O presente trabalho teve como foco um problema que vem se tornando cada vez mais grave nos dias de hoje, já que, com o crescimento das zonas urbanas, algumas residências estão se aproximando dos transformadores de potência. Transformadores são máquinas cuja função é aumentar ou diminuir a diferença de potencial de uma rede elétrica, porém, eles geram um nível significativo de ruído, podendo ser prejudicial à saúde. Esse ruído é causado pela magnetostricção pelas chapas de Fe-Si as quais compõem o núcleo. Assim, o intuito desse trabalho foi estudar duas ligas de Fe-Ti, para averiguar seu comportamento magnetostrictivo. Além disso, é importante estudar as propriedades magnéticas dessas ligas, a fim de se analisar quais são as perdas magnéticas associadas a essas ligas. Portanto, também foram feitas medidas de indução magnética, permeabilidade magnética e resistividade elétrica. Também foram feitas análises de microscopia eletrônica de varredura, para análise do tamanho e morfologia dos grãos, difratometria de raios X, para identificação das fases presentes e difração de elétrons retroespalhados, para identificação da textura. Todas essas medidas foram feitas para as ligas de Fe-Ti e uma liga de Fe-Si comercial de grão orientado e os resultados foram comparados entre si. As ligas de Fe-Ti apresentaram valores de magnetostricção menores do que a liga de Fe-Si, porém, apresentaram valores bem maiores quando analisadas as perdas magnéticas. Com isso, foi possível fazer uma primeira análise das ligas de Fe-Ti, criando diversas possibilidades para estudos futuros. / The present research had as focus a problem that is becoming very serious nowadays, since with the growth of urban areas, some households are approaching the power transformers. Power transformers are machines whose function is to increase or decrease the potential difference of a power grid, but they generate a significant level of noise, which can be harmful to human health. This noise is created by the magnetostriction of the Fe-Si plates that compose the core. Thus, the purpose of this research was to study two Fe-Ti alloys to investigate their magnetostrictive behavior. In addition, it is important to study the magnetic properties of these alloys in order to analyze the magnetic losses associated with these samples. Therefore, measurements of magnetic induction, magnetic permeability and electrical resistivity were also made. Were made analyzes of scanning electron microscopy to investigate the size and morphology of the grains, X-ray diffraction, to identify the phases that are present in the material and electron backscatter diffraction to identify the texture.These characterizations were made for the Fe-Ti alloys and a commercial grain-oriented Fe-Si alloy. The results were compared to each other. Fe-Ti alloys showed lower magnetostriction values than the Fe-Si alloy, however they presented highest values of magnetic losses. As a result, it was possible to make a first analysis of the Fe-Ti alloys properties, creating several possibilities for future studies in order to improve Fe-Ti alloys properties.

In paleomagnetism, practical measurements are rarely made using perfect, isolated, single-phase, ferromagnetic crystals. Experimental observations are typically made using magnetic materials formed by a variety of natural processes. In this thesis, we will look at bridging the gap between current numerical modelling capability and experimental observations. First, we work towards micromagnetic modelling of multi-phase magnetic materials, including magnetostriction, embedded in a rocky matrix, along with crystal defects. We present a derivation of the Boundary Element Method formulation used by the micromagnetics package, MERRILL, and provide an extension of this from single-phase materials to multi-phase. After discussing issues with previous approaches to modelling magnetostriction, we derive and present a more robust and flexible approach. This model of magnetostriction is suitable for non-uniformmagnetizations, for multi-phase materials, and for arbitrary boundary conditions, and can be incorporated into MERRILL.We then outline a method for extending our model to materials embedded in an infinite elastic matrix of arbitrary elasticity. Finally, we present a method for modelling the magnetic response of a material due to crystal defects, along with a concrete example of a magneto-dislocation coupling energy at a magnetite-ilmenite boundary where stress due to lattice misfit is eased by regular edge dislocations. Second, we work towards being able to verify micromagnetic models against nano-scale experimental data. To do this, we present two techniques for simulating electron holograms from micromagnetic modelling results, a technique capable of imaging magnetic structures at the nano-scale. We also present example electron holograms of commonly occurring magnetic structures in nano-scale rock and mineral magnetism, and highlight some distinguishing features, which may be useful for interpreting experimental electron holography data.

