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Thesis. 1977. Ph.D.--Massachusetts Institute of Technology. Dept. of Physics. / M̲i̲c̲ṟo̲f̲i̲c̲ẖe̲ c̲o̲p̲y̲ a̲v̲a̲i̲ḻa̲ḇḻe̲ i̲ṉ A̲ṟc̲ẖi̲v̲e̲s̲ a̲ṉḏ S̲c̲i̲e̲ṉc̲e̲. / Includes bibliographical references. / Ph.D.

No description available.

Materiais amorfos demonstraram possuir um comportamento magnetomecânico superior ao de qualquer outro material magnético. Isso vêm permitindo sua utilização para um crescente número de finalidades de sensoriamento. A capacidade de interrogar remotamente a frequência de ressonância de fitas de material amorfo através de campos magnéticos permite a aplicação destas como sensores em situações que não permitem acesso direto à superfície de medição. Essa qualidade pode ser útil no monitoramento de risers que trazem petróleo do fundo do mar até plataformas na superfície. A frequência de ressonância das fitas amorfas depende, entre outras propriedades, da intensidade do campo magnético no qual estão inseridas. Desta forma, a deformação de um substrato pode ser monitorada através do uso de um transdutor nele colado, o qual se magnetiza à medida que o substrato deforma, consequentemente mudando o campo magnético imposto sobre o ressonador e a sua frequência de ressonância. Neste trabalho, a construção de um sensor magnetoelástico de deformação é investigada, onde uma liga policristalina de FeAlB foi utilizada como transdutor, e fitas de materiais amorfos, de nomes comerciais Metglas 2826 MB3 e 1K501, foram utilizadas como ressonadores. A liga de Fe80Al20, com 2%at. de B, mostrou ter uma magnetostricção de 80 ppm, o que inspirou o seu uso como transdutor, o que possibilita a substituição das fitas amorfas utilizadas anteriormente. Uma bancada de testes, capaz de aplicar tensão mecânica a um substrato de latão, foi construída com o objetivo de testar a sensibilidade do sensor magnetoelástico à deformação. Foi observado um comportamento altamente linear da frequência de ressonância do sensor com a tensão aplicada sobre o substrato de latão, com Gauge Factors de 120 e 90 para os sensores que utilizaram Metglas 2028 MB3 e 1K501 como ressonadores, respectivamente. Este resultado instigou a exploração da aplicabilidade do sensor magnetoelástico em substratos ferromagnéticos. Por fim, ensaios de tração foram realizados, nos quais a deformação dos substratos de aço SAE 1010 foram monitoradas simultaneamente pelo sensor magnetoelástico e por um Strain Gauge. A variação de frequência de ressonância do sensor nestes esaios apresentou uma forma mais sigmoidal, com uma região quase linear. O monitoramento de um riser com este dispositivo seria factível / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior, CAPES / Amorphous metals have been shown to have magnetomechanical properties which are superior to those of any other magnetic materials. This has allowed their usage in a growing number of sensing purposes. The capacity of remotely interrogating the resonant frequency of amorphous material stripes trough magnetic fields allows their application as sensor in situations that do now allow direct contact with the measurement surface. This quality may be useful for the monitoring of risers that bring petrol from deep sea to platforms on the surface. The resonant frequency of the stripes is a function of, alongside other properties, the intensity of the magnetic field in which they are inserted. Thus, a substrate’s deformation may be monitored trough the use of a transducer in him affixed, which magnetizes as the substrate deforms, consequently altering the magnetic field imposed over the resonator, and its resonant frequency. In this work, the construction of a magnetoelastic strain sensor is investigated, where a polycrystalline FeAlB alloy was used as transducer, and amorphous materials, by the commercial name of Metglas 2826 MB3 and 1K501, were used as resonators. The Fe80Al20 alloy, with 2%at. B, was shown to have an 80 ppm magnetostriction, which inspired its use as transducer, which enabled the substitution of the amorphous ribbons previously used. A testing bench, capable of applying mechanical stress to a brass substrate, was built with the goal of teste the sensibility of the magnetoelastic sensor to strain. A highly linear behavior of the sensor’s resonant frequency to the applied stress on the brass substrate was observed, with Gauge Factors of 120 for the sensors that used Metglas 2826 MB3 and 1K501 as resonators, respectively. This result instigated the exploration of the magnetoelastic sensor’s applicability on ferromagnetic surfaces. Finally, mechanical stress tests were conducted, in which the deformation of the SAE 1010 steel substrate were simultaneously monitored by the magnetoelastic sensor, and a Strain Gauge. The resonant frequency of the sensor is this test showed a sigmoidal form, with a nearly linear region. The monitoring of a riser with this device is feasible

