Dissertations / Theses on the topic 'GMR'

Die Messung magnetischer Felder ist in der Sensorik von großem Interesse. Benötigt werden dazu physikalische Effekte, die magnetische Größen in elektrische Größen umsetzen. Ein interessanter Vertreter ist dabei der Riesenmagnetowiderstand (GMR). Systeme, die den GMR zeigen, sind Thema dieser Arbeit. Die untersuchten Systeme lassen sich in zwei Typen einteilen: Multilagen bestehen aus einer großen Zahl (30-40) nominell identischer Doppellagen aus abwechselnd ferromagnetischem und nichtmagnetischem Metall. Diese Systeme zeigen eine Widerstandsänderung mit der Stärke des externen Magnetfeldes. Untersucht wurden Schichten Co/Cu und NiFe/Cu. Es konnten Schichten mit einer Sensitivität von 3.2%/mT präpariert werden. Für den Rückgang der Signalstärke bei erhöhten Temperaturen sind, abhängig von der Cu-Dicke, zwei unterschiedliche Mechanismen verantwortlich. Diese werden diskutiert. Spin Valves bestehen aus Einzellagen unterschiedlicher Materialien (antiferro-, ferro- und paramagnetisch), meist Metalle, die eine Widerstandsänderung mit der Richtung des externen Magnetfeldes zeigen. Untersucht wurden Systeme, die auf NiO, FeMn und IrMn basieren. Die Temperaturabhängigkeit dieser Systeme zeigt Eigenschaften, die für die kommerzielle Nutzung wichtig sein können. Die mikroskopischen Ursachen werden diskutiert. Ein neu entwickeltes, leistungsfähiges Modell kann das sensorische Verhalten dieser Systeme sehr gut nachbilden und erlaubt so einen Einblick in die internen Vorgänge.

Die Messung magnetischer Felder ist in der Sensorik von großem Interesse. Benötigt werden dazu physikalische Effekte, die magnetische Größen in elektrische Größen umsetzen. Ein interessanter Vertreter ist dabei der Riesenmagnetowiderstand (GMR). Systeme, die den GMR zeigen, sind Thema dieser Arbeit. Die untersuchten Systeme lassen sich in zwei Typen einteilen: Multilagen bestehen aus einer großen Zahl (30-40) nominell identischer Doppellagen aus abwechselnd ferromagnetischem und nichtmagnetischem Metall. Diese Systeme zeigen eine Widerstandsänderung mit der Stärke des externen Magnetfeldes. Untersucht wurden Schichten Co/Cu und NiFe/Cu. Es konnten Schichten mit einer Sensitivität von 3.2%/mT präpariert werden. Für den Rückgang der Signalstärke bei erhöhten Temperaturen sind, abhängig von der Cu-Dicke, zwei unterschiedliche Mechanismen verantwortlich. Diese werden diskutiert. Spin Valves bestehen aus Einzellagen unterschiedlicher Materialien (antiferro-, ferro- und paramagnetisch), meist Metalle, die eine Widerstandsänderung mit der Richtung des externen Magnetfeldes zeigen. Untersucht wurden Systeme, die auf NiO, FeMn und IrMn basieren. Die Temperaturabhängigkeit dieser Systeme zeigt Eigenschaften, die für die kommerzielle Nutzung wichtig sein können. Die mikroskopischen Ursachen werden diskutiert. Ein neu entwickeltes, leistungsfähiges Modell kann das sensorische Verhalten dieser Systeme sehr gut nachbilden und erlaubt so einen Einblick in die internen Vorgänge.

This thesis describes a translation project carried out within the framework of the Language Toolkit program, which is the result of a collaboration between the Department of Interpretation and Translation and the Chamber of Commerce of Romagna. For this translation project, technical and promotional materials were translated from Italian into Russian for GMR ENLIGHTS S.r.l., a local company that specializes in lighting technology. Materials that were assigned for this translation project combine technical and promotional writing, which is a common feature of business-to-business promotional texts. The first chapter explores the main characteristics of texts belonging to this category and analyzes the tools and skills that a translator needs to perform promotional and technical translation. More information about the Language Toolkit program and GMR ENLIGHTS S.r.l. can be found in the second chapter. Here the work of the program is analyzed in the context of economic development and internationalization of the region of Emilia-Romagna. This is followed by a brief history of the company's development and a description of the task assigned by the company. The third chapter describes the tools that were chosen for this translation project and the resources that were used in order to acquire the relevant terminology. The fourth chapter provides a detailed analysis of all the source texts. Given the promotional nature of the texts, it was decided to adopt the functional approach to translation and analyze the texts along Nord's (2005) model of translation-oriented text analysis, which revolves greatly around the analysis of the prospective target reader. The most interesting and recurrent translation problems that were encountered in this project, and strategies adopted to solve them are described in the fifth and final chapter.

The electrodeposition is a technique that day by day is gaining positions among the mainly employed physical methods. This is due to the fact that electrodeposition shows some advantages over the physical techniques such as: versatility, selectivity, room temperature, high deposition rates, high thicknesses, among others. Therefore, the aim of this thesis is the use of the electrochemical technology to prepare Co-Ag nanostructured materials for magntoresistive applications.

The first step was the preparation of granular films. However, the big difference in the standard potentials of both metals discards their codeposition and therefore, the main problem to overcome was to reduce this difference. Different electrolytic baths containing different complexing agents (Bath 1: Thiourea, bath 2: Thiosulphate and bath 3: Chloride) were employed in order to favour the codeposition. After optimizing the composition of each solution, Co-Ag films with a distribution of nanometric cobalt particles into the silver matrix were obtained. However, the deposits prepared from baths 1 and 2 only showed giant magnetoresistnace (GMR) at low temperatures, fact that was attributed to the presence of sulphur in the magnetic/non-magnetic interfaces which hindered the magnetoresistance effect to take place. The use of a sulphur-free bath (bath 3) allowed obtaining films with GMR values up to 7% at room temperature, values higher than those published by others. The numerical analysis of the magnetoresistance curves, which allowed the decomposition of the magnetoresistance curves into its ferromagnetic (FM) and superparamagnetic (SPM) contribution, indicated the higher SPM contribution over the FM one in all the electrodeposition conditions.

On the other hand and taking profit of the versatility of the electrodeposition, Co-Ag multilayers were prepared. The magnetic (Co) and non-magnetic (Ag) layer deposition condition optimization was crucial to obtain the highest GMR values.

The electrochemical technology was also useful to prepara Co-Ag nanowires (both granular and multilayered nanowires) into the pores of polycarbonate membranes. Moreover, nanoparticles of the Co-Ag system were also prepared with a core-shell structure and by the microemulsion method. A voltammetric method was developed to univocally determine the correct core-shell structure formation. An strategy was also developed to measure the magnetoresistance of the last two kinds of nanomaterials (nanowires and nanoparticles) which corroborated their magnetoresistive behaviour.
L'electrodeposició és una tècnica que, dia rere dia, escala posicions entre les més habitualment emprades tècniques físiques de deposició. Aquest fet es deu principalment als avantatges que presenta la tècnica electroquímica front als mètodes físics, essent aquests: versatilitat, selectivitat, equipament senzill, temperatura ambient, elevades velocitats de deposició, gruixos importants,..Aquest projecte de tesi desenvolupa la preparació electroquímica de materials nanoestructurats cobalt-plata, material que potencialment és útil en aplicacions magnetorresistives.

El nostre objectiu inicial va ser la preparació de pel·lícules granulars. El primer problema que va haver de superar-se per aconseguir la codeposició d'ambdós metalls va ser reduir l'elevada diferència entre els seus potencials de deposició. Es van utilitzar diferents banys electrolítics contenint agents complexants (bany 1:Tiourea, bany 2: Tiosulfat i bany 3: Clorurs) per tal d'afavorir la codeposició, Les formulacions optimitzades d'aquests banys van permetre aconseguir dipòsits amb una dispersió de partícules nanomètriques de cobalt a la matriu de plata. No obstant això els dipòsits preparats a partir dels banys 1 i 2 únicament presentaren magnetorresistència gegant a temperatures criogèniques, fet que es va relacionar amb la presència de sofre a les interfases magnètiques/no magnètiques, proposta que es va confirmar posteriorment.

Afortunadament el bany base-clorurs (bany 3) va permetre obtenir dipòsits amb valors de GMR de fins a un 7% a temperatura ambient, valors sensiblement superiors als trobats a la literatura. Un tractament de les dades experimentals amb un model teòric va permetre establir la contribució a la magnetoresistència de les partícules de cobalt d'acord amb la seva mida.

D'altre banda aprofitant la versatilitat de l'electrodeposició, es va procedir a la preparació de multicapes Co-Ag. L'optimització de les condicions d'electrodeposició tant de la capa magnètica (Co) com de la capa no magnètica (Ag) va ser decisiva per tal d'obtenir estructures amb GMR.

El mètode electroquímic va ser útil per obtenir fils de mida nanomètrica de Co-Ag a partir de templates de membranes de policarbonat, tant granulars com en forma de multicapa. D'aquest material, Co-Ag, s'han preparat nanoparticules amb estructura nucli-corona pel mètode de la microemulsió, per les que s'ha desenvolupat un mètode electroquímic de caracterització que ha permès comprovar la correcta formació de les nanoparticles. Per la mesura de GMR d'aquests sistemes nanomètrics (nanofils i nanoparticles) s'ha dissenyat un procediment experimental de mesura que ha confirmat el caràcter magnetoresistiu de les nanoestructures.

PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO
COORDENAÇÃO DE APERFEIÇOAMENTO DO PESSOAL DE ENSINO SUPERIOR
PROGRAMA DE SUPORTE À PÓS-GRADUAÇÃO DE INSTS. DE ENSINO
PROGRAMA DE SUPORTE À PÓS-GRADUAÇÃO DE INSTITUIÇÕES COMUNITÁRIAS DE ENSINO PARTICULARES
Amperímetros convencionais devem ser inseridos em série com o elemento no qual se deseja medir a corrente, constituindo uma forma de medição invasiva. Amperímetros alicate, baseados em bobinas, realizam medições de forma não invasiva, mas são limitados a correntes alternadas. Para medição de correntes contínuas, amperímetros baseados no efeito Hall são utilizados, mas possuem baixo nível de tensões de saída e pouca estabilidade em relação à temperatura. O objetivo desta dissertação foi desenvolver um protótipo de amperímetro baseado em magnetômetros de magnetorresistência gigante (GMR) capaz de medir correntes contínuas, de forma não invasiva e com alta resolução em relação aos amperímetros alicate. A metodologia dividiu-se em: (i) utilização de dois magnetômetros GMR para medir o campo magnético gerado pela corrente elétrica em um condutor; (ii) projeto e implementação de um solenoide para polarizar os sensores na faixa de operação linear; (iii) aprimoramento e desenvolvimento de circuitos eletrônicos dedicados à excitação e leitura dos GMRs; (iv) implementação de algoritmos para solução do problema inverso, isto é, a partir da saída do circuito, em mV, estimar a corrente que passa pelo condutor e a distância entre este e o amperímetro. Foram realizados 60 testes, com correntes variando de -3 A a 3 A, com passos de 0,1 A. O protótipo foi capaz de estimar a corrente elétrica com incerteza expandida, do tipo A, de 0,091 A e 0,07 cm para a distância. Os resultados comprovam a viabilidade da realização de medições de corrente, por aproximação, utilizando sensores GMR.
Conventional ammeters should be inserted in series with the element in which the current is to be measured, thus constituting an invasive measurement form. Clamp ammeters, based on coils, are able to measure non-invasively but are limited to alternating currents. For measurement of direct currents, Hall-based ammeters are used, but have low output voltages and little temperature stability. Thus, the objective of this dissertation was to develop a prototype based on giant magnetoresistance (GMR) magnetometers capable of measuring direct currents, non-invasively and with high resolution in relation to clamp ammeters. The methodology was divided into: (i) the use of two GMR magnetometers to measure the magnetic field generated by the electric current in a conductor; (ii) design and implementation of a solenoid to polarize the sensors in the linear operating range; (iii) improvement and development of electronic circuits dedicated to the excitation and reading the GMRs; (iv) implementation of algorithms to solve the inverse problem, that is, from the outputs of the circuit, in mV, estimate the current passing through the conductor and the distance between it and the ammeter. Sixty tests were performed, with currents varying from -3 A to 3 A, with steps of 0.1 A. The prototype was able to estimate the electrical current with type A expanded uncertainty of 0.091 A and 0.07 cm for the distance. The results demonstrate the feasibility of conducting current measurements by approximation using GMR sensors.

Heusler alloys are a class of materials with some of the greatest potential for the advancement of magnetic recording and memory. Their combination of high magnetisations, Curie temperatures and spin polarisations make them ideal for device applications. However perpendicular anisotropy is difficult to achieve in GMR devices as an interface with an oxide is required. To develop these materials for GMR application the perpendicular anisotropy must be induced in other ways. In this work polycrystalline Co2FeSi and Co2FeAl0.5Si0.5 Heusler alloys have been deposited on body-centred cubic seed layers of vanadium and tungsten. Their magnetic and crystallographic properties have been measured and quantified using a range of techniques, significantly mangnetometry and X-ray diffractometry. With the use of vanadium seed layers Co2FeSi was deposited with a strong {110} texture out-of-plane, ideal for the crystallisation of the material. In Co2FeSi layers < 5 nm thick perpendicular anisotropy is induced by strain at the interface with vanadium. This is further enhanced by the addition of a top layer of vanadium, doubling the interface area and increasing the anisotropy. When tungsten seed layers are used instead there is a significant increase in the perpendicular anisotropy of Co2FeSi. This anisotropy is maintained in films with thicknesses up to and beyond 12.5 nm. When incorporated into GMR stacks both Co2FeSi and Co2FeAl0.5Si0.5 are found to exhibit layer thickness dependent switching, ideal for device application. The heating of the film pre-deposition is found to heavily influence the structure and anisotropy of the samples, even at modest temperatures < 70 ±C for less than two minutes. GMR devices were fabricated and a proof of principle for a perpendicular CPP-GMR device based on Heusler alloys presented.

Magnetic fluid or magnetic liquid are colloidal solutions of ultra-fine magnetic materials. Ferromagnet-ic materials consist of magnetic or other compound containing iron, nickel or cobalt, by a particle size of 5 to 50 nanometers, generally in a superparamagnetic, ferromagnetic or diamagnetic state. Magnetic fluids have a unique combination of strength and ability to interact with the magnetic field. This paper proposes to estimate and detect magnetic fluid weight density (concentration as low as 1%) by giant magnetore-sistance (GMR) sensor. The high sensitivity of the sensor is around 11 μV/μT. We propose to use it for bio-applications to characterize magnetic microfluides. For this application a Helmholtz coil was simulated and fabricated to make more uniform magnetic flux density. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/34967

L'objectif de cette thèse est de développer des bio-capteurs à base de magnétorésistance géante (GMR), ainsi que l'électronique de conditionnement associée, en vue de caractériser magnétiquement des ferrofluides biologiques. Ce travail a été réalisé en collaboration avec le Pr Sotoshi YAMADA de l'Institut « Nature and Environmental Technology» de l'Université de Kanazawa. La première partie porte sur l'état de l'art et les méthodes de mesures des propriétés magnétiques des ferrofluides et la physique de l'effet GMR. La deuxième partie concerne la mise en place d'un dispositif de mesure pour déterminer et caractériser la valeur de la sensibilité de chaque capteur. Cette sensibilité est une caractéristique cruciale pour toute application biomédicale. Sa connaissance et son optimisation permettent d'envisager des mesures précises et justes des propriétés magnétiques des ferrofluides notamment à bas niveau de signal. La troisième partie, également expérimentale, décrit les mesures de la perméabilité relative (µr) et de la susceptibilité (X) de fluides magnétiques (ferrofluides) par des capteurs GMR I, II. En outre, afin de confirmer les résultats expérimentaux obtenus avec ces capteurs, nous les avons comparés à ceux obtenus avec d'autres méthodes comme la magnétométrie à échantillon vibrant (VSM) ou à des calculs théoriques. Le quatrième et dernier chapitre présente les résultats expérimentaux de la perméabilité relative et de la susceptibilité d'un marqueur magnétique permettant la détection de la bactérie pathogène Escherichia coli O157: H7
The intent of this thesis is to develop bio-sensors based on giant magnetoresistance (GMR) and the associated conditioning electronics, to characterize magnetically organic ferrofluids. This work was done in collaboration with Pr Sotoshi YAMADA of the Institute "Nature and Environmental Technology" at the University of Kanazawa. The first part focuses on the state of the art and the methods for magnetic properties measurements of ferrofluids and the description of the GMR effect. The second part concerns the introduction of a measuring device to determine and characterize the value of the sensitivity of each sensor. This sensitivity is a crucial parameter for any biomedical application. Its knowledge allows optimization of sensors ability to measure very low magnetic parameters of ferrofluids very precisely. The third experimental part describes measurements of relative permeability (µr) and susceptibility (X) of magnetic ferrofluids with GMR sensors I, II. In addition, to confirm the experimental results obtained with these sensors, we have compared them to those obtained with other methods such as vibrating sample magnetometer (VSM) or by theoretical calculations. The fourth and last chapter presents the experimental results of the relative permeability and susceptibility of a magnetic marker used to detect pathogenic bacteria (Escherichia coli O157: H7)

L'objectif de cette thèse est de développer des bio-capteurs à base de magnétorésistance géante (GMR), ainsi que l'électronique de conditionnement associée, en vue de caractériser magnétiquement des ferrofluides biologiques. Ce travail a été réalisé en collaboration avec le Pr Sotoshi YAMADA de l'Institut « Nature and Environmental Technology» de l'Université de Kanazawa. La première partie porte sur l'état de l'art et les méthodes de mesures des propriétés magnétiques des ferrofluides et la physique de l'effet GMR. La deuxième partie concerne la mise en place d'un dispositif de mesure pour déterminer et caractériser la valeur de la sensibilité de chaque capteur. Cette sensibilité est une caractéristique cruciale pour toute application biomédicale. Sa connaissance et son optimisation permettent d'envisager des mesures précises et justes des propriétés magnétiques des ferrofluides notamment à bas niveau de signal. La troisième partie, également expérimentale, décrit les mesures de la perméabilité relative (µr) et de la susceptibilité (X) de fluides magnétiques (ferrofluides) par des capteurs GMR I, II. En outre, afin de confirmer les résultats expérimentaux obtenus avec ces capteurs, nous les avons comparés à ceux obtenus avec d'autres méthodes comme la magnétométrie à échantillon vibrant (VSM) ou à des calculs théoriques. Le quatrième et dernier chapitre présente les résultats expérimentaux de la perméabilité relative et de la susceptibilité d'un marqueur magnétique permettant la détection de la bactérie pathogène Escherichia coli O157: H7
The intent of this thesis is to develop bio-sensors based on giant magnetoresistance (GMR) and the associated conditioning electronics, to characterize magnetically organic ferrofluids. This work was done in collaboration with Pr Sotoshi YAMADA of the Institute "Nature and Environmental Technology" at the University of Kanazawa. The first part focuses on the state of the art and the methods for magnetic properties measurements of ferrofluids and the description of the GMR effect. The second part concerns the introduction of a measuring device to determine and characterize the value of the sensitivity of each sensor. This sensitivity is a crucial parameter for any biomedical application. Its knowledge allows optimization of sensors ability to measure very low magnetic parameters of ferrofluids very precisely. The third experimental part describes measurements of relative permeability (µr) and susceptibility (X) of magnetic ferrofluids with GMR sensors I, II. In addition, to confirm the experimental results obtained with these sensors, we have compared them to those obtained with other methods such as vibrating sample magnetometer (VSM) or by theoretical calculations. The fourth and last chapter presents the experimental results of the relative permeability and susceptibility of a magnetic marker used to detect pathogenic bacteria (Escherichia coli O157: H7)

