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Ernandes, Cyrine. "Manipuler l'émission et l'absorption de transitions dipolaires magnétiques par l'utilisation de nano-antennes optiques." Electronic Thesis or Diss., Sorbonne université, 2019. http://www.theses.fr/2019SORUS091.
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Au cours des dernières années, les progrès technologiques dans le domaine de la nanophotonique ont permis le développement des nanostructures optiques. Ces dernières possèdent la particularité de modifier l'émission lumineuse de nanoémetteurs quantiques .Cependant, l’interaction lumière-matière est considérée comme étant véhiculée par le champ électrique. Les études se sont alors concentrées sur le contrôle et la modification des propriétés d'excitation et d'émission des transitions dipolaires électriques.Récemment, il a été décrit qu’il existe dans la nature des nanoémetteurs possédant des transitions magnétiques détectables : ces nanoémetteurs sont les ions lanthanides.Les nanostructures optiques développant des résonances magnétiques pourraient alors modifier l’émission et l’excitation de transitions dipolaires magnétiques, de la même manière que leurs homologues électriques.Dernièrement , il a été démontré théoriquement que certain type de nanostructure, peuvent renforcer le champ magnétique optique par deux ordres de grandeur et qu’une fois couplé à un dipôle magnétique, ils peuvent augmenter fortement la fluorescence des transitions magnétiques comme celle qui que se trouve dans les ions de lanthanide.Une étude publiée dans Physical review letters, a rapporté qu’il était aussi possible d’étudier l’excitation de transitions dipolaires magnétiques.L’objectif de ma thèse a donc été d’utiliser certaines nanostructures ayant des affinités particulières avec le champ magnétique afin d’étudier et de manipuler l’émission et l'absorbption de transitions dipolaires magnétiquesDuring the last years, technological progresses in the field of nanophotonic have allowed the development of optical nanostructures to manipulate the emission of fluorescent nanoemitters . However, light-matter interactions are usually considered to be mediated by the optical electric field only, discarding the magnetic side of it. Indeed, most of the past studies have been only studying the modification of the excitation or emission properties of electric dipole transitions. Recently, it was demonstrated that magnetic dipole could also be found in lanthanide ions. It was also shown that by changing the magnetic local density of states near these ions, the emission fluorescent of the magnetic transitions could be enhanced or decreased with respect to their electric counterpart. In here, we demonstrate experimentally, in perfect agreement with numerical simulations, the manipulation of magnetic and electric dipolar transitions by means of plasmonic cavities. Using a near-field scanning optical microscope (NSOM), we bring in close proximity a nanoparticle doped with trivalent europium to plasmonic cavities of different sizes made of aluminum , allowing perfect control over the interactions between the emitter and the nanostructures. In this study, we show both an increase and decrease of electric and magnetic signal from the particle, and we also display the spatial distribution of both the electric and magnetic radiative local density of state at the surface of the cavities.Therefore, this work pave the way to the understanding of ‘magnetic light’ and matter interactions
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Shen, Jianqi. "Quantum Coherence and Quantum-Vacuum Effects in Some Artificial Electromagnetic Media." Doctoral thesis, KTH, Elektroteknisk teori och konstruktion, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-10074.
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The author of this thesis concentrates his attention on quantum optical properties of some artificial electromagnetic media, such as quantum coherent atomic vapors (various multilevel electromagnetically induced transparency vapors) and negative refractive index materials, and suggests some possible ways to manipulate wave propagations inside the artificial electromagnetic materials based on quantum coherence and quantum vacuum effects. In Chapters 1 and 2, the author reviews the previous papers on quantum coherence as well as the relevant work such as electromagnetically induced transparency (EIT), atomic population trapping and their various applications. The basic concepts of quantum coherence (atomic phase coherence, quantum interferences within atomic energy levels) and quantum vacuum are introduced, and the theoretical formulations for treating wave propagations in quantum coherent media are presented. In Chapter 3, the author considers three topics on the manipulation of light propagations via quantum coherence and quantum interferences: i) the evolutional optical behaviors (turn-on dynamics) of a four-level N-configuration atomic system is studied and the tunable optical behavior that depends on the intensity ratio of the signal field to the control field is considered. Some typical photonic logic gates (e.g. NOT and NOR gates) are designed based on the tunable four-level optical responses of the N-configuration atomic system; ii) the destructive and constructive quantum interferences between two control transitions (driven by the control fields) in a tripod-type four-level system is suggested. The double-control quantum interferences can be utilized to realize some photonic devices such as the logic-gate devices, e.g., NOT, OR, NOR and EXNOR gates; iii) some new quantum coherent schemes (using EIT and dressed-state mixed-parity transitions) for realizing negative refractive indices are proposed. The most remarkable characteristic (and advantage) of the present scenarios is such that the isotropic left-handed media (with microscopic structure units at the atomic level) in the optical frequency band can be achieved. Quantum vacuum (the ground state of quantized fields) can exhibit many interesting effects. In Chapter 4, we investigate two quantum-vacuum effects in artificial materials: i) the anisotropic distribution of quantum-vacuum momentum density in a moving electromagnetic medium; ii) the angular momentum transfer between quantum vacuum and anisotropic medium. Such quantum-vacuum macroscopic mechanical effects could be detected by current technology, e.g., the so-called fiber optical sensor that can measure motion with nanoscale sensitivity. We expect that these vacuum effects could be utilized to develop sensitive sensor techniques or to design new quantum optical and photonic devices.In Chapter 5, the author suggests some interesting effects due to the combination of quantum coherence and quantum vacuum, i.e., the quantum coherent effects, in which the quantum-vacuum fluctuation field is involved. Two topics are addressed: i) spontaneous emission inhibition due to quantum interference in a three-level system; ii) quantum light-induced guiding potentials for coherent manipulation of atomic matter waves (containing multilevel atoms). These quantum guiding potentials could be utilized to cool and trap atoms, and may be used for the development of new techniques of atom fibers and atom chips, where the coherent manipulation of atomic matter waves is needed.In Chapter 6, we conclude this thesis with some remarks, briefly discuss new work that deserves further consideration in the future, and present a guide to the previously published papers by us.QC 20100810
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Paineau, Erwan-Nicolas. "Transitions de phases dans les argiles : influence de la minéralogie et de la morphologie : comportement sous écoulement et sous champs." Thesis, Vandoeuvre-les-Nancy, INPL, 2011. http://www.theses.fr/2011INPL005N/document.
