京都大学 / 0048 / 新制・課程博士 / 博士(理学) / 甲第22114号 / 理博第4541号 / 新制||理||1652(附属図書館) / 京都大学大学院理学研究科化学専攻 / (主査)教授 寺西 利治, 教授 島川 祐一, 教授 若宮 淳志 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DGAM

Superconducting Magnetic Energy Storage (SMES) offers many advantages over conventional forms of energy storage. The higher unit costs of SMES make it economically feasible only for large-scale applications (5000 MWh or more). Early studies showed that low aspect ratio solenoids have the lowest overall costs and most of the subsequent research and conceptual design was centered around low to moderate aspect ratio solenoidal designs. Toroids, poloids and force-reduced magnets are some alternate magnet structures that can be used for SMES but have not received much attention. These structures have some advantages over solenoidal designs such as lower peak fields with greater energy storage capability (poloid), lower support structure requirement (force-reduced magnet) and zero external field (toroid). For some applications of SMES such as pulsed power for fusion reactors or particle accelerators, where the large external field of the solenoid may be unacceptable but the fast response and high efficiency of SMES are required, alternate magnet structures or geometries must be used even if the costs are somewhat higher. Therefore it is useful to study the relative costs of each magnet structure in order to choose a suitable magnet structure for a given application. Four magnet structures viz. the solenoid, toroid, poloid and a force-reduced magnet are evaluated for their energy storage capability, support structure requirements and stray field characteristics. The variation of these parameters with the geometry of the magnet as well as the size of the SMES system are also studied. The objective of this study is to provide a quantitative comparison of important magnet parameters as well as to develop a simple procedure for the preliminary magnetic design of SMES magnets of any size, based on the detailed analysis of a reference design. Due to the high costs of SMES particularly for smaller sizes, it is important to optimize magnet design as well as to look for new magnet configurations to make SMES more cost effective. Superconductor and support structure material are major components of the overall cost of SMES magnets. Various methods of optimizing these parameters are explored. Force-reduced magnets have attracted some controversy in SMES research due to various claims made for and against them. The virial theorem and its implications for force-reduced magnets are analyzed with reference to a specific force-reduced configuration and it is shown that the claims that force-reduced magnets do not offer any savings in structure are unjustified. Methods for further reducing the structure requirements in force-reduced magnets and toroidal magnets are discussed. Due to the unique and highly desirable characteristic of zero stray field of toroidal magnets, it is important to seek ways of increasing its energy storage capability. A variational problem is formulated to determine the optimal cross-sectional shape which maximizes the stored energy with a given quantity of superconductor. The optimal shape stores 16 p.c. more energy than the circular cross section toroid and is shown to be identical to the structurally superior constant tension D shape. The desired characteristics of an ideal SMES magnet are shown to be a uniform magnetic field within a closed magnet configuration. A twisted toroidal magnet combining the features of an ideal solenoid and the general toroidal configuration is studied as a candidate for the ideal magnet. Geometric arguments are used to prove that no such closed surface can be found in three dimensions with the minimum smoothness conditions required from physical considerations. / Ph. D.

