Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Neste trabalho foram estudadas as propriedades estruturais e termomagnéticas dos pseudobinários Ho1-yGdyAl2, através de abordagens experimentais e teóricas. A parte experimental envolveu a preparação de cinco amostras, com as concentrações y = 0, 0,25, 0,5, 0,75 e 1, assim como medidas de magnetização, calor especifico e da variação adiabática da temperatura. Na parte teórica usamos um hamiltoniano modelo que leva em consideração a interação dos íons com o campo magnético aplicado, com o campo elétrico cristalino e a troca entre os íons magnéticos. A entropia da rede foi considerada na aproximação de Debye e a entropia eletrônica na aproximação do gás de elétrons livres. A influência das reorientações de spin, espontâneas e induzidas pelo campo magnético, na magnetização e no calor especifico foram investigadas sistematicamente tanto a partir de dados experimentais quanto teoricamente. Também obtemos resultados teóricos para a variação de entropia e variação adiabática da temperatura alterando a intensidade ou a direção do campo magnético. / In this work the structural and thermomagnetic properties of the pseudobinaries Ho1-yGdyAl2 have been studied by experimental and theoretical approaches. The experimental part included the preparation of five samples, with concentrations y = 0, 0,25, 0,5, 0,75 and 1, as well as magnetization, specific heat and adiabatic temperature change measurements. In the theoretical part we used a model Hamiltonian which includes the interaction of the ions with the applied magnetic field, the crystalline electrical field and exchange interactions with others magnetic ions. The lattice entropy has been considered within Debyes approach and the electronic entropy as that of a free electron gas. The spin reorientation influence, spontaneous and magnetic field induced ones, in magnetization and specific heat has been systematically investigated either from experimental data as well as theoretically. We have also obtained theoretical results for the isothermal entropy change and the adiabatic temperature change by modifying either the magnetic field strength or its direction.

Le comportement mécanique de matériaux granulaires est intrinsèquement lié aux propriétés individuelles des grains constitutifs ainsi qu’à leur assemblage (texture, distribution des vides, contact entre grains…). Soumis à un chargement extérieur, cet assemblage se déforme incluant le déplacement relatif entre les particules mais également la déformation propre des grains jusqu’à leur rupture si elle se produit. Pour étudier la rupture d'une seule particule, des études expérimentales et numériques ont été réalisées. Quatre particules sphériques formées de billes d’argile expansée légère ont été testées en compression à déplacement contrôlé jusqu’à la rupture (essai brésilien). Des photos ont été prises avec une fréquence d’acquisition de 4 images par seconde pour suivre la déformation des grains durant l’essai. La structure interne d'une particule a une influence significative sur l'initiation de la fissure. Pour approfondir cet effet, une micro-tomographie par rayons X a été utilisé pour scanner une particule afin d'obtenir la structure géométrique réelle en 3D. Ensuite, un modèle numérique 3D basé sur la géométrie des particules incluant la porosité interne a été construit avec Abaqus pour les mêmes conditions de chargement. Une comparaison des résultats des tests de laboratoire et des simulations a été faite. Sur la base des résultats, l’initiation des fissures, leur localisation dans le grain et la classification des ruptures de particules ont été établies. Afin d’étudier le rôle de l’anisotropie et en particulier de la fabrique d’un matériau granulaire soumis à un chargement externe, cinq essais de compression biaxiaux ont été réalisé sur un assemblage de grains quasi-sphériques placés dans une chambre confinée. Des photos ont été prises pendant les tests et ont été enregistrées selon une fréquence définie. Un programme écrit sous Matlab a été utilisé pour traiter les photos, obtenir le champ de déplacement et analyser les résultats. Un intérêt particulier a concerné l’orientation des contacts, le tenseur de fabrique et son évolution durant le chargement. L'impact de certains facteurs clés tels que la densité de compactage, la pression de confinement, la taille des plateaux de chargement, la taille des particules et l’épaisseur des échantillons sur la déformation des échantillons ont été étudiés. Une attention particulière s’est portée sur les grains subissant une rupture. Nous avons déterminé le nombre de contact sur ces grains et les avons reproduits, dans le modèle numérique (grain 3D) soumis à un chargement diamétral, par le biais de contraintes cinématiques / The mechanical behaviour of granular materials is deeply related to both the individual particle properties and to the assembly of grains (fabric, void distribution …). Subjected to an external loading, the assembly deforms which is not only dependent on relative grain displacements but also on the grain deformation and to grain breakage when occurring. Experimental and numerical studies of single particles were performed. Four approximately spherical particles of light expanded clay were tested to investigate the breakage phenomenon under diametric