O desenvolvimento de motores e equipamentos elétricos de alta eficiência energética tem representado um desafio para o desenvolvimento tecnológico. Além da criação de novos materiais, a busca pela melhoria nas propriedades daqueles já existentes surge como uma rota para otimização energética de motores elétricos. É nesse contexto que nos últimos anos as pesquisas em aços para aplicações magné-ticas, os aços elétricos, foram retomadas buscando novas rotas e processos de fa-bricação desses materiais aliando a redução de custos com a otimização das propri-edades do material. Com o aumento da produção surge a necessidade de desenvol-ver-se formas de inspeção para o controle de qualidade desses materiais que forne-çam resposta rápida e de baixo custo. Assim, surge como alternativa os métodos eletromagnéticos como ferramenta de inspeção por ensaios não destrutivos. Neste trabalho, buscou-se a otimização das propriedades de aços elétricos variando sua composição química e microestrutura, com o objetivo de estudar a influência nas propriedades magnéticas e, então, a aplicação dos métodos micromagnéticos para a inspeção da microestrutura do material com foco na criação de um método de inspe-ção para controle de qualidade que permita sua implementação durante o processo produtivo, sem a necessidade de extração de material para a detecção de defeitos e, dessa forma, foi possível verificar a viabilidade da ferramenta para esse fim. / The development of highly efficient electrical devices and engines comes up as a challenge for technological development. Summed up to new materials devel-opment, the improvement of material’s properties rises as a route for optimization of electrical machines. In this context, in the last years the researches on electrical steels have been focused on finding new manufacturing routes focused on cost re-duction and achievement of better magnetic properties, in order to waste less energy during work. Increases in steel volume production lead to a need to finding Low cost methods which supply fast results , for quality control and assurance for these mate-rials.. Electromagnetic methods show up as nondestructive tool for this purpose. In this work, several non-oriented electrical steel were prepared , with various micro-structural conditions which caused varying magnetic properties among the samples; micromagnetic methods were used as a tool for non-destructive evaluation of their microstructure and magnetic properties. The inspection aimed at building a model for in-production line quality assurance of this sort of material.

Trens de pouso de aeronaves podem vir a apresentar defeitos induzidos termicamente devido a condições severas que podem ocorrer durante pousos e inspeções rotineiras em que são submetidos periodicamente. A microestrutura resultante das regiões que compreendem os defeitos pode comprometer o bom desempenho em fadiga do componente devido a alteração das propriedades mecânicas envolvidas. Sua detecção no cenário atual atualmente faz-se de maneira dispendiosa em tempo e custo, sendo executada invasivamente através da remoção da camada de cromo presente, seguida da imersão do componente em tanques contendo o reagente químico de nital, que irá revelar possíveis queimas no substrato. Posteriormente, se o componente apresentar danos, estes são reparados e então a eletrodeposição de cromo novamente é realizada e o componente é posto em uso. O objetivo deste trabalho é apresentar uma metodologia de inspeção micromagnética não destrutiva para a detecção de danos térmicos, baseada em norma interna da BOEING. Estas técnicas são baseadas na aplicação de um campo magnético no material a ser inspecionado, o qual irá interagir e revelar as características microestruturais presentes, sem a remoção do cromo, tornando possível uma inspeção confiável, rápida e de baixo valor. Aqui será apresentado como foi desenvolvido um padrão para servir de gabarito a futuras inspeções, além de melhorias sugeridas à norma da BOEING para um melhor aproveitamento da técnica nesta aplicação específica. A metodologia empregada utilizou de uma chapa de aço 300M que sofreu processos de tratamento térmico e shot-peening, posteriormente submetida a danos térmicos impostos através de laser de CO2 de baixa potência, e parcialmente revestida com cromo duro. As regiões danificadas foram avaliadas micromagneticamente através da imposição de um campo magnético alternado sob diferentes frequências de excitação, através de um equipamento comercial disponível no laboratório, e a influência do revestimento de cromo foi estudada. Os resultados apresentaram elevada sensibilidade da técnica na avaliação de danos térmicos na presença e ausência de cromo na superfície, porém para o sensor utilizado neste estudo, há uma limitação quanto a espessura da camada de cromo existente. / The landing gear of aircrafts may present thermally induced defects due to the severe conditions that can occur during landings and also during the routine inspections to which they are submitted periodically. The microstructure resulting from the regions comprising the defect may impair the proper fatigue performance of the component due to the change of the mechanical properties involved. Its detection, in the current scenario, is expensive time and costwise, being executed invasively by removing the existing layer of chromium followed by immersion of the component in tanks containing the chemical reagent Nital, which will show possible burnings on the substrate. Subsequently, if the component presents damages, they are repaired and then the re-chrome plating on the component is carried out and it is put to use. The aim of this dissertation is to present a non-destructive, micromagnetic inspection methodology, for the detection of thermal damage, based