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L’objectif de ce travail est d’étudier les transitions de phases sol-gel et isotrope-nématique dans des suspensions de smectites dioctaédriques en fonction de la morphologie et de la nature minéralogique des argiles. Bien que tous les systèmes étudiés présentent une transition sol-gel à de faibles fraction volumique, la transition cristal-liquide isotrope-nématique n’a pu être identifiée que dans le cas de suspensions de smectites ayant un déficit de charge tétraédrique. L’effet de la localisation de la charge sur le comportement colloïdal a été déterminée à l’aide de la diffusion des rayons X aux petits angles (SAXS) et par des mesures rhéologiques. La nature des interactions électrostatiques dans ces suspensions est purement répulsive et rejette l’idée d’une structure tridimensionnelle de type « château de carte ». Cependant, les smectites ayant un déficit de charge tétraédrique sont plus répulsives et ont des propriétés viscoélastiques plus faibles que celles ayant un déficit octaédrique. Il a également été montré que la dépendance en taille de particules de la position de la transition sol-gel était liée à une statistique de piégeage hydrodynamique des plaquettes d’argile. Finalement, l’application de champs externes (électrique et magnétique) a permis d’obtenir l’alignement de la phase nématique tandis que dans la phase isotrope, le champ électrique induit un ordre antinématique parfait. Afin de préserver l’ordre induit, ces suspensions ont été polymérisées sous champ permettant l’obtention de nanocomposites orientées et structurésThe aim of this work is to study sol-gel and isotropic-nematic phases transitions in suspensions of dioctahedral smectites depending on the morphology and mineralogical nature of clays. Although all the systems studied exhibit a sol-gel at low volume fraction, the liquid-crystalline isotropic-nematic transition could be identified only in the case of smectites with tetrahedral charge deficit. The effect of charge location on the colloidal behavior was determined using small-angle X-ray scattering (SAXS) and rheological measurements. The nature of electrostatic interactions in these suspensions is purely repulsive and rejects the idea of the so-called “house of card” network. However, smectites with a charge deficit located in the tetrahedron are more repulsive and their viscoelastic properties are lower than octahedrally substituted clays. It was also shown that the particle size dependence of the volume fraction corresponding to the sol-gel transition c was related to a simple statistical hydrodynamic trapping of clay platelets. Finally, the application of external fields (electric and magnetic) has resulted in the alignment of the nematic phase while in the isotropic phase, the electric field induces a perfect antinematic order. To preserve the induced alignment, these suspensions were polymerized under the field to obtain perfectly aligned and patterned nanocomposites
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Cherifi, Ryan. "Experimental design of a strong Magneto-Electric coupling system between a ferroelectric and a magnetic phase transition alloy : BaTiO3/FeRh, and theoretical study of the metamagnetic transition of FeRh." Thesis, Paris 6, 2015. http://www.theses.fr/2015PA066309.
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Aujourd'hui, la puissance de calcul des processeurs et la capacité de stockage des disques durs tels que conçus dans l'électronique moderne sont limités par la limite thermodynamique aux systèmes finis. Pour garder une vitesse de développement tel que prédit par la loi de Moore, il est donc nécessaire de considérer de nouveaux types d’architecture d’unité de calcul et stockage d’information. Un autre problème réside dans la gestion des pertes de courant par effet Joule, qui deviennent critiques dès lors que l’on atteint de très fortes densités de transistors et bits magnétiques. Notre étude s’inscrit dans ces problématiques, par la conception de nouveaux systèmes à fort couplage magnéto-électrique qui permettrait de contrôler l’information magnétique par l’injection de faibles courants électriques. Notre objectif a été de concevoir un système à fort couplage magnéto-électrique. Il existe des matériaux possédant un couplage entre ordre magnétique et ordre ferroélectrique de façon intrinsèque. Ce type de structures représente une bonne base d’analyse conceptuelle sur la nature d’hybridation des ordres férroiques. Cependant le couplage y est généralement faible, et ne permet pas l’intégration de ces matériaux dans l’électronique moderne.Une autre option consiste à artificiellement générer un couplage magnéto-électrique à travers l’interface entre deux matériaux possédant chacun un des ordres férroiques. Nous avons travaillé essentiellement sur ce type d’hétérostructure binaire, alliant un substrat ferroélectrique type, (BaTiO3) avec, dans un premier temps, un film ultra-mince ferromagnétique type (Fe, Co, FeNi). Nous avons montré la présence d’une signature d’un couplage magnéto-électrique faible à l’interface de ces systèmes. Nous avons ensuite proposé de remplacer le matériau ferromagnétique typique par un film mince de FeRh, un alliage qui possède une transition de phase magnétique d’antiferromagnétique à ferromagnétique juste au-dessus de la température ambiante, qui dépend à la fois de la température, de la pression et du champ magnétique.Nous avons alors réalisé une étude de croissance de FeRh en films ultra-minces. Nous avons pu montrer que l’alliage garde une température de transition bulk et une transition assez abrupte jusqu’à 5nm d’épaisseur. Nous avons ensuite étudié le couplage magnéto-électrique dans le système FeRh(22nm)/BaTiO3 par magnétométrie SQUID sous champ électrique. Nous avons démontré un très fort effet magnéto-électrique induit par contrainte mécanique, possédant une constante de couplage record, α = 1.6 x 10-5 s.m-1, un ordre de grandeur au-dessus des valeurs rapportées dans la littérature.Utilisant notre connaissance du système, nous avons montré l’intérêt conceptuel d’utiliser un matériau à transition de phase dans les architectures novatrices de mémoire, en proposant une description mathématique d’un comportement memristif dans le système FeRh/piézoélectrique.Finalement, l’utilisation pratique de FeRh nous a amené à étudier l’alliage par calculs Ab Initio sous contrainte mécanique et sous injection de charges, pour comprendre plus fondamentalement la nature et les mécanismes de la transitionOne of the most practical concept used in physics and engineering is the concept of triggeror switch, consisting of a means to start a controlled chain of energy transformation.A switch can lead to reversible or irreversible consequences. Technological developmentusually seeks to make use of the former because it allows for repetitive logical tasks. Suchtriggers exist via the coupling between two or more types of energetic transformations.It is formally described by the interaction between two or more distinct fields and theirexpression on a system. Amongst the most studied coupling in material physics, we findelectro-mechanical couplings such as piezoelectricity or ferroelectricity, electro-caloric ormagneto-caloric couplings such as pyroelectricity and pyro-magnetism, magneto-electric,etc. The fundamental and experimental domestication and understanding of these couplingsis usually followed (and very often motivated) by the design of practical applicationin electronics engineering technology
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Alexeev, Arseny. "Quantum rings in electromagnetic fields." Thesis, University of Exeter, 2013. http://hdl.handle.net/10871/8021.