displacement-controlled compression load. Photos were taken with a frame rate of 4 images per second during the testing. Since the interior of a heterogeneous particle has significant influence on the failure initiation, an X-Ray micro tomography system was used to scan particles. Moreover, the post-processing enables us to obtain the real 3D volumetric structure. Then a 3D numerical model including pore structure was built in Abaqus for the same loading conditions. A comparison of results from laboratory tests and simulations was made. Based on the results, the crack initiation process, its location and classification of particle failures were set. For purpose of understanding the anisotropy and in particular fabric of packing of granular material when disturbed under external loading, five biaxial compression tests were performed on an assembly of approximately spherical particles settled in a chamber under confining pressure. During the test, photos were taken by the camera and saved to a computer at periodic intervals. Software written with Matlab codes was used to process the photos, determine the displacement field and analyse the results. Focus on contact orientation, fabric tensor and its evolution during testing were put on. Impact of some key factors such as packing density, confining pressure, sizes of the covers, sizes of the particles and thickness of samples on the packing characteristic were analysed. In order to understand mechanical behaviour and kinematic of multiple particles under external load considering particle breakage, six biaxial compression tests were performed on an assembly of approximately spherical particles. Photos were taken to record the location of each particle during the tests. Software written with of Matlab codes was used to process the photos and trace the displacement of all particles in order to analyze kinematical behaviour of the particles. A particular attention was payed to given particles subjected grain breakage within the assembly. Their contacts and relative displacements were introduced in the numerical model of single grain breakage and conclusions were derived

Made available in DSpace on 2014-06-11T19:32:21Z (GMT). No. of bitstreams: 0 Previous issue date: 2006-05-19Bitstream added on 2014-06-13T19:21:56Z : No. of bitstreams: 1 cabanasnavarro_f_dr_rcla.pdf: 4430700 bytes, checksum: a93015794da4e288862dea20ef0e01d3 (MD5) / Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) / Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) / Considerando um conjunto de 21 tipos de rochas utilizadas como revestimento e subdivididas em quatro conjuntos por afinidade da composição mineral (rochas carbonáticas, quartzosas, feldspáticas e quartzo-feldspáticas) foram realizados ensaios tecnológicos para a determinação do coeficiente de dilatação térmica linear e da resistência à compressão uniaxial, bem como a anisotropia dessas propriedades. Os dados tecnológicos obtidos foram correlacionados com informações petrográficas qualitativas e quantitativas referentes à composição mineral, variações texturais e estruturais determinadas em seções ortogonais entre si a partir de um sistema de referência (xyz) baseado na foliação e lineação macroscopicamente visíveis. A análise integrada dos dados utilizando estatística convencional e multivariada procurou apontar as variáveis petrográficas mais relevantes para as duas propriedades tecnológicas enfocadas e suas respectivas anisotropias. A dilatação térmica e sua anisotropia são influenciadas principalmente pela composição mineral e pela orientação preferencial dos minerais embora as microfissuras desempenhem papel importante em alguns casos. A tensão de compressão mostra sua variabilidade e anisotropia influenciadas pela granulação média, tipos de contatos minerais predominantes e padrões de microfissuras mais ou menos definidos por influência da foliação presente. Constatou-se que no conjunto analisado a presença da foliação não implica necessariamente em anisotropia das duas propriedades estudadas. / The anisotropy of thermal expansion coefficient and compressive tensile strength were determined for 21 commercially used stones gathered in four set according the main mineral composition named carbonatic, quartz-rich, feldspar-rich and quartz-feldspar-rich rocks. Using a coordinate reference system (xyz) based on the macroscopic visible foliation and lineation the samples were submitted to normalized laboratorial analyses for determination of the both technological properties and the petrographical features such as mineral composition, texture and fabric. Additionally was carried out measurements of weathered area and microcrack quantification by image analysis and texture quantification by U-stage methods. In order to understand the relationship between the anisotropy measured and petrographical data it was applied traditional and multivariate statistical analysis. The results pointed to the great significance of mineral composition and the crystallographic preferred orientation for thermal expansion and respective anisotropy, especially to monomineralic and/or foliated rocks, in spite of some cases microcracks play this role. The compressive strength is mainly controlled by a complex interaction between grain size distribution, grain boundary and microcrack patterns related or not to foliation.

