The goal of this thesis is to design, build and test a new measurement system for comprehensive studies of the magnetoelectric and the converse magnetoelectric effect. The research on multiferroic composites is an emerging field of research and there is no commercially available equipment. The method proposed here for testing magnetoelectric properties of the multiferroics is relatively inexpensive and versatile. The advantage of the new method described below is that the same set of instruments in different configurations enables multiple measurements of various parameters characterizing multiferroic composites. The system was tested using two samples Fe78Si10B12/AIN and Fe78Si10B12/PZT consisting of ferromagnetic and magnetostrictive ribbon of metallic glass glued to piezoelectric AlN or PZT. The final result was a working system that enables selective measurements of different responses of the multiferroic composites to the static and dynamic electric and magnetic fields. This demonstrates the versatility of the system. Magnetoelectrical effect, Piezoelectric, Piezomagnetic, magneticmechanical, electromechanical, magnetoelectrical measurement

Coupling between the electric field, magnetic field, and strain of composite materials is achieved when electro-elastic (piezoelectric) and magneto-elastic (piezomagnetic) particles are joined by an elastic matrix. Although the matrix is neither piezoelectric nor piezomagnetic, the strain field in the matrix couples the E field of the piezoelectric phase to the B field of the piezomagnetic phase. This three-phase electro-magneto-elastic composite should have greater ductility and formability than a two-phase composite in which E and B are coupled by directly bonding two ceramic materials with no compliant matrix. A finite element analysis and homogenization of a representative volume element is performed to determine the effective electric, magnetic, mechanical, and coupled-field properties of an elastic (epoxy) matrix reinforced with piezoelectric and piezomagnetic fibers as functions of the phase volume fractions, the fiber (or particle) shapes, the fiber arrangements in the unit cell, and the fiber material properties with special emphasis on the symmetry properties of the fibers and the poling directions of the piezoelectric and piezomagnetic fibers. The effective magnetoelectric moduli of this three-phase composite are, however, less than the effective magnetoelectric coefficients of a two-phase piezoelectric/piezomagnetic composite, because the epoxy matrix is not stiff enough to transfer significant strains between the piezomagnetic and piezoelectric fibers.

Coupling between the electric field, magnetic field, and strain of composite materials is achieved when electro-elastic (piezoelectric) and magneto-elastic (piezomagnetic) particles are joined by an elastic matrix. Although the matrix is neither piezoelectric nor piezomagnetic, the strain field in the matrix couples the E field of the piezoelectric phase to the B field of the piezomagnetic phase. This three-phase electro-magneto-elastic composite should have greater ductility and formability than a two-phase composite in which E and B are coupled by directly bonding two ceramic materials with no compliant matrix. A finite element analysis and homogenization of a representative volume element is performed to determine the effective electric, magnetic, mechanical, and coupled-field properties of an elastic (epoxy) matrix reinforced with piezoelectric and piezomagnetic fibers as functions of the phase volume fractions, the fiber (or particle) shapes, the fiber arrangements in the unit cell, and the fiber material properties with special emphasis on the symmetry properties of the fibers and the poling directions of the piezoelectric and piezomagnetic fibers. The effective magnetoelectric moduli of this three-phase composite are, however, less than the effective magnetoelectric coefficients of a two-phase piezoelectric/piezomagnetic composite, because the epoxy matrix is not stiff enough to transfer significant strains between the piezomagnetic and piezoelectric fibers.