Le travail effectué dans cette thèse a pour thème central la conception d’un aimant quadripolaire supraconducteur en Nb-Ti destiné à remplacer à l’horizon 2014 les aimants d’insertions actuellement utilisés dans le grand collisionneur de Hadrons (LHC) du CERN de Genève. Ce nouveau quadripôle, caractérisé par un diamètre d’ouverture encore jamais atteint (120 mm), ouvre la voie vers les quadripôles à grandes ouvertures. Tout d’abord, pour rapidement estimer l’énergie magnétique stockée dans un quadripôle de type cos2?, une formule analytique basée sur la décomposition en série de Fourier du courant et permettant d’estimer l’énergie avec une précision de 10 % est développée. Le design magnétique de la section transverse de la bobine du quadripôle est ensuite réalisé en utilisant une nouvelle méthode d’optimisation basée sur les équations analytiques du champ magnétique. Puis, pour la première fois, une estimation de la reproductibilité dans le positionnement des blocs de conducteurs dans des aimants Nb3Sn est faite. Elle a été réalisée à l’aide d’une méthode existante et grâce à la production récente de deux séries d’aimants Nb3Sn. Une comparaison avec les valeurs obtenues pour des aimants en Nb-Ti est présentée. Ensuite, une méthode analytique basée sur les statistiques et permettant d’expliquer certains phénomènes observés sur la dispersion des mesures magnétiques dans une série de quadripôles est développée. Enfin, on montre que l’incertitude sur la moyenne des harmoniques de champ est due pour la majorité des harmoniques à un phénomène statistique lié au nombre limité d’aimants dans la série et non à des erreurs systématiques / The main objective of the work presented in this thesis is the design of a quadrupole magnet based on Nb-Ti. It aims at replacing the current insertion quadrupoles used in the Large Hadron Collider (LHC) at CERN by 2014. This new quadrupole features an unprecedented large aperture (120 mm) and opens the way toward large aperture quadrupoles. First, to rapidly estimate the magnetic energy stored in a cos2?-type quadrupole, an analytical formula based on the Fourier transform of the current is developed. It allows estimating the energy with a precision of 10 %. Secondly, the magnetic design of the quadrupole coil cross-section is realized using a novel optimization method based on analytical equations of the magnetic field. Subsequently, for the first time, an estimate of the reproducibility in the coil-blocks positioning in Nb3Sn magnets is given. The estimate has been obtained by using an existing method and from tow recently built Nb3Sn magnet series. A comparison with values obtained for Nb-Ti magnets is also presented. Following this, an analytical method based on statistics is developed. It makes possible to explain some phenomenon observed on the dispersion of the magnetic measurement in a quadrupole series. Finally, we show that the uncertainty in the mean of the magnetic field errors is for most of the harmonics related to statistical errors due to the limited number of magnets in the series, and not because of systematic defects in the coil

The synthesis and characterisation of a large family of hexametallic [MnIII 6] Single-Molecule Magnets with general formula [MnIII 6O2(R-sao)6(X)2(L)4-6] (where sao2- = dianion of salicylaldoxime; R = H, Me, Et, Ph; X = O2CR' (R' = H, Me, Ph etc), Hal , O2PHPh or O2P(Ph)2; L = solvent) are presented. Deliberate structural distortions of the [Mn3O] trinuclear moieties within the complexes are used to tune the observed magnetic properties. These findings highlight a qualitative magnetostructural correlation whereby the type (anti- or ferromagentic) of each Mn2 pairwise magnetic exchange is dominated by the magnitude of each individual Mn-N-O-Mn torsion angle. To shed further light on this intriguing family of nanomagnets, a large family of the analogous “half” molecules has been synthesised and fully characterised. These trimetallic [MnIII 3] complexes can be divided into three categories with general formulae (type 1) [MnIII 3O(R-sao)3(X)(sol)3-4] (where R = H, Me, tBu; X = O2CR (R = H, Me, Ph etc); sol = py and / or H2O), (type 2) [MnIII 3O(R-sao)3(X)(sol)3-5] (where R = Me, Et, Ph, tBu; X = O2CR (R = H, Me, Ph etc); sol = MeOH, EtOH and / or H2O), and (type 3) [MnIII 3O(R-sao)3(sol)3](XO4) (where R = H, Et, Ph, Naphth; sol = py, MeOH, -pic, Et-py, tBu-py; X = Cl, Re). In the crystals the ferromagnetic triangles are involved in extensive inter-molecular H-bonding which is clearly manifested in the magnetic behaviour, producing exchange-biased SMMs. These interactions can be removed by ligand replacement to give “simpler” SMMs. The [MnIII 6] and [MnIII 3] molecular nanomagnets are then exploited as building blocks to construct supramolecular architectures by means of host-guest interactions and coordination driven self-assembly. A number of discrete and infinite architectures based on the molecular triangle [Mn3] and various pyridyl-type ligands were obtained and structurally and magnetically characterised.