Made available in DSpace on 2016-06-02T20:16:43Z (GMT). No. of bitstreams: 1 1968.pdf: 1149213 bytes, checksum: 8acdd67fec9e555998a18561b9fbf007 (MD5) Previous issue date: 2008-07-23 / Financiadora de Estudos e Projetos / A study about surface melting on silver using equilibrium molecular dynamics simulation is the proposal of this work. We applied the Embedded Atom Method as the many-body interaction potential to describe Ag properties. Simulations were done in the microcanonical ensemble, for the study of bulk properties, and in the canonical ensemble, for simulations of the solid with surfaces. As a preliminary result, we obtained the equilibrium melting point Tm equal 1264(12)K from solid-liquid coexistence configurations. Surfaces were simulated using repeated slabs separated by vacuum in the z direction, while keeping periodic boundary conditions in the remaining directions. Results showed that Ag[110] is the lone orientation that has surface melting. Ag[111] maintains its crystalline structure even after reaching Tm, while it could be overheated by 100K. Other properties like density of states, thermal expansion and surface relaxation were in good agreement with experimental data. / Um estudo sobre a fusão de superfícies da prata (Ag) utilizando dinâmica molecular de equilíbrio é a proposta deste trabalho. Aplicamos o método Embedded Atom como potencial de interação de muitos corpos para descrever as propriedades da prata. As simulações foram feitas nos ensembles microcanônico, para o estudo de propriedades de bulk, e canônico, para as simulações do sólido com superfícies. Como resultado de estudo preliminar, obtivemos a temperatura de fusão de equilíbrio Tm igual a 1264(12)K a partir das configurações do sistema com as fases sólida e líquida em coexistência. As superfícies foram simuladas incluindo uma separação com vácuo acima e abaixo do cristal na direção z e utilizando condições periódicas de contorno nas outras direções cartesianas. Os resultados mostraram que a superfície [110] é a única que possui fusão de superfície. A superfície [111] mantém sua estrutura cristalina até mesmo após atingir Tm, podendo esse sistema ser superaquecido em 100K. Outras propriedades como densidade de estados, dilatação térmica e relaxação de superfície tiveram boa concordância com os dados obtidos experimentalmente.

Made available in DSpace on 2014-06-11T19:33:38Z (GMT). No. of bitstreams: 0 Previous issue date: 2011-02-01Bitstream added on 2014-06-13T20:45:35Z : No. of bitstreams: 1 panosso_ar_dr_jabo.pdf: 805581 bytes, checksum: ae9e7cfe85602f581a11930028a83d72 (MD5) / Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) / Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) / Neste trabalho, foram avaliados aspectos diversos da emissão de CO2 (FCO2) em um Latossolo Vermelho em áreas de cana-de-açúcar sobre os sistemas de manejo de cana queimada (CQ) e cana crua (CC), no nordeste do Estado de São Paulo. No experimento 1 (ano de 2007), a média da FCO2 foi 39% superior na área de CQ (2,87 μmol m-2 s-1) quando compara à CC (2,06 μmol m-2 s-1) ao longo de um período de 70 dias de avaliação. Os modelos ajustados aos semivariogramas experimentais de FCO2 foram, na sua maioria, exponenciais em ambas as áreas. Os mapas de emissão foram homogêneos após um período de seca. O teor de matéria orgânica do solo e o estoque de carbono do solo (0-0,25 m) foram 13 e 20%, respectivamente, superiores em CQ quando comparados à CC. O grau de humificação da matéria orgânica do solo e a sua interação com a densidade do solo foi um importante fator, não somente na diferenciação da emissão de CO2 entre os diferentes sistemas de manejo. No experimento 2 (ano de 2008), foi conduzida a caracterização anisotrópica das variáveis estudadas por meio da dimensão fractal (DF), para diferentes direções (0o, 45o, 90o e 135o) em relação às linhas de plantio (0o). A propriedade porosidade livre de água (PLA) foi