<p>Materials with new or improved properties are crucial for technological development. To provide the foundation for future successful products, it is important to prepare and characterise new chemical compounds that could show unusual properties. The properties of magnetic materials are closely related to their crystal, magnetic and electronic structures. This thesis focuses on the novel synthesis and structural characterisation of a number of new ternary or <i>pseudo</i>-ternary silicides and germanides of manganese with iridium, cobalt or palladium. To provide a more complete picture of the complex magnetic properties, crystal and magnetic structure refinements by the Rietveld method of X-ray and neutron powder diffraction data are complemented by single-crystal X-ray diffraction, electron diffraction, magnetisation measurements and Reverse Monte Carlo simulations of magnetic short-range order. The experimental results are corroborated by first-principles electronic structure and total energy calculations. </p><p>A commensurate non-collinear antiferromagnetic structure is found for most compounds of the solid solution Mn₃Ir_1-yCo_ySi_1-xGe_x. The non-collinearity is a result of geometric frustration in a crystal structure with magnetic Mn atoms located on a three-dimensional network of triangles. The close structural similarity to the β-modification of elemental manganese, which does not order magnetically, inspired a closer theoretical comparison of the Mn₃Ir_1-yCo_ySi_1-xGe_x propertieswith β-Mn.</p><p>Magnetic frustration is also observed for Mn₄Ir_7-xMn_xGe₆, and is an important factor underlying the dramatic change from commensurate antiferromagnetic order to spin glass properties induced by a small variation in Mn concentration. Magnetic short-range order with dominant antiferromagnetic correlation is observed for Mn₈Pd₁₅Si₇, and results from a random distribution of Mn atoms in-between the geometrically frustrated magnetic moments on the Mn octahedra. </p><p>An incommensurate cycloidal magnetic structure, observed for IrMnSi, is stabilised by an electronic structure effect, which also accounts for the non-collinearity of the Mn₃IrSi type magnetic structure.</p>

Materials with new or improved properties are crucial for technological development. To provide the foundation for future successful products, it is important to prepare and characterise new chemical compounds that could show unusual properties. The properties of magnetic materials are closely related to their crystal, magnetic and electronic structures. This thesis focuses on the novel synthesis and structural characterisation of a number of new ternary or pseudo-ternary silicides and germanides of manganese with iridium, cobalt or palladium. To provide a more complete picture of the complex magnetic properties, crystal and magnetic structure refinements by the Rietveld method of X-ray and neutron powder diffraction data are complemented by single-crystal X-ray diffraction, electron diffraction, magnetisation measurements and Reverse Monte Carlo simulations of magnetic short-range order. The experimental results are corroborated by first-principles electronic structure and total energy calculations. A commensurate non-collinear antiferromagnetic structure is found for most compounds of the solid solution Mn3Ir1-yCoySi1-xGex. The non-collinearity is a result of geometric frustration in a crystal structure with magnetic Mn atoms located on a three-dimensional network of triangles. The close structural similarity to the β-modification of elemental manganese, which does not order magnetically, inspired a closer theoretical comparison of the Mn3Ir1-yCoySi1-xGex propertieswith β-Mn. Magnetic frustration is also observed for Mn4Ir7-xMnxGe6, and is an important factor underlying the dramatic change from commensurate antiferromagnetic order to spin glass properties induced by a small variation in Mn concentration. Magnetic short-range order with dominant antiferromagnetic correlation is observed for Mn8Pd15Si7, and results from a random distribution of Mn atoms in-between the geometrically frustrated magnetic moments on the Mn octahedra. An incommensurate cycloidal magnetic structure, observed for IrMnSi, is stabilised by an electronic structure effect, which also accounts for the non-collinearity of the Mn3IrSi type magnetic structure.