La Spectroscopie par Résonance Magnétique Nucléaire (NMRS) est une technique largement connue pour l'analyse de molécules chimique et biologiques. Cependant, en raison de la faible intensité des signaux de RMN, il est très difficile de travailler sur des volumes inférieurs à un mm³. Cette limitation a conduit à la mise au point de capteurs miniaturisés tels que les microbobines, les centres NV et des magnétomètres atomiques. Au cours de cette thèse nous avons développé une approche basée sur l'utilisation de capteurs à MagnétoRésistance Géante (GMR), capteurs magnétiques à large de la bande, capable de détecter localement le signal RMN. Les capteurs GMR, sur différents substrats tels que le silicium, le verre et l’alumine, ainsi que la configuration du montage RMN ont été spécifiquement conçus pour avoir une détectivité dans la gamme de 20pt/sqrt(Hz) et capable de travailler avec un champ magnétique externe jusqu'à 1 Tesla. Nous allons d’abord présenter les résultats obtenus à 0.3T sur de l’eau, dans la configuration où la RMN locale est effectuée dans un grand volume, mettant en évidence le caractère fonctionnel du montage. Puis les résultats obtenus, également à 0.3T, de la spectroscopie RMN de liquides modèle comme l'éthanol où le volume sondé estimé est de l’ordre de 20x20x20μm³. Finalement un résultat à un champ magnétique plus élevé, 0.6T, a également été montré sur de l’eau
Nuclear Magnetic Resonance Spectroscopy (NMRS) is a widely known technique for chemical and biological molecule analysis. However due to the weakness of the NMR signals, it is very difficult to work on volumes lower than a mm³. That limitation has led to the development of miniaturized sensors such as microcoils, NV centers and atomic magnetometers. We will present our approach based on the use of Giant Magnetoresistive sensors (GMR) as wide band magnetic sensors to detect locally the NMR signal. GMR sensors and NMR set up have been specifically designed to have a detectivity in the range of 20pt/sqrt(Hz) and able to work with external magnetic field up to 1T. We will first present the results obtained at 0.3T on water, in the configuration where the local NMR is done on a high volume, highlighting the functionality of the set-up. Then we will show the results obtained also at 0.3T, of NMR spectroscopy of model liquids like Ethanol on a volume of the order of 20x20x20μm³. Finally, a result at a higher magnetic field, 0.6T, has also been obtained on water

L’activité cérébrale se traduit par des courants ioniques circulant dans le réseau neuronal.La compréhension des mécanismes cérébraux implique de sonder ces courants, via des mesures électriques ou magnétiques, couvrant différentes échelles spatiales. A l’échelle cellulaire, les techniques d’électrophysiologie sont maitrisées depuis plusieurs décennies, mais il n’existe pas actuellement d’outils de mesure locale des champs magnétiques engendrés par les courants ioniques au sein du réseau neuronal. La magnéto-encéphalographie(MEG) utilise des SQUIDs(Superconducting QUantum Interference Devices)fonctionnant à très basse température, placés en surface du crâne, qui fournissent une cartographie des champs magnétiques mais dont la résolution spatiale est limitée du fait de la distance séparant les capteurs des cellules actives. Le travail présenté dans cette thèse propose de développer des capteurs magnétiques à la fois suffisamment sensibles pour être capable de détecter le champ magnétique extrêmement faible générés par les courants neuronaux (de l’ordre de 10⁻⁹ T), et dont la géométrie est adaptable aux dimensions des cellules, tout en fonctionnant à température ambiante. Ces capteurs,basés sur l’effet quantique de magnétorésistance géante (GMR, sont suffisamment miniaturisables pour être déposés à l’extrémité de sondes d’une finesse de l’ordre de 100 μm. L’utilisation de capteurs GMR pour la mesure de signaux biomagnétiques fut d’abord testée lors d’expériences in-vitro, réalisées sur le muscle soléaire de souris. Ce système biologique a été choisi pour sa simplicité,rendant la modélisation accessible, ainsi que pour sa robustesse, permettant d’avoir des résultats fiables et reproductibles. Le parfait accord entre les prédictions théoriques et les signaux magnétiques mesurés valide cette technologie. Enfin, des expériences in vivo dans le cortex visuel du chat ont permis de réaliser la toute première mesure de la signature magnétique de potentiels d’action générés par des neurones corticaux, ouvrant la voie à la magnétophysiologie
Information transmission in the brain occurs through ionic currents flowing inside the neuronal network. Understanding how the brain operates requires probing this electrical activity by measuring the associated electric or magnetic field. At the cellular scale, electrophysiology techniques are well mastered, but there is no tool to perform magnetophysiology. Mapping brain activity through the magnetic field generated by neuronal communication is done via magnetoencephalography (MEG). This technique is based on SQUIDs (Superconducting Quantum Interference Devices) that operate at liquid Helium temperature. This parameter implies to avoid any contact with living tissue and a shielding system that increases the distance between the neurons and the sensors, limiting spatial resolution. This thesis work aims at providing a new tool to performmagnetic recordings at the neuronal scale. The sensors developed during this thesis are based on the Giant Magneto-Resistance (GMR) effect. Operating at room temperature, they can be miniaturize and shaped according to the experiment, while exhibiting a sensitivity that allows to measure amplitude of 10⁻⁹ T. Before targeting neurons, the use of GMR-based sensors for magnetic recordings of biological activity has been validated through invitro experiments on the mouse soleus muscle. This biological system has been chosen because of its simple organization, allowing for a realistic modelling, and for its robustness, in order to get reliable and replicable results. The perfect agreement between the measurements and the theoretical predictions represents a consistent validation of the GMR technology for biological applications. Then a specially adapted needle-shaped probe carrying micron-sized GMR sensors has been developed for in-vivo experiment in cat visual cortex. The very first magnetic signature of action potentials inside the neuropil has been measured, paving the way towards magnetophysiology

An ultra-short echo time (UTE) magnetic resonance imaging (MRI) sequence was used together with other MRI sequences to evaluate the possibility of segmenting air, soft tissues and bone. Three patients were imaged with the UTE sequence and other sequences as well as with computed tomography (CT). An algorithm using Gaussian mixture models was developed and applied to the problem of segmenting the MR images. A similar algorithm was developed and used to generate an artificial CT image from the MR data. The images of the first patient were used as training data for the algorithms and the images of the other two patients were used for validation. It was found that less than 20 percent of the volume inside the head was misclassified and that the root mean square error of the artificial CT image was less than 420 Hounsfield units. Finally a volunteer was imaged in the same way but with an additional UTE sequence with a larger flip angle. The results suggested that the additional image may improve segmentation further.
En sekevens för bildgivande magnetresonans (MRI) med ultrakort ekotid (UTE) användes tillsammans med andra MRI-sekvenser till att utvärdera möjligheten att segmentera luft, mjukvävnad och ben. Bilder togs av tre patienter med UTE-sekvensen och med övriga sekvenser samt med datortomografi (CT). En algoritm baserad på en blanding av normalfördelningar utvecklades och tillämpades på MR-segmenteringsproblemet.En likande algoritm utvecklades och användes till att skapa en konstgjord CT-bild utifrån MR-bilderna.Bilderna tagna av den första patienten användes till att träna algoritmerna medan bilderna av de två andra patienterna användes för validering. Mindre än 20 procent av volymen inuti huvudet felklassificerades och det kvadratiska medelvärdet av avvikelserna i den konstgjorda CT-bilden var mindre än 420 hounsfieldenheter. Slutligen togs bilder av en frivillig på samma sätt men med ytterligare en UTE-sekvens med en större flippvinkel. Resultatet antyder att den nya bilden kan bidra till en förbättrad segmentering.

Il presente lavoro di tesi è il risultato dell’adesione al progetto “Language Toolkit”, promosso dalla Camera di Commercio della Romagna e dal Dipartimento di Interpretazione e Traduzione (DIT) di Forlì con lo scopo di garantire un maggiore grado di internazionalizzazione alle imprese romagnole nonché un primo approccio al mondo del lavoro agli studenti laureandi. Nello specifico, l’elaborato è stato redatto in seguito a un tirocinio di 300 ore svolto con l’azienda forlivese GMR Enlights, che ha riguardato la traduzione in tedesco di documentazione promozionale e tecnica (il company profile e la scheda tecnica di un proiettore). La tesi è composta da cinque capitoli che ripercorrono l’intero processo traduttivo. Il primo capitolo fornisce una descrizione generale del progetto, dell’internazionalizzazione delle PMI, dell’azienda GMR Enlights e della traduzione verso la lingua straniera. Nel secondo capitolo si procede a discutere l’importanza storica della traduzione tecnica, le teorie di traduzione più importanti in tale ambito, la comunicazione tecnica e le caratteristiche dei linguaggi specialistici. Nel terzo capitolo viene affrontato il concetto di “tipo testuale” e viene svolta un’analisi approfondita dei testi di partenza. Il quarto capitolo è dedicato alle risorse e alle tecnologie traduttive utilizzate prima e durante il processo di traduzione, ossia i corpora monolingui specialistici e comparabili per lo studio di testi paralleli e per l’estrazione terminologica; SDL MultiTerm per la creazione di un termbase; SDL Trados Studio per la traduzione assistita. Infine, nel quinto e ultimo capitolo vengono riportate le procedure ascrivibili alla macrostrategia generale di traduzione e le microstrategie adoperate per risolvere i problemi traduttivi ai vari livelli testuali.