The effect of pressure on a number of magnetically interesting compounds such as single-molecule magnets and dimeric copper and manganese molecules has been investigated to probe the validity of ambient magneto-structural correlations. The first chapter is an introduction to the equipment and methodologies that have been adopted to carry out the experimental high-pressure work. The second chapter reports the first combined high-pressure single crystal X-ray diffraction and high pressure magnetism study of four single-molecule magnets (SMMs). At 1.5 GPa the structures [Mn6O2(Et-sao)6(O2CPh(Me)2)2(EtOH)6] (1) – an SMM with a record effective anisotropy barrier of ~86 K – and [Mn6O2(Etsao) 6(O2C-naphth)2(EtOH)4(H2O)2] (2) both undergo significant structural distortions of their metallic skeletons which has a direct effect upon the observed magnetic response. Up to 1.5 GPa pressure the effect is to flatten the Mn-N-O-Mn torsion angles weakening the magnetic exchange between the metal centres. In both compounds one pairwise interaction switches from ferro- to antiferromagnetic, with the Jahn-Teller (JT) axes compressing (on average) and re-aligning differently with respect to the plane of the three metal centres. High pressure dc χMT plots display a gradual decrease in the low temperature peak value and slope, simulations showing a decrease in |J| with increasing pressure with a second antiferromagnetic J value required to simulate the data. The “ground states” change from S = 12 to S = 11 for 1 and to S = 10 for 2. Magnetisation data for both 1 and 2 suggest a small decrease in |D|, while out-of-phase (χM //) ac data show a large decrease in the effective energy barrier for magnetisation reversal. The third SMM is the complex [Mn3(Hcht)2(bpy)4](ClO4)3·Et2O·2MeCN (3·Et2O·2MeCN) that at 0.16 GPa loses all associated solvent in the crystal lattice, becoming 3. At higher pressures structural distortions occur changing the distances between the metal centres and the bridging oxygen atoms making |J| between the manganese ions weaker. No significant variations are observed in the JT axis of the only MnIII present in the structure. Highpressure dc χMT plots display a gradual decrease in the low temperature peak value and slope. Simulations show a decrease in J with increasing pressure although the ground state is preserved. Magnetisation data do not show any change in |D|. The fourth SMM, [(tacn)6Fe8O2(OH)12](ClO4)3.9Br4.1⋅6H2O, (4) is the largest inorganic compound ever studied at high-pressure. Up to 2.0 GPa the conformation of the complex remains largely unaffected, with the counter ions and water molecules moving around to accommodate a compression of the unit cell volume. High pressure magnetic susceptibility data collected up to 0.93 GPa confirm minimal changes in the intra-molecular exchange interactions. The third chapter focuses on three hydroxo-bridged CuII dimers: [Cu2(OH)2(H2O)2(tmen)2](ClO4)2 (5), [Cu2(OH)2(tben)2](ClO4)2 (6) and [Cu2(OH)2(bpy)2](BF4)2 (7) have been structurally determined up to 2.5, 0.9 and 4.7 GPa, respectively. 6 and 7 have never been reported before. Pressure imposes important distortions in the structures of all three complexes, particularly on the bond distances and angles between the metal centres and the bridging hydroxo groups. 5 undergoes a phase transition between 1.2 and 2.5 GPa caused by the loss of a coordinated water molecule. This leads to a loss of symmetry and dramatic changes in the molecular structure of the complex. The structural changes are manifested in different magnetic behaviours of the complexes as seen in dc susceptibility measurements up to ~0.9 GPa: J becomes less antiferromagnetic in 5 and 6 and more ferromagnetic in 7. The fourth chapter shows the compression of two oxo-bridged MnII/MnIII mixed valence dimers: [Mn2O2(bpy)4](ClO4)3⋅3CH3CN, (8) has been squeezed up to 2.0 GPa whilst [Mn2O2(bpy)4](PF6)3⋅2CH3CN⋅1H2O, (9) could be measured crystallographically up to 4.55 GPa. 9 has never been reported before, while 8 has been reported in a different crystallographic space group. The application of pressure imposes significant alterations in the structures of both complexes. In particular, in 8 the Mn-Mn separation is reduced by the contraction of some of the Mn-O bond distances, 9 shows essentially analogous behaviour: the Mn-Mn distance and nearly all the Mn-N bonds shrink significantly. The magnetic behaviour of the complexes has been measured up to 0.87 GPa for 8 and 0.84 GPa for 9, but neither display any significant differences with respect to their ambient data.

