This thesis deals with the aspects of methods for pulsed high-level EM quantities measurement. Methods for current and voltage measurement in pulsed power generator and power measurement in pulse microwave generator are discussed. New approaches to single-shot measurement methods application are proposed. The theoretical analysis of suitable sensor designs is performed. The magneto-optic measurement method has been experimentally realized. On the basis of experimental results a fiber-optic current sensor has been designed and theoretically analyzed. For identification and measurement of the free-space electromagnetic pulse a combined calorimetric sensor has been designed and built.

Diese Arbeit befasst sich mit der Nanostrukturierung von magnetischen Schichtsystemen mit Tunnelmagnetowiderstandseffekt (TMR-Effekt), welche in der Form von Nanosäulen in magnetoresistiven Speichern (MRAM) eingesetzt werden. Solche Nanosäulen können zukünftig ebenfalls als Nanoemitter von Mikrowellensignalen eine Rolle spielen. Dabei wird von der Auswahl eines geeigneten TMR-Schichtsystems mit einer MgO-Tunnelbarriere über die Präparation der Nanosäulen mit Seitenisolierung bis hin zum Aufbringen der elektrischen Zuleitungen eine komplette Prozesskette entwickelt und optimiert. Die Strukturen werden mittels optischer Lithographie und Elektronenstrahllithographie definiert, die anschließende Strukturübertragung erfolgt durch Ionenstrahlätzen (teilweise reaktiv) sowie durch Lift-off. Rückmeldung über Erfolg oder Probleme bei der Strukturierung geben Transmissionselektronenmikroskopie (teilweise mit Zielpräparation per Ionenfeinstrahl, FIB), Rasterelektronenmikroskopie sowie die Lichtmikroskopie. Es können so TMR-Nanosäulen mit minimalen Abmessungen von bis zu 69 nm x 71 nm hergestellt werden, von denen Nanosäulen mit Abmessungen von 65 nm x 87 nm grundlegend magneto-elektrisch charakterisiert worden sind. Dies umfasst die Bestimmung des TMR-Effektes und des Widerstandes der Tunnelbarriere (RA-Produkt). Weiterhin wurde das Verhalten der magnetischen Schichten bei größeren Magnetfeldern bis +-200mT sowie das Umschaltverhalten der magnetisch freien Schicht bei verändertem Winkel zwischen magnetischer Vorzugsachse des TMR-Elementes und dem äußeren Magnetfeld untersucht. Der Nachweis des Spin-Transfer-Torque Effektes an den präparierten TMR-Nanosäulen ist im Rahmen dieser Arbeit nicht gelungen, was mit dem zu hohen elektrischen Widerstand der verwendeten Tunnelbarriere erklärt werden kann. Mit dünneren Barrieren konnte der Widerstand gesenkt werden, allerdings führt ein Stromfluss durch diese Barrieren schnell zur Degradation der Barrieren. Weiterführende Arbeiten sollten das Ziel haben, niederohmige und gleichzeitig elektrisch belastbare Tunnelbarrieren in einem entsprechenden TMR-Schichtsystem abzuscheiden. Eine erste Auswahl an Ansatzpunkten dafür aus der Literatur wird im Ausblick gegeben.:Einleitung I Grundlagen 1 Spinelektronik und Magnetowiderstand 1.1 Der Elektronenspin – Grundlage des Magnetismus 1.2 Magnetoresistive Effekte 1.2.1 AnisotroperMagnetowiderstand 1.2.2 Riesenmagnetowiderstand 1.2.3 Tunnelmagnetowiderstand 1.3 Spin-Transfer-Torque 1.4 Anwendungen 1.4.1 Festplattenleseköpfe 1.4.2 Magnetoresistive Random AccessMemory (MRAM) 1.4.3 Nanooszillatoren für drahtlose Kommunikation 2 Grundlagen der Mikro- und Nanostrukturierung 2.1 Belacken 2.2 Belichten 2.2.1 Optische Lithographie 2.2.2 Elektronenstrahllithographie 2.3 Entwickeln 2.4 Strukturübertragung 2.4.1 Die Lift-off Technik 2.4.2 Ätzen 2.5 Entfernen der Lackmaske 2.6 Reinigung 2.6.1 Quellen von Verunreinigungen 2.6.2 Auswirkungen von Verunreinigungen 2.6.3 Entfernung von Verunreinigungen 2.6.4 Spülen und Trocknen der Probenoberfläche 3 Ionenstrahlätzen 3.1 Physikalisches Ätzen – Sputterätzen 3.2 Reaktives Ionenstrahlätzen – RIBE 3.3 Anlagentechnik 3.3.1 Parameter 3.3.2 Homogenität 3.3.3 Endpunktdetektion II Ergebnisse und Diskussion 4 TMR-Schichtsysteme 4.1 Prinzipielle Schichtfolge 4.2 Verwendete TMR-Schichtsysteme 