M.Sc. / When a pure chromium single crystal is cooled through its Néel temperature, it undergoes a paramagnetic to a multi-wave vector incommensurate spin-density-wave magnetic transition. Should a chromium single crystal be cooled through its Neel temperature in the presence of a strong enough magnetic field, 4-5 T, then all the spin-density-wave vectors that occur as it undergoes the paramagnetic to incommensurate spin-density-wave magnetic transition, are forced to be aligned parallel to the direction of the applied magnetic field, producing what is called a single spin-density-wave wave vector state in the crystal. The single spin-density-wave wave vector state will remain in the crystal when the magnetic field is removed providing the crystal is not heated above its Neel temperature. If the crystal when in the single spin-density-wave wave vector state is orientated so that the single spin-density-wave wave vector is aligned perpendicular to the direction of an applied magnetic field, then the spin polarisation vectors of the magnetic moments will align themselves so that they are perpendicular to the applied magnetic field and perpendicular to the single wave vector, producing what is called a single spin-densitywave wave vector and single spin polarisation vector state in the crystal. There is a difference in value between the elastic constants measured when a chromium single crystal is in the single spin-density-wave wave vector state to the elastic constants measured when the crystal is in the multi-wave vector spin-density-wave state.When pure chromium is alloyed with other materials the topology of the Fermi surface is changed resulting in some of the alloys being able to undergo paramagnetic to commensurate spin-densitywave magnetic transitions, as well as being able to undergo commensurate spin-density-wave to incommensurate spin-density wave transitions. This study makes use of a magnetic field of strength 4.5 Tin an attempt to produce a single spin-density-wave wave vector state in a Cr + 0.3 at.% Ru and a Cr + 1.6 at.% Si single crystals. Both single crystals undergo paramagnetic to commensurate spin-density-wave transitions when cooled through their, respective Neel temperatures, as well as the Cr + 0.3 at.% Ru single crystal being able to undergo a commensurate spin-density-wave to an incommensurate spin-density-wave transition if cooled further, down to 77 K, well below it's Neel temperature. The effects of the applied magnetic field on the Cr + 0.3 at.% Ru and Cr + 1.6 at.% Si single crystals was determined by measuring the elastic constants of the respective crystals.

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No description available.

Master of Science

Ces dernières années, les performances des matériaux multiferroïques ont beaucoup progressé avec les composites à deux phases : magnetostrictive et piézoélectrique. Les composites utilisent le couplage entre le magnétisme et la piézoélectricité par le biais de la magnétostriction. On obtient ainsi le contrôle de l’aimantation par le champ électrique électrique et à l’inverse celui de la polarisation électrique par un champ magnétique (ce qui nous intéresse ici). Cela pousse l’électronique vers des solutions plus vertueuses pour l’environnement avec une baisse de la consommation électrique des circuits (les commandes en courant sont remplacées par des commandes en tension) et le remplacement des piles d’alimentation, qui doivent être changées périodiquement, par des systèmes de récupération d’énergie pérenne. La récupération d’énergie est très présente avec l’Internet des Objets (IoT). Malgré leur performance, ces composites restent perfectibles, notamment au niveau de la phase magnetostrictive. Son optimisation est indispensable. Le matériau courant est le Terfenol-D à cause de sa magnétostriction géante, dans sa forme massive et monocristalline. Ce matériau historique demeure rare, cher, fragile et son procédé de tirage n’est pas adapté à la fabrication de dispositifs miniatures. Ce travail a donc porté sur l’étude comparative des voies de fabrication de disques miniatures de Terfenol-D pour la réalisation de récupérateurs d’énergie. Une étude de fond a été menée sur des séries de disques découpés dans des lingots d’alliages commerciaux (monocristallins et polycristallins). Ensuite, nous sommes tournés vers la méthode du frittage isotrope de poudre avec très peu de recul sur ce matériau. Le frittage conventionnel a conduit aux premiers disques fonctionnels sans découpe mais manquant de densité et de tenue mécanique. Ces défauts ont ensuite été corrigés grâce à la technique de SPS (Spark Plasma Sintering) mais la reproductibilité dans le temps reste à améliorer. Les disques de Terfenol-D (découpés et fabriqués) ont été assemblés avec la phase piézoélectrique (PZT commercial). Des caractérisations électriques par la méthode sans contact ont validé leur aptitude à récupérer de l’énergie, en proportion moindre quand on le compare au Terfenol-D monocristallin comme attendu, mais en quantité suffisante pour les applications ciblées. Enfin, une solution alternative a été explorée avec l’alliage magnétique à mémoire de forme NiMnGa offrant de très grandes déformations. Une perspective vers un bouton poussoir autonome sans fil est présentée en toute fin. / In recent years, performances of multiferroïc materials have considerably improved with two-phase composites: magnetostrictive and piezoelectric. These composites take advantage of the coupling between magnetism and piezoelectricity through magnetostriction. Thus they allow control of magnetization with electrical voltage, and conversely, to get an electrical polarization depending on the magnetic field (our focus in this case). This drives electronics towards more environmental friendly solutions, namely with lower circuit power consumption (current controls are replaced by voltage controls) and the replacement of batteries, which must be periodically changed, by sustainable energy harvesting systems. Energy harvesting solutions are popular with the Internet of Things (IoT). Despite their performance, these multiferroïc composites remain perfectible, especially regarding the magnetostrictive phase. Its optimization is essential. The common material is Terfenol-D because of its giant magnetostriction, used in its massive and monocrystalline form. This material remains rare, expensive, fragile and its growing method is not adapted to the manufacturing of miniature devices. This work focuses on a comparative study of Terfenol-D miniature disk manufacturing pathways for the production of energy harvesters. A benchmark study was carried out on a series of disks cut in commercial alloy ingots (monocrystalline and polycrystalline). Next, the isotropic powder sintering method was investigated with very little background on this material. Conventional sintering led to the first functional disks needing no ulterior machining but with low density and mechanical strength. These defects were then corrected using the SPS technique (Spark Plasma Sintering) but the reproducibility over time has yet to be improved. The Terfenol-D disks (both cut and manufactured) were assembled with the piezoelectric phase (commercial PZT). Electrical characterizations using a contactless method have validated their potential to harvest energy, in lesser amounts than monocrystalline Terfenol-D as expected, but in a large enough quantity regarding most of applications. Finally, an alternative solution has been explored with NiMnGa shape magnetic alloys offering very large deformations. A perspective to a wireless autonomous push button prototype is presented at the very end.