This dissertation presents the development of a novel linear magnetostrictive actuator. The magnetostrictive material used here is Terfenol-D, an alloy of the formula Tb0.3Dy0.7Fe1.92. In response to a traveling magnetic field inside the Terfenol-D element, it moves in the opposite direction with a peristaltic motion. The proposed design offers the flexibility to operate the actuator in various configurations including local and conventional three-phase excitation. The conceptual design of the linear magnetostrictive actuator was performed during which different configurations were analyzed. Finite Element Analysis (FEA) was extensively used for magnetic circuit design and analysis in conceptual design. Eventually one of these designs was chosen based on which detailed design of linear magnetostrictive actuator was carried out. A new force transmission assembly incorporates spring washers to avoid the wear due to the sudden collision of Terfenol-D element with the force transmission assembly. All mechanical parts were then fabricated at the mechanical engineering machine shop. The power electronics to operate the motor in a local three-phase mode was designed and implemented. It was demonstrated that the power consumption can be reduced significantly by operating the magnetostrictive linear actuator in the local excitation mode. A finite-element model of the actuator was developed using ATILA and an empirical model was presented using the data gathered from numerous tests performed on the actuator. The closed-loop control system was implemented using relay control which resulted in an optimal closed-loop performance. The magnetostrictive actuator has demonstrated 410-N load capacity with a travel range of 45 mm, and the maximum speed is 9 mm/min. The maximum power consumption by the motor is 95 W. The sensorless control of the linear magnetostrictive actuator was successfully conducted using two different approaches. First, using a linear-approximation method, we achieved a position estimation capability with ±1 mm error. Then, an adaptive neuro-fuzzy inference system was employed for estimating the position which resulted in a position estimation capability with only a ±0.5 mm error.

The aim of this thesis work was to develop magnetoelectric (ME) composites consisting of piezoelectric and magnetostrictive components. The piezoelectric constituent was selected as a PZT ceramic modified by strontium, bismuth and manganese. The magnetostrictive phase was nickel ferrite (NF) ceramic doped by cobalt, copper and manganese. The properties of component phases were optimized in order to enhance the ME effect in the composite. In the first part of the thesis, effects of sintering temperature on the dielectric and piezoelectric properties of PZT and on the electrical and magnetic properties of NF ceramics were investigated in the temperature range covered from 1150 to 1250 &deg / C. The best piezoelectric properties in PZT were attained at 1250 &deg / C. At this sintering temperature, values of piezoelectric strain coefficient, dielectric constant, and electromechanical coupling coefficient were 434 pC/N, 1320 and 0.48, respectively. NF ceramics showed poor densification / 80 %TD was attained at 1250 &deg / C. In order to obtain higher densities in ferrites, Bi2O3 was used as a sintering aid. Addition of Bi2O3 enhanced densification up to 97 %TD, and improved electrical and magnetic properties of ferrites. Highest DC-resistivity of 1.15*10^8 ohm-cm and highest magnetostriction of ~26 ppm were attained in NF ceramics doped with 1 wt% Bi2O3. In the second part of the thesis, ME composites were manufactured either as bulk composites or as laminated composites. The efficiency of different composite types was evaluated in terms of voltage output in response to the applied magnetic field. Higher outputs were observed in laminated composites.

<p>A magnetostrictive material elongates when it is subjected to a magnetic field. This effect can then be used to design powerful actuators. The department of electromagnetic engineering has been working with magnetostricitve material and their applications since the 1980s and is presently engaged in a project focusing on magnetostrictive transducer utilisation for the aeronautic field.</p><p>The focus of the presented work has been to develop and improve methods and tools supporting the development of magnetostrictive actuators.</p><p>The axial-radial model was previously developed at the department and is well suited for circular cross sections of magnetostrictive rods. It is, however, common to laminate the magnetostrictive rods resulting in rectangular cross sections. The use of Cauer circuits allows modelling of the shielding effect. This shielding effect results in non-homogenous magnetisation and stress in both rectangular and circular cross sections of the rod. A model based on Cauer circuits, including a hysteresis model based on experimental data, was developed during the project. Furthermore, it is demonstrated how figures of merit and the use of finite element methods can be used to find optimised designs in a systematic and computational efficient way. The<i> modified generalised Fabry factor</i> <i>and the magnetisation inhomogeneity coefficient</i> are two proposed new figures of merit.</p><p>A Magnetostricitve material is characterised through an experimental procedure. Usually, magnetostrictive material exhibit large hysteresis. An important part of the material characterisation is the post-processing of the measurement data, including a de-hysterisation procedure. In the thesis, a de-hysterisation method which ensures energy consistent data is presented. Energy consistent material data is essential to achieve energy consistent simulations of magnetostrictive systems.</p><p>It is also demonstrated how the knowledge at the department can be utilised in international projects. In an ongoing project, the department is engaged in two sub tasks. In one of these sub tasks a high torque actuator is to be developed for the helicopter industry. The developed magnetostrictive models are used to perform system simulations of such actuator systems. In the other sub task a device for power harvesting from vibrations is analysed. It has now been shown how to adapt the load impedance in order to extract maximal electric power from the device.</p>