Les valvulopathies cardiaques sont des maladies cardiaques fréquentes. Certaines se traduisent par un manque de coaptation des valves, on désigne ce type de pathologie sous le terme d’insuffisance. Le traitement standard de ces valvulopathies consiste à remplacer les valves malades par des valves prothétiques. L'absence de substitut valvulaire idéal et les inconvénients inhérents au matériel prothétique et à la nécessité d’un traitement anticoagulant, incitent à favoriser, chaque fois que cela est possible, les techniques de chirurgie conservatrice des valves. Actuellement, la réparation de la valve aortique demeure un défi chirurgical. En revanche en ce qui concerne la valve mitrale une réparation est plus souvent réalisable. Cependant, la faisabilité et le résultat final, dépends du mécanisme de la fuite, de l’extension des lésions ainsi que de la technique de réparation chirurgicale utilisée. C’est pour tenter de surmonter tous ces obstacles qu’est né le projet d’étude des forces magnétiques d’aimants permanents comme traitement complémentaire à une plastie ou comme traitement exclusif, pour rétablir une coaptation valvulaire efficace. Pour concrétiser cette idée, nous avons réalisé notre recherche en trois étapes essentielles : 1- La conception d’un système magnétique d’aide à la coaptation. 2- Une étude de faisabilité portant sur la vérification du fonctionnement des aimants in vitro et in vivo. 3- La vérification de l’efficacité de la force magnétique pour atteindre la coaptation nécessaire pour corriger l’insuffisance valvulaire. Cette recherche a été réalisée en étroite collaboration entre le service de Chirurgie Thoracique et Cardio-vasculaire du groupe hospitalier Pitié-Salpêtrière à Paris et le groupe de recherche électrodynamique - GREM3 - du Laboratoire LAPLACE à Toulouse. Les aimants ont été fabriqués en tenant compte des facteurs suivants : la biocompatibilité, la conservation de l'aimantation en milieu sanguin, la flexibilité mécanique des éléments implantés, et la nécessité de stérilisation. L'une des préoccupations principales était d’obtenir une force magnétique adaptée pour fermer la valve et permettre son ouverture en fonction du cycle cardiaque. Dans un deuxième temps, sur la base des concepts précédemment décrits, et après réalisation des tests in vitro, une étude expérimentale a été réalisée in vivo en vue de démontrer la faisabilité du projet. Cette phase d’expérimentation animale a consisté en l’implantation d’aimants permanents sur la valve aortique chez sept moutons gardés en vie pendant 3 mois. Les résultats ont été satisfaisants : aucun prolapsus iatrogène, parfaite bio-tolérance des aimants implantés sans nécessité de traitement anticoagulant, absence de réaction inflammatoire visible à l’autopsie après sacrifice des moutons au troisième mois postopératoire. En dernier lieu, afin d’étudier la valeur de la force magnétique nécessaire pour atteindre la coaptation souhaitée dans l’insuffisance valvulaire, trois modèles d’aimants ont été implantés chez quatre moutons. Malheureusement les résultats n’ont pas été entièrement satisfaisants. Actuellement, forts des enseignements tirés de ces expériences, nous tentons d’améliorer le problème de fabrication des aimants ; de nouveaux aimants sont en cours de réalisation. A notre connaissance, l’utilisation de la force magnétique pour corriger l'insuffisance valvulaire n'a jamais été rapportée dans la littérature. Même si la phase d’expérimentation des aimants destinés à traiter ces insuffisances valvulaires n’est pas arrivée à son terme, nous avons montré la faisabilité du concept sur valve saine. Ce champ d'investigation doit continuer à être exploré compte tenu des avantages qu’ont ces aimants. D’une part, ils sont techniquement faciles à poser et pourraient donc permettre de réaliser une réparation rapide et reproductible des valves. D’autre part, en raison de cette simplicité, on pourrait envisager une implantation par voie percutanée exclusive, ouvrant alors une voie nouvelle, en matière de chirurgie conservatrice des insuffisances valvulaires cardiaques (aortique et mitrale). / Valvular heart diseases are important cardiac pathology and valvular heart insufficiency is one of them. The standard treatment is valve replacement with prosthetic valve. Lacks of ideal prosthetic valve and the drawbacks inherent in prosthetic material and anticoagulant therapy, encourage us to develop techniques of conservative surgery of the valve. Today, repair of the aortic valve remains a surgical challenge, but mitral valve repair is frequently possible. However, the result and possibility of repair depends on the mechanism of insufficiency and the extension of the lesion of the mitral valve. For overcoming all these obstacles, we proposed the theory to study of the magnetic forces of permanent magnets as an adjuvant, or as exclusive treatment to restore effective valve coaptation. To realize this idea, we based our research on three steps: 1 - Characterization of magnets required. 