on BOEING internal standards. These techniques are based on applying a magnetic field in the material to be inspected, which will interact and disclose the microstructural characteristics of the part without removal of the microstructural characteristics of the part without removal of the chrome, making possible a reliable, fast and low cost inspection. Here it will be presented how a standard was developed to serve as a norm for future inspections, and suggested improvements to BOEING's rule for a better use of the technique in this specific application. The methodology employed used a steel plate to 300M which had undergone heat treatment processes and shot-peening and thereafter subjected to thermal damage imposed through low power CO2 laser , and partially coated with hard chrome. The damaged regions were evaluated micromagnetically through the imposition of an alternating magnetic field under different excitation frequencies, through a commercially available equipment in the laboratory, and the influence of chromium coating was studied. The results showed high sensitivity of the technique to assess thermal damage in the presence and absence of chromium on the surface, but for the sensor used in this study, there is a limit on the thickness of the existing chromium.

Trens de pouso de aeronaves podem vir a apresentar defeitos induzidos termicamente devido a condições severas que podem ocorrer durante pousos e inspeções rotineiras em que são submetidos periodicamente. A microestrutura resultante das regiões que compreendem os defeitos pode comprometer o bom desempenho em fadiga do componente devido a alteração das propriedades mecânicas envolvidas. Sua detecção no cenário atual atualmente faz-se de maneira dispendiosa em tempo e custo, sendo executada invasivamente através da remoção da camada de cromo presente, seguida da imersão do componente em tanques contendo o reagente químico de nital, que irá revelar possíveis queimas no substrato. Posteriormente, se o componente apresentar danos, estes são reparados e então a eletrodeposição de cromo novamente é realizada e o componente é posto em uso. O objetivo deste trabalho é apresentar uma metodologia de inspeção micromagnética não destrutiva para a detecção de danos térmicos, baseada em norma interna da BOEING. Estas técnicas são baseadas na aplicação de um campo magnético no material a ser inspecionado, o qual irá interagir e revelar as características microestruturais presentes, sem a remoção do cromo, tornando possível uma inspeção confiável, rápida e de baixo valor. Aqui será apresentado como foi desenvolvido um padrão para servir de gabarito a futuras inspeções, além de melhorias sugeridas à norma da BOEING para um melhor aproveitamento da técnica nesta aplicação específica. A metodologia empregada utilizou de uma chapa de aço 300M que sofreu processos de tratamento térmico e shot-peening, posteriormente submetida a danos térmicos impostos através de laser de CO2 de baixa potência, e parcialmente revestida com cromo duro. As regiões danificadas foram avaliadas micromagneticamente através da imposição de um campo magnético alternado sob diferentes frequências de excitação, através de um equipamento comercial disponível no laboratório, e a influência do revestimento de cromo foi estudada. Os resultados apresentaram elevada sensibilidade da técnica na avaliação de danos térmicos na presença e ausência de cromo na superfície, porém para o sensor utilizado neste estudo, há uma limitação quanto a espessura da camada de cromo existente. / The landing gear of aircrafts may present thermally induced defects due to the severe conditions that can occur during landings and also during the routine inspections to which they are submitted periodically. The microstructure resulting from the regions comprising the defect may impair the proper fatigue performance of the component due to the change of the mechanical properties involved. Its detection, in the current scenario, is expensive time and costwise, being executed invasively by removing the existing layer of chromium followed by immersion of the component in tanks containing the chemical reagent Nital, which will show possible burnings on the substrate. Subsequently, if the component presents damages, they are repaired and then the re-chrome plating on the component is carried out and it is put to use. The aim of this dissertation is to present a non-destructive, micromagnetic inspection methodology, for the detection of thermal damage, based on BOEING internal standards. These techniques are based on applying a magnetic field in the material to be inspected, which will interact and disclose the microstructural characteristics of the part without removal of the microstructural characteristics of the part without removal of the chrome, making possible a reliable, fast and low cost inspection. Here it will be presented how a standard was developed to serve as a norm for future inspections, and suggested improvements to BOEING's rule for a better use of the technique in this specific application. The methodology employed used a steel plate to 300M which had undergone heat treatment processes and shot-peening and thereafter subjected to thermal damage imposed through low power CO2 laser , and partially coated with hard chrome. The damaged regions were evaluated micromagnetically through the imposition of an alternating magnetic field under different excitation frequencies, through a commercially available equipment in the laboratory, and the influence of chromium coating was studied. The results showed high sensitivity of the technique to assess thermal damage in the presence and absence of chromium on the surface, but for the sensor used in this study, there is a limit on the thickness of the existing chromium.