Conventional wire bond power modules have limited application for high-current operation, mainly because of their poor thermal management capability. Planar power modules have excellent thermal management capability and lower parasitic inductance, which means that the planar packaging method is desirable for high-power applications. For these reasons, a planar power module for an automotive motor drive system was developed, and a gate-driver circuit with an over-current protection was planned to integrate into the module. This thesis discusses a current-sensing method for the planar module, and the integrated gate driver circuit with an over-current protection. After reviewing several current-sensing methods, it becomes clear that most popular current-sensing methods, such as the Hall-Effect sensor, the current transformer, the Shunt resistor, and Rogowski coils, exhibit limitations for the planar module integration. For these reasons, a giant magneto resistive (GMR) magnetic-field detector was chosen as a current-sensing method. The GMR sensor utilizes the characteristics of the giant magneto resistive (GMR) effect in that it changes its resistance when it is exposed to the magnetic-flux. Because the GMR resistor can be fabricated at the wafer level, a packaged GMR sensor is very compact when compared with conventional current sensors. In addition, the sensor detects magnetic-fields, which does not require direct contact to the current-carrying conductor, and the bandwidth of the sensor can be up to 1 MHz, which is wide enough for the switching frequencies of most of motor drive applications. However, there are some limiting factors that need to be considered for accurate current measurement: â ¢ Operating temperature â ¢ Magnetic-flux density seen by a GMR resistor â ¢ Measurement noise If the GMR sensor is integrated into the power module, the ambient temperature of the sensor will be highly influenced by the junction temperature of the power devices. Having a consistent measurement for varying temperature is important for module-integrated current sensors. An experiment was performed to see the temperature characteristics of a GMR sensor. The measurement error caused by temperature variation was quantified by measurement conditions. This thesis also proposes an active temperature error compensation method for the best use of the GMR sensor. The wide current trace of the planar power module helps to reduce the electrical/thermal resistance, but it hinders having a strong and constant magnetic-field-density seen by the GMR sensor. In addition, the eddy-current effect will change the distribution of the current density and the magnetic-flux-density. These changes directly influence the accurate measurement of the GMR sensor. Therefore, analyzing the magnetic-flux distribution in the planar power module is critical for integrating the GMR sensor. A GMR sensor is very sensitive to noise, especially when it is sensing current flowing in a wide trace and exposed to external fields, neither of which can be avoided for the operation of power modules. Post-signal processing is required, and the signal-conditioning circuit was designed to attenuate noise. The signal-conditioning circuit was designed using an instrumentation amplifier, and the circuit attenuated most of the noise that hindered accurate measurement. The over-current protection circuit along with the gate driver circuit was designed, and the concept was verified by experiments. The main achievements of this study can be summarized as: â ¢ Characterization of conventional current-sensing methods â ¢ Temperature characterization of the GMR resistor â ¢ Magnetic-flux distribution of the planar power module â ¢ Design of the signal-conditioning circuit and over-current protection circuit
Master of Science

L’effet de magnétorésistance géante (GMR) permet de fabriquer des capteurs magnétiques avec une bonne sensibilité dont la résistance est proportionnelle au champ magnétique. De plus, ils sont sensibles à petite taille (quelques microns), à température ambiante et selon une direction de sensibilité unique. Ce sont donc des capteurs intéressants pour mesurer les champs magnétiques générés par l’activité électrique des neurones à l’échelle locale, comme les potentiels d’action, dont l’amplitude est attendue entre 10 et 100 pT à 1 kHz. Comme les capteurs GMR ont une limite de détection (LOD) de l‘ordre du nT à basse fréquence, plusieurs études ont été menées, notamment sur la taille et la composition du capteur GMR pour l’améliorer. La sonde qui implémente ces capteurs pour les mesures in-vivo, appelée magnétrode, a également été optimisée selon deux axes particuliers : sa pointe est affinée pour en limiter l’invasivité d’une part et intègre plusieurs capteurs GMR qui peuvent notamment réaliser des mesures en 2D d’autre part. Ces magnétrodes ont ainsi été appliquées à la mesure in-vivo sur des rongeurs. Les sondes ainsi développées et optimisées conservent une LOD de 1 nT autour de 1 kHz et ont gagné en stabilité ce qui a permis de réduire le niveau de bruit pendant les expériences in-vivo en moyennant sur un nombre important d’évènements. De plus, une magnétrode permettant de mesurer un champ magnétique en 2D a été développée. Enfin, les capteurs GMR sont à l’état de l’art sur une magnétrode dont la pointe a été affinée pour une épaisseur finale de 25 µm. Les sondes réalisées permettent de mesurer in-vivo des signaux magnétiques d’une amplitude de l’ordre de 250 pT
Magnetic sensors based on the Giant Magnetoresistance (GMR) effect have a good sensitivity with a resistance which is proportional to the external magnetic field. In addition, they are sensitive at small scale (a few microns), at room temperature and along a unique axis of sensitivity. Thus, they are good candidates to measure the magnetic fields generated by the electrical activity of neurons at local scale like action potentials which have an amplitude expected between 10 and 100 pT at 1 kHz. As GMR sensors have a limit of detection (LOD) in the nT range at low frequency, several studies were conducted, including on the size and composition of the GMR sensor, to improve it. A probe that implements GMR sensors to conduct in-vivo experiments, called magnetrode, was also optimized in two ways. First, the tip thickness is reduced to decrease its invasiveness. Second, several GMR sensors are embedded on the magnetrode and in particular for 2D measurements. The optimized magnetrodes were then used for in-vivo recordings on rodents. They keep a limit of detection of 1 nT around 1 kHz for an increased stability which enables the reduction of the noise level of in-vivo experiments thanks to an averaging over a large number of events. In addition, a magnetrode for 2D measurements was developed. Finally, GMR sensors at the state of the art are implemented on a magnetrode with a tip thickness decreased down to 25 µm. Magnetrodes are able to detect in-vivo a magnetic signal with an amplitude around 250 pT

High target utilisation sputtering (HiTUS) is a relatively new thin film deposition technique that generates a high density plasma remotely from the sputter target. This method has been employed firstly to investigate FePt and FePtN thin films for high density data storage media applications and secondly to investigate the production of a GMR/PZT hybrid structure (multi-ferroism) for improvements to magneto-resistive read-sensor devices in hard disk drives and potentially for other novel multi-ferroic applications. The magnetic and structural properties of FePt and FePtN films, prepared by the HiTUS method, on both silicon and glass substrates have been investigated before and after annealing at temperatures in the range of 300 to 800 ◦C. It is shown that during thermal annealing there is a degradation in magnetic properties of the FePt films at around 400 ◦C due to the formation of silicides as the thermal processing promotes the reaction of the film with the substrate. However, in the FePtN samples coercivity values continue to rise with annealing temperatures above 400 ◦C. XRD analysis confirms that silicide formation is suppressed in films containing nitrogen up to 800 ◦C. Using the HiTUS technique, there is evidence that L10 ordering of FePt has occured at annealing temperature of 400 ◦C with in plane and out of plane coercivities of 7180 Oe and 6300 Oe respectively. Finally, it is shown that HiTUS is capable of depositing ultra thin multilayer GMR structures onto a variety of substrates; silicon, glass, flexible kapton film and PZT. It is interesting to find that the GMR ratio obtained on kapton film (14.39 %) is almost as high as that on silicon (16.15 %), with much scope for improve- ment. Multi-ferroic composite films consisting of the GMR multilayer structure [Co(8 °A)/Cu(21 °A)]×20/Co(12 °A) on PZT substrates were fabricated and magneto- electric coupling effects explored. It was found that AC voltages applied across the composite GMR/PZT structure produced a marked decrease in the coercivity of the GMR layer. However, DC voltages did not produce any measurable magnetic effects. Careful investigation revealed that the reduction in coercivity observed during AC measurements was, in fact, due to sample heating effects.

Dans cette thèse, nous présentons la conception et les performances de capteurs magnétiques basés sur les technologies AMR et GMR en vue d'une utilisation dans la navigation. Afin d'obtenir une sensibilité et une linéarité optimales à champ nul, le design des capteurs utilise des barberpoles et un pont de wheatstone pour l'un et prend avantage des différentes anisotropies et couplages pour l'autre. Les capteurs sont fabriqués par pulvérisations cathodiques et photolithographies et leurs performances en terme de sensibilité, de linéarité et de bruit sont testées et comparées. La conception de gradiomètres nécessaires à la navigation magnéto-inertielle repose sur l'utilisation de magnétorésistances placées aux extrémités du capteur reliées par un pont de WheatStone dont la sortie est proportionnelle au gradient du champ magnétique. Des concentrateurs de Flux destinés à amplifier le champ afin d'améliorer la sensibilité sont conçus et testés sur les capteurs. Un concentrateur de flux destiné à amplifier un champ ayant la forme du gradient est proposé comme amélioration des gradiomètres. Des solutions innovantes pour le swithching d'anisotropie et la compensation d'offset utilisant l'effet Hall de spin et le couplage spin-transfer sont étudiées. Dans cette optique, un dispositif de mesure du couplage spin-transfer appelé spin-torque-bridge est conçu et utilisé pour étudier l'effet Hall de spin et le spin transfer dans différentes multi-couches
In this work, we present the conception and the performances of AMR and GMR-based sensors for navigation applications In order to obtain the best sensitivity and linearity at zero field, the design include barberpoles and a Wheatstone bridge for the first and takes advantage of the different anisotropies and coupling for the other. The sensor are fabricated by magnetron sputtering and photolithography and their performances in terms of sensitivity, linearity and noise are compared. The concept of gradiometers used for magneto-inertial navigation is based on the utilisation of magnetoresistances placed at each extremity of the sensor connected by a wheatstone bridge whose output is proportional to the gradient of the magnetic field. Flux concentrators designed to amplify the incoming field in order to improve the sensitivity are fabricated and tested on the sensors. A flux concentrator designed to amplify a magnetic gradient is proposed as an improvement of the gradiometers. Innovant solutions for low consumption anisotropy switching and offset compensation are being experimented using spin Hall effect and spin transfer torque with adjacent Pt and AuW layers. In that regard a spin torque measurement device: the spin-torque-bridge, is designed and used to study the spin hall effect and the spin transfer couplings in different multi layers

Thesis (M.S.)--University of New Orleans, 2004.
Title from electronic submission form. "A thesis ... in partial fulfillment of the requirements for the degree of Master of Science in the Department of Physics."--Thesis t.p. Vita. Includes bibliographical references.