um dos principais fatores relacionados à variabilidade espacial de FCO2, independentemente das direções. Os valores de DF foram significativamente inferiores no sentido de plantio da cultura da cana-de-açúcar, indicando, além de anisotropia dessa propriedade, maior homogeneidade de FCO2 na direção de 0o. A PLA mostrou ser uma importante propriedade na compreensão da variabilidade espaçotemporal de FCO2, especialmente nas áreas de cana queimada / In this work was studied various aspects of soil CO2 emission (FCO2) of a bare Dark Red Latosol in sugarcane areas submitted to burned (B) and green (G) management systems in northeastern of São Paulo State. In the experiment 1 (year 2007), mean FCO2 emission was 39% higher in the B plot (2.87 μmol m-2 s-1) when compared to the G plot (2.06 μmol m-2 s-1) throughout the 70-day period after harvest. FCO2 Semivariogram models were mostly exponential in both areas. The emission maps are clearly more homogeneous after a drought period in both sites. Organic matter content and carbon stock (0-25 cm) were 13% and 20% higher in B, respectively, when compared to G. Regression analysis indicates that the humification index of soil organic matter, and its interaction with soil bulk density, is an important factor not just to differentiate emissions in each plot. In the experiment 2 (2008) the anisotropic characterization of the studied variables, was performed by deriving the fractal dimension (DF) calculated for different directions (0o, 45o, 90o and 135o) in relation to the crop line (0o). The air-filled pore space (AFPS) was the main factor affecting the spatial variability of FCO2 in all directions. The FCO2 DF values were significantly lower in the direction of planting of sugarcane crop, indicating anisotropy of this property and greater homogeneity in this direction. The AFPS was an important property in understanding the spatiotemporal variability of FCO2, especially in the areas submitted to burn

Pour ce travail de thèse, nous nous sommes intéressés dans une première partie à la conception et à la synthèse de nouveaux matériaux multifonctionnels (LC, photosensible, systèmes moléculaires dendritiques) capables d'être élaborés en films minces anisotropes et doués de propriétés photo-induites. Nous avons réalisé l'étude complète des propriétés mésomorphes de ces nouveaux matériaux et de dérivés structuraux (en fonction de la connectivité dendritique intrinsèque) par la diffraction des rayons X aux petits angles; l’étude de leurs propriétés optiques a également été effectuée. Dans une seconde partie, nous avons fonctionnalisé des nanoparticules d'or avec des ligands dendritiques mésogènes afin d'organiser ces particules dans des structures mésomorphes. Les objectifs principaux de cette partie sont tout d’abord la synthèse d'une "bibliothèque" de nanoparticules mésomorphes dendronisées, et ensuite la caractérisation de réseaux simples formée par l’auto-assemblage des particules précédentes. / The need to expand further the range of mesomorphic organization, develop original materials where different functionalities can be added (i.e. multifunctional), and to design “multitask materials” with tunable properties are particularly interesting and crucial challenges for potential uses in future technologies. On the one hand, we focused on the design and synthesis of multifunctional materials (liquid crystalline, dendritic, photoresponisve) which are suitable for making thin films where photoinduced optical anisotropy and surface relief gratings can be generated. The mesomorphic behaviour of these dendrimers was investigated and also their optical properties. On the other hand, we grafted structurally related protodendritic mesogenic ligands to monodisperse gold nanoparticles to elaborate liquid crystalline hybrids in order to self-organize NPs in periodic arrays. A set of dendronized gold nanohybrids was synthesized to carry out this study.