4.3 Rekristallisation von Kupfer 4.4 Formierung der TMR-Schichtsysteme 4.4.1 Antiferromagnetische Kopplung an PtMn 4.4.2 Rekristallisation an der MgO-Barriere 4.5 Anpassung der MgO-Schicht – TMR-Effekt und RA-Produkt 4.6 Magnetische Charakterisierung 5 Probendesign 5.1 Beschreibung der vier lithographischen Ebenen 5.2 Layout für statische und dynamischeMessungen 5.2.1 Geometrie 5.2.2 Anforderungen für die Hochfrequenzmessung 5.3 Layout für Zuverlässigkeitsmessungen 5.3.1 Geometrie 5.3.2 Voraussetzungen für die Funktion 5.4 Chiplayout 5.4.1 Zusatzstrukturen 5.4.2 Anordnung der Elemente 6 Fertigung eines Maskensatzes für die optische Lithographie 6.1 Vorbereitung desMaskenrohlings 6.2 Strukturierung mittels Elektronenstrahllithographie 6.3 Ätzen der Chromschicht 7 Ergebnisse und Diskussion der Probenpräparation 7.1 Definition der Grundelektrode 7.1.1 Freistellen der Grundelektrode 7.1.2 Gratfreiheit der Grundelektrode 7.1.3 Oberflächenqualität nach der Strukturierung 7.2 Präparation der magnetischen Nanosäulen 7.2.1 Aufbringen einer Ätzmaske 7.2.2 Ionenstrahlätzen der TMR-Nanosäule 7.2.3 Abmessungen der präparierten Nanosäulen 7.3 Vertikale Kontaktierung 7.3.1 Seitenwandisolation 7.3.2 Freilegen der Kontakte 7.3.3 Aufbringen der elektrischen Zuleitungen 7.4 Die komplette Prozesskette und Ausbeute 8 Magneto-elektrische Charakterisierung 8.1 Messung des Tunnelmagnetowiderstandes 8.2 Stabilität der magnetischen Konfiguration 8.3 Spin-Transfer-Torque an TMR-Nanosäulen 9 Zusammenfassung und Ausblick Literaturverzeichnis / This thesis deals with the fabrication of nanopillars with tunnel magnetoresistance effect (TMR-effect), which are used in magnetoresistive memory (MRAM) and may be used as nanooscillators for future near field communication devices. Starting with the selection of a suitable TMR-layer stack with MgO-tunnel barrier, the whole process chain covering the fabrication of the nanopillars, sidewall isolation and preparation of the supply lines on top is developed and optimised. The structures are defined by optical and electron beam lithography, the subsequent patterning is done by ion beam etching (partially reactive) and lift-off. Techniques providing feedback on the nanofabrication are transmission electron microscopy (partially with target preparation by focused ion beam, FIB), scanning electron microscopy and optical microscopy. In this way nanopillars with minimal dimensions reaching 69 nm x 71 nm could be fabricated, of which nanopillars with a size of 65 nm x 87 nm were characterized fundamentally with respect to their magnetic and electric properties. This covers the determination of the TMR-effect and the resistance of the tunnel barrier (RA-product). In addition, the behaviour of the magnetic layers under higher magnetic fields (up to +-200mT) and the switching behaviour of the free layer at different angles between the easy axis of the TMR-element and the external magnetic field were investigated. The spin transfer torque effect could not be detected in the fabricated nanopillars due to the high electrical resistance of the tunnel barriers which were used. The resistance could be lowered by using thinner barriers, but this led to a quick degradation of the barrier when a current was applied. Continuative work should focus on the preparation of tunnel barriers in an appropriate TMR-stack being low resistive and electrically robust at the same time. A first selection of concepts and ideas from the literature for this task is given in the outlook.:Einleitung I Grundlagen 1 Spinelektronik und Magnetowiderstand 1.1 Der Elektronenspin – Grundlage des Magnetismus 1.2 Magnetoresistive Effekte 1.2.1 AnisotroperMagnetowiderstand 1.2.2 Riesenmagnetowiderstand 1.2.3 Tunnelmagnetowiderstand 1.3 Spin-Transfer-Torque 1.4 Anwendungen 1.4.1 Festplattenleseköpfe 1.4.2 Magnetoresistive Random AccessMemory (MRAM) 1.4.3 Nanooszillatoren für drahtlose Kommunikation 2 Grundlagen der Mikro- und Nanostrukturierung 2.1 Belacken 2.2 Belichten 2.2.1 