Dans la première partie, nous présentons les résultats de l'étude du supraconducteur sans inversion de symétrie LaRhSi3 par spectroscopie muonique. En champ nul, nous n'avons pas détecté de champ interne. Ceci indique que la fonction d'onde de l'état supraconducteur n'est pas dominée par l'état triplet. Les mesures en champ transverse de 35G présentent une transition en accord avec la transition de phase attendue sous le champ critique Hc1. Nous avons répété ces mesures pour un champ entre Hc1 et Hc2, 150G. Le spectre obtenu pour ces mesures conserve l'asymétrie et relaxe rapidement à basse température tel que prédit pour un supraconducteur dans la phase d'Abrikosov. Néanmoins, les relaxations produites par ce balayage en température présentent une transition à près de 2 fois la température critique attendue. Dans la deuxième partie de ce mémoire, nous donnons l'interprétation des résultats de la diffraction neutronique inélastique par l'étude des champs électriques cristallins. Ces mesures ont été effectuées sur des aimants frustrés SrHo2O4 et SrDy2O4 sous la forme de poudre. L'étude des niveaux produits par les champs cristallins par la méthode des opérateurs de Stevens indique une perte du moment cinétique dans les deux matériaux. Pour le SrDy2O4, l'état fondamental serait constitué de quatre états dégénérés quasi accidentellement qui portent un moment magnétique total non-nul. Toute fois, nos mesures de susceptibilité magnétique ne montrent aucun ordre au-dessus de 50mK. Pour le SrHo2O4, le fondamental est formé d'une paire accidentelle. Nous obtenons un moment magnétique de 6.94(8)$\mu_B$ ce qui s'accorde avec les données expérimentales. / In the first part of this thesis, we present our muon spectroscopy results of the non-centrosymmetric superconductor LaRhSi3. Zero magnetic field measurements showed no internal field, suggesting at most a very small triplet component in the superconducting wave function. A temperature scan taken in 35G transverse-field geometry showed a phase transition at Hc1. The asymmetry of the muon relaxation spectrum measured at 20mK and field of 150G, which is between the lower and upper critical fields, shows a faster relaxation rate compared to the spectrum obtained at 4K, a behaviour expected in the presence of vortices in the type II superconductor. However, the temperature dependence of the relaxation rate begins to increase all the way to a temperature twice Tc of LaRhSi3 in a field of 150G. In the second part of this document, we present the interpretation of inelastic neutron scattering by crystalline electric fields. These measurements were carried out on powder samples of frustrated quantum magnets SrHo2O4 and SrDy2O4. Using Stevens operators method, we determined the level scheme du to crystalline electric field effects using a point charge model and fitted it to the experimental data. For the SrDy2O4 we found a ground state that appears to be composed of four quasi-accidental degenerate states that carry a non zero magnetic moment even though susceptibility measurements did not indicate magnetic order above 50mK. For the SrHo2O4, the ground state is a pair with a 6.98(8)$\mu_B$ magnetic moment. This lat value fots with experimental data.

Cette thèse s'interesse à la nature dynamique de la transition vitreuse. Dans une première partie, nous nous intéressons à une classe de modèles de verres de spins en champ moyen. Nous montrons que la nature continue -avec brisure complète de la symétrie des répliques- ou structurelle -avec brisure à un pas de la symétrie des répliques- de la transition vitreuse peut être prédite en regardant le spectre de la matrice des couplages et plus précisément la zone de ce spectre située au voisinage de la valeur propre la plus grande, c'est-à-dire correspondant à l'état d'énergie minimale. La transition dynamique correspondant à l'apparition d'une multitude d'états métastables, nous nous intéressons au nombre de ceux-ci dans le modèle orthogonal aléatoire généralisé, qui est un modèle analogue au modèle de Hopfield avec un nombre extensif de motifs, mais où les motifs sont strictement orthogonaux. Nous étudions l'influence de l'orthogonalité des motifs sur le nombre d'états 1-stables (états stables par retournement d'un spin quelconque). Les études analytiques précédentes par la méthode des répliques sont appuyées par des simulations numériques. Nous réalisons à la fois des simulations Monte-Carlo et des énumérations exactes sur des petits systèmes qui permettent d'obtenir les grandeurs thermodynamiques d'équilibre ou le nombre d'états 1-stables en excellent accord avec les prédictions analytiques.\\ Dans une deuxième partie, nous étudions un modèle sans désordre dont le paramètre d'ordre possède la symétrie $O(N)$ et dont les états fondamentaux ne sont pas tous équivalents. Ce modèle décrivant de manière schématique l'évolution vers une phase cristallisé ou amorphe d'un système de colloïdes de sphéres dures. Nous montrons que l'état amorphe est favorisé par la dynamique. Nous étudions alors les bassins d'attraction de chaque phase pour la dynamique à température nulle : analytiquement à la limite où $N$ est grand, et numériquement lorsque $N$ est fini.