Ce travail de thèse porte sur l'étude de composites magnétoélectriques laminaires dans le but de réaliser des dispositifs innovants intégrés sur silicium tel que l'inductance RF variable. Grâce au couplage mécanique entre des couches adjacentes magnétostrictive ultra douce et piézoélectrique, il est possible d'obtenir un couplage magnétoélectrique indirect qui est supérieur de plusieurs ordres de grandeur à celui des matériaux multiferroïques naturels. Dans un premier temps, nous avons utilisé l'approche phénoménologique basée sur les énergies pour décrire le panorama des effets attendus dans des composites magnétoélectriques laminaires (multicouches). Ensuite, des composites magnétoélectriques macroscopiques à base de substrats piézoélectriques de type MFC et de couches minces de FeCoB ont été réalisés. L'étude du couplage magnétoélectrique en fonction de la composition de FeCoB a permis de déterminer les propriétés clés des matériaux, notamment le rapport λs/Ms, qui sont essentielles pour obtenir un effet magnétoélectrique élevé. Un coefficient magnétoélectrique record de 250 V∙cm‐1Oe‐1 a été obtenu. Par ailleurs, un microscope à effet Kerr a été spécialement développé pour pouvoir observer de manière quasi-instantanée la modification de la structure en domaines sous l'effet de la tension électrique dans ces composites. Pour la première fois, l'observation directe de la rotation de l'axe facile d'aimantation sous commande électrique a été réalisée. La deuxième partie de ce manuscrit est consacrée à la conception, simulation, fabrication et caractérisation d'un dispositif MEMS hybride d'inductance variable intégrée. Ce dispositif exploite l'effet magnétoélectrique indirect entre un élément moteur en PZT (sol gel) et un élément inductif à base de FeCoB. Etant donné le caractère multiphysique hors norme de ce dispositif, un ensemble de tests électriques, mécaniques, optiques et magnétiques a été déployé tout au long de la fabrication. Les résultats concluent à une preuve de concept partiellement fonctionnelle en raison principalement d'une mauvaise gestion des contraintes internes liées à la fabrication. Les pistes d'amélioration aux niveaux du design, des matériaux et des procédés sont identifiées. / This work is focused on the study of laminated magnetoelectric composites aiming at the realization of novel components integrated on silicon, such as variable inductors. Thanks to the mechanical coupling between two adjacent layers of ultra-soft magnetostrictive and piezoelectric materials it is possible to obtain an indirect magnetoelectric effect which is several orders of magnitude higher than in natural multiferroics. Firstly, we used an energy-based phenomenological approach to describe a range of expected effects in such laminated magnetoelectric composites. Thereupon, macroscopic magnetoelectric composites based on piezoelectric MFC substrates and magnetostrictive thin films of FeCoB were realized. The study of the magnetoelectric coupling vs. FeCoB composition leads to the identification of the key material parameters, such as λs/Ms, that are essential for high magnetoelectric effect. A record magnetoelectric coefficient of 250 V∙cm‐1Oe‐1 is obtained. In parallel, a specific Kerr effect microscope devoted to live observation of the magnetic domains change vs. applied electrical field was developed. For the first time, direct observation of the magnetic easy-axis rotation with voltage in such composites is reported. The second part of this work concerns the design, simulation, fabrication and characterization of a hybrid MEMS variable inductor. This device exploits the indirect magnetoelectric effect between a PZT sol gel driving element and a FeCoB-based inductive element. The unusual multi-physics nature of the device prompted us to deploy a set of electrical, mechanical, optical and magnetic tests throughout the manufacturing. The results conclude with partially functional proof of concept, mainly due to the lack of management of internal stress during the fabrication. Areas for improvement of design, materials and process are identified.