Optische Lithographie 2.2.2 Elektronenstrahllithographie 2.3 Entwickeln 2.4 Strukturübertragung 2.4.1 Die Lift-off Technik 2.4.2 Ätzen 2.5 Entfernen der Lackmaske 2.6 Reinigung 2.6.1 Quellen von Verunreinigungen 2.6.2 Auswirkungen von Verunreinigungen 2.6.3 Entfernung von Verunreinigungen 2.6.4 Spülen und Trocknen der Probenoberfläche 3 Ionenstrahlätzen 3.1 Physikalisches Ätzen – Sputterätzen 3.2 Reaktives Ionenstrahlätzen – RIBE 3.3 Anlagentechnik 3.3.1 Parameter 3.3.2 Homogenität 3.3.3 Endpunktdetektion II Ergebnisse und Diskussion 4 TMR-Schichtsysteme 4.1 Prinzipielle Schichtfolge 4.2 Verwendete TMR-Schichtsysteme 4.3 Rekristallisation von Kupfer 4.4 Formierung der TMR-Schichtsysteme 4.4.1 Antiferromagnetische Kopplung an PtMn 4.4.2 Rekristallisation an der MgO-Barriere 4.5 Anpassung der MgO-Schicht – TMR-Effekt und RA-Produkt 4.6 Magnetische Charakterisierung 5 Probendesign 5.1 Beschreibung der vier lithographischen Ebenen 5.2 Layout für statische und dynamischeMessungen 5.2.1 Geometrie 5.2.2 Anforderungen für die Hochfrequenzmessung 5.3 Layout für Zuverlässigkeitsmessungen 5.3.1 Geometrie 5.3.2 Voraussetzungen für die Funktion 5.4 Chiplayout 5.4.1 Zusatzstrukturen 5.4.2 Anordnung der Elemente 6 Fertigung eines Maskensatzes für die optische Lithographie 6.1 Vorbereitung desMaskenrohlings 6.2 Strukturierung mittels Elektronenstrahllithographie 6.3 Ätzen der Chromschicht 7 Ergebnisse und Diskussion der Probenpräparation 7.1 Definition der Grundelektrode 7.1.1 Freistellen der Grundelektrode 7.1.2 Gratfreiheit der Grundelektrode 7.1.3 Oberflächenqualität nach der Strukturierung 7.2 Präparation der magnetischen Nanosäulen 7.2.1 Aufbringen einer Ätzmaske 7.2.2 Ionenstrahlätzen der TMR-Nanosäule 7.2.3 Abmessungen der präparierten Nanosäulen 7.3 Vertikale Kontaktierung 7.3.1 Seitenwandisolation 7.3.2 Freilegen der Kontakte 7.3.3 Aufbringen der elektrischen Zuleitungen 7.4 Die komplette Prozesskette und Ausbeute 8 Magneto-elektrische Charakterisierung 8.1 Messung des Tunnelmagnetowiderstandes 8.2 Stabilität der magnetischen Konfiguration 8.3 Spin-Transfer-Torque an TMR-Nanosäulen 9 Zusammenfassung und Ausblick Literaturverzeichnis

L’objectif principal de ce travail de thèse est de formuler un matériau nanocomposite doté de propriétés magnéto-optiques (MO) et photostructurable pour, in fine, réaliser des dispositifs optiques non-réciproques pouvant être intégrés au sein de puces optiques. Le matériau nanocomposite MO est obtenu en dispersant des nanoparticules magnétiques (NP) de ferrite de cobalt dans une matrice sol-gel d’alcoxydes de silicium et de titane. Les NP confèrent au matériau ses propriétés MO. La formulation du matériau est photostructurable en UV profond (193, 266 nm) sans ajout de photoamorceur et se comporte comme une photo-résine négative. La formulation est flexible en termes de ratio molaire Si/Ti et de dopage en NP pouvant atteindre 20 %vol. La photochimie du matériau en films minces a été étudiée par ellipsométrie spectroscopique, FTIR et spectroscopie UV-visible. Les techniques de photolithographies UV interférométriques et par masques binaires ont permis de réaliser des réseaux périodiques de lignes bien définis et couvrant une large gamme de périodes, de 500 nm à 100 µm. Les propriétés optiques et MO (rotation Faraday) du matériau ont été étudiées. En couches minces, l’indice de réfraction peut être modulé entre 1,4 et 1,7 selon la composition du matériau. Il a été établi que l’ensemble des NP introduites dans le matériau contribuent à la rotation Faraday. Des dispositifs microstructurés ont été réalisés en espace libre et en configuration guidée en se basant sur les dimensionnements opto-géométriques déterminés par des simulations optiques et MO. Leurs caractérisations démontrent l’intérêt de ce matériau et son caractère prometteur pour réaliser des dispositifs intégrés. / The main objective of this PhD work is to formulate a nanocomposite material with magneto-optical (MO) properties which is also photostructurable, in order to