optical Kerr effect magnetometer is used to measure the magnetic response of the soft ferromagnetic films and details of its construction are also discussed. A simple model of uniaxial anisotropy is described, then applied, to the uniaxial NiFe film and deviations from the model are critically analyzed. The exchange bias and coercive fields of NiFeCuMo/FeMn are reported for the first time and studied as a function of buffer layer material. The influence of the different buffer layer materials on the magnetization response of the bilayer is explained from a structural standpoint.

<p>The heating of the solar corona has been investigated during four of decades and several mechanisms able to produce heating have been proposed. It has until now not been possible to produce quantitative estimates that would establish any of these heating mechanism as the most important in the solar corona. In order to investigate which heating mechanism is the most important, a more detailed approach is needed.</p><p>In this thesis, the heating problem is approached ”ab initio”, using well observed facts and including realistic physics in a 3D magneto-hydrodynamic simulation of a small part of the solar atmosphere. The ”engine” of the heating mechanism is the solar photospheric velocity field, that braids the magnetic field into a configuration where energy has to be dissipated. The initial magnetic field is taken from an observation of a typical magnetic active region scaled down to fit inside the computational domain. The driving velocity field is generated by an algorithm that reproduces the statistical and geometrical fingerprints of solar granulation. Using a standard model atmosphere as the thermal initial condition, the simulation goes through a short startup phase, where the initial thermal stratification is quickly forgotten, after which the simulation stabilizes in statistical equilibrium. In this state, the magnetic field is able to dissipate the same amount of energy as is estimated to be lost through radiation, which is the main energy loss mechanism in the solar corona.</p><p>The simulation produces heating that is intermittent on the smallest resolved scales and hot loops similar to those observed through narrow band filters in the ultra violet. Other observed characteristics of the heating are reproduced, as well as a coronal temperature of roughly one million K. Because of the ab initio approach, the amount of heating produced in these simulations represents a lower limit to coronal heating and the conclusion is that such heating of the corona is unavoidable.</p>

The heating of the solar corona has been investigated during four of decades and several mechanisms able to produce heating have been proposed. It has until now not been possible to produce quantitative estimates that would establish any of these heating mechanism as the most important in the solar corona. In order to investigate which heating mechanism is the most important, a more detailed approach is needed. In this thesis, the heating problem is approached ”ab initio”, using well observed facts and including realistic physics in a 3D magneto-hydrodynamic simulation of a small part of the solar atmosphere. The ”engine” of the heating mechanism is the solar photospheric velocity field, that braids the magnetic field into a configuration where energy has to be dissipated. The initial magnetic field is taken from an observation of a typical magnetic active region scaled down to fit inside the computational domain. The driving velocity field is generated by an algorithm that reproduces the statistical and geometrical fingerprints of solar granulation. Using a standard model atmosphere as the thermal initial condition, the simulation goes through a short startup phase, where the initial thermal stratification is quickly forgotten, after which the simulation stabilizes in statistical equilibrium. In this state, the magnetic field is able to dissipate the same amount of energy as is estimated to be lost through radiation, which is the main energy loss mechanism in the solar corona. The simulation produces heating that is intermittent on the smallest resolved scales and hot loops similar to those observed through narrow band filters in the ultra violet. Other observed characteristics of the heating are reproduced, as well as a coronal temperature of roughly one million K. Because of the ab initio approach, the amount of heating produced in these simulations represents a lower limit to coronal heating and the conclusion is that such heating of the corona is unavoidable.

Magneto-rheological damper is a nonlinear system. In this case study, system has been identified using Neural Network tool. Optimization between number of neurons in the hidden layer and number of epochs has been achieved and discussed by using multilayer perceptron Neural Network.

This thesis provides a summary of the laser system constructed in the Quantum Degenerate Gases Laboratory for laser cooling and trapping of 85/87Rband 6Li as well as of experiments that have been pursued in our lab to date. The first chapter provides an overview of the experimental focus of the QDG lab. The second and third chapters provide the fundamental theory behind laser cooling and trapping. The fourth chapter provides details of the laser system. The fifth chapter describes an experiment performed on the subject of dual-injection, performed in collaboration with Dr. James Booth of the British Columbia Institute of Technology (BCIT) involving the dual-injection of a single slave amplifier. The last chapter describes the progress made on the experimental setup needed for the study of Feshbach resonances between 85/87Rb and 6Li and the photoassociative formation of molecules.

No description available.

Abstract Recently, the large magneto-resistance effects in epitaxial manganite thin films has interested in the doped manganite perovskite materials for magnetic random access memory (MRAM) and read-head application. The relation between the magneto-resistance and microstructure of the colossal magneto-resistance materials has been evaluated in this study. Different thickness of La0.67Ca0.33Mn03 (LCMO) thin films were grown on (001) MgO and (001) SrTi03 (STO) substrates at growth temperature 750 degree C with RF magnetron sputtering technique, respectively. These substrates provide two different lattice-mismatch conditions for the LCMO films (+9% for MgO and +1% for STO). The crystal structure of LCMO films were characterized with X-ray diffraction (XRD), the surface morphology of LCMO films were observed by scanning electron microscope (SEM), the interface of microstructure between LCMO films and substrate were studied by transmission electron microscope (TEM), the thickness and chemical composition of LCMO films were determined by Rutherford backscattering spectrometer (RBS), and finally the resistance and I-M transition temperature were evaluated at temperature range from 77K to 300K. The results show that the epitaxial LCMO films with a superlattice structure were obtained on STO substrate and polycrystal structure of LCMO films were on MgO substrate due to larger lattice mismatch.. The transition temperature of magneto-resistance of LCMO thin film is quite sensitive with film thickness. The transition temperature increases with film thickness increased. When the film with thickness excess of 2000A, the transition temperature is nearly same as that of LCMO bulk material.. The existed strain and the microstructure of LCMO films are two important factors related with magnetic resistance and electrical properties of LCMO films.