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This thesis is devoted to optical properties of Aharonov-Bohm quantum rings in external electromagnetic fields. It contains two problems. The first problem deals with a single-electron Aharonov-Bohm quantum ring pierced by a magnetic flux and subjected to an in-plane (lateral) electric field. We predict magneto-oscillations of the ring electric dipole moment. These oscillations are accompanied by periodic changes in the selection rules for inter-level optical transitions in the ring allowing control of polarization properties of the associated terahertz radiation. The second problem treats a single-mode microcavity with an embedded Aharonov-Bohm quantum ring, which is pierced by a magnetic flux and subjected to a lateral electric field. We show that external electric and magnetic fields provide additional means of control of the emission spectrum of the system. In particular, when the magnetic flux through the quantum ring is equal to a half-integer number of the magnetic flux quantum, a small change in the lateral electric field allows tuning of the energy levels of the quantum ring into resonance with the microcavity mode, providing an efficient way to control the quantum ring-microcavity coupling strength. Emission spectra of the system are calculated for several combinations of the applied magnetic and electric fields.
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Bouba, Oumarou. "Théories quantique et semi-classique des intégrales radiales de transitions dipolaires et multipolaires des états excités : Applications au calcul des forces d'oscillateur et des probabilités de transition dans l'approximation à une configuration." Orléans, 1986. http://www.theses.fr/1986ORLE0010.
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Calcul des intégrales radiales à l'approximation quasi classique (JWKB) des fonctions d'onde radiales, complétée par une description en termes de trajectoires elliptiques de l'électron optique. Obtention d'expressions analytiques de ces intégrales dont on simplifie le calcul à l'aide d'une méthode basée sur le développement limite d'une fonction bien adaptée à des calculs par interpolation ou extrapolation : elles s'expriment toutes en termes de deux fonctions fondamentales qui ne dépendent que de la différence entre deux nombres quantiques principaux effectifs des états initial et final. Déduction de forces d'oscillateur et probabilités de transition aussi précises que celles obtenues par quantique.
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Amzal, Nora. "Measurement of electric and magnetic dipole moments in octupole nuclei." Thesis, University of Liverpool, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.398582.
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Mainos, Constantinos. "Etude des transitions mutiphotoniques dans des molécules diatomiques." Paris 13, 1986. http://www.theses.fr/1986PA132001.
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Etude des transitions rovibroniques multiphotoniques de type dipolaire électrique pour des états moleculaires présentant un couplage de hund (a),(b) ou un couplage intermediaire entre (a) et (b), à l'approximation adiabatique pour décrire la vibration et la rotation. Expressions de l'intensité des raies rotationnelles dans le cas d'une polarisation linéaire ou circulaire et pour des photons identiques. Régles de sélection pour la rotation et le couplage ou se trouvent les états moléculaires (initial et final) pour le cas général d'une transition à "n" photons et d'une multiplicité quelconque. Rapport d'intensités polarisationlinéaire / polarisation circulaire. Expérience à 2 photons pour la bande gamma (o,o) de no et comparaison aux valeurs théoriques calculées
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Grozier, James R. "The cryogenic neutron electric dipole moment experiment : magnetic challenges and solutions." Thesis, University of Sussex, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.444372.
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Nouri, Nima. "MAGNETIC FIELD NON-UNIFORMITY CHALLENGES IN NEUTRON ELECTRIC DIPOLE MOMENT EXPERIMENTS." UKnowledge, 2016. http://uknowledge.uky.edu/physastron_etds/38.
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A new neutron Electric Dipole Moment (nEDM) experiment was proposed to be commissioned at the Fundamental Neutron Physics Beamline at the Spallation Neutron Source (SNS) of the Oak Ridge National Laboratory (ORNL). The underlying theme of this experiment (first conceived by Golub and Lamoreaux in 1994) is the search for new physics beyond the Standard Model of particle physics. The discovery of a non-zero nEDM would be of revolutionary importance to physics, with the discovery of such providing for evidence for new-beyond-the-Standard-Model physics required for a resolution to the unresolved puzzle of why the universe is dominated by matter, as opposed to anti-matter. A first demonstration of a new magnetic field monitoring system for a neutron electric dipole moment experiment is presented. The system is designed to reconstruct the vector components of the magnetic field in the interior measurement region solely from exterior measurements. The results highlight the potential for the implementation of an improved system in an upcoming neutron electric dipole moment experiment to be carried out at the Spallation Neutron Source at Oak Ridge National Laboratory.
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Choi, Tin Chau. "An ultra-wideband magnetic-electric dipole antenna and a shielded slot antenna." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp01/MQ38622.pdf.
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Zolj, Adnan. "Electrically Small Dipole Antenna Probe for Quasi-static Electric Field Measurements." Digital WPI, 2018. https://digitalcommons.wpi.edu/etd-theses/202.
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The thesis designs, constructs, and tests an electrically small dipole antenna probe for the measurement of electric field distributions induced by a transcranial magnetic stimulation (TMS) coil. Its unique features include high spatial resolution, large frequency band from 100 Hz to 300 kHz, efficient feedline isolation via a printed Dyson balun, and accurate mitigation of noise. Prior work in this area is thoroughly reviewed. The proposed probe design is realized in hardware; implementation details and design tradeoffs are described. Test data is presented for the measurement of a CW capacitor electric field, demonstrating the probe’s ability to properly measure conservative electric fields caused by a charge distribution. Test data is also presented for the measurement of a CW solenoidal electric field, demonstrating the probe’s ability to measure non-conservative solenoidal electric fields caused by Faraday’s law of induction. Those are the primary fields for the transcranial magnetic stimulation. Advantages and disadvantages of this probing system versus those of prior works are discussed. Further refinement steps necessary for the development of this probe as a valuable TMS instrument are discussed.
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He, Weiping. "Characterizing near-field circuit board radiation using crossed electric and magnetic dipole sources." Diss., Rolla, Mo. : Missouri University of Science and Technology, 2010. http://scholarsmine.mst.edu/thesis/pdf/He_09007dcc807256ca.pdf.
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Thesis (M.S.)--Missouri University of Science and Technology, 2010.Vita. The entire thesis text is included in file. Title from title screen of thesis/dissertation PDF file (viewed Dec. 23, 2009). Includes bibliographical references (p. 60).
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Dadisman, James Ryan. "MAGNETIC FIELD DESIGN TO REDUCE SYSTEMATIC EFFECTS IN NEUTRON ELECTRIC DIPOLE MOMENT MEASUREMENTS." UKnowledge, 2018. https://uknowledge.uky.edu/physastron_etds/53.