ultimately create non-reciprocal optical devices that can be integrated into optical chips. The nanocomposite MO material is obtained by homogenously dispersing magnetic nanoparticles (NP) of cobalt ferrite in a sol-gel matrix based on silicon and titanium alkoxides. NP confer the material its MO properties. The material is photostructurable with deep UV wavelengths (193, 266 nm) without any addition of photoinitiator and behaves like a negative photoresist. The formulation is versatile in terms of Si/Ti molar ratio and NP doping, up to 20 %vol. The photochemistry of this material as thin films has been studied by spectroscopic ellipsometry, FTIR and UV-visible spectroscopy. UV photolithography techniques using interferometry setups and binary masks have achieved well-defined periodic lines patterns over a wide range of periods, from 500 nm to 100 microns. The optical and MO (Faraday rotation) properties of the material were studied. In thin layers, the refractive index can be modulated between 1.4 and 1.7 depending on the Si/Ti material stoichiometry and its NP doping. It has been established that all the NP introduced in the material contribute to the Faraday rotation. Micro-structured devices in free space and in guided configuration have been realized using the opto-geometrical features determined using optical and MO simulations. Their characterizations demonstrate the high interest of this material and clearly show its promising character to realize integrated devices.

A systematic development of a continuum model is presented, which is capable of describing the magneto-mechanical behavior of magnetic polymer gels commonly referred to as ‘‘ferrogels’’. In the present research, ferrogels are treated as multicomponent, multiphase materials. They consist of a polymer network (P), fixed magnetic particles (f), mobile magnetic particles (m), and liquid (L). By considering ferrogels as multicomponent materials, interaction among constituents of ferrogels can be captured. This helps in understanding the process occurring inside ferrogels under the influence of external stimuli, such as magnetic fields. In our modeling approach, the field equations of ferrogels are derived within the framework of the theory of mixtures. The basic equations include Maxwell’s equations, balance of mass, linear momentum, angular momentum, energy, and entropy. In the framework of the theory of mixtures, balance relations are first presented at the constituent level also referred to as partial balance relations. By summing partial balance relations over all constituents and imposing the restrictions of theory of mixtures, balance relations of mixture (for the ferrogel) are obtained. In the current work the specific magnetization (magnetization per density) is considered as an evolving variable. It is demonstrated that balance of angular momentum is satisfied using the evolution equation of specific magnetization and constitutive laws. In the process of modeling, a suitable free energy function is introduced and thermodynamically consistent constitutive laws are formulated. Introducing certain assumptions, a reduced model of the ferrogel, a coupled magneto-mechanical formulation, is subsequently presented. The reduced model consists only of a polymer network (P) and fixed magnetic particles (f). It is concluded that the reduced model compares well to the existing ones in the literature. The magneto-mechanical problem based on the reduced model is solved in 2D using the finite element method. The only unknowns for the finite element method implementation are mechanical displacement and magnetic potential. Deformation of a ferrogel in a magnetic field is subsequently investigated. Elongation and contraction of a ferrogel are observed when a magnetic field is applied in the x- and y-directions, respectively. The numerical results were compared with existing experimental work in the literature. A good qualitative agreement was found between numerical and experimental results.