Registered nurses are exposed to the risk of Human Immunodeficiency Virus (HIV) infection and contracting the Acquired Immunodeficiency Syndrome (AIDS). Qualitative phenomenological research was conducted to explore registered nurses' experiences of working in such a high-risk environment and how their experiences influence the therapeutic relationship. A sample of registered nurses who care for HIV-infected persons or persons who suffer from AIDS was purposefully selected. Focus group interviews were conducted. Qualitative data analysis was performed. Frankl's theory of meaning of life served as a theoretical foundation for interpreting the research findings. The research results revealed that registered nurses experience existential frustration due to the intentional and unintentional risks that they are exposed to. This negatively impacts upon their ability to maintain a healthy therapeutic relationship with patients. However, evidence was obtained indicating that some factors support their quest for finding meaning in life in the workplace. / Health Studies / M.A. (Health Studies)

Identification of aggression in Junior Primary school learners often becomes a difficult task due to the lack of appropriate measuring instruments. The assessment instruments used presently are unable to identify the subtypes of aggression. In order to address this limitation in the field of aggression, the present investigation was undertaken. A literature study was done where the concept aggression was defined and the relationship and differences between the subtypes of aggression (physical, verbal, reactive and proactive aggression) were examined. The factors that relate to aggression, namely, biological, personality, environmental and social, parental influence, frustration and media influences were identified. A reliable measuring instrument was developed to identify the four main subtypes of aggression in junior primary learners. The results of the empirical investigation indicated that there were significant positive correlations between the subtypes of aggression. Gender and intellectual potential do not appear to have a significant bearing on childhood aggression. The educational implications of the findings are discussed and guidelines regarding treatment of childhood aggression are given for both educators and parents. / Education Studies / M.Ed.

Made available in DSpace on 2016-06-02T20:15:29Z (GMT). No. of bitstreams: 1 5202.pdf: 3904832 bytes, checksum: c623a581c3cdb03d9cc81fc16ecef935 (MD5) Previous issue date: 2013-04-08 / Universidade Federal de Minas Gerais / This thesis presents a study of the magnetization plateau and the phenomenon of geometrical frustration in spin systems applied to lattices with triangular structure, as well as the results achieved by applying the differential operator technique of the Ising and Heisenberg models with external magnetic field applied to the easy magnetization axis z, their phase diagrams, behavior plateaus observed and analyzed according to the Haldane conjecture and appearance of plateaus presented by Oshikawa, Yamanaka and Affleck, and also to study the behavior of the magnetic susceptibility in order to verify the behavior of frustrated systems using the frustration factor f= &#952;WC/TN to verify frustration encountered at various stages of the study models / Este trabalho apresenta um estudo da magnetização de platô e do fenômeno de frustração geométrica em sistemas de spins, aplicados às redes com estrutura triangular, bem como os resultados alcançados aplicando-se a técnica do operador diferencial a modelos de Ising e Heisenberg com campo magnético externo aplicado sobre o eixo fácil de magnetização z, seus diagramas de fases e comportamento de platôs observados e analisados segundo a conjectura de Haldane e a condição de aparecimento de platôs apresentada por Oshikawa, Yamanaka e Affleck, e ainda, o estudo do comportamento da susceptibilidade magnética com o objetivo de verificar o comportamento dos sistemas frustrados utilizando-se o fator de frustração f= &#952;WC/TN para verificar a frustração nas diversas fases encontradas ao longo do estudo dos modelos.