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Charge-Conjugation (C) and Charge-Conjugation-Parity (CP) Violation is one of the three Sakharov conditions to explain via baryogenesis the observed baryon asymmetry of the universe (BAU). The Standard Model of particle physics (SM) contains sources of CP violation, but cannot explain the BAU. This motivates searches for new physics beyond the standard model (BSM) which address the Sakharov criteria, including high-precision searches for new sources of CPV in systems for which the SM contribution is small, but larger effects may be present in BSM theories. A promising example is the search for the electric dipole moment of the neutron (nEDM), which is a novel system to observe CPV due to the initial and final state being identical. A non-zero measurement necessarily requires violation of P and T discrete symmetries; invoking CPT invariance requires that CP is violated. There are BSM theories which predict a magnitude for the nEDM larger than SM predictions, so that such studies are beneficial at setting constraints on new physics. The current experimental limit of dn < 3.0 x 10-26 e cm at 90% CL as set by the Institut Laue-Langevin (ILL) [1] was largely limited by systematic effects related to the magnetic field. The research presented here supported technical progress toward a new measurement of the nEDM, with the goal of improving the result by an order of magnitude. A novel approach to the problem of limiting systematics is proposed, studied in Monte Carlo simulations, and an optimized prototype was constructed for use in a magnetic resonance experiment.
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Bowlan, John. "Electric dipole moments, cluster metallicity, and the magnetism of rare earth clusters." Diss., Georgia Institute of Technology, 2010. http://hdl.handle.net/1853/34751.
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One of the fundamental properties of bulk metals is the cancellation of electric
fields. The free charges inside of a metal will move until they find an arrangement where
the internal electric field is zero. This implies that the electric dipole moment of a metal
particle should be exactly zero, because an electric dipole moment requires a net separation
of charge and thus a nonzero internal electric field.
This thesis is an experimental study to see if this property continues to hold for tiny sub-
nanometer metal particles called clusters (2 - 200 atom, R < 1 nm). We have measured the
electric dipole moments of metal clusters made from 15 pure elements using a molecular
beam electric deflection technique. We find that the observed dipole moments vary a great
deal across the periodic table. Alkali metals have zero dipole moments, while transition
metals and lanthanides all have dipole moments which are highly size dependent. In most
cases, the measured dipole moments are independent of temperature (T = 20 - 50 K), and
when there is a strong temperature dependence this suggests that there is a new state of
matter present. Our interpretation of these results are that those clusters which have a non-
zero dipole moment are non-metallic, in the sense that their electrons must be localized
and prevented from moving to screen the internal field associated with a permanent dipole
moment.
This interpretation gives insight to several related phenomena and applications. We
briefly discuss an example cluster system RhN where the measured electric dipole moments
appear to be correlated with a the N2O reactivity.
Finally, we discuss a series of magnetic deflection experiments on lanthanide clusters
(Pr, Ho, Tb, and Tm). The magnetic response of these clusters is very complex and highly
sensitive to size and temperature. We find that PrN (which is non-magnetic in the bulk) becomes magnetic in clusters and TmN clusters have magnetic moments lower than the atomic value as well as the bulk saturation value implying that the magnetic order in the cluster involves non-collinear or antiferromagnetic order. HoN and TbN show very similar size dependent trends suggesting that these clusters have similar structures.
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Aleksandrova, Alina. "Magnetic Field Monitoring in the SNS Neutron EDM Experiment." UKnowledge, 2019. https://uknowledge.uky.edu/physastron_etds/68.
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It is a well known fact that the visible universe is made almost entirely of baryonic matter. Yet, this is also one of the greatest puzzles that physicists are trying to solve: Where did all of this matter come from in the first place? The Standard Model (SM) of particle physics predicts a baryon asymmetry that is much smaller than what is observed in nature. In order to try and explain this discrepancy, Sakharov (1967) postulated three necessary conditions for baryogenesis in the early universe. One of these is the requirement that charge conjugation (C) and the product of C and parity (P) symmetries are violated. Because the SM fails to generate the observed baryon asymmetry, additional sources of CP violation are needed in order to help reconcile theory and observation. Thus, physicists have been looking for extensions to the SM in search of an answer. The presence of a neutron Electric Dipole Moment (nEDM) would signal a new source of CP violation. A non-vanishing nEDM would provide evidence for the breaking of both parity (P) and time-reversal symmetry (T). Because CPT symmetry is assumed to be conserved and has not been found to be broken, this would signal CP violation.
To look for an nEDM, stored ultracold neutrons are placed in parallel and anti-parallel magnetic and electric fields and the Larmor precession frequency is carefully measured. A difference in the precession frequency of the neutrons in the two states of the fields would signal the existence of an nEDM. The current upper limit of the nEDM was set by the RAL-Sussex-ILL collaboration and stands at dn < 3.0x10-26 e cm (90% CL). Currently a new cryogenic apparatus is under construction at the Spallation Neutron Source (SNS) at the Oak Ridge National Laboratory (ORNL) which aims to reduce the current upper limit by two orders of magnitude.
A central problem to all neutron EDM experiments is the generation of a highly uniform and stable magnetic field. Because the suppression of systematic effects that arise from magnetic field nonuniformities and temporal drifts is vital to the success of these experiments, it is important to have the ability to precisely control and monitor the magnetic field gradients inside of the experimental volume. However, it is not always possible to measure the field gradients within the region of interest directly. To remedy this issue in the SNS nEDM experiment, a field monitoring system has been designed and tested that will allow for the reconstruction of the field gradients inside of the fiducial volume using noninvasive measurements of the field components at discrete locations external to this volume. This document will outline the theoretical framework of our method and present the results of experimental and simulated studies performed and the engineering design for such a field monitoring system.
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Malkowski, Susan Kate. "MAGNETIC SHIELDING STUDIES FOR THE NEUTRON ELECTRIC DIPOLE MOMENT EXPERIMENT AT THE SPALLATION NEUTRON SOURCE." UKnowledge, 2011. http://uknowledge.uky.edu/physastron_etds/1.
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The neutron Electric Dipole Moment Experiment at the Spallation Neutron Source requires an overall magnetic shielding factor of order 105 to attenuate external background magnetic fields. At present, the shielding design includes an external (room-temperature) multi-layer μ-metal magnetic shield, a cryogenic (4 Kelvin) Pb superconducting shield, and a cryogenic (4 Kelvin) ferromagnetic shield composed of Metglas ribbon. This research determined how to construct a Metglas shield using minimal material that produced axial and transverse shielding factors of ~267 and ~1500. In addition, the μ-metal and Metglas shields were modeled using finite element analysis. The FEA model includes external coils and their effect on the residual magnetic fields. This study will help with the design of the shielding.
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Flaux, Pierrick. "Measurement of the neutron electric dipole moment at the Paul Scherrer Institute : production of magnetic fields." Thesis, Normandie, 2019. http://www.theses.fr/2019NORMC222/document.