Les développements récents en physique, et technologiques, ont permis l’élaboration de nouveaux matériaux magnéto-électro-élastique, comme les composites multicouches piézoélectriques / piézomagnétiques. Leur coefficient magnétoélectrique, très grand en comparaison de celui des matériaux constitués d’une seule phase, a suscité récemment un grand nombre de travaux, menant au développement de capteurs, d’actionneurs, de systèmes de conversion d’énergie magnétique-électrique, et dans les mémoires à état solide.Cette thèse porte sur l’étude théorique et expérimentale des ondes acoustiques de surface dans des structures multicouches piézomagnétiques. Une description théorique des matériaux magnéto-élastiques, reposant sur la dérivation d’un modèle de matériau piézomagnétique équivalent, est utilisée conjointement à une technique numérique afin de calculer les courbes de dispersion et les formes des modes des ondes acoustiques se propageant dans des composites piézo-électro-magnétiques déposés sur un substrat. Ce modèle, très général, peut être utilisé pour différents types de structures et pour une intensité et une direction quelconques du champ magnétique externe appliqué. Les structures réalisées en salle blanche sont constituées d’un film mince de 20 couches de TbCo2 (5nm)/FeCo(5nm) déposé sur un substrat de LiNbO3 entre deux peignes interdigités. Une comparaison, entre les variations de la vitesse de phase d’ondes acoustiques de surface induites par l’application d’un champ magnétique externe modélisées et mesurées, est réalisée. Un bon accord quantitatif entre les mesures et les calculs théoriques, et cela pour toutes les orientations du champ magnétique (suivant l’axe facile ou l’axe difficile) et pour différents modes acoustiques, est obtenu. Le mode transverse horizontal présente les plus grandes variations de vitesse, proche de 20% pour un film dont l’épaisseur serait celle de la longueur d’onde acoustique / Recent developments in physics and technology allow the elaboration of new magneto-electro- elastic materials such as multilayered piezoelectric-piezomagnetic composites. Their large magne- toelectric coefficient, compared to the one of single phase materials, recently attracted a large number of studies, and they are now widely used in the development of sensors, actuators, magnetic- electric energy converting devices, and solid state memories.This PhD thesis addresses the experimental and theoretical investigations of guided elastic waves propagation in piezomagnetic multi-layered structure. A theoretical description of magneto- elastic materials, based on the derivation of an equivalent piezomagnetic material of a magnetostric- tive thin film, is used in conjunction with a numerical method to compute propagation constants, i.e. dispersion curves, and mode shapes of elastic waves in layered piezoelectric-piezomagnetic com- posites deposited on a substrate. This model can be used for different structures, and for an applied external magnetic field of any intensity and direction.The realized structures are composed of a 20xTbCo2(5nm)/FeCo(5nm) nanostructured multi- layer deposited between two Aluminum Inter-Digitals Transducers forming a surface acoustic wave delay line, on a LiNbO3 substrate. A comparison between the calculated and measured phase velocity variation under the action of the external magnetic field orientation and magnitude is made. A quantitative agreement between the measured and modeled phase velocity shift for all external magnetic field configurations (hard axis and easy axis) and for different shape modes of elastic waves at their first and third harmonic operation frequencies is obtained. The shear horizontal mode exhibits a maximum phase velocity shift close to 20% for a ratio close to 1 between magneto-elastic film thickness and wavelength

L’objectif des travaux de cette thèse est la réalisation de capteurs magnétiques à ondes élastiques de surface (SAW). Nos études réalisées dans ce cadre se sont focalisées sur la modélisation et la réalisation de dispositifs magnéto-élastique SAW à base de structures multicouches sensibles au champ magnétique. Une géométrie multicouche offrant plusieurs degrés de libertés permettant d’agir sur les performances du capteur a été considérée. La configuration de cette structure est : Substrat piézoélectrique/électrodes interdigitées/Couche isolante/Couche sensible magnéto-élastique. Les différents paramètres de la structure, notamment les épaisseurs des différentes couches et leurs natures ont été optimisées théoriquement au regard du facteur de qualité, du facteur de couplage électromécanique et de la sensibilité au champ magnétique. Des dispositifs utilisant les configurations optimales ont été réalisés et caractérisés et leurs performances comparées au prédiction théoriques. Nous avons montré que le capteur peut être conçu pour répondre aux besoins de l’application en ce qui concerne la gamme de l’intensité du champ à mesurer et de la sensibilité visée. Ainsi le CoFeB utilisé comme couche sensible magnéto-élastique permet une meilleure sensibilité mais sur une étendue étroite du champ magnétique alors que le nickel permet d’étendre la gamme de mesure mais avec moins de sensibilité. Nous avons également montré que l’utilisation comme couche isolante de matériau dur comme l’alumine permet une meilleure sensibilité. Cette sensibilité est également fortement augmentée pour un fonctionnement à hautes fréquences / The aim of this Ph.D. Thesis is to study piezo-magnetic surface acoustic wave (SAW) sensor. Accurate and fully coupled physical model was numerically implemented in order to investigate the sensitivity of SAW devices using the magneto-elastic interaction with an external magnetic field. The different parameters of the structure, including the thicknesses of the various layers and their natures were theoretically optimized with regard to the quality factor, the electromechanical coupling factor and the sensitivity to the magnetic field. Devices using the optimal settings have been made and characterized, and their performance compared to the theoretical prediction. We have shown that the sensor can be designed to meet the needs of the application as regards the range of the field strength to be measured and the target sensitivity. Thus the CoFeB used as magneto-elastic sensitive layer provides better sensitivity but on a narrow stretch of the magnetic field while the nickel expands the measurement range but with less sensitivity. We have also shown that the use of hard material as insulating layer, such as alumina, allows better sensitivity. This sensitivity is also greatly increased when the sensor is operating at high frequencies