Eisen-Gallium-Legierungen sind aufgrund ihrer hohen Magnetostriktion und ihrer hervorragenden mechanischen Eigenschaften sehr interessant für Anwendungen sowohl in Form von Sensoren als auch Aktoren. Die fortschreitende Miniaturisierung erfordert die Herstellung von Bauteilen in eindimensionaler Struktur und komplexen Geometrien. Beide Herausforderungen sind mit templatbasierter elektrochemischer Abscheidung zugänglich. Es konnte gezeigt werden, dass dünne Fe-Ga-Schichten schon aus einfachen wässrigen Elektrolyten abgeschieden werden können. Gallium kann nur in Anwesenheit von Fe induziert reduziert werden. Gleichzeitig konnte nachgewiesen werden, dass durch die Hydrolyseneigung der Ga-Ionen immer Hydroxide gebildet und in das Deposit eingebunden werden. Durch die Einführung einer alternierenden potentiostatischen Abscheidung mit einem Reduktions- und einem Relaxationsschritt können dennoch dichte und homogene Fe80Ga20-Schichten mit wenigen Defekten und einem vernachlässigbar kleinen Sauerstoffgehalt hergestellt werden. Die Übertragung der so gefundenen Abscheideparameter zur templatbasierten Nanodrahtherstellung ist nur bis zu einem Porendurchmesser von 100nm möglich. Wird der Durchmesser der Porenkanäle weiter verringert, führt aufgrund eingeschränkter Diffusionsvorgänge die Abscheidung zu segmentierten und sauerstoffreichen Depositen. Die Modifizierung des Elektrolyten durch Komplexierung der Metallionen verhindert die Bildung und Einbindung der Hydroxide. Damit können auch für Porendurchmesser kleiner 100nm Drähte in AAO-Template abgeschieden werden. Diese sind dicht, defektfrei und weisen keinen Zusammensetzungsgradienten entlang der Wachstumsrichtung auf. Detaillierte TEM-Untersuchungen konnten zeigen, dass die Herstellung durch ein einfacheres potentiostatisches Abscheideregime zu weniger verspannten und dennoch homogenen und defektfreien Drähten führt. Für die Herstellung von magnetisch aktiven Drähten sollte daher die potentiostatische der gepulsten Abscheidung vorgezogen werden.

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.

In this work, a 3-terminal capacitance dilatometer was set up and used for measurements of the thermal expansion and magnetostriction of novel superconducting iron pinictides and related materials. In particular, \re~with R\,=\,La, Ce, Pr, Sm, Gd, \laf~and Ca(Fe$_{1-x}$Co$_x$)$_2$As$_2$ have been investigated. The data on polycrystalline \laf~are the first published thermal expansion data on this material. The lattice effects at the structural and the magnetic phase transition have been investigated and the phase diagram upon F-doping has been studied. A main result is the observation of a previously unknown fluctuation regime for the doping level $\mathnormal{x}\leqslant$ 0.04 over a large $T$ range above the structural transition temperature \ts. The absence of any structural anomalies in the normal state of the superconducting \laf~samples with $\mathnormal{x}\geqslant$ 0.05 corroborates the discontinuous character of the phase boundary not only for the magnetism but also for the structural degrees of freedom. Similarly, the presence of high-temperature fluctuations is found for all \re~undoped materials under study. The discussion of the probable origin of the fluctuations as well as the definition of the structural transition temperature \ts~are done. The low temperature features shown by the thermal expansion data for \re~are caused by the onset of long range magnetic order of the $4f$-moments and their different configurations. In particular, \pr, which has a very pronounced anomaly associated with Pr-ordering exhibits a large magnetostriction at low temperatures. By discussing this effect along with the magnetization, resistivity and other measurements, it is found that this large magneto-elastic effect may originate from the correlations between the momentum from Fe$^{3+}$ and Pr$^{3+}$. Last, the thermal expansion of Ca(Fe$_{1-x}$Co$_x$)$_2$As$_2$ 122 single crystals is investigated. Ca(Fe$_{1-x}$Co$_x$)$_2$As$_2$ is one of the first materials where single crystals are available. The thermal expansion results on the undoped compound with $x=0$ show a large anomaly at the combined magnetic and structural transition which is far sharper than that for polycrystalline systems. Upon doping, both transitions are suppressed and their splitting is visible in the thermal expansion data. The high precision thermal expansion and magnetostriction results presented in this work are among the first data on the novel family of iron-based superconductors. A valuable insight in the respective ordering phenomena and the thermodynamic properties is provided.