L'Agence nationale pour la gestion des déchets radioactifs (Andra) a commencé en 2000 la construction du Laboratoire Souterrain de Meuse / Haute-Marne (LS-M/HM) avec l'objectif principal de démontrer la faisabilité d’un stockage géologique dans l’argilite du Callovo-Oxfordien. Un réseau de galeries expérimentales a été excavé, principalement en suivant les directions des contraintes horizontales (majeure et mineure), avec des variations sur : la méthode d'excavation, la géométrie de la structure et le soutènement. Chaque galerie a été instrumentée en différentes sections pour suivre le comportement hydromécanique de la roche face à l’excavation. Le suivi de la zone autour des galeries excavées au niveau principal (-490 m) a révélé le développement d'une zone fracturée (fractures en extension et en cisaillement) induite par l'excavation. La distribution de la zone fracturée dépend à la fois de l'orientation de la galerie et du champ de contraintes in-situ et a une influence importante sur la déformation des galeries. En effet, les mesures de convergence ont montré une fermeture anisotrope de la section de la galerie. De plus, il a été observé un champ de distribution anisotrope de la pression de pores ainsi que des surpressions autour des galeries.Afin d’analyser la réponse anisotrope du massif pendant l’excavation et après celle-ci, les travaux effectués dans le cadre de la thèse sont axés principalement sur une étude directe des mesures de convergence in-situ. Cette analyse s’effectue à l’aide de la loi semi-empirique proposée par Sulem et al. (1987) [Int J Rock Mech Min Sci Geomech Abstr 24: 145–154]. A cet égard, différentes galeries excavées dans le LS-M/HM ont été étudiées. Ces galeries présentent certaines différences dans leurs orientations et l’état initial des contraintes, dans la méthode et la vitesse d’excavation ainsi que dans les diamètres de la section et les types de soutènements installées. Cette analyse permet d’obtenir des prédictions fiables de la convergence à long-terme, ce qui peut servir pour le dimensionnement et la prévision de la performance du soutènement à long-terme.En outre, nous avons étudié la réponse anisotrope du champ de pression interstitielle observée in-situ. Cette analyse est basée sur une approche poroélastique anisotrope. L’objectif principal est de reproduire qualitativement l’évolution de la pression des pores autour des galeries avec une approche simple qui prend en compte l’anisotropie intrinsèque du matériau. Enfin, une analyse de l’apparition de la rupture montre le rôle clé que joue le couplage hydromécanique dans l’extension de la zone fracturée / The French National Radioactive Waste Management Agency (Andra) began in 2000 the construction of an Underground Research Laboratory (URL) with the main goal of demonstrating the feasibility of a geological repository in Callovo-Oxfordian claystone. Several research programs have taken place to improve the knowledge of the rock properties and its response to the excavation progress. A network of experimental drifts has been constructed with variations on: excavation method, structure geometry, supports system and orientations with respect to principal stresses’ directions. In each drift different sections have been instrumented to monitor the hydro-mechanical behavior of the rock mass formation. Continuous monitoring of the excavated zone around the drifts in the main level (-490 m) revealed the development of a fractured zone (extensional and shear fractures) induced by the excavation. The extent of this fractured zone depends on the drift orientation regarding the in-situ stress field. Accordingly, the convergence measurements showed an anisotropic closure which depends also on the drifts’ orientations. Moreover, marked overpressures and an anisotropic pore pressure field around the drifts have been also observed.The approach proposed in this work is mainly based on a direct analysis of the convergence measurements, for studying the anisotropic response of the rock formation during and after excavation. The convergence evolution is analyzed on the basis of the semi-empirical law proposed by Sulem et al. (1987) [Int J Rock Mech