2 - Feasibility study of the magnets in vitro and in vivo 3 - Verification of the effectiveness of the magnetic force to achieve the desired coaptation in valvular insufficiency. This research is done in collaboration between the department of Thoracic and Cardiovascular surgery of Pitié-Salpêtrière hospital in Paris and the research group Electrodynamics - GREM3 LAPLACE Laboratory in Toulouse. The magnets were fabricated by taking into account the following factors: lowprofile and permanency; biocompatibility; the conservation of magnetization in a blood medium; mechanical flexibility of the implanted elements; and the possibility of sterilization. One of the main concerns was to elaborate the adapted intensity of the magnetic force, such that it would be sufficiently strong to close the valve, yet be weak enough to allow valve opening during cardiac cycle. To assess the feasibility, before conducting experiments in animals, in vitro data were obtained and judged appropriate by using a circulating pig heart model with a paracorporeal pneumatic (Thoratec®) ventricular assist device. The phase of animal testing was carried out by the establishment of three permanent magnets on the aortic valve in seven sheep kept alive for 3 months and the results were satisfactory: - No iatrogenic prolepses, - Perfect bio-tolerance without the need for anticoagulation - No visible inflammatory reaction at autopsy on the third postoperative month. Finally, to study the effectiveness of the magnetic force to achieve the desired coaptation in valvular insufficiency, three models of magnets have been tested on 4 sheep, but the results were not satisfactory. Currently we try to solve the problem and new magnets are by the way of conception. To our knowledge, the use of magnetic force to correct valvular incompetence has never been reported. Even if the experimental phase of magnets for treating valvular insufficiency has not reached its conclusion, we demonstrated the feasibility of the concept of healthy valve. This field of investigation must continue to be explored because the magnets have several advantages. On the one hand, they are technically easy to perform, and could thus allow a rapid repair. On the other hand, because of this simplicity, we could consider a percutaneous implantation, which will open a new way for conservative surgery in valvular insufficiency.

Ímãs híbridos aglomerados foram preparados por compactação uniaxial de pós magnéticos e curados ao ar e sob vácuo. Correlações entre tratamentos de cura, propriedades mecânicas e propriedades magnéticas foram estabelecidas com base em resultados obtidos por Histeresigrafia, Magnetometria de Amostra Vibrante, ensaios de Compressão e análises de Microscopia Óptica e Eletrônica de Varredura. Parâmetros como pressão de compactação, tempo e influência da temperatura e da atmosfera de cura nas propriedades mecânicas e magnéticas de ímãs aglomerados utilizados como padrão de referência, preparados com pós MQEP de NdFeB (partículas magnéticas impregnadas com resina epóxi), foram discutidos na primeira parte deste trabalho. A melhor condição de cura foi à temperatura de 200°C por cinco horas, sob vácuo. O produto de energia máximo (BHMáx) obtido para os ímãs padrão, curados ao ar e sob vácuo, foi de 76,2 KJ/m³ e 80,5 KJ/m³, respectivamente. Na segunda parte deste trabalho, ímãs híbridos foram produzidos a partir da mistura do pó MQEP aditivado com diferentes quantidades de pós de ferrite de estrôncio e NdFeB reprocessado por HDDR. O melhor resultado de BHMáx obtido para os ímãs híbridos de MQEP com ferrite de estrôncio e MQEP com pó reprocessado por HDDR, curados sob vácuo, foi de 73,2 KJ/m³ e 78,3 kJ/m³, respectivamente. Ímãs híbridos de MQEP com pó reprocessado por HDDR apresentaram melhor desempenho magnético que os ímãs híbridos de MQEP com pós de ferrite de estrôncio. / Bonded hybrid magnets were prepared by uniaxial pressing of magnetic powders cured in air and under vacuum. Correlations between cure treatments, mechanical properties and magnetic properties were established based on results obtained by Hysteresigraphy, Vibrating Sample Magnetometry, Compression tests, Optical Microscopy and Scanning Electron Microscopy. Parameters such as compaction pressure and the influence of time, temperature and atmosphere during the curing step in the mechanical and magnetic properties of the bonded magnets used as reference patterns, produced with NdFeB MQEP powder (epoxy encapsulated magnetic particles) were discussed in the first part of this work. The better cure condition was that performed at 200 oC for 5 hours under vacuum. The maximum energy product (BHMax) obtained for the patterns bonded magnets cured in air and under vacuum was 76.2 KJ/m³ and 80.5 KJ/m³, respectively. In the second part of this work, hybrid bonded magnets were produced by the mixture of MQEP powder with different amounts of strontium ferrite powder and NdFeB powder reprocessed by HDDR. The best results of BHMax obtained for the hybrid MQEP magnets with strontium ferrite powder and NdFeB reprocessed by HDDR, cured under vacuum were 73.2 KJ/m³ and 78.3 kJ/m³, respectively. Hybrid MQEP bonded magnets produced with the addition of HDDR reprocessed powder presented better magnetic performance than that obtained with strontium ferrite powders.