Thesis (MSc)--University of Stellenbosch, 2011. / ENGLISH ABSTRACT: A magneto optical trap (MOT) is capable of trapping a vapor cloud consisting of atoms cooled down to the micro Kelvin range. Three orthogonal pairs of counter-propagating laser beams of the correct circular polarisation form an optical molasses which facilitates the cooling of neutral atoms. Additionally a spatially non-uniform magnetic field produced by two current carrying coils in a Maxwell gradient configuration is used to trap the cooled atoms. In this report the effects of the trap parameters, including the laser beam intensity and frequency detuning, beam diameter and magnetic field gradient, on the number of trapped atoms are discussed. Secondly the development of an experimental setup for laser cooling and trapping of 87Rb atoms in vacuum with the aid of a MOT is presented. All trap components were implemented and characterised. The vacuum system and trapping chamber in which the cooling takes place were designed and constructed. A rubidium getter to act as a source of atoms was integrated into the vacuum system. The two external cavity diode lasers used for trapping and optical re-pumping were characterised. The optical setup required for the optical molasses was designed, constructed and characterised. Saturated absorption spectroscopy was performed to investigate the hyperfine structure of 87Rb and to frequency lock the lasers. We report on the current status of the project with regards to progress, results and future work. / AFRIKAANSE OPSOMMING: 'n Magneto-optiese val (magneto optical trap, MOT) kan 'n dampwolk van atome vang en afkoel tot in die mikro Kelvin bereik. Drie ortogonale pare laserbundels, elke paar voortplantend in teenoorgestelde rigtings, met die korrekte sirkelvormige polarisasie vorm 'n sogenaamde optiese molasse wat die afkoeling van neutrale atome moontlik maak. Bykomend word 'n ruimtelik nie-uniforme magneetveld geproduseer deur twee stroomdraende spoele in 'n Maxwell gradient-opstelling gebruik om die afgekoelde atome te vang. In hierdie verslag word die invloed van die val parameters, insluitend die laserbundel intensiteit en frekwensie afstemming, die laserbundel deursnit en magneetveld gradiënt, op die aantal atome in die val bespreek. Tweedens word die ontwikkeling van 'n eksperimentele opstelling vir laser afkoeling en vang van 87Rb atome in vakuum met die hulp van 'n MOT voorgelê. Alle komponente van die val is geïmplementeer en gekarakteriseer. Die vakuumsisteem en val-kamer waarin die afkoeling plaasvind is ontwerp en gebou. 'n Rubidium gasbinder is in die vakuumsisteem ingebou om as 'n bron van atome te dien. Die twee eksterne resonator diodelasers wat gebruik is vir die val en die optiese terugpomp is gekarakteriseer. Die optiese opstelling wat nodig is vir die optiese molasse is ontwerp, gebou en gekarakteriseer. Versadigde absorpsiespektroskopie is uitgevoer om die hiperfynstruktuur van 87Rb te ondersoek en om die lasers se frekwensies te stabiliseer. Verslag word gedoen oor die huidige stand van die projek wat betref vordering, resultate en toekomstige werk.

Les développements récents des nanotechnologies ont permis d’accéder à des dimensions qui permettent d’’étudier les spins des électrons. Ceci ouvre la voie à l’utilisation du degré de liberté du spin des électrons dans des dispositifs électroniques de nouvelle génération. C’est l’origine d’un nouveau domaine de recherche prometteur baptisé spintronique.Dans ce travail, on présente des expériences dans le domaine de la spintronique en utilisant deux matériaux très prometteurs : les nanotubes de carbone (CNT) et le palladiumnickel (PdNi), un ferromagnet versatile dans le but de manipuler le spin électronique dans les deux régimes, classiques et quantiques. Une compréhension détaillée des caractéristiques magnétiques de PdxNi 100-x devient cruciale à la fois pour comprendre les caractéristiques de basculement d’un tel dispositif mais aussi pour optimiser ses propriétés électroniques.Une étude sur des structures micrométrique et nanométrique en PdNi a été menée grâce à des mesures de l’effet Hall extraordinaires (EHE sur des croix lithographiées). Les analyses montrent que la géométrie, l’épaisseur, la composition chimique ainsi que la couche de recouvrement, ont tous une influence sur l’aimantation des électrodes de PdNi, en particulier celles de taille nanométrique. Cela est dû à la relaxation des contraintes sur les bords qui devient important pour les dispositifs de petites dimensions.On met en place un point quantique connecté `a deux contacts ferromagnétiques non colinéaires (source et drain), évaporées sur le CNT; le nanotube est connecté à une tension de grille pendant qu’une source de tension source-drain est utilisée pour varier le potentiel chimiques des ferromagnets. Les électrodes sont conçues pour former un angle téta = Pi/2. On attend alors un comportement similaire à celui d’une vanne de spin, donc un effet fini de magnétorésistance à effet tunnel est à prévoir.Des mesures de transport de spin ont révélé un régime de blocage de Coulomb, confirmé par la spectroscopie de transport. Les régimes linéaires et non-linéaires ont été également testés.En régime linéaire, les résultats montrent un signal de TMR lorsqu’il est placé dans un champ qui est balayé, un comportement typique pour