Download or read book Etude des parois de domaines dans les nanofils magn tiques written by Ségolène Jamet and published by . This book was released on 2015 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Ce travail de thèse porte sur l'étude des parois de domaines dans des nanofils magnétiques. Nous avons étendu le diagramme de phase des parois de domainesdéjà connu pour des géométries allant des nanobandes aux nanofils. Les différents types de parois et des transitions de phases sont présentés.Nous avons introduit de nouveaux estimateurs s'appuyant sur des grandeurs physiques connues, pour mieux caractériser les configurations magnétiques des parois et prédire leur type en fonction de la géométrie.Pour valider notre approche théorique, nous nous sommes ensuite intéressés à les observer par microscopie.Nous avons choisi le Dichroisme Circulaire Magnétique des rayons X associé à la Microscopie par Emission de PhotoElectrons (XMCD-PEEM). Ce type de microscopie permet d'atteindre une résolution spatiale suffisante pour observer les parois de domaine. Les configurations expérimentales (échantillons et dispositif expérimental) permettent d'avoir accès à la fois à l'aimantation de surface maisaussi à l'ombre du fil projetée sur le substrat. Cette ombre contient l'information sur l'aimantation dans le volume, moyennée le long du chemin desrayons X dans le matériau. Cette configuration donne lieu à des contrastes magnétiques complexes. Nous avons donc développé un modèle permettant de simuler le contraste XMCD à partir de configurations micromagnétiques à l'équilibre. La comparaison entre les contrastes expérimentaux et les contrastes simulés donne lieu à un très bon accord quantitatif.De plus, les paramètres expérimentaux ont été étudiés afin d'obtenir le meilleur contraste réflétant au mieux la configuration micromagnétique de l'échantillon.La suite de ce travail consistera, notamment, à étudier la propagation de la paroi point de Bloch dans les nanofils.

Download or read book Mouvement de Parois de Domaines Magn tiques Dans Des Nanofils Cylindriques Modul s written by Alexis Wartelle and published by . This book was released on 2018 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: The thesis is concerned with the observation of ferromagnetic domain walls in cylindrical nanowires, as well as their dynamics under applied magnetic fields. These nanostructures were electrodeposited by colleagues of mine into nanoporous alumina templates with a tailored pore geometry. The materials are soft FeNi or CoNi alloys; the diameters range from 150 nm to 250-300 nm, with a typical length of 30 μm.My work first comprised experimental developments of sample holders and high-frequency electronics towards field-induced domain wall motion. The latter I investigated with X-ray Magnetic Circular Dichroism coupled to transmission PhotoEmission Electron Microscopy (XMCD-PEEM). This synchrotron-based technique allows to monitor the internal domain wall configuration before and after displacement; due to the stringent requirements of time-resolved XMCD-PEEM experiments in terms of reproducibility, the real-time dynamics is out of reach as of yet.The response of ferromagnetic domain walls to applied magnetic fields is notably characterized by their mobility, i.e. the ratio of attained velocity to field strength. In cylindrical nanowires, a novel ingredient emerges in the case of one domain wall type that is absent in flat strips: the Bloch point domain wall. Not only does this domain wall host a micromagnetic singularity, that is to say a point where magnetization vanishes (the Bloch point), but it also possesses a discrete degree of freedom representing the sense of magnetization winding around the nanowire axis. It has been predicted that Bloch point wall motion under sufficiently high fields leads to this degree of freedom selecting one of its only two possible values. In other words, one winding becomes unstable. I report in this thesis experimental evidence of such a selection in a majority of Bloch point wall motion events.Although mobility measurements could not be carried out, my experiments have furthermore evidenced transformations between domain wall types that had not been predicted in simulations. Since the Bloch point wall contains a topological defect (the Bloch point itself), this unexpected behaviour questions the sometimes argued protection attributed to topologically non-trivial textures. While reminiscent of the well-known conversion between transverse and vortex walls in strips, these transformations in cylindrical nanowires involve topologically non-equivalent micromagnetic configurations, in contrast with the aforementioned transverse and vortex walls. Moreover, the observed only relative stability of domain wall types suggests caution in the interpretation of future mobility measurements in such systems, if the internal wall configuration cannot be resolved.Aside from such electrodeposited samples, I have also studied an upright core-shell nanowire grown by colleagues with Focused-Electron-Beam-Induced Deposition. This nanostructure featured a nanocrystalline cobalt core and a platinum shell. Its magnetic configuration was investigated with transmission XMCD-PEEM as well. Contrary to the aforementioned horizontally-lying wires, the core-shell sample was vertical with no diameter modulations. On the other hand, the geometry featured bends engineered to favour domain wall pinning. In this novel imaging configuration, the challenge was to recover as much of the nanowire's magnetic state as possible. I was able to demonstrate the presence of at least one domain wall.

Download or read book Nanomagnetism and Spintronics written by Teruya Shinjo and published by Elsevier. This book was released on 2013-10-07 with total page 373 pages. Available in PDF, EPUB and Kindle. Book excerpt: The concise and accessible chapters of Nanomagnetism and Spintronics, Second Edition, cover the most recent research in areas of spin-current generation, spin-calorimetric effect, voltage effects on magnetic properties, spin-injection phenomena, giant magnetoresistance (GMR), and tunnel magnetoresistance (TMR). Spintronics is a cutting-edge area in the field of magnetism that studies the interplay of magnetism and transport phenomena, demonstrating how electrons not only have charge but also spin. This second edition provides the background to understand this novel physical phenomenon and focuses on the most recent developments and research relating to spintronics. This exciting new edition is an essential resource for graduate students, researchers, and professionals in industry who want to understand the concepts of spintronics, and keep up with recent research, all in one volume. - Provides a concise, thorough evaluation of current research - Surveys the important findings up to 2012 - Examines the future of devices and the importance of spin current

Download or read book Multiscale Multimodel Simulation of Micromagnetic Singularities written by Christian Andreas and published by Forschungszentrum Jülich. This book was released on 2014 with total page 217 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Spintronic 2D Materials written by Wenqing Liu and published by Elsevier. This book was released on 2019-06-15 with total page 320 pages. Available in PDF, EPUB and Kindle. Book excerpt: Spintronic 2D Materials: Fundamentals and Applications provides an overview of the fundamental theory of 2D electronic systems that includes a selection of the most intensively investigated 2D materials. The book tells the story of 2D spintronics in a systematic and comprehensive way, providing the growing community of spintronics researchers with a key reference. Part One addresses the fundamental theoretical aspects of 2D materials and spin transport, while Parts Two through Four explore 2D material systems, including graphene, topological insulators, and transition metal dichalcogenides. Each section discusses properties, key issues and recent developments. In addition, the material growth method (from lab to mass production), device fabrication and characterization techniques are included throughout the book. Discusses the fundamentals and applications of spintronics of 2D materials, such as graphene, topological insulators and transition metal dichalcogenides Includes an in-depth look at each materials system, from material growth, device fabrication and characterization techniques Presents the latest solutions on key challenges, such as the spin lifetime of 2D materials, spin-injection efficiency, the potential proximity effects, and much more

Download or read book Magnetism in Carbon Nanostructures written by Frank Hagelberg and published by . This book was released on 2017 with total page 420 pages. Available in PDF, EPUB and Kindle. Book excerpt: A comprehensive survey of carbon nanostructure magnetism, emphasizing both the fundamental nature of the field and its groundbreaking nanotechnological applications.