Manipulation de l'anisotropie magnétique dans les semiconducteurs ferromagnétiques

The subject of this thesis is the experimental study of the magnetic anisotropy in thin ferromagnetic semiconductor films and the magnetic coupling in bilayers formed with ferromagnetic metals. I have focussed my studies on two different systems: quaternary ferromagnetic GaMnAsP thin films and MnAs/GaMnAs bilayers. In these systems I have investigated how the magnetic anisotropies are influenced by the lattice mismatch induced biaxial strain and the hole concentration. The principal experimental techniques used are ferromagnetic resonance spectroscopy, SQUID magnetization measurements as well as transport and high resolution X-ray diffraction. Two series of GaMnAsP layers characterized by different Mn concentrations of 7% and 10% were investigated. For each series the P concentration has been varied over a wide range from 0 to 20%. Of particular interest is the case of highly P doped layers where the conductivity regime changes from metallic to impurity band conduction. This change induces a profound modification of all pertinent magnetic parameters. The variation of the four anisotropy constants as a function of temperature and P has been determined. For intermediate P concentrations layers with zero uniaxial strain can be obtained. The temperature induced magnetization reorientations have been evidenced for 6% doped P. High frequency FMR measurements have been used to study the magnetic anisotropy of MnAs epitaxial films on (111) and (100) GaAs. A ferromagnetic exchange coupling has been evidenced for MnAs/GaMnAs bilayers. I have further studied the magnetization relaxation via the Gilbert damping factor which has been deduced from FMR linewidth studies at two different microwave frequencies.Cette thèse présente une étude de l'anisotropie magnétique de semiconducteurs ferromagnétiques en couches minces et du couplage magnétique dans des bicouches formées à partir de ces matériaux et de métaux ferromagnétiques. Je me suis focalisé sur deux systèmes distincts : des films minces de l'alliage quaternaire GaMnAsP et des bicouches : MnAs/GaMnAs. Dans ces systèmes, j'ai étudié l'influence sur les anisotropies magnétiques d'une part, de la déformation biaxiale induite par le désaccord de maille avec le substrat et d'autre part, de la concentration en trous. Ces études ont été menées principalement par résonance ferromagnétique, mesures d'aimantation par SQUID, ainsi que grâce à des mesures de transport et de diffraction de rayons X à haute résolution. Deux séries de films de GaMnAsP caractérisées par des concentrations en Mn de 7% et 10% ont été étudiées. Pour chaque série, la concentration en P a été variée sur une large gamme de 0 à 20%. Les forts dopages en P sont intéressants car le régime de conduction peut changer, passant de métallique à bande d'impuretés. Ceci induit de profondes modifications de tous les paramètres magnétiques pertinents. Nous avons étudié les variations d'anisotropie magnétique avec la concentration en P. Une réorientation de l'aimantation avec la température a pu être mise en évidence pour une concentration 6% P. Des mesures de RFM à haute fréquence ont permis d'étudier l'anisotropie magnétique de films de MnAs épitaxiés sur (111) et (100) GaAs. Un couplage d'échange ferromagnétique est mis en évidence pour les bicouches MnAs/GaMnAs. La relaxation de l'aimantation de ces systèmes a été étudiée via le facteur de Gilbert, déterminé à partir de l'étude de la largeur des résonances en fonction de la fréquence des microondes utilisées