Extant research on terrorism has predominantly examined conditions associated with transnational terror. Considerably less is known about home-grown or domestic terrorism despite its accounting for much of the non-state violence seen in the international system. While some have examined the relationship between education and political violence, less has been done to investigate qualitatively the relationship between education and domestic terrorism, particularly under the condition of corruption. Comparing the cases of Morocco, Libya, Jordan and Egypt between 1970-2010, I find that increases in education bear little connection with levels of domestic terror. However, empirics suggest that increases in education may play a role in individual abilities to recognise and react against, sometimes violently, perceived state corruption. Findings suggest a need for further disaggregated data on the perpetrators of terrorist violence to better understand the complex relationship between education and domestic terror.

Esta tese tem como tema o inadimplemento antecipado do contrato no direito civil brasileiro. O ponto de partida para o estudo consiste na análise de jurisprudência que originariamente utilizou a figura, desprovida de consagração legal expressa. Posteriormente, é examinada a doutrina. Diante deste material, propõe-se um modelo teórico para o entendimento do inadimplemento antecipado do contrato, ajustando-o às categorias básicas do direito das obrigações brasileiro. São apresentados seus pressupostos, elementos constitutivos e efeitos. No decorrer do trabalho, são abordados aspectos do compromisso de compra e venda, a relação obrigacional complexa, deveres acessórios e laterais, fim contratual, inadimplemento, culpa e imputabilidade, impossibilidade, perda da função social, exceção de contrato não cumprido, resolução, indenização e demanda de cumprimento. / This work has as its theme the anticipatory breach of contract in the Brazilian civil law. The starting point for the study is the analysis of cases that originally used the figure, devoid of explicit legal recognition. Subsequently, the doctrine is examined. Faced with this material, we propose a theoretical model for understanding the anticipatory breach of contract, adjusting it to the basic categories of Brazilian law of obligations. Their assumptions, constitutive elements and effects are presented. Throughout his work, aspects of purchase and sale, the complex obligatory relationship, accessories and side duties, contractual order, breach of contract, non-performance, responsability, frustration, loss of social function, termination, rescission, and action for damages.

Submitted by Renata Lopes (renatasil82@gmail.com) on 2017-06-28T14:29:11Z No. of bitstreams: 1 damiaodesousavieirajunior.pdf: 10265456 bytes, checksum: 8b1ceaeb4c4be0e91a46c2d30add7349 (MD5) / Approved for entry into archive by Adriana Oliveira (adriana.oliveira@ufjf.edu.br) on 2017-08-07T21:17:55Z (GMT) No. of bitstreams: 1 damiaodesousavieirajunior.pdf: 10265456 bytes, checksum: 8b1ceaeb4c4be0e91a46c2d30add7349 (MD5) / Made available in DSpace on 2017-08-07T21:17:55Z (GMT). No. of bitstreams: 1 damiaodesousavieirajunior.pdf: 10265456 bytes, checksum: 8b1ceaeb4c4be0e91a46c2d30add7349 (MD5) Previous issue date: 2016-02-03 / CAPES - Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / O contínuo desenvolvimento das técnicas de fabricação de estruturas em escala nanométrica, com considerável precisão e reprodutibilidade, tem permitido e estimulado a investigação científica em torno das propriedades básicas e novas aplicações tecnológicas desses sistemas. Especialmente a partir dos anos 90, é crescente o interesse da comunidade científica no comportamento de sistemas magnéticos nano-estruturados. Nestes, a quebra da simetria espacial devido às pequenas dimensões faz com que exibam comportamentos completamente distintos dos observados em amostras macroscópicas. A anisotropia de forma resultante das interações clássicas entre os dipolos magnéticos permite a formação de estruturas magnéticas exóticas em nanomagnetos como vórtices, skyrmions, paredes de domínio individuais e, até mesmo, excitações topológicas similares a monopolos magnéticos. A compreensão e controle do comportamento magnético estático e dinâmico dessas estruturas é fundamental para o desenvolvimento de novos dispositivos tecnológicos baseados em spintrônica. Neste trabalho foram estudadas nanopartículas planares, alongadas na forma elíptica, de material ferromagnético macio, especificamente o Permalloy-79. Tais nanopartículas tem atraído atenção devido ao seu potencial de aplicação