un dispositif vanne de spin. Dans le régime non linéaire, ont été obtenues des variations du signal d’hystérésis lorsque la polarisation change de signe. De plus, la TMR affiche un comportement presque antisymétrique avec la conductance. Les mesures réalisées pour différentes valeurs de la tension grille et celle source drain prouvent la non trivialité de ce comportement. Cette variation antisymétrique, qui a la même symétrie que le courant, indique un courant de spin induite par un phénomène de précession. Des simulations théoriques appuient également cette hypothèse: une combinaison de phénomènes d’accumulation de spin (induite par la polarisation en spin du courant) et des phénomènes de relaxation de spin (qui agissent contre la première catégorie) déterminent une précession du spin lors de son passage dans le nanotube. / Recent developments in the field of nanotechnology allowed the access to adequate length scale necesary to closely investigate spins and opened large prospects of using electrons spin degree of freedom in new generation electronic devices. This have lead to the development of a vibrant field dubbed spintronics.Here, we present experiments that combine two very promising materials: namely cardon nanotubes and palladium-nickel (PdNi), with the purpose to manipulate the electronic spin both in the classical and in the quantum regime. We implement a quantum dot connected to two non-collinear ferromagnetic leads that acts as a spin-valve device. The versatility of carbon nanotubes to fabricate quantum dots when connected to PdNi electrodes via tunneling barriers is combined with the particular transversal anisotropy of the PdNi when shaped in nanometric stripes.For devices exploiting actively the electronic spin, however control over classical or quantum spin rotations has still to be achieved. A detailed understanding of the magnetic characteristics of PdxNi 100-x alloy is crucial both for understanding the switching characteristics of such the spin-valve device and for optimizing its electronic properties. We present a magnetic study of Pd20Ni80 and Pd90Ni10 nanostripes by means of extraordinary Hall effect measurements, at low temperature, for various dimensions, thicknesses and capping films. In the case of Pd20Ni80, this experiment is a first at low temperature.The CNT-based device proposed here was tested both in linear and nonlinear transportregimes. While the linear spin dependent transport displays the usual signatures of electronicconfinement, the finite bias magnetoresistance displays an impressive magnetoresistance antisymmetric reversal in contrast with the linear regime. This effect can only be understood if electronic interactions are considered. It is accompanied by a linear dispersion of the zeromagnetoresistance point in the bias-field plane. Simulations based on a proposed model confirm a current induced spin precession, electrically tunable due to the quantum nature ofthe device.

Medidas de atenuação ultrassônica e constante elástica em ligas de Cr-V, utilizando técnicas de pulso eco foram realizadas e as transições na temperatura de Neel, TN, estudadas. Um modelo teórico é proposto para descrever os comportamentos da atenuação e constante elástica perto da transição em TN. De acordo com o modelo proposto a adição de vanádio diminui drasticamente o coeficiente de difusão, modificando a natureza da transição. Foram utilizadas amostras de cromo contendo 0,2%V; 0,5%V; 0,67%V; 1,0%V e 1,5%V. A partir da dependência aproximadamente linear de TN com a concentração de vanádio conclui-se que 3,3% V corresponderá à TN= 0K. O efeito do campo magnético até 4,5T revelou-se insuficientemente para a obtenção de monodomínio magnético e não causa nenhuma variação mensurável em TN / Measurements of ultrasonic attenuation and elastic Constant in Cr-V alloys, using pulse echo techniques were realized and the transitions at the Neel temperature, TN, were studied. We propose a theoretical model which describe the behavior of the ultrasonic attenuation and elastic Constant near the transition in TN. According to the theoretical model the addition of Vanadium to chromium, drastically diminishes the diffusion coefficient thus changing the nature of the transition. It was used samples of chromium containing 0,2%V; 0,5%V; 0,67%V; 1,0%V and 1,5%V. From the approximately linear dependence of TN with the vanadium concentration it was concluded that 3,3%V corresponds to TN= 0. The effect of magnetic fields up to 4,5T was insufficient to produce single-Q samples, and did not cause any mensurable variation in TN