Âge et Langue dans L'utilisation des Stratégies D'apprentissage

This study examines how language difference, age, and proficiency are related to the choice and use of learning strategies by students completing a reading comprehension task. The aim of this study is to determine the learning strategies employed by two groups of students of different ages and with different foreign language proficiency levels. Participants of the study were 94 university students and 105 secondary school students. Participants were given a reading comprehension task in their native language, Turkish, and another in English, with the learning strategies they employed in the two languages categorized according to the Learning Strategies Determining Scale. It was observed that language difference, age and proficiency were influential factors in determining which learning strategies individuals used.Este estudio examina cómo la diferencia del idioma, la edad y la competencia se relacionan con la elección y el uso de estrategias de aprendizaje en una tarea de comprensión de lectura. El objetivo de este estudio es descubrir el uso de estrategias de aprendizaje de dos grupos de diferentes edades y con diferentes niveles de competencia en lenguas extranjeras. Los participantes del estudio fueron 94 estudiantes universitarios y 105 estudiantes de secundaria. A los participantes se les asignó una tarea de comprensión lectora en turco e inglés, y luego se determinaron las estrategias de aprendizaje que utilizaron en los dos idiomas con la ayuda de la escala de Estrategias de Aprendizaje. Como resultado, se observó que la diferencia de idioma, la edad y la competencia eran factores efectivos en el uso de estrategias de aprendizaje.Cette étude examine comment la différence de langue, l'âge et la compétence sont liés au choix et à l'utilisation de stratégies d'apprentissage dans une tâche de compréhension en lecture. Le but de cette étude, menée avec des sondages, est d´explorer l'utilisation des stratégies d'apprentissage chez deux groupes d´étudiants de différents âges et avec des niveaux variés de maîtrise de langues étrangères. Les participants étaient 94 étudiants universitaires et 105 lycéens. Ils ont reçu une tâche de compréhension de lecture en turc et en anglais puis, l´on a déterminé les stratégies d'apprentissage utilisées dans les deux langues à l'aide d´une échelle. Les résultats ont montré que les différences de langue, d'âge et la compétence étaient des facteurs efficaces dans l'usage des stratégies d'apprentissage

Manipulation of magnetic anisotropy in ferromagnetic semiconductors

Cette thèse présente une étude de l anisotropie magnétique de semiconducteurs ferromagnétiques en couches minces et du couplage magnétique dans des bicouches formées à partir de ces matériaux et de métaux ferromagnétiques. Je me suis focalisé sur deux systèmes distincts : des films minces de l alliage quaternaire GaMnAsP et des bicouches : MnAs/GaMnAs. Dans ces systèmes, j ai étudié l influence sur les anisotropies magnétiques d une part, de la déformation biaxiale induite par le désaccord de maille avec le substrat et d autre part, de la concentration en trous. Ces études ont été menées principalement par résonance ferromagnétique, mesures d aimantation par SQUID, ainsi que grâce à des mesures de transport et de diffraction de rayons X à haute résolution. Deux séries de films de GaMnAsP caractérisées par des concentrations en Mn de 7 et 10% ont été étudiées. Pour chaque série, la concentration en P a été variée sur une large gamme de 0 à 20%. Les forts dopages en P sont intéressants car le régime de conduction peut changer, passant de métallique à bande d impuretés. Ceci induit de profondes modifications de tous les paramètres magnétiques pertinents. Nous avons étudié les variations d anisotropie magnétique avec la concentration en P. Une réorientation de l aimantation avec la température a pu être mise en évidence pour une concentration 6% P. La relaxation de l aimantation de ces systèmes a été étudiée via le facteur de Gilbert. Des mesures de RFM à haute fréquence ont permis d étudier l anisotropie magnétique de films de MnAs épitaxiés sur (111) et (100)GaAs. Un couplage d échange ferromagnétique est mis en évidence pour les bicouches MnAs/GaMnAsPARIS-BIUSJ-Physique recherche (751052113) / SudocSudocFranceF

Mobile Game Development for Children with Down Syndrome

Children with diagnosis of down syndrome has different kinds of personalities, mental states, and talents similar to other children. The key point is that every child needs proper support at the right time. There are options like special education programs, physical and other therapies, and play groups. However, there are not any electronic games to support the education and improvement of these children. The goal of this study is to develop a mobile game for children with down syndrome, in order to help them learn everyday knowledge by using a mobile device such as a smart phone or a tablet. In most cases pedagogues use puzzle or paper based card games to teach these children the necessary knowledge they need to maintain their lives. This study aims to optimize the learning process of children with down syndrome by providing educators electronic games they can use to teach them in a mobile application which will enrich the teaching process in addition to update their teaching methods to Industry 4.0 standards