No presente trabalho foram produzidas duas ligas policristalinas de Fe-Ga e Fe-Ga-B para estudar a influência do boro nas propriedades piezomagnéticas da liga Fe-Ga. As propriedades piezomagnéticas foram obtidas a partir de medidas de magnetostricção (&lambda;) em função de campo magnético (H) pelo coeficiente d33 = d&lambda;/dH e medidas de indução magnética (B) em função da tensão compressiva aplicada (&sigma;) pelo coeficiente d*33 = dB/d&sigma;. A composição escolhida foi com 18,6% de Ga para ambas as ligas, que é a composição que possui o maior valor de magnetostricção na liga binária. A análise da microestrutura indicou a presença das fases Fe(Ga)-&alpha; (A2) e Fe3Ga (D03) para ambas as ligas e da fase Fe2B para a liga ternária. A presença da fase Fe2B causou o refinamento dos grãos e consequentemente um pequeno aumento do campo coercitivo da liga Fe-Ga-B se comparada à liga Fe-Ga e, além disto, aumentou o campo de saturação. Consequentemente os coeficientes piezomagnéticos da liga com boro foram duas vezes menores que da liga Fe-Ga. A igualdade d33* = d33 não é satisfeita para a liga Fe-Ga nem para a Fe-Ga-B, significando que os experimentos não foram realizados em condições estritamente reversíveis. Atribui-se esta irreversibilidade à alta velocidade de carregamento usada nos experimentos de B vs &sigma;. No entanto, a dependência dos coeficientes piezomagnéticos do campo magnético e da tensão compressiva aplicada da liga Fe-Ga-B é bem menor que da liga Fe-Ga e os valores obtidos de ~ 4 nm/A são suficientemente adequados para muitas aplicações. / In this work were maked two polycrystalline alloys of Fe-Ga e Fe-Ga-B for to study the influence of borun in the piezomagnetc properties of the Fe-Ga alloys. The piezomagnetc properties were obteined from magnetostrictive measuments (&lambda;) in function of magnetic field (H) by the coefficient d33 = d&lambda;/dH and magnetic induction measuments (B) in function of compressive stress applied (&sigma;) by the coefficient d*33 = dB/d&sigma;. The chosen composition were 18.6% of Ga to both alloys, which is the composition for the largest magnetostriction to the binary alloy. The microstructural analysis indicated the presence of the phases Fe(Ga)-&alpha; and Fe3Ga (D03) for the both alloys and Fe2B phases to the ternary alloy. The presence of the Fe2B caused the refinament of the grains and consequently a small increase in the coercive field of the Fe-Ga alloy and, in addition, increased the saturation field. Consequently, the piezomagnetic coefficients of the boron alloys were twice as low as that of the Fe-Ga alloy. The equality d33* = d33 was not satisfied for the Fe-Ga and to Fe-Ga-B meaning that the experiments were not performed under strictly reversible conditions. This irreversibility was attributed to the high loading speed used in the experiments of B vs &sigma;. However, the dependence of the piezomagnetic coefficients of the magnetic field and the applied compressive stress of the Fe-Ga-B alloy is much lower than that of the Fe-Ga alloy and the values obtained from ~ 4nm/A are sufficiently suitable for many applications.

M.Sc. / The aim of this study is to show that there exists a parallelism between the effect of the concentration of the itinerant electrons per atoom, and the applied hydrostatic pressure, p, on the magnetic phase diagram of a Cr + 0.2 at.% Ir alloy. This Cr-Ir alloy was chosen, because it contains all possible magnetic phases that can exist in a Cr alloy.