Min Sci Geomech Abstr 24: 145–154]. The monitoring and analysis of convergence data can provide a reliable approach of the interaction between rock mass and support. Therefore, the anisotropy and the variability of the closure are analyzed taking into account different field cases: drifts excavated in two different orientations (i.e. influence of the initial stress state), different methods, sizes and rates of excavation and different supports systems with different conditions of installation. This broad range of cases permits to refine the analysis for reliable predictions of the convergence evolution in the long term. This approach can thus be used for the design of various types of support and the evaluation of its performance in the long term.On the other hand, the pore pressure evolution induced by excavation of drifts as recorded in situ has been analyzed. The anisotropic response observed in-situ suggests that the intrinsic anisotropy of the material plays a key role in the response of the rock formation. To understand these phenomena, an anisotropic poroelastic analysis of the pore pressure evolution induced by the drift excavation is performed. The main goal is to simulate the main trends of the pore pressure evolution with a simple model taking into account the inherent anisotropy of the material. Finally, an analysis of the onset of failure shows the key role of the hydro-mechanical coupling on the extension of the failed zone around the drifts

Phénomènes de spintronique dans les jonctions tunnel magnétiques et des films minces sont très prometteurs des deux points fondamentaux et l'application de vue. Elles sont basées sur l'exploration de spin d'électron en plus de sa charge et comprennent intercalaire couplage d'échange (CEI), l'anisotropie magnétique perpendiculaire (PMA), géante (GMR) et magnétorésistance tunnel (TMR), Couple de transfert de spin (STT), Spin effet Hall (SHE) et même induire du magnétisme dans les éléments non compris d graphène. Cette thèse comprendra premiers principes des études de phénomènes spintronique qui ont été d'un grand intérêt récemment. La première partie est consacrée à intercalaire couplage d'échange à travers les matériaux isolants dont le MgO, SrTiO3, GaAs et ZnSe. La deuxième partie comprendra des études ab initio d'anisotropie magnétique perpendiculaire au Fe | interfaces MgO et MTJ y compris le mécanisme et sa corrélation avec le spin Bloch symétrie Etat fondé de filtrage. Dans les enquêtes troisième partie de l'anisotropie magnétique et la fonction de travail dans les Co | interfaces graphène seront présentés. Ensuite, il sera montré possibilité d'induire et d'optimiser le magnétisme intrinsèque dans nanomeshes graphène. Dernière partie sera consacrée à l'induction de polarisation de spin et le réglage de Dirac point et ordre magnétique dans le graphène à l'aide d'effets de proximité magnétiques substrat. / Spintronic phenomena in magnetic tunnel junctions and thin films are very promising from both fundamental and application points of view. They are based on exploring spin of electron in addition to its charge and include interlayer exchange coupling (IEC), perpendicular magnetic anisotropy (PMA), giant (GMR) and tunnel magnetoresistance (TMR), Spin Transfer Torque (STT), Spin Hall Effect (SHE) and even inducing magnetism in non d elements including graphene. This thesis will include first-principles studies of spintronic phenomena which have been of high interest recently. First part is devoted to interlayer exchange coupling across insulating materials including MgO, SrTiO3, GaAs and ZnSe. The second part will include ab initio studies of perpendicular magnetic anisotropy at Fe|MgO interfaces and MTJs including the mechanism and its correlation to the Bloch state symmetry based spin filtering. In third part investigations of magnetic anisotropy and work function in Co|graphene interfaces will be presented. Next, it will be shown possibility of inducing and optimizing intrinsic magnetism in graphene nanomeshes. Final part will be devoted to inducing spin polarization and tuning Dirac point and magnetic order in graphene by means of magnetic substrate proximity effects.