A Análise de Elementos Finitos (AEF) vem sendo utilizada em diversos trabalhos na Odontologia, pois possibilita que o estudo in vitro simule uma situação clínica real. Neste estudo utilizou-se a Análise de Elementos Finitos para avaliar as tensões geradas por prótese total obturadora maxilar Classe II de Okay retida por implantes e utilizando os sistemas de retenção O\'ring e magneto. Avaliaram-se as tensões geradas no tecido ósseo, gengivo-mucoso e barras metálicas após a aplicação de cargas nas mesas oclusal e incisal. A Análise de Elementos Finitos foi realizada empregando-se um modelo digital desenvolvido a partir de uma tomografia computadorizada de um indivíduo edentado adulto, onde se simulou uma perda óssea condizente com uma maxilectomia, simulando a Classe II de Okay. Foram posicionados quatro implantes na maxila, na região de incisivo lateral, canino, segundo pré-molar e primeiro molar esquerdos, todos unidos por barra metálica onde se instalaram os sistemas de retenção escolhidos para esse estudo. Utilizou-se o programa Rhinoceros® versão 5.0 para gerar o modelo BioCAD 3D, onde foram incorporados os modelos CAD dos implantes, UCLAS e dos sistemas de retenção, obtendo-se dois modelos, Modelo 1, O\'ring e Modelo 2, magneto. A malha de elementos finitos foi gerada pelo programa Ansys® e nela foi aplicada uma força de 80 N na plataforma oclusal e 35 N na plataforma incisal, simultaneamente. Foi realizada uma análise qualitativa, correspondente à escala de tensão máxima principal e os valores quantitativos expressos em MPa. O deslocamento da prótese obturadora, no sentido da região sem suporte ósseo, foi maior no Modelo 1, O\'ring. A mucosa de revestimento, o osso cortical e o osso medular sofreram tensões de tração e compressão que variaram de acordo com o sistema de retenção utilizado, sendo que o Modelo 2, magnetos, transferiu mais tensões para essas estruturas. O Modelo 2, magnetos, apresentou tensões na região cervical de três implantes, enquanto o Modelo 1, O\'ring, apresentou somente em um implante. A barra metálica com retenções do tipo magneto sofreu tensões equivalentes de von Mises com valores semelhantes a barra metálica com O\'ring, no entanto a área envolvida foi maior em abrangência. Baseando-se nos resultados apresentados neste estudo, a utilização de ambos sistemas de retenção é indicada para reabilitação com próteses obturadoras implantorretidas, no entanto o modelo que utilizou retenção com O\'ring, apresentou comportamento biomecânico mais favorável para esse tipo de reabilitação. / The Finite Elements Analysis (FEA) has been used in several studies in Dentistry, as it allows that an in vitro study simulates a clinical scenario. In this study the Finite Element Analysis was used to evaluate the bone stress generated by an Okay Class II obturator implant retained prosthesis having Ball/O\'ring and magnetic attachment. The tensions generated over bone, soft tissue and metallic bars were evaluated after applied loads which simulated the masticatory activity. The Finite Elements Analysis, were done utilizing a digital model developed from a computer tomography of an adult subject, where it was simulated a bone loss in accordance with a maxillectomy, simulating an Okay Class II. Four implants were set in the left maxilla, on the lateral incisor, canine, second premolar and first molar, all linked by a metallic bar where the retention system chosen for this study was installed. The Rhinoceros® program, version 5.0 was used to generate the BioCAD 3D model, where the implant CAD models, UCLAS and retention systems were incorporated, obtaining two models, Model 1, Ball/O\'ring and Model 2, magnetic attachment. The finite elements mesh was generated by Ansys® program and an 80 N force was applied over it on the occlusal platform and 35 N on the incisal platform. A qualitative analysis was performed, corresponding to the maximum main stress and the quantitative values expressed on MPa. The obturator prosthesis movement in the direction of the area without the bone support was greater on the Model 1, O´Ring. The soft tissue, the cortical and medullar bones suffered compression and tensions which variated according with the retention system used, the Model 2, magnetic attachment, was the one transferring more stress to these structures. The Model 2, magnetic attachment, presented tensions on the cervical region at 03 implants, while the Model 1, Ball/O\'ring, presented only at one implant. The metallic bar with magnetic attachment suffered von Mises equivalent tensions with similar values to the metallic bar with Ball/O\'ring, however it covered a greater area. Based on the results obtained in this study, the use of both retention systems is indicated in the rehabilitation with implant retained obturator prosthesis, though the Model 1, Ball/O\'ring, presented a biomechanical behavior more suitable to this type of rehabilitation.

Submitted by Irvana Coutinho (irvana@ufpa.br) on 2013-01-16T15:26:59Z No. of bitstreams: 2 license_rdf: 23898 bytes, checksum: e363e809996cf46ada20da1accfcd9c7 (MD5) Dissertacao_EstudoEfeitosFaraday.pdf: 2830184 bytes, checksum: a65a882a543c4f569716126c34a612bb (MD5) / Approved for entry into archive by Ana Rosa Silva(arosa@ufpa.br) on 2013-01-17T13:08:36Z (GMT) No. of bitstreams: 2 license_rdf: 23898 bytes, checksum: e363e809996cf46ada20da1accfcd9c7 (MD5) Dissertacao_EstudoEfeitosFaraday.pdf: 2830184 bytes, checksum: a65a882a543c4f569716126c34a612bb (MD5) / Made available in DSpace on 2013-01-17T13:08:36Z (GMT). No. of bitstreams: 2 license_rdf: 23898 bytes, checksum: e363e809996cf46ada20da1accfcd9c7 (MD5) Dissertacao_EstudoEfeitosFaraday.pdf: 2830184 bytes, checksum: a65a882a543c4f569716126c34a612bb (MD5) Previous issue date: 2012 / CNPq - Conselho Nacional de Desenvolvimento Científico e Tecnológico / Neste trabalho foi investigada e otimizada uma nova heteroestrutura planar de três camadas com efeitos magneto-ópticos de Faraday e de Kerr aprimorados e transmissão óptica extraordinária na região de comprimento de onda de 925 a 1200 nm. Esta estrutura consiste