O desenvolvimento de motores e equipamentos elétricos de alta eficiência energética tem representado um desafio para o desenvolvimento tecnológico. Além da criação de novos materiais, a busca pela melhoria nas propriedades daqueles já existentes surge como uma rota para otimização energética de motores elétricos. É nesse contexto que nos últimos anos as pesquisas em aços para aplicações magné-ticas, os aços elétricos, foram retomadas buscando novas rotas e processos de fa-bricação desses materiais aliando a redução de custos com a otimização das propri-edades do material. Com o aumento da produção surge a necessidade de desenvol-ver-se formas de inspeção para o controle de qualidade desses materiais que forne-çam resposta rápida e de baixo custo. Assim, surge como alternativa os métodos eletromagnéticos como ferramenta de inspeção por ensaios não destrutivos. Neste trabalho, buscou-se a otimização das propriedades de aços elétricos variando sua composição química e microestrutura, com o objetivo de estudar a influência nas propriedades magnéticas e, então, a aplicação dos métodos micromagnéticos para a inspeção da microestrutura do material com foco na criação de um método de inspe-ção para controle de qualidade que permita sua implementação durante o processo produtivo, sem a necessidade de extração de material para a detecção de defeitos e, dessa forma, foi possível verificar a viabilidade da ferramenta para esse fim. / The development of highly efficient electrical devices and engines comes up as a challenge for technological development. Summed up to new materials devel-opment, the improvement of material’s properties rises as a route for optimization of electrical machines. In this context, in the last years the researches on electrical steels have been focused on finding new manufacturing routes focused on cost re-duction and achievement of better magnetic properties, in order to waste less energy during work. Increases in steel volume production lead to a need to finding Low cost methods which supply fast results , for quality control and assurance for these mate-rials.. Electromagnetic methods show up as nondestructive tool for this purpose. In this work, several non-oriented electrical steel were prepared , with various micro-structural conditions which caused varying magnetic properties among the samples; micromagnetic methods were used as a tool for non-destructive evaluation of their microstructure and magnetic properties. The inspection aimed at building a model for in-production line quality assurance of this sort of material.