Dans cette thèse nous avons évalué l'effet de la substitution partielle du cobalt par des éléments non-magnétiques de type p (M) sur les propriétés structurales et magnétiques des composés RCo5. Les échantillons ont été synthétisées par fusion dans un four à induction, puis caractérisés en utilisant des nombreuses techniques expérimentales: diffraction de rayons X et de neutrons, microscopie électronique à balayage, magnétométrie, susceptométrie en courant alternatif et spectroscopie photoélectronique par rayons X.Tous les composés de type RCo5-xMx (R= Pr, Sm, Tb, Er et Tm; M= Si, Ge, Al, Ga; x=0,5 et x=1) étudiés gardent la structure cristalline de type CaCu5 des composés de départ RCo5, mais les paramètres de la maille cristalline sont modifiés par la présence des éléments M. Le domaine de stabilité thermique des phases RCo5-xMx est notablement modifié par la présence d'élément métalloïde en substitution sur les sites du cobalt. Il peut être étendu pour Al et Ga et réduit pour Si et Ge. Les atomes de l'élément M sont localisés préférentiellement sur le site cristallographique Co 3g. La solubilité des éléments Ge et Si dans la structure RCo5 est trouvée être inférieure à celle des métalloïdes ayant un électron de moins tels que Al et Ga.La substitution M/Co a une influence importante sur les propriétés magnétiques des composés RCo5. La température d'ordre et l'aimantation spontanée diminuent significativement après le remplacement partiel du cobalt par l'élément métalloïde. Ces modifications sont induites par l'évolution des interactions d'échange en particulier Co-Co mais aussi par la réduction de l'aimantation du Co liée à sa sensibilité au voisinage atomique et magnétique local. La direction de facile aimantation à la température ambiante est préservée le long de l'axe cristallographique c pour tous les échantillons étudiés. Dans quelques composés RCo5-xMx (R = Sm, Er et Tm) la substitution de M au cobalt change le mécanisme de coercitivité par rapport aux composés de départ RCo5. Une coercitivité élevée a été détectée à basse température, surtout pour les composés SmCo4Al et SmCo4Ga, qui présentent aussi des champs d'anisotropie énormes, bien supérieurs à ceux de phase SmCo5.Les expériences XPS sur les composés de type RCo5-xMx ont détecté la réduction de la densité d'états électroniques au niveau de Fermi par rapport aux composés de type RCo5. La bande 3d du cobalt est remplie lors de la substitution M/Co et conduit à un moment magnétique du cobalt réduit. / In this work we have evaluated the effect of the partial substitution of cobalt with non-magnetic p-type elements (M) on the structural and magnetic properties of RCo5 compounds. The samples were prepared by alloying in an induction furnace and were characterized using various experimental techniques: X-ray and neutron diffraction, scanning electron microscopy, magnetometry, AC susceptometry and X-ray photoelectron spectroscopy.All of the studied RCo5-xMx compounds (R=Pr, Sm, Tb, Er and Tm; M=Si, Ge, Al and Ga; x=0.5 and x=1) maintain the CaCu5 crystal structure of the RCo5 compounds, however the lattice parameters are modified due to the presence of M elements. The thermal stability range of the RCo5-xMx phases is modified significantly due to the Co site substitutions. The thermal stability increases for Al and Ga substitutions and decreases when M is Si or Ge. The M atoms were found to preferentially occupy the Co 3g site. The solubility of Ge and Si in the RCo5 structure is inferior to that of metalloid elements with one less electron, such as Al and Ga. The M/Co substitution has an important influence on the magnetic properties of RCo5 compounds. The ordering temperature and the spontaneous magnetization are significantly reduced after the partial substitution of cobalt by the metalloid elements. These changes are induced in particular by the evolutions of the Co-Co exchange interactions and also by the reduction of the Co magnetization due to the sensitivity of Co to the local atomic and magnetic vicinity. The easy magnetization direction at room temperature is preserved along the c-axis for all of the studied samples. In several RCo5-xMx (R = Sm, Er and Tm) compounds the substitution of Co with M atoms changes the coercivity mechanism compared to RCo5. A higher coercivity was found at low temperatures, especially for SmCo4Al and SmCo4Ga compounds, which also show huge values of the anisotropy field, well above the ones found in SmCo5.The XPS measurements on RCo5-xMx compounds show a reduction of the density of states at the Fermi level compared to the RCo5 compounds. There is a filling of the Co 3d band following the M/Co substitution, leading to a lower Co moment.

In an attempt to improve the quality in finite element analysis of thermoformed components, a method for predicting the thickness distribution is presented. The strain induced anisotropic material behaviour in the amorphous polymers of concern is also taken into account in the method. The method comprises of obtaining raw material data from experiments, followed by a simulation of the vacuum thermoforming process where hyperelastic material behaviour is assumed. The theory of hyperelasticity that was applied was based on the Ogden model and implemented in the FE-software LS-DYNA. Material behaviour from thermoformed prototypes is examined by experiments and implemented together with the mapped results from the thermoforming simulation in a succeeding FE-model. For the latter, the three-parameter Barlat model was suggested, giving the possibility to account for anisotropic material behaviour based on an initial plastic strain.