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Le travail réalisé au cours de cette thèse concerne le développement du système de bobines de l'expérience n2EDM à l'Institut Paul Sherrer (PSI). Le but de cette expérience est de mettre en évidence de nouvelles sources de violation CP à travers la mesure du moment dipolaire électrique du neutron. L'actuelle limite supérieure sur la mesure de nEDM, $2.9 \cross 10^{-26}$ e.cm (90\% C.L.) à été obtenue par la collaboration RAL-Sussex-ILL en 2006.L'expérience n2EDM vise à améliorer d'un ordre de grandeur la sensibilité statistique en gardant sous contrôle les effets systématiques. Cela requiert la production d'un champ magnétique très uniforme. Les non-uniformités de ce dernier sont en effet responsable de la dépolarisation des neutrons et impliqués dans plusieurs effets systématiques.Dans le premier chapitre, les motivations physiques sont discutées.Le second chapitre décrit le principe de mesure de l'expérience n2EDM, ainsi que l'importance de l'uniformité du champ magnétique. Le chapitre s'achève par une présentation globale du dispositif expérimental.Le troisième chapitre présente le logiciel COMSOL et discute du design et des performances de la bobine B$_{0}$, en charge de la production du champ magnétique principal.Dans le quatrième chapitre, le système de bobines correctrices chargées de corriger les non-uniformités du champ magnétique et celles devant produire des gradients spécifiques sont présentées.Finalement, le cinquième et dernier chapitre présente l'étude des dipôles magnétiques localisés et de leur influence sur l'expérienceThis work presents the design of the coils system developed for the n2EDM experiment at the Paul Sherrer Institute (PSI). The goal of this experiment is to reveal new sources of CP violation through the measurement of the neutron electric dipole moment. The current upper limit of the nEDM measurement, $2.9 \cross 10^{-26}$ e.cm (90\% C.L.) was achieved by the RAL-Sussex-ILL collaboration in 2006.The n2EDM experiment aims at improving by one order of magnitude the statistical sensitivity while keeping under control the systematics effects. It requires to produce a very uniform field, its non-uniformities being responsible of the neutron's depolarization and of severals systematic effects.In the first chapter, the theoretical motivation are discussed.The second chapter describes the measurement principle of the n2EDM experiment, as well as the importance of the magnetic field uniformity. This chapter ends by an overview of the apparatus.The third chapter introduces the COMSOL software and discuss the design and the performances of the B0 coil, in charge of the production of the main magnetic field.In the fourth chapter, the correcting coils used to suppress the non-uniformities of the magnetic field and the ones which produce specific gradients are presented.Finally, the fifth and last chapter talks about the study of localised magnetic dipoles and their influence on the experiment
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Bergmann, Ryan M. "Characterization of low-frequency electric potential oscillations near the edge of a plasma confined by a levitated magnetic dipole." Thesis, Massachusetts Institute of Technology, 2009. http://hdl.handle.net/1721.1/53240.
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Thesis (S.M. and S.B.)--Massachusetts Institute of Technology, Dept. of Nuclear Science and Engineering, 2009.Cataloged from PDF version of thesis.
Includes bibliographical references (p. 95-96).
A vertically adjustable electrostatic probe array was made to observe the previously seen low-frequency angular oscillations in LDX and identify if they are related to computationally expected convective cells. The array rests one meter from the centerline and measures edge fluctuations at field lines near the separatrix. It spans ninety degrees and has 24 probes mounted on it for total probe tip separation of 6.8cm. Bispectral analysis of the fluctuations show that that an inverse cascade of energy is present at times in LDX. The cascade transfers energy from small spatial scale structures to large scale structures. The wavenumber spectrum is xc k-1.4 to cx k-25 at high wavenumbers, which encompasses the inverse energy cascade regime of c k-5/3. The plasma also has a linear dispersion relation which gives a phase velocity of 2-16 k. This phase velocity is inversely correlated with neutral gas pressure in the vessel. The velocity also has a local maximum at 5 pTorr which is the pressure that produces maximum plasma density. The radial E x B drift velocities are observed to have a mean near zero, which indicates a closed structure like a convective cell. The instantaneous radial drift velocities are on the order of the ion sound speed, which is 35 km/s.
by Ryan M. Bergmann.
S.M.and S.B.
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Gök, Şafak. "Electrical and magnetic investigations on transition metal implanted GaAs." [S.l.] : [s.n.], 2006. http://deposit.ddb.de/cgi-bin/dokserv?idn=983511020.
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Seo, Jiwon. "Electronic and magnetic properties of transition metal oxide heterostructures." Thesis, University of Cambridge, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.611390.
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Bingham, Stephen John. "Magnetic circular dichroism and electron paramagnetic resonance of transition ions." Thesis, University of East Anglia, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.357179.
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Alcaraz, de la Osa Rodrigo. "Nanostructured systems with arbitrary electric and magnetic properties: Development and Application of an Extension of the Discrete Dipole Approximation (E-DDA)." Doctoral thesis, Universidad de Cantabria, 2013. http://hdl.handle.net/10803/117776.
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The discrete dipole approximation (DDA) has been successfully applied to many light scattering problems. Simply stated, the DDA is an approximation of the continuum target by a finite array of polarizable points. The points acquire dipole moments in response to thelocal fields. The dipoles of course interact with one another via their electric and magnetic fields, so the DDA is also sometimes referred to as the coupled dipole approximation. As of today, the method has established itself as one of the best solutions to calculate the scattering of radiation by particles of arbitrary shape. Hitherto, however, the main existing implementations include materials with relative magnetic permeability equal to 1 only, which is correct for all materials in the optical frequency range.
Nonetheless, materials with unusual optical properties have arisen recently. This includes the possibility of having both electric and magnetic anisotropic properties (bianisotropic materials) in the most general case. The situation where both the real part of the electric permittivity and the magnetic permeability are negative corresponds to what is known as "left-handed materials", or negative index materials (NIM), with unconventional properties such as negative refraction. The treatment of these materials with a method as contrasted as the DDA provides several advantages, apart from possibly being the only method available in many cases.
This PhD Thesis has explored nanostructured systems with arbitrary anisotropic optical properties (both electric and magnetic) by means of an Extension of the Discrete Dipole Approximation (E-DDA). During the development of this dissertation, a computational code (E-DDA code) has been implemented, able to produce comparative results with existing DDA codes, obtaining an excellent agreement.
After validation, the method was then applied to a wide range of materials and situations, making a special reference to its application to magneto-optical materials (with an antisymmetric electric permittivity tensor) and composite materials.