The Cu/NiFe/Cu/Co/(CoOx) spin-valves have been prepared by the ion-beam sputtering method. Their GMR ratio and the time stability have been investigated by the magnetoresistance and the MOKE measurements at room temperature. The reproducibility of the preparation of the samples have been studied as well, i.e. two identically configurations of the layers should have the same magnetotransport properties.

Im Rahmen der vorliegenden Arbeit werden ab initio Berechnungen des Restwiderstandes von metallischen Nanostrukturen vorgestellt. Die elektronische Struktur der idealen Systeme wird mit Hilfe einer Screened KKR Greenschen Funktionsmethode im Rahmen der Vielfachstreutheorie auf der Grundlage der Dichtefunktionaltheorie berechnet. Die Potentiale von Punktdefekten werden selbstkonsistent mit Hilfe einer Dyson-Gleichung für die Greensche Funktion des gestörten Systems berechnet. Unter Nutzung der ab initio Ubergangswahrscheinlichkeiten wird der Restwiderstand durch Lösung der quasi-klassischen Boltzmann-Gleichung bestimmt. Ergebnisse für ultradünne Cu-Filme und die Leitfähigkeitsanomalie während des Wachstums von Co/Cu-Vielfachschichten werden vorgestellt. Der Einfluss von Oberflächen, geordneten und ungeordneten Grenzflächenlegierungen und von Defekten an verschiedenen Positionen in der Vielfachschicht auf den Effekt des Giant Magnetoresistance wird untersucht. Die selbstkonsistente Berechnung der Streueigenschaften und die verbesserte Lösung der Boltzmann-Transportgleichung unter Einbeziehung der Vertex-Korrekturen stellen ein leistungsfähiges Werkzeug zur umfassenden theoretischen Beschreibung dar. Sie verhelfen zu nützlichen Einsichten in die mikroskopischen Prozesse, die die Transporteigenschaften von nanostrukturierten Materialen bestimmen
A powerful formalism for the calculation of the residual resistivity of metallic nanostructured materials without adjustable parameters is presented. The electronic structure of the unperturbed system is calculated using a screended KKR multiple scattering Green's function formalism in the framework of density functional theory. The scattering potential of point defects is calculated self-consistently by solving a Dyson equation for the Green's function of the perturbed system. Using the ab initio scattering probabilities the residual resistivity was calculated solving the quasiclassical Boltzmann equation. Examples are given for the resistivity of ultrathin Cu films and the conductance anomaly during the growth of a Co/Cu multilayer. Furthermore, the influence of surfaces, ordered and disordered interface alloys and defects at different positions in the multilayer on the effect of Giant Magnetoresistance is investigated. The self-consistent calculation of the scattering properties and the improved treatment of the Boltzmann transport equation including vertex corrections provide a powerful tool for a comprehensive theoretical description and a helpful insight into the microscopic processes determining the transport properties of magnetic nanostructured materials

Bien que la physique des effets de transfert de spin ne soit pas complètement comprise, il est déjà clair que leurs applications seront de première importance pour la microélectronique: le renversement de l'aimantation induit par le courant polarisé est étudié comme méthode d'écriture alternative dans les mémoires magnétiques, et la précession de l'aimantation générée par le transfert de spin est envisagée comme principe de fonctionnement des nouveaux oscillateurs RF pour la téléphonie mobile. Cependant, si des nombreuses études on été menés dans des piliers métalliques de type Co/Cu/Co, peu de travail a été accompli sur des structures plus sophistiquées. Cette étude est l'une des premières à analyser les effets de transfert de spin dans des vannes de spin complexes, développées pour des têtes CPP-GMR, contenant un couche piégée synthétique et des couches laminées. Comme les densités de courant utilisées dans les têtes sont comparables à celles nécessaires pour générer des effets de transfert de spin, ces derniers peuvent induire du bruit parasite et affecter le fonctionnement du dispositif. Le transfert de spin dans ces multicouches a été étudié par des mesures statiques et dynamiques. L'influence de la nature des couches de lamination sur la GMR et les courants critiques a été aussi analysée. Alors que les diagrammes de phase statiques peuvent être interprétés à partir du modèle macrospin de Sionczewski, des simulations micromagnetiques sont nécessaires pour comprendre les spectres hyperfréquence. Pour la première fois, des modes de précession dans la couche piégée ont été observés. Ces modes de plus forte puissance semblent plus prometteurs pour les applications
Though the physics of spin-transfer effects is still not fully understood, it is already cIear that the applications would be of major importance for microelectronics : current induced magnetization switching is under evaluation as a new write scheme for magnetic memories, while spin-torque excitec magnetization precession may be the working principle of new RF oscillators for telecom devices. If much is known nowadays about spin-transfer in simple metallic pillars of the type Co/Cu/Co, more complicated structures have only started to be investigated recently. The present study was the first to analyze spin-transfer effects in complex spin-valves developed for CPP-GMR heads, containing exchanged biased synthetic antiferromagnetic layers, with laminated reference and free layers. As the current densities used in such devices are of the same order of magnitude as the currents at which spin-torque induced excitations are observed, these effects can generate parasitic noise and influence the functionin of the magnetic heads. Spin-transfer has been investigated in these multilayers through static and dynamic measurements and the influence ofthe laminating material on the CPP-GMR and the switching currents was analyzed as weil. While the static phase diagrams can be fairly weil understood based on Sionczewski's macrospin model, full micromagnetic simulations are required to interpret the microwave spectra. For the first time, precession states excited by the spin-polarized current in the pinned layer, considerably more coherent than the dynamics of the free layer, were unequivocally demonstrated, suggestin a new possible structure for microwave oscillators

Im Rahmen der vorliegenden Arbeit werden ab initio Berechnungen des Restwiderstandes von metallischen Nanostrukturen vorgestellt. Die elektronische Struktur der idealen Systeme wird mit Hilfe einer Screened KKR Greenschen Funktionsmethode im Rahmen der Vielfachstreutheorie auf der Grundlage der Dichtefunktionaltheorie berechnet. Die Potentiale von Punktdefekten werden selbstkonsistent mit Hilfe einer Dyson-Gleichung für die Greensche Funktion des gestörten Systems berechnet. Unter Nutzung der ab initio Ubergangswahrscheinlichkeiten wird der Restwiderstand durch Lösung der quasi-klassischen Boltzmann-Gleichung bestimmt. Ergebnisse für ultradünne Cu-Filme und die Leitfähigkeitsanomalie während des Wachstums von Co/Cu-Vielfachschichten werden vorgestellt. Der Einfluss von Oberflächen, geordneten und ungeordneten Grenzflächenlegierungen und von Defekten an verschiedenen Positionen in der Vielfachschicht auf den Effekt des Giant Magnetoresistance wird untersucht. Die selbstkonsistente Berechnung der Streueigenschaften und die verbesserte Lösung der Boltzmann-Transportgleichung unter Einbeziehung der Vertex-Korrekturen stellen ein leistungsfähiges Werkzeug zur umfassenden theoretischen Beschreibung dar. Sie verhelfen zu nützlichen Einsichten in die mikroskopischen Prozesse, die die Transporteigenschaften von nanostrukturierten Materialen bestimmen.
A powerful formalism for the calculation of the residual resistivity of metallic nanostructured materials without adjustable parameters is presented. The electronic structure of the unperturbed system is calculated using a screended KKR multiple scattering Green's function formalism in the framework of density functional theory. The scattering potential of point defects is calculated self-consistently by solving a Dyson equation for the Green's function of the perturbed system. Using the ab initio scattering probabilities the residual resistivity was calculated solving the quasiclassical Boltzmann equation. Examples are given for the resistivity of ultrathin Cu films and the conductance anomaly during the growth of a Co/Cu multilayer. Furthermore, the influence of surfaces, ordered and disordered interface alloys and defects at different positions in the multilayer on the effect of Giant Magnetoresistance is investigated. The self-consistent calculation of the scattering properties and the improved treatment of the Boltzmann transport equation including vertex corrections provide a powerful tool for a comprehensive theoretical description and a helpful insight into the microscopic processes determining the transport properties of magnetic nanostructured materials.