Materiais magnetostrictivos, como o TERFENOL-D (Tb0,27-0,30Dy0,73-0,70Fe2) e o GALFENOL (Fe72-82Ga18-28), são aplicados em diversos tipos de atuadores, sensores e coletores de energia. Contudo, existe a necessidade de novos materiais que sejam mais baratos, ambientalmente amigáveis e com melhores propriedades mecânicas. Por essa razão, as ligas de Fe-Al são uma alternativa, já que o alumínio é mais abundante na natureza e é sete vezes mais barato que o gálio. O objetivo desse trabalho foi estudar a influência de dois tratamentos termomecânicos nas propriedades magnéticas das ligas (Fe1-xAlx)98,4B1,6, onde x = 0,18; 0,13 e 0,21. No primeiro processamento, as ligas foram submetidas a um tratamento térmico sob compressão para introduzir uma anisotropia magnetocristalina extrínseca. Para compressões de até 180 MPa, as ligas tratadas sob tensão obtiveram valores de magnetostricção e dos coeficientes piezomagnéticos maiores que o das ligas sem tratamento. Ou seja, este processamento aumentou a sensibilidade das ligas como atuador (d33) e sensor (d33 *). No segundo processamento termomecânico, amostras com formato de chapa foram laminadas e tratadas termicamente para induzir um crescimento anormal de grãos e consequentemente uma textura. Embora não tenha ocorrido crescimento de grão anormal durante o tratamento térmico, os valores de magnetostricção foram maiores que o das amostras como fundidas. Ambos processamentos termomecânicos foram efetivos para melhorar as propriedades magnéticas e a liga (Fe0,87Al0,13)98,4B1,6 foi a que obteve os maiores valores de magnetostricção e dos coeficientes piezomagnéticos. Em outras palavras, dentre as ligas estudadas, esta composição foi mais promissora para ser aplicada em atuadores e sensores. / Magnetostrictive materials, like TERFENOL-D (Tb0.27-0.30Dy0.73-0.70Fe2) and GALFENOL (Fe72-82Ga18-28), are applied in several types of sensors, actuators and energy harvesting. Nevertheless, there is the necessity of new materials that are cheaper, environmentally friendly and with good mechanical properties. For that reason, the Fe-Al alloys are an alternative, since the aluminum is more abundant in nature and is seven times cheaper than gallium. The goal of this work is to study the influence of two thermomechanical proceeding at magnetic properties of the (Fe1- xAlx)98.4B1.6 alloys, which x = 0.18; 0.13 e 0.21. At the first proceeding, the alloys were submitted to a stress annealing to introduce an extrinsic magnetocrystalline anisotropy. Up to 180 MPa of compression stress, stress annealed alloys have magnetostriction and piezomagnetic coefficient values higher than the alloys without annealing. In other words, this proceeding increased the alloys sensibility to be applied like actuators (d33) and sensors (d33 *). At the second thermomechanical proceeding, samples with sheet format were rolled and annealed to induce an abnormal grain growth and, consequently, a texture. Although the annealing not produced an abnormal grain growth, the magnetostriction values are higher than for the as-cast samples. Both proceedings were efficient to improve the magnetic properties and the (Fe0.87Al0.13)98.4B1.6 alloy achieved the higher values of magnetostriction and piezomagnetic coefficient. In another words, between the studied alloys, this composition was the most promising to be applied like actuators and sensors.