As a summary, the status of the E-DDA code is mature enough to be applied to very different configurations, making it a very useful, flexible and stable computational tool for calculating scattering and absorption of light by irregular particles, including anisotropic materials both electrically and magnetically at the same time in the most general case.La aproximación de dipolo discreto (o DDA por sus iniciales en inglés) ha sido empleada con éxito en multitud de aplicaciones dentro del ámbito de la difusión de luz. Básicamente consiste en discretizar el blanco difusor en elementos polarizables. Los elementos adquieren momentos dipolares en respuesta a los campos locales. Los dipolos por supuesto interaccionan entre ellos por medio de sus campos eléctricos y magnéticos, por eso a la DDA también se la conoce como aproximación de dipolo acoplado. A día de hoy, el método se afianza como una de las mejores soluciones para calcular la radiación difundida por partículas de forma arbitraria. Hasta ahora, sin embargo, las principales implementaciones existentes sólo incluyen materiales en los que la permeabilidad magnética relativa puede aproximarse por la unidad, lo cual es acertado para todos los materiales en el dominio de las frecuencias del rango óptico. No obstante, últimamente están apareciendo materiales con propiedades ópticas inusuales, como por ejemplo el caso de que algunas de sus constantes ópticas efectivas sean negativas (sus partes reales), o bien que presenten anisotropía tanto para el campo eléctrico como para el magnético (materiales bianisótropos). El caso doble negativo correspondería a lo que se ha venido en llamar “materiales zurdos”, o materiales con índice negativo, con propiedades sorprendentes como la refracción negativa. El tratamiento de estos materiales con un método tan bien contrastado como es el DDA presenta bastantes ventajas, aparte de que en muchos casos puede ser el único método disponible. Esta Tesis Doctoral ha explorado sistemas nanoestructurados con propiedades eléctricas y magnéticas anisótropas por medio de una Extensión de la Aproximación de Dipolo Discreto (E-DDA). Durante el desarrollo de esta tesis, se ha implementado un código computacional (código E-DDA), capaz de producir resultados comparativos con otros códigos DDA existentes, obteniendo un acuerdo excelente. Después de validarse, el método se ha aplicado a un amplio rango de materiales y situaciones, haciendo mención especial a su aplicación a materiales magneto-ópticos (con un tensor de permisividad eléctrica antisimétrico) y materiales compuestos. En resumen, el estado del código desarrollado es suficientemente maduro como para poder aplicarse a muchas configuraciones diferentes, haciendo de él una herramienta computacional útil, flexible y estable para calcular la difusión y absorción de luz por partículas irregulares, incluyendo materiales anisótropos tanto eléctricos como magnéticos en el caso más general.
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Delange, Pascal. "Many-electron effects in transition metal and rare earth compounds : Electronic structure, magnetic properties and point defects from first principles." Thesis, Université Paris-Saclay (ComUE), 2017. http://www.theses.fr/2017SACLX040/document.
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Le sujet de cette thèse est la théorie à partir des premiers principes de la structure électronique de matériaux présentant de fortes corrélations électroniques. D’importants progrès ont été faits dans ce domaine grâce aux implémentations modernes de Théorie de la Fonctionelle de Densité (DFT). Néanmoins, la méthode DFT a certaines limitations. D’une part, elle est faite pour décrire les propriétés de l’état fondamental mais pas des états excités des matériaux, bien que ces derniers soient également importants. D’autre part, les approximations de la fonctionnelle employées en pratique réduisent la validité de la DFT, conceptuellement exacte : en particulier elles décrivent mal les matériaux aux effets de corrélations les plus importants.Depuis les années 1990, différentes théoriques quantiques à N corps ont été utilisées pour améliorer ou compléter les simulations à base de DFT. Une des plus importantes est la Théorie du Champ Moyen Dynamique (DMFT), dans laquelle un modèle sur réseau est relié de manière auto-cohérente à un modèle plus simple d’impureté, ce qui donne de bons résultats à condition que les corrélations soient principalement locales. Nous présentons brièvement ces théories dans la première partie de cette thèse. Les progrès récents de la DMFT visent, entre autres, à mieux décrire les effets non-locaux, à comprendre les propriétés hors équilibre et à décrire de vrais matériaux plutôt que des modèles.Afin d’utiliser la DMFT pour décrire de vrais matériaux, il faut partir d’un calcul de structure électronique traitant tous les électrons au même niveau, puis appliquer une correction traitant les effets à N corps sur un sous-espace de basse énergie d’orbitales autour niveau de Fermi. La définition cohérente d’un tel sous-espace nécessite de tenir compte de la dynamique des électrons en-dehors de cet espace. Ces derniers, par exemple, réduisent la répulsion de Coulomb entre électrons dans le sous-espace. Néanmoins, combiner la DFT et la DMFT n’est pas aisé car les deux n’agissent pas sur la même observable. Dans la deuxième partie de cette thèse, nous étudions les modèles de basses énergies, comme la technique échange écranté + DMFT récemment proposée. Nous analysons l’importance de l’échange non-local et des interactions de Coulomb retardées, et illustrons cette théorie en l’appliquant aux états semi-cœur dans les métaux d10 Zn et Cd.Dans la dernière partie, nous utilisons ces méthodes pour étudier trois matériaux corrélés importants d’un point de vue technologique. Dans un premier temps, nous nous intéressons à la physique des mono-lacunes dans la phase paramagnétique du fer. De façon surprenante pour un défaut aussi simple, son énergie de formation n’a toujours pas été obtenue de manière cohérente par la théorie et l’expérience. Nous démontrons que cela est dû à de subtils effets de corrélations autour de la lacune dans la phase paramagnétique à haute température : cette phase est plus fortement corrélée que la phase ferromagnétique, où des calculs de DFT ont été faits.Dans un deuxième temps, nous étudions la transition métal-isolant dans la phase métastable VO2 B. Nous montrons que cette transition ressemble à celle entre la phase conventionnelle rutile et la phase M2 de VO2, mettant en jeu à la fois des liaisons covalentes dans les dimères et une transition de Mott sur les atomes V restants. Nous étudions également l’effet de lacunes d’oxygène sur la structure électronique de VO2.Enfin, nous proposons une technique au-delà de la DFT pour calculer le champ cristallin dans les oxydes et alliages de terres rares. Bien que l’amplitude de ce champ soit faible pour les orbitales localisées 4f des lanthanides, il est crucial pour leur caractère d’aimant permanent. En modifiant l’approximation Hubbard I pour résoudre les équations de DMFT, nous évitons une erreur d’auto-interaction faible en valeur absolue mais physiquement importante, démontrant l’importance de modèles de basse énergie correctement définisThe topic of this thesis is the first-principles theory of the electronic structure of materials with strong electronic correlations. Tremendous progress has been made in this field thanks to modern implementations of Density Functional Theory (DFT). However, the DFT framework has some limits. First, it is designed to predict ground state but not excited state properties of materials, even though the latter may be just as important for many applications. Second, the approximate functionals used in actual calculations have more limited validity than conceptually exact DFT: in particular, they are not able to describe those materials where many-electron effects are most important.Since the 1990's, different many-body theories have been used to improve or complement DFT calculations of materials. One of the most significant non-perturbative methods is Dynamical Mean-Field Theory (DMFT), where a lattice model is self-consistently mapped onto an impurity model, producing good results if correlations are mostly local. We briefly review these methods in the first part of this thesis. Recent developments on DMFT and its extensions were aimed at better describing non-local effects, understanding out-of-equilibrium properties or describing real materials rather than model systems, among others. Here, we focus on the latter aspect.In order to describe real materials with DMFT, one typically needs to