Atualmente, nanopartículas (NPs) são utilizadas em todos os ramos da tecnologia. Suas promissoras aplicações envolvem entre outros, o campo dos sensores e transdutores, mídia de gravação magnética, carreadores magnéticos de drogas medicinais. Com o objetivo de produzir NPs pelo método físico, um gerador de nanopartículas foi adaptado usando um dos canhões do sistema de magnetron sputtering, baseando-se no método de agregação gasosa. Com o gerador somos capazes de produzir NPs de diversos materiais e codepositá-las em matrizes dielétricas ou metálicas. Neste trabalho apresentamos o desenvolvimento da metodologia para a produção de nanopartículas de materiais magnéticos duros, usando alvos de SmCo5, Sm2Co17, Nd2Fe17B, FePt e CoPt. Investigamos a influência dos parâmetros de deposição (pressão, fluxo de gás e potência de sputtering), tipo de substrato e a existência de buffer e/ou codeposição, na obtenção das propriedades estruturais e magnéticas desejadas para esses materiais. As NPs produzidas são analisadas magneticamente pelo VSM e SQUID, sua morfologia e tamanho por TEM e SEM, a sua estequiometria pelo RBS, e a sua estrutura cristalina por XRD, a fim de obter nano-ímãs de alta anisotropia magnética. Da caracterização morfológica, através de microscopia eletrônica, encontramos para as NPs produzidas e estudadas diâmetros entre 5 e 17 nm. Através de análises de RBS obtemos para composição das NPs que as mesmas possuem estequiometria diferente dos alvos usados. Estudos estruturais e magnéticos mostram que para Sm-Co, Fe-Pt e Co-Pt é possível obter NPs cristalinas e com coercividade da ordem de 1 kOe. / In the recent years, nanoparticles (NPs) are being in all fields of technology. Their promising applications involve among others, the field of sensors and transducers, magnetic recording media, magnetic carriers of medicinal drugs. Aiming to produce NPs by physical method, a generator of nanoparticles was adapted using a system of guns \"magnetron sputtering\", based on the aggregation gas method. With the generator we are able to produce NPs with different types of material. In this work, we present the development of the methodology for the production of nanoparticles of hard magnetic materials, using targets of SmCo5, Sm2Co17, Nd2Fe17B, FePt and CoPt. We investigated the influence of the deposition parameters (pressure, gas flux and sputtering power), substrate type and the existence of the buffer and/or codeposition layers, to obtain the desired structural and magnetic properties for the nanoparticles. The produced NPs were magnetically analyzed by VSM and SQUID, the morphology and size by TEM and SEM, the stoichiometry by RBS and the crystal structure by XRD. The main objective of this work is to obtain nano-magnet with high magnetic anisotropy. Through the morphological characterization by electron microscopy, we found for NPs produced and studied have diameters between 5 and 17 nm. Through RBS analysis we have obtained the composition of the NPs, and also that they have different stoichiometry in relation to the used targets. Structural and magnetic studies have show that for Sm-Co, Fe-Pt and Co-Pt it is possible to obtain crystalline NPs with coercive field around 1 kOe.