Giant radicular cyst with bilateral maxillary sinus involvement

Radicular cysts are the most common cysts of the jaws. They are localized on the apex of the teeth with necrotic pulp. They are classified as inflammatory cysts. Radiographically, they appear as an oval radiolucent lesion with well-defined radiopaque border. They develop slowly, and asymptomatic unless infected. Because of this they can reach big dimensions. Intraoral examination of an 21-year-old man revealed a fluctant swelling on the palatinal and vestibular mucosa of the incisor-canine region. Radiographic examination revealed well defined and uniformly radiolucent lesion present between the left and right molar regions. The lesion was extending to nasal cavity and left and right maxillary sinus regions. The result of the histopathological examination was reported as radicular cyst. In this report it was aimed to present a giant radicular cyst case

Memristive, Spintronic, and 2D-Materials-Based Devices to Improve and Complement Computing Hardware

Funder: Royal Academy of Engineering; Id: http://dx.doi.org/10.13039/501100000287Funder: Ministry of Education—Kingdom of Saudi ArabiaIn a data-driven economy, virtually all industries benefit from advances in information technology -- powerful computing systems are critically important for rapid technological progress. However, this progress might be at risk of slowing down if we do not address the discrepancy between our current computing power demands and what the existing technologies can offer. Key limitations to improving energy efficiency are the excessive growth of data transfer costs associated with the von Neumann architecture and the fundamental limits of complementary metal-oxide-semiconductor (CMOS) technologies, such as transistors. In this perspective article, we discuss three technologies that will likely play an essential role in future computing systems: memristive electronics, spintronics, and electronics based on 2D materials. We present how these may transform conventional digital computers and contribute to the adoption of new paradigms, like neuromorphic computing

Electrical nucleation and detection of single 360° homochiral Néel domain walls measured using the anomalous Nernst effect

International audienc

Spin-orbit torque magnetization switching of a three-terminal perpendicular magnetic tunnel junction

International audienc

Spin transport in organic semiconductors: from spin pumping by ferromagnetic resonance to lateral spin-valves

Summary form only given. Organic semiconductors (OSC) such as conjugated polymers/molecules are enabling flexible, large area optoelectronic devices, such as organic light-emitting diodes, transistors, and solar cells. Due to their exceptionally long spin lifetimes, these carbon-based materials could also have an important impact on spintronics, where carrier spins play a key role in transmitting, processing and storing information. Here, we combine three different approaches to study spin transport in OSC: spin pumping induced by ferromagnetic resonance (FMR), vertical and lateral spin-valves. i) We have recently demonstrated spin pumping by FMR in a ferromagnet (FM)/ conjugated polymer/nonmagnetic (NM) spin-sink trilayer to demonstrate the ability of polarons to carry pure spin currents over hundreds of nanometers with long spin relaxation times of up to a millisecond and to exhibit Hanle precession. Our trilayer architecture relies on spin pumping from a FM material for spin injection into the organic and on the inverse spin-Hall effect (ISHE) in a NM metal with strong spin-orbit coupling for detection of spins transmitted through the organic layer. This technique allows us to measure both spin and charge carrier transport through the organic in the same device. We have also studied spin pumping on different organic materials such as PBTTT, F4TCNQ doped PBTTT as well as P3HT with a thickness dependence in order to characterize the spin diffusion length of the organic layer. ii) We report the results of magnetoresistance (MR) measurements in vertical organic spin-valves where an organic material is contacted by two FM electrodes (Py) with the magnetic field oriented parallel to the layer stack. The organic layer is generally thick enough to avoid any coupling between the two FM electrodes. The MR is measured as a function of temperature, bias and orientation. iii) Finally, we report our attempts at spin injection into OSC using lateral organic spin-valves (LSV). We will present the fabrication method using electron beam lithography and evaporation/sputtering techniques. Typical LSV structures consist of two laterally separated ferromagnetic Co or other ferromagnetic electrodes (with and without tunnel barriers), connected by a patterned OSC ribbon of F4TCNQ doped PBTTT. In these structures, the charge and spin currents can be separated in order to rule out the MR effects of the electrodes and to avoid the presence of a background resistance coming from the contacts. We compared the devices where the FM layer is in direct contact with the organic to the one obtained using tunnel contacts such as FM/MgO and FM/Al2O3. These studies are very important in order to optimize the magnetic contacts to organic for future organic-based spintronic devices.info:eu-repo/semantics/publishe