start with an electronic structure calculation that treats all the electrons of the system on the same footing, and apply a many-body correction on a well-chosen subspace of orbitals near the Fermi level. Defining such a low-energy subspace consistently requires to integrate out the motion of the electrons outside this subspace. Taking this into account correctly is crucial: it is, for instance, the screening by electrons outside the subspace strongly reduces the Coulomb interaction between electrons within the subspace. Yet it is a complex task, not least because DFT and DMFT are working on different observables. In the second part of this thesis, we discuss low-energy models in the context of the recently proposed Screened Exchange + DMFT scheme. In particular, we study the importance of non-local exchange and dynamically-screened Coulomb interactions. We illustrate this by discussing semi-core states in the d10 metals Zn and Cd.In the third and last part, we use the methods described above to study the electronic structure of three fundamentally and technologically important correlated materials. First, we discuss the physics of point defects in the paramagnetic phase of bcc Fe, more precisely the simplest of them: the monovacancy. Surprisingly for such a simple point defect, its formation energy had not yet been reported consistently from calculations and experiments. We show that this is due to subtle but nevertheless important correlation effects around the vacancy in the high-temperature paramagnetic phase, which is significantly more strongly correlated than the ferromagnetic phase where DFT calculations had been done.Second, we study the metal-insulator phase transition in the metastable VO2 B phase. We show that this transition is similar to that between the conventional rutile and M2 VO2 phases, involving both bonding physics in the dimer and an atom-selective Mott transition on the remaining V atoms. Motivated by recent calculations on SrVO3, we study the possible effect of oxygen vacancies on the electronic structure of VO2.Finally, we propose a scheme beyond DFT for calculating the crystal field splittings in rare earth intermetallics or oxides. While the magnitude of this splitting for the localized 4f shell of lanthanides does not typically exceed a few hundred Kelvin, it is crucial for their hard-magnetic properties. Using a modified Hubbard I approximation as DMFT solver, we avoid a nominally small but important self-interaction error, stressing again the importance of carefully tailored low-energy models
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Campanini, Donato. "Nanocalorimetry of electronic phase transitions in systems with unconventional superconductivity and magnetic ordering." Licentiate thesis, Stockholms universitet, Fysikum, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-116202.
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In this thesis, low temperature specific heat measurements on small (μg) single crystals of different superconducting and magnetic systems are presented. The device used in this work features a combination of high sensitivity and good accuracy over the temperature range 1-400 K and allows measurements in high magnetic fields. It consists of a stack of thin films deposited in the center of a Si3N4 membrane. A batch process for the production of up to 48 calorimeters from a 2" silicon wafer was developed in order to overcome the scarcity of devices and allow systematic investigations. With abundance of calorimeters, single crystals of three different systems were studied. Fe2P is the parent compound of a broad family of magnetocaloric materials. The first-order para- to ferromagnetic phase transition at TC = 216 K was investigated for fields H up to 2 T, applied parallel and perpendicular to the easy axis of magnetization c. Strikingly different phase contours were obtained depending on the field direction. In particular, for H perpendicular to c, two different ferromagnetic phases, with magnetization parallel and perpendicular to c are found. It was also possible to observe the superheating/supercooling states, the latent heat, and the structural change associated to the first-order transition. BaFe2(As1-xPx)2 is a member of the recently discovered iron-based high-temperature superconductors family. Crystals with three different compositions were measured to study the doping dependence of the superconducting properties in the overdoped regime (x > 0.30). The electronic specific heat at low temperatures was analyzed with a two band α model, which allows to extract the gap amplitudes and their weights. The degree of gap anisotropy was investigated from in-field measurements. Additional information on the system was obtained by a combined analysis of the condensation energy and upper critical field. URu2Si2, a heavy fermion material, was studied around and above the hidden-order temperature THO = 17.5 K. The origin of the hidden-order phase is still not understood. High-resolution specific heat data were collected to help clarify if any pseudogap state is seen to exist above THO. We found no evidence for any bulk phase transition above THO.
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Rouzhaji, Tuerhong. "Effect of environment on the electronic and magnetic properties of transition metals and rare-earth complexes." Thesis, Strasbourg, 2017. http://www.theses.fr/2017STRAE006/document.
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Cette thèse présente les résultats de mesures expérimentales effectués à basse température par les techniques de microscopie tunnel à balayage et de spectroscopie par tunnel à balayage (STS) sur les métaux de transitions phthalocyanines déposées sur les surfaces de métaux nobles. Les mesures STM/STS ont été effectuées pour les molécules MnPc et CuPc adsorbées sur les surfaces Ag (111) et Au (111) à la température expérimentale de travail de 4,5 K. Ces deux types de molécules présentent une différence substantielle de configurations d'adsorption, des comportements électroniques et magnétiques et des structures vibratoires moléculaire. Les études STM/STS ont principalement porté sur les propriétés magnétiques de ces molécules à travers l’effet Kondo et une attention particulière a été accordée à la molécule de MnPc en raison de son comportement magnétique plus intéressant issu de l'atome Mn central. Particulièrement, nous avons étudié l'évolution spectrale des structures électroniques et magnétiques du MnPc partant d'une molécule unique jusqu'à la structure bicouche ordonnée sur la surface Ag (111). En outre, les études STM/STS ont montré une preuve de couplage magnétique entre les moments magnétiques de l'atome de Co et de la molécule de MnPc ainsi que sa forte dépendance vis-à-vis du site d'adsorption de l'atome de Co. Ces études STM/STS sur ce système nous ont permis de comprendre l'effet des interactions molécule-substrat, molécule-molécule et molécules-atome sur les propriétés électroniques et magnétiques des molécules de MnPcThis thesis presents the results of low-temperature scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS) studies on transition-metal phthalocyanines molecules on the noble metal surfaces. The STM/STS measurements have been performed for MnPc and CuPc molecules adsorbed on Ag(111) and Au(111) surfaces at the experimental working temperature of 4.5 K. These two types of molecules exhibit substantially different adsorption configurations, the electronic and magnetic behaviors and the molecule vibrational structures. The STM/STS studies have focused mainly on the magnetic properties of these molecules by means of Kondo effect, and special attention has been paid to MnPc molecule due to its more interesting magnetic behavior arising from the central Mn atom. Particularly we investigated the spectral evolution of electronic and magnetic structures of MnPc starting from a single molecule up to the ordered bilayer structures on Ag(111) surface. In addition, the STM/STS investigations showed an evidence of magnetic coupling between the magnetic moments of the Co atom and MnPc molecule and its strong dependence on the adsorption site of Co atom. These STM/STS investigations on this system allowed us to understand the effect of molecule-substrate, molecule-molecule and molecule-atom interactions on the electronic and magnetic properties of MnPc molecules
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Tilford, Claire. "Experimental investigations of the electronic interactions within multinuclear first row transition metal complexes." Thesis, University of East Anglia, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.302144.