This thesis presents the theoretical studies of chiral magnetic structures, which exist or are affected by antisymmetric Dzyaloshinskii-Moriya interactions. The theoretical approach is based on the phenomenological model of ferromagnetic materials lacking inversion symmetry. Equilibrium magnetic states are described as static structures in the micromagnetic low temperature limit with a fixed magnitude of the magnetization. The studies are focused on two cases: (i) magnetization structures that are affected by chiral exchange so that a particular chirality of these structures is selected, and (ii) novel solitonic states that are called chiral Skyrmions and only exist because of the chiral exchange. Vortex states in magnetic nanodisks provide the simplest example of a handed magnetization structure, where effects of the chiral couplings may become noticeable. A chiral exchange here favours one chirality of such a vortex state over the other. This effect can stem from surface-induced or other defect-related chiral Dzyaloshinskii-Moriya exchange. The different chiral versions of the vortex states are shown to display strong dependencies on the materials properties of such nanodisks. Within a micromagnetic model for these effects, numerical calculations of the shape, size, and stability of the vortices in equilibrium as functions of magnetic field and the material and geometrical parameters provide a general analysis of the influence of the broken mirror symmetry caused by the surface/interfaces or structural defect on their properties. The Dzyaloshinskii-Moriya interactions impose differences in the energies and sizes of vortices with different chirality: these couplings can considerably increase sizes of vortices with one sense of rotation and suppress vortices with opposite sense of rotation. Torsions related to lattice defects can cause similar to the surface-induced chiral couplings. A general phenomenological magneto-elastic formulation for this torsional chirality selection is given. It is applied to calculate similar effects on vortex states in magnetic disks with a screw dislocation at their center. In systems with strong chiral exchange the magnetic equilibrium states themselves become chiral twisted structures. The most interesting structures in this context are the two-dimensional solitonic states that are now known as chiral Skyrmions. The properties and stability of multiply twisted states composed of these particle-like units are the subject of the second part of this thesis. These states compete with the well known onedimensionally modulated helical states in non-centrosymmetric magnetic systems. Studies of modulated states in cubic helimagnets have shown, that in absence of additional effects, the only thermodynamically stable state is a cone helix. Uniaxial distortions, that can be caused by uniaxial stresses in the bulk samples or arise due to surface effects in thin films, suppress the helical states and stabilize Skyrmion lattices in a broad range of thermodynamical parameters. Using the phenomenological theory for modulated and localized states in chiral magnets, the equilibrium parameters of the Skyrmion and helical states have been derived as functions of applied magnetic field and induced uniaxial anisotropy. These results show that due to a combined effect of induced uniaxial anisotropy and an applied magnetic field, Skyrmion lattices can be formed as thermodynamically stable states. The theoretical results provide a comprehensive description of the evolution of modulated states in an applied magnetic field depending on type of anisotropy. The cases of a uniaxial anisotropy of easy axis and easy plane type with fields applied along its axis are investigated in detail. Existence of Skyrmion-lattice states in the easy axis case as thermodynamic field-induced phase is demonstrated. The results explain recent observation of Skyrmion lattices by magnetic Lorentz microscopy in thin foils of cubic chiral magnets. In systems with easy plane type of anisotropy, Skyrmion states do not form thermodynamic phases in applied fields along the axis. However, distorted Skyrmion phases can exist in fields applied perpendicularly to the axis. In this configuration of anisotropy axis and fields, both the helical states and the Skyrmions display elliptical distortions. The investigated micromagnetic model maps out the basic helical and Skyrmionic states expected to exist in cubic and nearly cubic chiral magnets.

Les composés intermétalliques à base d'éléments de terres rares et de métaux de transition présentent des propriétés magnétiques intéressantes pour les applications technologiques (aimants permanents, enregistrement magnétique,...). Ce travail est dédié à l'étude des propriétés structurales et magnétiques des nanomatériaux de type PrCo(3-x)Fex, dérivant de la structure PuNi3. L'état nanocristallin a pour but d'optimiser les propriétés magnétiques extrinsèques, il a été obtenu par broyage à haute énergie suivi d'un recuit. Les composés PrCo3 ont une anisotropie uniaxiale, une aimantation très importante et un champ coercitif de 12 kOe à température ambiante et de 55 kOe à T = 10 K. L'analyse des données de diffraction des rayons X par affinement Rietveld a montré que le système PrCo3-xFex est mono-phasé de type PuNi3 pour x < 1. La substitution du Co par Fe induit des améliorations significatives sur les propriétés magnétiques intrinsèques. Cette amélioration est due d'une part au renforcement du moment magnétique moyen 3d des composés substitués, et d'autre part à l'effet magnétovolumique. Parallèlement, nous avons complété cette étude expérimentale