La microscopie à sonde locale magnétorésistive repose sur la fabrication et l’utilisation de micro-bras de levier flexibles intégrant un ou plusieurs capteurs basés sur les technologies de magnétorésistance géante (GMR) ou tunnel (TMR). Ces sondes, dont le capteur peut atteindre une taille caractéristique typique inférieure à 1 µm, permettent de mesurer l’information topographique d’un échantillon ainsi que son information magnétique simultanément et de manière décorrélée. La mesure ainsi obtenue par le capteur GMR est sensible (limite de détection de l’ordre de 1 nT), quantitative, large bande (DC-100 MHz), robuste dans le temps et ne nécessite pas de recalibration ou de ré-aimantation régulière de la sonde. Les axes d’étude principaux de cette thèse portent sur le développement et l’intégration sur des micro-bras de leviers en nitrure de silicium de nanocapteurs magnétorésistifs. Ils visent à améliorer la résolution spatiale, tout en gagnant en linéarité de la réponse magnétique et en réduisant le bruit de mesure d’origine magnétique. Des stratégies de piégeage ont été utilisées pour stabiliser le bruit dans les GMR, améliorant typiquement la limite de détection et la répétabilité d’un ordre de grandeur. Des capteurs de taille caractéristique jusqu’à la centaine de nanomètres ont été fabriqués en se basant sur des empilements GMR dédiés et à l’état de l’art. L’implémentation des pointes GMR fabriquées sur un dispositif de microscopie à force atomique (AFM) ont permis de tester leur efficacité et leur fiabilité, posant ainsi les bases d’une méthode innovante d’imagerie magnétique locale, basée sur la mesure de susceptibilité magnétique
Magnetoresistive scanning probe microscopy is based on fabrication and use of micro-cantilevers integrating giant magnetoresistive (GMR) or tunnel magnetoresistive sensors (TMR). These probes enable simultaneous measurement of decorrelated topography and local magnetic signal of the sample. The sensor can be manufactured down to submicron characteristic size. GMR measurement is sensitive (detection limit around 1 nT), quantitative, broadband (DC-100 MHz), robust in time and does not require frequent remagnetization or recalibration of the probe. The main study topics of this PhD are focused on developping and integrating magnetoresistive nanosensors on silicon nitride micro-cantilevers. They enhance spatial resolution while improving the linearity of the magnetic response and reducing magnetic noise. Pinning strategies have been used to stabilize the noise so as to improve repeatability and detection limit by one order of magnitude Sensors down to a few hundreds of nanometers have been manufactured, using dedicated and state-of-the-art GMR stacks. We tested reliability and efficiency of the nano-GMR probes by integrating them on an atomic force microscope (AFM), thus paving the way for an innovative local magnetic imaging method based of magnetic susceptibility measurement

Cette thèse est consacrée à l'étude expérimentale du phénomène de transfert de spin. Ce mécanisme, introduit théoriquement en 1996 par J. Slonczewski, permet d'orienter l'aimantation d'un matériau ferromagnétique sans champ appliqué, mais seulement par injection d'un courant polarisé en spin et transfert de spin vers le matériau considéré. Les fortes densités de courant à injecter pour observer l'effet, de l'ordre de 107 A.cm-2, imposent le recours à des nanostructures. Nous avons suivi deux voies pour caractériser cet effet nouveau de transfert de spin depuis un courant vers une aimantation. D'une part, à l'instar des tout premiers résultats expérimentaux obtenus à Cornell University en 2000, nous avons étudié cet effet dans des piliers magnétiques submicroniques de Co/Cu/Co. Nous avons pu clairement mettre en évidence le renversement d'aimantation par un courant polarisé en spin a champ nul. Ensuite, nous nous sommes intéressés à la dépendance en champ des courants critiques. Cette étude approfondie nous a permis de tracer le diagramme de phase champ-courant, nous fournissant des informations importantes quant aux mécanismes microscopiques à l'origine du phénomène de renversement d'aimantation par injection de spin. La deuxième partie de ma thèse concerne le cas des barreaux de vanne de spin Co/Cu/NiFe dans lesquels la modification d'aimantation est due au déplacement de paroi magnétique induit par transfert de spin à partir d'un courant polarisé en spin. Pour des champs proche de zéro, une paroi magnétique peut être déplacée uniquement sous l'action du courant entre des centres de piégeage et, en accord avec les conclusions du modèle de Berger, le déplacement s'effectue dans des directions opposées pour des courants opposés. La densité de courant critique requise pour déplacer la paroi est de l'ordre de quelques 106 A/cm², un ordre de grandeur plus faible que les courants nécessaires pour entraîner un renversement d'aimantation dans les structures multicouches de type piliers. Ces mesures constituent la première mise en évidence directe et en temps réel de déplacement de parois par transfert de spin dans des nanostructures magnétiques.

Syfte: Syftet är att undersöka hur medarbetarnas välbefinnande och känsla av sammanhang (KASAM) uppfattas på arbetsplatser i Sverige och USA.  Metod: Studien är en kvalitativ studie med kvantitativt inslag. Den tar en deduktiv ansats och utgår ifrån teorierna Antonovskys Känsla av sammanhang (KASAM) (Antonovsky, 2005) och Hofstedes kulturdimensionsteori (Hofstede, 2020) Resultat & Slutsats: Ett starkt samband kan ses mellan en hög känsla av sammanhang (KASAM) och faktorerna begriplighet, hanterbarhet och meningsfullhet med en hög trivsel på arbetsplatsen. Det finns kulturella skillnader mellan de båda länderna som tydligt visar sig i studien, men studien kan inte med säkerhet förankra i vilken grad dessa påverkar resultatet. Uppsatsens bidrag: Studien bidrar till befintlig forskning om välbefinnande samt utvecklar området genom att sammankoppla teorierna KASAM och Hofstedes kulturdimensionsteori i undersökande syfte hur välbefinnande och känsla av sammanhang uppfattas på arbetsplatser i Sverige och USA. Förslag till vidare forskning: Denna studie har använt sig mindre population än önskvärt på grund av begränsningar i resurser. För att säkerställa resultaten behövs en mer omfattande studie. Nyckelord: Känsla av sammanhang (KASAM), Generella motståndsresurser - GMR, Välbefinnande, Kulturdimensionsteori.

Die vorliegende Arbeit ist ein Beitrag zur Theorie des spinabhängigen Transports in magnetischen Vielfachschichten. Es wird erstmalig eine parameterfreie Beschreibung des Giant Magnetoresistance (GMR) vorgelegt, welche detaillierte Einsichten in die mikroskopischen Vorgänge gestattet. Die ab-initio Berechnung der Elektronenstruktur der magnetischen Vielfachschichten basiert auf der Spindichtefunktionaltheorie unter Verwendung eines Screened Korringa-Kohn-Rostoker-Verfahrens. Die Streueigenschaften von Punktdefekten werden über die Greensche Funktion des gestörten Systems selbstkonsistent bestimmt. Die Transporteigenschaften werden durch Lösung der quasiklassischen Boltzmann-Gleichung unter Berücksichtigung der Elektronenstruktur der Vielfachschicht und der Anisotropie der Streuung an Fremdatomen berechnet. Die Boltzmann-Gleichung wird iterativ unter Einbeziehung der Vertex-Korrekturen gelöst. Der Formalismus wird auf Co/Cu- und Fe/Cr-Vielfachschichten, die Standardsysteme der Magnetoelektronik, angewandt. Es werden die Abhängigkeit der Streuquerschnitte, der spezifischen Restwiderstände und des GMR von der Art und der Lage der Übergangsmetalldefekte in Co/Cu- und Fe/Cr-Vielfachschichten diskutiert. Darüber hinaus wird der Einfluß des Quantum Confinements auf den GMR eingehend untersucht. Vorteile und Grenzen der vorliegenden theoretischen Beschreibung werden aufgezeigt
A new theoretical concept to study the microscopic origin of Giant Magnetoresistance (GMR) from first principles is presented. The method is based on ab-initio electronic structure calculations within the spin density functional theory using a Screened Korringa-Kohn-Rostoker method. Scattering at impurity atoms in the multilayers is described by means of a Green's-function method. The scattering potentials are calculated self-consistently. The transport properties are treated quasi-classically solving the Boltzmann equation including the electronic structure of the layered system and the anisotropic scattering. The solution of the Boltzmann equation is performed iteratively taking into account both scattering out and scattering in terms (vertex corrections). The method is applied to Co/Cu and Fe/Cr multilayers. Trends of scattering cross sections, residual resistivities and GMR ratios are discussed for various transition metal impurities at different positions in the Co/Cu or Fe/Cr multilayers. Furthermore the relation between spin dependence of the electronic structure and GMR as well as the role of quantum confinement effects for GMR are investigated. Advantages and limits of the approach are discussed in detail

L'histoire du GRM, fondé en 1958, au sein de la Radio Télévision Française, prend sa source à la radio, dès le début des années 1940. La première partie de cette recherche reconstruit la chronologie des événements : œuvres, publications, développements technologiques, élaborations de nouveaux concepts, évolution de l'institution. Les sept chapitres, un par décennie, prennent comme point de départ l'année 1948, date de naissance officielle de la Musique Concrète. Le premier chapitre est un peu particulier. Il s'attache à dégager les racines de la jeune musique concrète en remontant le temps, le plus loin possible, avant 1948, jusqu'aux mouvements futuristes des débuts du XXe siècle, ainsi qu'au dadaïsme, et au surréalisme. La seconde partie aborde l'histoire du GRM transversalement, suivant différentes thématiques. Un premier chapitre expose la prise d'identité de ce nouveau genre musical, et la lente évolution du Groupe de Recherche de Musique Concrète, vers un rôle d'École, à partir de 1951. Le second chapitre porte sur les concepts (écoute réduite, objet sonore, analyse typomorphologique. . . ), la pédagogie et les outils (des premiers phonogènes aux derniers logiciels GRM-Tools) développés au GRM, depuis cinquante ans. Le troisième chapitre expose la problématique de l'espace, du concert, et le lien au public. Le quatrième chapitre explore la lisière entre le musical et le visuel, à travers la question de l'écriture, une interrogation majeure qui se pose à tous les arts de support, aujourd'hui
Originating in radio at the beginning of the 1940's, the GRM was officially launched in 1958 by Radio Television Française. The first part of this research reconstructs the history, starting with the most visible manifestations: opuses, publications, technological developments. The research traces also the elaboration of new concepts and evolution of the movement. Beginning with 1948, the official birth date of the Concrete Music, the chronology is divided into seven chapters, one for each decade. The first chapter, however, moves back in time, delineating the roots of Concrete Music by recounting the events that preceded 1948 and eventually led to the dadaism and surrealism of the twentieth century. The second part of the research traces the themes of the GRM history. The first chapter identifies the emergence of this new musical genre and its slow progression from the Groupe de Recherche de Musique Concrete of the Paris Studio to its role as a musical School in 1951. The second chapter examines the concepts (reduced listening, sound object, typomorphological analysis. . . ). It traces the pedagogy and the tools (from the first phonogènes to the final software called GRM-Tools and Acousmographe) developed in the last fifty years. The third chapter studies the problems of space, concert presentation and connection with the audience. The fourth chapter explores the boundary between the Musical and the Visual, across the question of writing, a major issue in all the media arts today

This thesis is divided into three main sections that deal with optical and magnetic thin films properties and their measurements techniques. Principles of the spectroscopic reflectometry and measurements of optical properties are described in the first part. Results of imaging reflectometry are most important. This technique is based on in situ monitoring of optical properties of SiO2 thin films during etching over the area cca 10 × 13 mm2. In next section magnetic properties of thin films and new apparatus built on the Institute of Physical Engineering of BUT are shown. Magnetic properties were observed by longitudinal magneto-optical Kerr effect. The construction of the device is based on a light beam with rectilinear polarization reflected from magnetic material with turned polarization. For investigation of local magnetic properties of microstructures a microscope objective focusing laser beam on the sample is used. The last part of the thesis is aimed on improving of a spin valve structure Co/Cu/NiFe. This work was done within the frame of the Erasmus project in Laboratoire Louis Néel in Grenoble. The goal was to achieve the value of GMR (Giant Magnetoresistance) as high as possible by changing of deposition parameters. This value describes the rate of resistances in different mutual directions of magnetization in trilayers.