prática no desenvolvimento de novos sensores, dispositivos de lógica, mídias de armazenamento de dados de alta densidade e dispositivos MRAM (Magnetic Random Access Memory). Pelo viés do interesse científico básico, tais nano-ilhas ferromagnéticas são a unidade fundamental em arranjos magnéticos bidimensionais geometricamente frustrados, como sistemas de gelo de spin artificiais. Nestes sistemas o arranjo geométrico das ilhas quebra a degenerescência do estado fundamental da rede, caracterizando um estado de frustração geométrica que permite excitações de comportamento análogo ao de monopólos magnéticos. Sob tais aspectos, é essencial caracterizar as configurações magnéticas no estado fundamental e os processos de reversão da magnetização em nanopartículas individuais. A forma elíptica planar gera uma forte anisotropia magnética, definindo duas configurações fundamentais para a magnetização do estado fundamental das nanopartículas: o estado de vórtice ou o estado alinhado ao longo do maior eixo — estado tipo C. A partir de uma razão de aspecto limite, a magnetização do estado fundamental é confinada no plano e ao longo do eixo maior de cada nano ilha, definindo um nanomagneto monodomínio com dois estados degenerados de magnetização, útil às aplicações previamente descritas. Partindo desse intuito estudamos inicialmente, através de simulação por dinâmica de spin, a competição entre os estados de vórtice e os estados alinhados tipo C como uma função da forma de cada nano-ilha elíptica, construindo um diagrama de fases de estados vórtice - tipo C. Cada nanopartícula magnética é modelada por momentos magnéticos que interagem via interação de troca entre primeiros vizinhos e por interação dipolar clássica de longo alcance. Nossos resultados mostram que é possível fabricar nano-ilhas alongadas com estado fundamental alinhado tipo C em razões de aspecto menores que dois. Este é um resultado interessante do ponto de vista tecnológico, pois permite usar ilhas menores que as atuais em pesquisas com gelos de spin e MRAM. Geralmente, os arranjos experimentais são feitos com nanopartículas de razão de aspecto próximas a três para garantir o estado fundamental alinhado da magnetização. Acrescentando ao modelo um termo de interação Zeeman com um campo magnético externo, estudamos o comportamento da reversão da magnetização nas nanopartículas. Consideramos espessuras diferentes e duas razões de aspecto distintas: uma do tamanho experimental usual e outra menor proposta a partir de nossos resultados. Aplicando campo magnético senoidal em diferentes frequências e em direções distintas no plano das nanoilhas, observou-se a dependência dos processos de reversão em função da espessura das partículas e com a direção e frequência do campo aplicado. Os resultados permitem traçar linhas gerais acerca do comportamento da reversão da magnetização nas nanopartículas individuais sob campo magnético externo. Evidentemente para o desenvolvimento das possíveis aplicações tecnológicas, inclusive o controle de excitações como monopólos magnéticos em gelos de spin, é crucial entender os processos ultra rápidos de reversão da magnetização, o que envolve a aplicação de campo externo de alta frequência em direções cuidadosamente definidas. Com esse objetivo, também estudamos a reversão da magnetização nas nano-ilhas por pulsos curtos de campo magnético (da ordem de nanosegundos) aplicados em diferentes direções. Observamos uma forte dependência da coerência da reversão da magnetização com a direção do campo aplicado e uma significante diferença na dependência angular da coercividade em relação ao observado em trabalhos prévios para campos aplicados na condição quase-estática. Finalmente, baseado em nossos resultados, propomos um método para o controle da reversão coerente da magnetização de nanopartículas individuais em matrizes quadradas de gelos de spin artificiais. Acreditamos que nossos resultados poderão ser úteis no desenvolvimento ulterior de arranjos magnéticos artificiais geometricamente frustrados e no controle das excitações topológicas destes sistemas. / The continuous development of structures fabrication techniques at the nanometer scale with considerable precision and reproducibility has allowed and encouraged scientific research around the basic properties and new technological applications of these systems. Especially from the 90's, there is growing interest of the scientific community in the behavior of nanostructured magnetic systems. In these, the breaking of spatial symmetry due to small dimensionality causes quite different behaviors from those observed in the bulk. The resulting shape anisotropy