par deux études théoriques. La première approche, à l'échelle atomique, consiste à faire des calculs de type DFT des structures électroniques et des propriétés magnétiques intrinsèques des intermétalliques RCox, (R = Y, Pr et x = 2, 3, 5) et PrCo(3-x)Fex. La seconde approche correspondant à l'échelle mésoscopique a pour but d'interprêter le lien entre les propriétés magnétiques extrinsèques et la structure à l'échelle nanométrique. Elle est menée dans le cadre du micromagnétisme par une méthode de type éléments finis / The intermetallic based on rare earth and transition metal compounds present interesting magnetic properties for the technological applications (permanent magnets, magnetic recording,...). This work is dedicated to the study of the structural and magnetic properties of nanocrystalline PrCo(3-x)Fex, described in the PuNi3 type structure. The nanocrystalline state leads to optimize the extrinsic roperties, it has been obtained by high energy milling technique following by subsequent annealing. The compound PrCo3-xFex presents a very high uniaxial magnetocrystalline anisotropy, a very important magnetization and a coercive field of 12 kOe at room temperature and 55 kOe at T = 10 K. The analysis result of X-ray diffraction pattern of PrCo(3-x)Fex using the Rietveld refinement showed that these compounds are single phase with the rhombohedral PuNi3-type structure for x < 1. The substitution of the Co by Fe leads to significant improvement on the intrinsic magnetic properties. This improvement comes from on the one hand the increase of average 3d magnetic moment on substituted compounds, and on the other hand the magnetovolumic effect. We have completed this experimental study by two theoretical investigations. The first approach, at the atomic scale, with DFT based calculations of the electronic structure and intrinsic magnetic properties of RCox (R = Y, Pr and x = 2, 3, 5) and PrCo3-xFex intermetallics. The second approach is the simulation of the extrinsic magnetic properties in the framework of micromagnetism. It has been performed in order to get a qualitative picture of the microstructure effect on the macroscopic magnetization curve, this model is treated by using the finite elements method

In der vorliegenden Arbeit wurden die mikromagnetische Struktur sowie das Ummagnetisierungsverhalten epitaktisch gewachsener MnAs Filme auf dem Substrat GaAs untersucht. Im Mittelpunkt steht die mikromagnetischen Struktur von anisotrop erspannten MnAs Filmen auf GaAs(001). Die Verspannung führt zur selbstorganisierten Anordnung ferromagnetischer Streifen. Ihre Domänenstruktur wurde mittels MFM (magnetischer Kraftmikroskopie) bestimmt und mit den Resultaten der XMCDPEEM (X-ray magnetic circular dichroism photoemission electron microscopy) verglichen. Um eine vollständige Charakterisierung der mikromagnetischen Eigenschaften der Streifenstruktur zu erreichen, wurden die MFM Experimente in einem äusseren Magnetfeld durchgeführt. Die Beantwortung der zentralen Frage nach der Domänenstruktur ist mit der Entwicklung eines mikromagnetischen Simulators für dreidimensionale magnetische Strukturen auf mesoskopischer Skala gelungen. Die Stabilität der dreidimensionalen mikromagnetischen Struktur hängt von den Eigenschaften der selbstorganisierten Streifenstruktur ab, d.h. sowohl von der Filmdicke als auch vom Verhältnis ihrer Breite zur Filmdicke - und damit der Temperatur. Durch die Erkenntnis, dass eine magnetische Struktur in der Tiefe des Streifens vorhanden ist, können die verbleibenden Unterschiede in den XMCDPEEM- und MFM-Resultaten erklärt werden. Durch die Simulationsergebnisse in Kombination mit den Experimenten wird eine widerspruchsfreie Deutung der mikromagnetischen Struktur sowie deren Ummagnetisierungsverhalten ermöglicht. Zudem wird die mikromagnetische Struktur von MnAs auf GaAs(111) simuliert und damit das Verständnis der mikromagnetischen Strukturen auf alle vorhandenen Substratorientierungen vervollständigt. / In the present thesis the micromagnetic structure, as well as the magnetization reversal, of epitaxial MnAs films on GaAs substrates are studied. The investigation is focused on the micromagnetic structure of anisotropically strained MnAs films on GaAs(001). The strain originates a selforganized array of ferromagnetic stripes. The magnetic domains were investigated using MFM (magnetic force microscopy) and the results were compared with XMCDPEEM (X-ray magnetic circular dichroism photoemission electron microscopy). To completely characterize the micromagnetic properties of the stripe structure, MFM experiments were performed in the presence of an external field. To unambiguously determine the domain structure a three-dimensional micromagnetic simulator was developed capable to calculate magnetic structures with mesoscopic dimensions. The stability of the three-dimensional micromagnetic structure depends on the properties of the selforganized stripe structure, i.e., on the film thickness as well as on the ratio of the stipe width to thickness - and thus the temperature. Taking into account the magnetization distribution in-depth, the remaining differences between the XMCDPEEM and the MFM results can be explained by the disturbing effect of the MFM tip. The results of the micromagnetic simulations, in combination with the experimental results, allow for a determination of the micromagnetic structure in an applied field throughout the phase coexistence regime. Moreover, the micromagnetic structure of MnAs films on GaAs(111) is simulated and thus the understanding of the micromagnetic properties have been extended on all substrate orientations.