Materiais magnetostrictivos, como o TERFENOL-D (Tb0,27-0,30Dy0,73-0,70Fe2) e o GALFENOL (Fe72-82Ga18-28), são aplicados em diversos tipos de atuadores, sensores e coletores de energia. Contudo, existe a necessidade de novos materiais que sejam mais baratos, ambientalmente amigáveis e com melhores propriedades mecânicas. Por essa razão, as ligas de Fe-Al são uma alternativa, já que o alumínio é mais abundante na natureza e é sete vezes mais barato que o gálio. O objetivo desse trabalho foi estudar a influência de dois tratamentos termomecânicos nas propriedades magnéticas das ligas (Fe1-xAlx)98,4B1,6, onde x = 0,18; 0,13 e 0,21. No primeiro processamento, as ligas foram submetidas a um tratamento térmico sob compressão para introduzir uma anisotropia magnetocristalina extrínseca. Para compressões de até 180 MPa, as ligas tratadas sob tensão obtiveram valores de magnetostricção e dos coeficientes piezomagnéticos maiores que o das ligas sem tratamento. Ou seja, este processamento aumentou a sensibilidade das ligas como atuador (d33) e sensor (d33 *). No segundo processamento termomecânico, amostras com formato de chapa foram laminadas e tratadas termicamente para induzir um crescimento anormal de grãos e consequentemente uma textura. Embora não tenha ocorrido crescimento de grão anormal durante o tratamento térmico, os valores de magnetostricção foram maiores que o das amostras como fundidas. Ambos processamentos termomecânicos foram efetivos para melhorar as propriedades magnéticas e a liga (Fe0,87Al0,13)98,4B1,6 foi a que obteve os maiores valores de magnetostricção e dos coeficientes piezomagnéticos. Em outras palavras, dentre as ligas estudadas, esta composição foi mais promissora para ser aplicada em atuadores e sensores. / Magnetostrictive materials, like TERFENOL-D (Tb0.27-0.30Dy0.73-0.70Fe2) and GALFENOL (Fe72-82Ga18-28), are applied in several types of sensors, actuators and energy harvesting. Nevertheless, there is the necessity of new materials that are cheaper, environmentally friendly and with good mechanical properties. For that reason, the Fe-Al alloys are an alternative, since the aluminum is more abundant in nature and is seven times cheaper than gallium. The goal of this work is to study the influence of two thermomechanical proceeding at magnetic properties of the (Fe1- xAlx)98.4B1.6 alloys, which x = 0.18; 0.13 e 0.21. At the first proceeding, the alloys were submitted to a stress annealing to introduce an extrinsic magnetocrystalline anisotropy. Up to 180 MPa of compression stress, stress annealed alloys have magnetostriction and piezomagnetic coefficient values higher than the alloys without annealing. In other words, this proceeding increased the alloys sensibility to be applied like actuators (d33) and sensors (d33 *). At the second thermomechanical proceeding, samples with sheet format were rolled and annealed to induce an abnormal grain growth and, consequently, a texture. Although the annealing not produced an abnormal grain growth, the magnetostriction values are higher than for the as-cast samples. Both proceedings were efficient to improve the magnetic properties and the (Fe0.87Al0.13)98.4B1.6 alloy achieved the higher values of magnetostriction and piezomagnetic coefficient. In another words, between the studied alloys, this composition was the most promising to be applied like actuators and sensors.

In electromechanical measurement techniques, passive transducers and passive electrical networks often interact. In some applications, continua are considered as part of the system, where fields are formed and waves are propagated. In this article, networks, continua, and electromechanical transducers feature sufficient amplitude linear behavior in their environment (e.g. for operation around a bias) and are reciprocal. In addition, all elements of the system have constant parameters during the measurement. Then, the skillful application of the inherent reciprocity of these systems can lead to surprisingly useful benefits. This is shown by actual examples from metrology. The examples include the precise determination of transduction coefficients. It is also shown how the linearity of a system is checked by utilizing reciprocityrelations. Although the facts of the matter are well known, its potential is often overlooked or disregarded in measurement techniques.