de uma placa metálica não magnética de ouro perfurada periodicamente e colocada sobre duas finas camadas dielétricas, sendo uma composta por um material não magnético e outra composta por um material magnético (Bi-substituted Yttrium Iron Garnet) uniformemente magnetizado perpendicularmente ao seu plano. Analisando e otimizando esta estrutura, obteve-se rotação de Faraday e rotação de Kerr três vezes e nove vezes maior, respectivamente, que os de dispositivos análogos publicados na literatura. Além disso, esta estrutura foi otimizada para obter um aumento de 40% da transmissão óptica extraordinária, preservando o ângulo de rotação de Faraday. A heteroestrutura investigada pode ser utilizada em dispositivos ópticos não recíprocos. / In this work a new planar heterostructure of three layers with an enhanced magneto-optical Faraday and Kerr effects and extraordinary optical transmission in the wavelength region 925 to 1200 nm was investigated and optimized. This structure consists of a periodically perforated non-magnetic metallic (Au) plate, placed on two thin dielectric layers, one composed by non-magnetic material and other composed by magnetic material (Bi-Substituted Yttrium Iron Garnet) uniformly magnetized perpendicularly to its plane. Analyzing and optimizing this structure, we obtained Faraday rotation and Kerr rotation 3 times and 9 times larger, respectively, than those in analogues devices published in the literature. In addition, this structure was optimized to obtain a 40% increase of extraordinary optical transmission, preserving the angle of Faraday rotation. The investigated heterostructure can be used in non-reciprocal optical devices.

Este trabalho apresenta uma proposta para o controle da suspensão veicular utilizando o amortecedor magneto-reológico, sendo o controle proposto composto pela associação de duas estratégias de controle, o controle ótimo e o controle fuzzy. O Controle ótimo é utilizado para determinar a força a ser utilizada pelo amortecedor magneto-reológico, e o controle fuzzy é utilizado para determinar a corrente elétrica, a ser utilizada no amortecedor magento-reológico e é obtido considerando o modelo de Mandani. Para o controle fuzzy, são consideradas duas entradas, a velocidade de deslocamento do pistão do amortecedor e a força prevista pelo controle ótimo, e uma saída, a corrente elétrica [A]. Para demonstrar a eficiência do controle proposto são consideradas simulações computacionais, utilizando um modelo matemático não-linear de um quarto de veículo. A análise do desempenho do controle é realizada, considerando excitações provocadas por irregularidades na pista, as irregularidades são representadas por entradas tipo degrau, impulso e senoidal. As simulações computacionais são realizadas, utilizando o Matlab® e o Simulink. Os resultados das simulações demonstram que o controle proposto aumenta a segurança do veículo e melhora sua dirigibilidade, reduzindo o deslocamento vertical do conjunto eixo e roda e o espaço de trabalho do amortecedor, quando comparado como o sistema passivo. Também contribui com o conforto dos passageiros, reduzindo as oscilações da carroceria, mantendo os níveis de aceleração abaixo dos considerados desconfortáveis pela norma BS 6841, 1987. Para verificar o comportamento do controle proposto, diante de incertezas, são realizadas simulações computacionais, considerando a possibilidade de erros paramétricos. As simulações, considerando os erros paramétricos, demonstram que o controle ótimo, mesmo quando sujeito a incertezas, permanece sendo estável e ótimo. / This work presents a proposal for control of vehicular suspension using the magneto-rheological damper, the proposed control is composed by association of two control strategy, the optimal control and the fuzzy control. The optimal control is used to determine the power to be applied by the magneto-rheological damper, and the fuzzy control is used to determine the electric current to be used in the magneto-rheological damper and is obtained considering the Mandani's model. For the fuzzy control two inputs are considered, the velocity of the piston's damper and the force provided by the optimal control, and one output, the electric current [A]. To demonstrate the efficiency of the proposed control, computational simulations are considered using a nonlinear mathematical model for a quarter-car. The performance of the control is analyzed considering excitements provoked by irregularities in the track, the irregularities are represented by entrances step type, pulse and sinusoidal. The computational simulations are performed using the Matlab® and the Simulink. The results of simulations show that the proposed control increases the vehicle security and improves the drive ability by reducing the vertical wheel displacement and the workspace to be used by the damper when compared to the passive system. It also helps with the comfort of passengers, reducing the bodywork oscillations, maintaining levels of accelerating below considered uncomfortable by standard BS 6841, 1987. To verify the behavior of the proposed control, in the face of uncertainty, computational simulations are carried out, considering the possibility of parametric errors. The simulations, show that the Optimal Control, even when subject to uncertainties, remains stable and optimal.