L'étude des excitations magnétiques de faible amplitude existant dans des films minces à aimantation non uniforme dans la gamme des hautes fréquences, typiquement entre quelques dizaines de MHz et quelques dizaines de GHz, constitue le sujet de ce mémoire. Le cas idéal de films magnétiques possédant une anisotropie perpendiculaire et présentant une configuration d'équilibre de l'aimantation sous forme de rubans parallèles et périodiques est étudié en détail. Dans le cas de films à forte anisotropie perpendiculaire, les spectres théoriques de susceptibilité dynamique calculés à l'aide de modèles analytiques puis, à partir de simulations numériques 2D de micromagnétisme dynamique, font apparaître des excitations localisées soit à l'intérieur des domaines magnétiques soit à l'intérieur des parois magnétiques. Ces résultats ont été comparés de façon satisfaisante avec des résultats expérimentaux issus de mesures de résonance ferromagnétique réalisées sur des films monocristallins de grenats ferrimagnétiques. Toutefois, les largeurs de raie expérimentales associées aux excitations de parois excèdent celles calculées en utilisant le terme dissipatif de Gilbert. Dans le cas de films à faible anisotropie perpendiculaire, les spectres théoriques de susceptibilité dynamique présentent de multiples excitations magnétiques liées à la forte hétérogénéité des configurations d'équilibre de l'aimantation de type rubans faibles. Les analyses modales effectuées à partir des simulations micromagnétiques dynamiques indiquent l'existence de modes de surface et de volume localisés dans différentes régions de spins à l'intérieur du film. L'influence de différents paramètres (anisotropie perpendiculaire, épaisseur du film, champ magnétique statique) sur les principales caractéristiques des spectres (nombre de résonances, fréquences de résonance, intensités et largeurs de raie) est ensuite étudiée. Ces simulations micromagnétiques dynamiques permettent d'interpréter des spectres expérimentaux complexes de perméabilité dynamique mesurés sur des films ferromagnétiques amorphes. Quelques perspectives concernant la dynamique de l'aimantation de faible amplitude dans différents objets magnétiques sont ensuite présentées.

D'un point de vu fondamental, la structure micromagnétique d'un point de Bloch est prédite depuis plus de 50 ans, mais représente cependant une singularité topologique dans le cadre de la théorie du micromagnétisme. Par conséquent, une description purement micromagnétique du point deBloch s'avère difficile. Ce manuscrit décrit les outils mathématiques et un ensemble d'algorithmes permettant de combiner un modèle d'Heisenberg classique avec des simulations micromagnétiques sur la base des éléments finis. A l'aide de ces algorithmes, nous pouvonsrigoureusement étudier les propriétés caractéristiques d'un point de Bloch d'une paroi de domaine de type vortex localisée dans un nanofil cylindrique ferromagnétique. Cette thèse décrit le pinning/depinning des points de Bloch au réseau atomique ainsi que les différents modes depropagation détectables pour des parois de domaine sous l'influence d'un champ magnétique externe, qui peut conduire le système à des vitesses supermagnoniques. / The fundamental micromagnetic structure of Bloch points was predicted by micromagnetic theory more than 50 years ago, but represents a topological singularity within the theory of micromagnetism. This complicates a pure micromagnetic description. This thesis describes thenecessary mathematical background and a set of algorithms to combine a classical atomistic Heisenberg model with micromagnetism on the basis of the finite element method. By means of those algorithms the characteristic properties of Bloch points in vortex domain walls inferromagnetic solid cylindrical nanowires can be studied rigorously. ln addition to the pinning/depinning of Bloch points at the atomistic lattice the thesis reports on the different modes of propagation detectable for vortex domain walls in that system under the influence of an externalmagnetic field, which can drive the system of the domain wall and the Bloch point with supermagnonic velocities.