Дисертаційна робота присвячена експериментальному і теоретичному вивченню особливостей електротранспорту при зміні температури і зовнішнього магнітного поля в нанорозмірних плівкових матеріалах у вигляді обмежених твердих розчинів (т.р.) атомів Fe або Co у ГЦК решітках Ag або Au, в яких формуються елементи гранульованого стану сферичної або неправильної форми та у вигляді острівців плівки магнітної компоненти. В останньому випадку плівкові зразки отримали назву "квазігранульовані". Відповідно до мети та поставлених задач, дослідження мали характер комплексних, оскільки були використані ряд методів і методик, які знайшли своє застосування у металофізиці плівкових матеріалів. Зокрема, формування гранульованих плівкових т.р. здійснювалося методом одночасної або пошарової конденсації компонент із наступною гомогенізацією фазового складу шляхом відпалювання до температури Tв = 700 – 900 К. Квазігранульовані плівки конденсувалися у вигляді тришарової системи, у якій середній шар представляв острівцеву плівку. Кристалічна структура, фазовий і елементний склад плівок досліджувався із використанням підкладок у вигляді плівки вуглецю товщиною d = 30 – 50 нм (для електронографічних і електроно-мікроскопічних досліджень методом ПЕМ) або природньо окисленої пластини Si із поверхневим шаром SiOx (х~2) товщиною до 60 нм (для досліджень методом растрової мікроскопії РЕМ та мікроаналізу хімічного складу методом енергодисперсійної спектрометрії ЕДС). Електрофізичні та магніторезистивні властивості досліджувалися методом високоточної резистометрії із використанням відповідних комп'ютеризованих комплексів лабораторного виробництва. Інтепретація результатів здійснювалась із використанням класичної моделі M.Csontos et all. і запропонованої нами напівкласичної моделі для магнітного коефіцієнту β_mB=(dInρ_m)/dB (ρm − т.зв. магнітний питомий опір) для розбавлених т.р., в яких ще не сформувалися гранули магнітної компоненти. Перший етап роботи був присвячений освоєнню методики формування гранульованих плівкових сплавів при різних загальних концентраціях магнітної компоненти (тобто сумарних концентраціях атомів, на основі яких формується решітка розбавлених т.р. і система гранул) та паспортизації їх фазового і елементного складу та системи гранул. У результаті було встановлено, що фазовий склад завжди відповідає ГЦК решітці т.р. Ag (Fe), Ag (Co), Au (Fe) або Au (Co) із слідами ОЦК - Fe або ГЩП - Co (на електронограмах фіксуються слабкі лінії при надлишку магнітної компоненти або точкові рефлекси від гранул). Обробка ПЕМ - мікрознімків дозволяє розрахувати середній розмір гранул 2 ro = 2 − 12 нм та їх поверхневу концентрацію − (8 · 1014 − 2·1015) · м-2. На першому етапі досліджень особлива увага була приділена питанню про концентрацію атомів магнітної компоненти та легких газових атомів (O, C, N та ін). Перед тим, як скористатися методом ЕДС були вперше отримані розрахункові формули для концентрації атомів магнітної компоненти у гранулах і в розбавлених т.р. із урахуванням середнього радіусу r0 гранул та товщини плівки т.р. Розрахункові величини могли уточнюватися при використанні високоточного методу ЕДС. Паралельно вперше була установлена максимально можлива концентрація легких атомів у плівці т.р. при умові конденсації в вакуумі 10-4 Па. Виявилося, що концентрація атомів кисню, вуглецю і азоту має такі значення: до 2 ат.% О; до 1 ат.% С і близько нуля ат. % N (ці дані отримувалися шяхом порівняння ЕДС спектрів плівки (т.р. + гранули)/SiOx/Si та підкладки SiOx/Si. Додаткові дослідження методом Венда функції розподілу дефектів типу "вакансія - інорідний атом" показали, що енергія активації заліковування цих вакансійних комплексів менше 1 еВ, що має типове значення для комплексів ("вакансія-легкий атом газу"). Це означає, що легкі атоми газів локалізуються у своєрідних "пастках" у вигляді вакансій металевих атомів (при таких умовах вони не будуть утворювати хімічні з'єднання, і приймати участь в електроперенесенні шляхом дифузії в т.р.). У результаті зроблено висновок, що атоми кисню і вуглецю не можуть помітним чином впливати на кінетичні властивості плівкових т.р. На другому етапі вивчалися електрофізичні властивості (питомий опір та ТКО) гранульованих т.р. Як і слід було очікувати, виходячи із аналізу літературних даних, величина ρ має велике значення порядка 10-7 Ом.м, що на порядок більше, ніж у масивних металевих зразках, а ТКО має порядок 10-3 · К-1, що в декілька разів менше у порівнянні і масивними зразками. Основна увага на цьому етапі досліджень була приділена питанню про внесок у загальну величину ТКО процесів розсіювання електронів на гранулах (мова йде про т.зв. термічний магнітний коефіцієнт або На момент постановки задачі досліджень була відома єдина феноменологічна модель для ТКО гранульованих т.р., яка дозволяла більш-менш коректно оцінити βmт як різницю βекс - βроз. Було встановлено, що дана різниця має порядок (0,10 − 0,15) · 10-3 К-1 для гранульованих плівок на основі Ag і Co, отриманих як одночасною, так і пошаровою конденсацією, а також у випадку плівок Pd/Co/П та Pt/Fe/П. Відмітимо, що вказані величини βмВ на даний момент можна розглядати як найбільш коректні, хоча використана феноменологічна модель має свої обмеження, точність і границі застосування. На третьому етапі проведені дослідження магніторезистивних властивостей плівок і була звернута увага на аномально малі величини МО, який у більшості випадків має усі ознаки ГМО, але при певних умовах реалізовувався анізотропний MО iз такою ж аномально малою амплітудою. Відмітимо, що у цьому випадку практично повторилася ситуація із TKρm. Виникла необхідність у розробці теоретичної моделі для βв розбавлених т.р. без магнітних гранул. Запропонована нами напівкласична модель, на відміну від використаної феноменогічної моделі, більш коректно враховує можливі варіанти розсіювання електронів і залежність від магнітного поля не тільки середньої довжини вільного пробігу, але і коефіцієнтів дзеркальності і проходження межі та інтерфейсів (в останньому випадку - при умові повного або часткового збереження індивідуальності окремих шарів). Це дало можливість оцінити максимально коректно величину βмВ, яка приймає значення 10-3-10-2 Тл-1. Адаптувавши класичну модель M.Csontos et all., яка описує залежність ρm від величини магнітного момента (спіна S) гранули, ми вперше отримали співвідношення для і у залежності від S. При фізично коректних величинах S (від 1 до 50 магнетонів Бора) розрахункові і співпадають із експериментальними. На основі цих результатів сформульовано висновок про те, що малі величини βмТ і βмВ реалізуються у плівках із відносно малими значеннями ТКО (1 - 3) 10-3 К-1 і аномально малими величинами ГМО (0,01 - 0,40 %). Критерії малості до деякої міри умовні і нами вибрані таким чином: ТКО менше 5 · 10-3 К-1 , а ГМО менше 0,5 %. Фізична природа цього пов’язана із недосконалою системою гранул (багато із них знаходяться у суперпарамагнтіному стані або мають відносно малий спін), що не дозволяє реалізацію ефективного спін-залежного розсіювання електронів. У результаті основний внесок у питоми опір плівки дає питомий опір т.р., оскільки в об’ємі наногранул реалізується балістичний механізм провідності. Недосконалий низькоомний спіновий канал не шунтує у повній мірі високоомний омічний канал провідності, що обумовлює малі величини ТКО і ГМО. На феноменологічному рівні проаналізовані питання про температурну і концентраційну залежності ГМО і АМО, що може бути використано при вирішенні задач прикладного характеру.
The thesis is devoted to the experimental and theoretical study of electrotransport features in changing temperature and external magnetic field in nanoscale film materials in the form of limited solid solutions (s.s.) Fe or Co atoms in hcc lattices Ag or Au, in which granular state elements of spherical or irregular shape in the form of islands of magnetic film component. In the latter case, the film samples were called "quasi-granular". In accordance with the purpose and the study objectives were complex in nature, because they used a number of methods and techniques that have found application in the metallophysics of film materials. In particular, the formation of granular film soils. were carried out by the method of simultaneous or layered condensation of the components, followed by homogenization of the phase composition by annealing to a temperature Tan = 700 − 900 K. Quasi-granular films were condensed in the form of a three-layer system, in which the middle layer was an island film. The crystalline structure, phase and elemental composition of the films were investigated using carbon film substrates with a thickness d = 30 − 50 nm (for electron diffraction and electron microscopy studies using the TEM method) or a naturally oxidized Si plate with a SiOx surface layer (х ~ 2) thickness up to 60 nm (for REM scanning microscopy and chemical composition by energy dispersion spectrometry EDS). Electrophysical and magnetoresistive properties were investigated by the method of high-precision resistometry using appropriate computerized laboratory complexes. The results were interpreted using the classic M.Csontos et all. model and our proposed semiclassical model for the magnetic coefficient (ρm − so-called magnetic resistivity) for diluted s.s. in which magnetic component granules have not yet formed. The first stage of the work was devoted to the development of the method of formation of granular film alloys at different total concentrations of the magnetic component (i.e. the total atoms concentrations, based on diluted s.s. and the granule system is formed) and certification their of phase and elemental composition and granules system. As a result, it was found that the phase composition always corresponds to the FCC lattice s.s. Ag (Fe), Ag (Co), Au (Fe) or Au (Co) with traces of BCC-Fe or HPC-Co (weak lines are recorded on the electrongrams with excess magnetic component or point reflexes from the granules). TEM micro-images processing allows us to calculate the average granule size of 2ro = 2 − 12 nm and their surface concentration - (8 · 1014 − 2 · 1015) m -2 . In the first stage of research, particular attention was paid to the magnetic component atoms concentration and light gas atoms (O, C, N, etc.). Before using the EDS method, the first formulas were obtained for the concentration of magnetic component atoms in granules and in diluted s.s. given the average granules radius r0 and the thickness of the film, etc. Estimated values should be specified when using the high-precision EDS. For the first time, the maximum possible concentration of light atoms in the socalled film was established. subject to condensation in a vacuum of 10-4 Pa. It was found that the concentration of oxygen, carbon and nitrogen atoms has the following values: up to 2 at % O; up to 1 at % C and about zero at % N (these data were obtained by comparing the EDS of the film spectra (s.s.+granules)/SiOx/Si and SiOx/Si substrates. Additional studies by the Vend method of the function of the distribution of defects of the type "vacancy - foreign atom" showed that the activation energy of healing of defects of these vacancy complexes is less than 1 eV, which has a typical value of complexes ("vacancy-light atom of gas"). This means that light atoms of gases are localized into peculiar "traps" in the form of vacancies of metal atoms (under such conditions they will not form chemical compounds, and participate in electrical transfer by diffusion in s.s.). As a result, it is concluded that atoms oxygen and carbon cannot appreciably affect the kinetic properties of s.s. films. In the second stage, the electrophysical properties (resistivity and TCR) of granular soils were studied. As expected, based on the analysis of the literature data, the ρ value is of great importance on the order 10-7 Ohm, which is an order of magnitude larger than in massive metal samples, and the TCR has an order 10-3 K -1 , which in several times smaller compared to bulk samples. The main focus at this stage of the research was on the contribution to the total value of the TCR of electron scattering processes on the granules (we are talking about the socalled thermal magnetic coefficient or ). At the time of formulation of the research problem, a single phenomenological model was known for TCR the granular s.s., which allowed more or less correct estimation β mT of the difference βеxp - . βcal. This difference was found to be of the order (0,10 − 0,15). 10-3 K -1 granular films based on Ag and Co obtained by both simultaneous and layer condensation in the case Pd / Co / S and Pt / Fe / S. Note that these values can currently be regarded as the most correct, although the phenomenological model used has its limitations, accuracy and limits of application. In the third stage, the studies of the magnetoresistive properties of the films were carried out and attention was paid to the abnormally small values of the MR, which in most cases has all the features of GMR, but under certain conditions anisotropic MR with the same abnormally small amplitude was realized. It should be noted that in this case the situation with TCρm practically repeated. There was a need to develop a theoretical model for βВ of dilute s.s. without magnetic granules. Our semiclassical model, unlike the phenomenological model used, more correctly takes into account possible electron scattering and dependence on the magnetic field not only of the average free path length, but also the parameter of specular reflection from external surfaces and the transmission parameter at the grain boundary аnd іnterfаces of electrons (in the latter case, provided that they are complete). This made it possible to estimate the maximum correct value βmB , which takes on value 10-3 − 10-2 Т -1 . Adapting the classic model of M.Csontos et all., which describes the dependency ρm from the magnitude of the magnetic moment (spin S) of the granule we first obtained the relation for β mT and β mB depending on S. At physically correct values S (from 1 to 50 Bohr magnets) are calculated S (від 1 до 50) Bohr magneton settlement β mT and β mB coincide with experimental ones. Based on these results, we conclude that small quantities βmT and βmB are implemented in films with relatively small values ТCR (1-3) 10-3К -1 і abnormally small quantities of GMR (0,01 − 0,40 %). The smallness criterion is to some extent conditional and we are chosen as follows: TCR is smaller 5. 10-3 К -1 and GMR less than 1 %. The physical nature of this is due to the imperfect granule system (many of which are in superparamagnetic state or have relatively small spin), which does not allow efficient spin-dependent electron scattering. As a result, the main contribution to the resistivity of the film is given by the resistivity of the so-called, since the ballistic mechanism of conductance is implemented in the nanogranule volume. The imperfect low-ohmic spin channel does not completely shunt the high-ohmic conductivity channel, which causes small values of TCR and GMR. At the phenomenological level the questions of temperature and concentration dependence of GMR and AMR are analyzed, which can be used in solving problems of applied character.