of the classical interaction between magnetic dipoles allows the formation of exotic magnetic structures in nanomagnets as vortices, skyrmions, single domain walls and even topological excitations similar to magnetic monopoles. The understanding and control of static and dynamic magnetic behavior of these structures is essential for the development of new technological devices based on spintronics. In this work we studied planar elongated nanoparticles in the elliptical shape of soft ferromagnetic material, specifically the Permalloy-79. Such nanoparticles have attracted attention because of their potential to practical application in the development of new sensors, logic devices, high density data storage media and MRAM (Magnetic Random Access Memory) devices. By the bias of basic scientific interest, such ferromagnetic nano-islands are the fundamental unit in two-dimensional magnetic arrangements geometrically frustrated as artificial spin ice systems. In these systems, the geometric arrangement of islands break the degeneracy of the network ground state featuring a state of geometrical frustration that allows excitations with analogous behavior of magnetic monopoles. Under these aspects, it is essential to characterize the magnetic configurations in the ground state and the magnetization reversal processes in individual nanoparticles. The elliptical planar shape generates a strong magnetic anisotropy which defines two basic configurations for the magnetization of the ground state of the nanoparticles: the vortex state or the aligned state along the major axis - type C state. As from an aspect ratio limit value, the magnetization of the ground state is confined in the plane and along the major axis of each nano-island defining mono-domain nanomagnet with two degenerate states of magnetization, useful for the applications previously described. Starting from this purpose we study initially, through simulation by spin dynamics, the competition between the vortex states and aligned type C states as a function of the shape of each elliptical nano-island to build a states diagram. Each magnetic nanoparticle is modeled by magnetic moments that interact by exchange interaction between nearest neighbors and by the classical long-range dipolar interaction. Our theoretical results indicate the possibility to manufacture elongated nano-islands with ground state like aligned C state for aspect ratios less than two. This is an interesting result from the technological point of view because it will be possible to use smaller islands in researches on spin ice and MRAM. Generally, the experimental arrangements are made with nanoparticles of aspect ratio close to three to ensure aligned magnetization in the ground state. Adding to the model a Zeeman interaction term between the magnetic moments and an external magnetic field we study the behavior of the magnetization reversal in nanoparticles. We consider different thickness and two different aspect ratios: one in the usual experimental size and a smaller proposed from our results. Applying sinusoidal magnetic field at different frequencies along the anisotropy axis in directions of ten and forty-five degrees from this, we observed the dependence of the reversal processes on the thickness of the particles and with the direction and frequency of the applied field. The results allow to establish general guidelines about the magnetization reversal behavior of the individual nanoparticles under external magnetic field. Evidently, for the development of possible technological applications, including the control of excitation like magnetic monopoles in spin ice, it is crucial to understand the ultrafast magnetization reversal processes which involves the application of high frequency magnetic fields in carefully defined directions. With this aim, we also studied the magnetization reversal of the nano-islands by short pulses of magnetic field (of the nanosecond order) applied in different directions. We observed a strong dependence on the coherence of the magnetization reversal with the direction of the applied field and a significant difference in the angular dependence of the coercivity compared to those seen in previous studies with applied magnetic fields in quasistatic conditions. Finally, based on our results we propose a method for the control of the coherent magnetization reversal of individual nanoparticles in square artificial spin ice arrays. We believe that our results may be useful in further developments of geometrically frustrated magnetic artificial arrangements and in the control of the topological excitations of these systems.