Submitted by isabela.moljf@hotmail.com (isabela.moljf@hotmail.com) on 2017-03-03T15:39:30Z No. of bitstreams: 1 josehenriquesilva.pdf: 38531594 bytes, checksum: c78eae9aa6726299a310f26bfa565039 (MD5) / Approved for entry into archive by Adriana Oliveira (adriana.oliveira@ufjf.edu.br) on 2017-03-06T20:17:02Z (GMT) No. of bitstreams: 1 josehenriquesilva.pdf: 38531594 bytes, checksum: c78eae9aa6726299a310f26bfa565039 (MD5) / Made available in DSpace on 2017-03-06T20:17:02Z (GMT). No. of bitstreams: 1 josehenriquesilva.pdf: 38531594 bytes, checksum: c78eae9aa6726299a310f26bfa565039 (MD5) Previous issue date: 2011-11-09 / CAPES - Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Nos últimos anos, o estudo do comportamento da magnetização em nanodiscos magnéticos tem atraído à atenção de muitos pesquisadores da área de nanomagnetismo. Devido a possibilidade dos nanodiscos apresentarem um estado de magnetização em forma de vórtice com componente fora-do-plano no seu centro, estes podem ser os possíveis substitutos dos dispositivos de armazenamento magnético utilizados atualmente. Para que os nano discos possam ser utilizados para fins de armazenamento,precisa-se conhecer com detalhes o comportamento do vórtice em diversas situações. Em trabalho recente verificou-se experimentalmente que a frequência do modo girotrópico na presença de impureza é maior que a frequência caso não houvesse impureza no nanodisco e que a frequência diminui com o aumento do diâmetro. No presente trabalho estudamos o comportamento do modo girotrópico, quando colocamos a impureza numa distância, em relação ao centro do nanodisco, menor que o raio do Modo Girotrópico e também quando colocamos a impureza numa distância maior que o raio do modo girotrópico. A impureza magnética é definida a partir da constante de acoplamento J da interação de troca entre Spin-Spin. Se a constante de acoplamento J' da interação entre impureza-Spin vizinho for maior que J(J' > J), temos uma impureza repulsiva e para J' < J a impureza é atrativa. Para estudar a influência de impurezas na frequência do modo girotrópico foram feitas simulações micromagnéticas em nanodiscos magnéticos usando valores conhecidos das constantes do Permalloy-79. Foram feitas simulações em nanodiscos com diversos diâmetros (125nm, 145nm, 175nm, 195nm, 225nm e 275nm), todos com 10nm de espessura. Nossos resultados mostram que existe uma flutuação na frequência do modo girotrópico na presença de impurezas magnéticas, o que está de acordo com resultados experimentais recentes. / In recent years, to study the behavior of magnetization in magnetic nanodisks has attracted the attention of many researchers in nanomagnetism. Due to the possibility of nanodisks to present a state of magnetization with vortex-shaped component out-of-plane at its center, this can substitute the magnetic storage devices used today. For nanodisks that can be used for storage purposes, one needs to know in detail the behavior of the vortex in many situations. In a recent study, it was experimentally found that the frequency of the gyrotropic mode in the presence of impurities is greater than the frequency, if there were no impurity in nanodisks, so that the frequency decreases with increasing the diameter. In this paper we study the behavior of gyrotropic mode when we place the impurity at a distance from the center of the nanodisks, smaller than the gyrotropic radius mode and also when the impurity placed at a distance greater than the radius of the gyrotropic mode. The magnetic impurity is defined as the coupling constant J of the exchange interaction between the Spin-Spin interaction. If the coupling constant J' from the interaction between impurity-neighbor spin is greater than J (J0 > J), we have a repulsive impurity and if J' <J the impurity is attractive. To study the influence of impuritiesin the gyrotropic frequency mode, micromagnetic simulations were made in magnetic nanodisks using known values of constants of the Permalloy-79. Nanodisks simulations were made with different diameters (125nm,145nm,175nm,195nm,225nmand275nm), all of with10nm thick. Our results show that there is a fluctuation in the gyrotropic frequency mode in the presence of magnetic impurities, which is in agreement with recent experimental results.