Ímãs híbridos aglomerados foram preparados por compactação uniaxial de pós magnéticos e curados ao ar e sob vácuo. Correlações entre tratamentos de cura, propriedades mecânicas e propriedades magnéticas foram estabelecidas com base em resultados obtidos por Histeresigrafia, Magnetometria de Amostra Vibrante, ensaios de Compressão e análises de Microscopia Óptica e Eletrônica de Varredura. Parâmetros como pressão de compactação, tempo e influência da temperatura e da atmosfera de cura nas propriedades mecânicas e magnéticas de ímãs aglomerados utilizados como padrão de referência, preparados com pós MQEP de NdFeB (partículas magnéticas impregnadas com resina epóxi), foram discutidos na primeira parte deste trabalho. A melhor condição de cura foi à temperatura de 200°C por cinco horas, sob vácuo. O produto de energia máximo (BHMáx) obtido para os ímãs padrão, curados ao ar e sob vácuo, foi de 76,2 KJ/m³ e 80,5 KJ/m³, respectivamente. Na segunda parte deste trabalho, ímãs híbridos foram produzidos a partir da mistura do pó MQEP aditivado com diferentes quantidades de pós de ferrite de estrôncio e NdFeB reprocessado por HDDR. O melhor resultado de BHMáx obtido para os ímãs híbridos de MQEP com ferrite de estrôncio e MQEP com pó reprocessado por HDDR, curados sob vácuo, foi de 73,2 KJ/m³ e 78,3 kJ/m³, respectivamente. Ímãs híbridos de MQEP com pó reprocessado por HDDR apresentaram melhor desempenho magnético que os ímãs híbridos de MQEP com pós de ferrite de estrôncio. / Bonded hybrid magnets were prepared by uniaxial pressing of magnetic powders cured in air and under vacuum. Correlations between cure treatments, mechanical properties and magnetic properties were established based on results obtained by Hysteresigraphy, Vibrating Sample Magnetometry, Compression tests, Optical Microscopy and Scanning Electron Microscopy. Parameters such as compaction pressure and the influence of time, temperature and atmosphere during the curing step in the mechanical and magnetic properties of the bonded magnets used as reference patterns, produced with NdFeB MQEP powder (epoxy encapsulated magnetic particles) were discussed in the first part of this work. The better cure condition was that performed at 200 oC for 5 hours under vacuum. The maximum energy product (BHMax) obtained for the patterns bonded magnets cured in air and under vacuum was 76.2 KJ/m³ and 80.5 KJ/m³, respectively. In the second part of this work, hybrid bonded magnets were produced by the mixture of MQEP powder with different amounts of strontium ferrite powder and NdFeB powder reprocessed by HDDR. The best results of BHMax obtained for the hybrid MQEP magnets with strontium ferrite powder and NdFeB reprocessed by HDDR, cured under vacuum were 73.2 KJ/m³ and 78.3 kJ/m³, respectively. Hybrid MQEP bonded magnets produced with the addition of HDDR reprocessed powder presented better magnetic performance than that obtained with strontium ferrite powders.

In this thesis, I present my research into the development and use of a magneto-spectrometer operating at terahertz frequencies. Molecular samples with unpaired electrons were studied using electron paramagnetic resonance (EPR) spectroscopy and the properties of semiconducting samples were measured by cyclotron resonance. A terahertz time-domain spectrometer was constructed, fine-tuned and benchmarked. The use of a large area photoconductive antenna (PCA), with a bias voltage modulated at 1 MHz, allowed for a signal-to-noise ratio of 13800:1 to be achieved, which was equal or superior to comparable systems in use. The thermal behaviour of the PCA was studied and modelled to find that a 28% increase in emission occurred when the PCA was cooled to 100 K and a 22% increase in the maximum usable bias voltage was possible when the emitter substrate was cooled in a liquid nitrogen cryostat. The spectrometer was used to study a mixed type I/type II GaAs quantum well heterostructure as a test sample, in the process extending the existing research performed on this controllable terahertz filter. Together with a Gunn diode, bolometer and a Schottky diode, a pulsed magnet was developed into a 135 GHz, continuous-wave EPR spectrometer. EPR was detected in DPPH allowing for the spectrometer magnetic field accuracy to be determined and in ruby, which provided the crystal orientation of the sample and the base temperature of the spectrometer. Following this, three novel mixed-metal fluoride-centred triangles were studied on a multiple frequency EPR spectrometer allowing for the exchange interactions to be calculated along with the g-factors for two energy states. Two dimetallic cobalt complexes were studied to find that small changes to the molecules resulted in significant changes in the measured EPR spectra and so these molecules could be a useful part of the study of exchange coupled systems. The terahertz time-domain spectrometer was then combined with the pulsed magnet and an asynchronous optical sampling (ASOPS) system. Use of ASOPS allowed the number of waveforms measurable during a magnetic field pulse to be increased by at least a factor of 20 compared to contemporary alternatives. The spectrometer was used study cyclotron resonance in a two-dimensional electron gas (2DEG) formed at a GaAs/AlGaAs interface. Cyclotron resonance was successfully measured in the 2DEG at frequencies up to 1.6 THz, finding an electron effective mass of 0.071 m e , a sheet electron density of 3.3 × 10 11 cm -2 and a mobility of 1.5 × 10 5 cm 2 V -1 s -1 . Furthermore, using this system, the detection of EPR in a ruby sample was achieved, providing the first demonstration of ASOPS being used to study EPR at terahertz frequencies.