This thesis is focused on a creating supporting drivers and algorithms for electrical motor control using CPU TriCore TC275 CA. The first part is devoted to processor description and selected peripherals, which are A/D converter, a timer for creating the PWM signals and the second timer for processing singnals from encoder. All drivers are tested on an aplication kit, which is equipped with TC275 CA processor. The second part analyzes the measurement quality of GMR sensor TLE5009. Special testbench was prepared for sin cos data capturing and for their comparison with precise encoder position measurement. It was composed from DC motor having both sensor types on commons shaft. Data are acquired using LabView. Subsequently, it analyzes the sensor data, their compensation and subsequent comparison with measured data from the encoder.

Die vorliegende Arbeit ist ein Beitrag zur Theorie des spinabhängigen Transports in magnetischen Vielfachschichten. Es wird erstmalig eine parameterfreie Beschreibung des Giant Magnetoresistance (GMR) vorgelegt, welche detaillierte Einsichten in die mikroskopischen Vorgänge gestattet. Die ab-initio Berechnung der Elektronenstruktur der magnetischen Vielfachschichten basiert auf der Spindichtefunktionaltheorie unter Verwendung eines Screened Korringa-Kohn-Rostoker-Verfahrens. Die Streueigenschaften von Punktdefekten werden über die Greensche Funktion des gestörten Systems selbstkonsistent bestimmt. Die Transporteigenschaften werden durch Lösung der quasiklassischen Boltzmann-Gleichung unter Berücksichtigung der Elektronenstruktur der Vielfachschicht und der Anisotropie der Streuung an Fremdatomen berechnet. Die Boltzmann-Gleichung wird iterativ unter Einbeziehung der Vertex-Korrekturen gelöst. Der Formalismus wird auf Co/Cu- und Fe/Cr-Vielfachschichten, die Standardsysteme der Magnetoelektronik, angewandt. Es werden die Abhängigkeit der Streuquerschnitte, der spezifischen Restwiderstände und des GMR von der Art und der Lage der Übergangsmetalldefekte in Co/Cu- und Fe/Cr-Vielfachschichten diskutiert. Darüber hinaus wird der Einfluß des Quantum Confinements auf den GMR eingehend untersucht. Vorteile und Grenzen der vorliegenden theoretischen Beschreibung werden aufgezeigt.
A new theoretical concept to study the microscopic origin of Giant Magnetoresistance (GMR) from first principles is presented. The method is based on ab-initio electronic structure calculations within the spin density functional theory using a Screened Korringa-Kohn-Rostoker method. Scattering at impurity atoms in the multilayers is described by means of a Green's-function method. The scattering potentials are calculated self-consistently. The transport properties are treated quasi-classically solving the Boltzmann equation including the electronic structure of the layered system and the anisotropic scattering. The solution of the Boltzmann equation is performed iteratively taking into account both scattering out and scattering in terms (vertex corrections). The method is applied to Co/Cu and Fe/Cr multilayers. Trends of scattering cross sections, residual resistivities and GMR ratios are discussed for various transition metal impurities at different positions in the Co/Cu or Fe/Cr multilayers. Furthermore the relation between spin dependence of the electronic structure and GMR as well as the role of quantum confinement effects for GMR are investigated. Advantages and limits of the approach are discussed in detail.

Dans l'ère actuelle de l'informatique la quantité d'informations à stocker à connu un essor considérable. Dans ce contexte l'évolution des mémoires a été importante, tant pour les mémoires vives que pour les enregistreurs magnétiques sur bande. Ainsi le travail proposé vise à améliorer ces deux types de dispositifs. Une première partie traite de la modélisation et de la conception d'une tête de lecture pour enregistrer sur bande magnétique. Pour cela, un nouveau type de design " yoke " a été mis en avant couplé à l'utilisation d'un matériau à magnétorésistance géante. Dans un deuxième temps, nous avons mené une réflexion sur les diverses approches pour modéliser le processus d'écriture dans le cas d'une mémoire vive magnétique à accès aléatoire (MRAM). Ceci nous a ensuite conduit à étudier le phénomène de diaphonie lorsque la densité de la mémoire augmente
In the current computer age, large amount of information to be stored made considerable great expansion. In this context, memories evolution is significant, for both, random access memories and magnetic tape recorder. Thus, this work suggests improving these two types of devices. A first part, mix the modelling and design of a reading head for magnetic tape recorder. In this purpose, a new type of "yoke" design is proposed, coupled with the use of a giant magneto-resistance material. In the second time, we carried out a reflexion on the various possible approaches to model the writing process in the case of a magnetic random access memory (MRAM). This then led us to study the phenomen of cross talk when the density of the memory increases