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Li, Peng. "Novel quantum magnetic states in low dimensions." Click to view the E-thesis via HKUTO, 2006. http://sunzi.lib.hku.hk/hkuto/record/B36883062.
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Li, Peng, and 李鵬. "Novel quantum magnetic states in low dimensions." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2006. http://hub.hku.hk/bib/B36883062.
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Kitada, Atsushi. "Magnetic and Electrical Properties of Transition Metal Oxides Obtained using Structurally Related Precursors." 京都大学 (Kyoto University), 2012. http://hdl.handle.net/2433/157604.
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Peleckis, Germanas. "Studies on diluted oxide magnetic semiconductors for spin electronic applications." Access electronically, 2006. http://www.library.uow.edu.au/adt-NWU/public/adt-NWU20070821.145447/index.html.
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Xu, Yang. "Performance Analysis of Point Source Model with Coincident Phase Centers in FDTD." Digital WPI, 2014. https://digitalcommons.wpi.edu/etd-theses/214.
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The Finite Difference Time Domain (FDTD) Method has been a powerful tool in numerical simulation of electromagnetic (EM) problems for decades. In recent years, it has also been applied to biomedical research to investigate the interaction between EM waves and biological tissues. In Wireless Body Area Networks (WBANs) studies, to better understand the localization problem within the body, an accurate source/receiver model must be investigated. However, the traditional source models in FDTD involve effective volume and may cause error in near field arbitrary direction. This thesis reviews the basic mathematical and numerical foundation of the Finite Difference Time Domain method and the material properties needed when modeling a human body in FDTD. Then Coincident Phase Centers (CPCs) point sources models have been introduced which provide nearly the same accuracy at the distances as small as 3 unit cells from the phase center. Simultaneously, this model outperforms the usual sources in the near field when an arbitrary direction of the electric or magnetic dipole moment is required.
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Martin, Claudia. "Density functional study of the electronic and magnetic properties of selected transition metal complexes." Doctoral thesis, Technische Universitaet Bergakademie Freiberg Universitaetsbibliothek "Georgius Agricola", 2014. http://nbn-resolving.de/urn:nbn:de:bsz:105-qucosa-134958.
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Die vorliegende Promotionsarbeit “Density functional study of the electronic and magnetic properties of selected transition metal complexes” beschäftigt sich mit dem Zusammenhang zwischen strukturellen Merkmalen sowie elektronischen und magnetischen Eigenschaften von Einzelmolekül-Magneten. Im Wesentlichen konnte dabei gezeigt werden, dass die magnetischen Eigenschaften sowohl von strukturellen Merkmalen als auch von den elektronischen Eigenschaften bestimmt werden. Des Weiteren ergab sich, dass verschiedene Kenngrößen der magnetischen Eigenschaften (im speziellen der magnetische Grundzustand S sowie die magnetische Anisotropie D) miteinander korreliert sind. Dies ist im Besonderen für eine mögliche Anwendung von Einzelmolekül-Magneten im Bereich der Datenspeicherung von Bedeutung.
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SANLI, AYDIN. "Transition Dipole Moment and Lifetime Study of Sodium Dimer and Lithium Dimer Electronic States via Autler-Townes and Resolved Fluorescence Spectroscopy." Diss., Temple University Libraries, 2017. http://cdm16002.contentdm.oclc.org/cdm/ref/collection/p245801coll10/id/444569.
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PhysicsPh.D.
This dissertation consists of three major studies. The first study, described in Chapter 3, focuses on the experimental work we carried out; experimental study of the electronic transition dipole moment matrix elements (TDMM) for the and electronic transitions of the sodium dimer molecule. Here we obtained the electronic transition dipole moments through Autler-Townes and resolved fluorescence spectroscopy and compared them to the theory. The second study, described in Chapter 4, is on sodium dimer ion-pair states. In this work, we calculated the radiative lifetimes and electronic transition dipole moments between Na2 ion-pair states ( , , , ) and state. This study was published in 2015. The last study, described in Chapter 5, is the total lifetime (bound-bound plus bound-free) and transition dipole moment calculations of the ion-pair electronic states, , of the lithium dimer molecule.
Temple University--Theses
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Baskar, Dinesh. "High temperature magnetic properties of transition metal oxides with perovskite structure /." Thesis, Connect to this title online; UW restricted, 2008. http://hdl.handle.net/1773/9812.
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Tabookht, Zahra. "Theoretical study of magnetic and conducting properties of transition metal nanowires." Doctoral thesis, Universitat Rovira i Virgili, 2011. http://hdl.handle.net/10803/52798.
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En la presente tesis doctoral se ha realizado un estudio computacional de las propiedades electrónicas de sistemas basados en cadenas metálicas monodimensionales de la familia de los llamados nanowires, concretamente su magnetismo y conductividad. Estas cadenas lineales se sustentan gracias a los ligandos orgánicos que se organizan a su alrededor, cuyo número de sitios de unión determina la nuclearidad de la cadena. Para estas moléculas, llamadas cadenas metálicas extendidas, se han calculado los parámetros de acoplamiento magnético con el método CASPT2. El uso del Hamiltoniano de Heisenberg estándar para los sistemas M3(dpa)4Cl2 cuando hay dos electrones no desapareados en cada centro, ha sido examinado mediante el cálculo del valor de λ mediante cálculos DFT. Las diferentes conductividades eléctricas observadas en las cadenas MMX [Ni2(dta)4I]∞ y [Pt2(dta)4I]∞ (dta = CH3CS2) y sus estados de ordenación de carga han sido analizados con parámetros de estructura electrónica extraídos a partir de cálculos DFT periódicos y de correlación combinados con la teoría del Hamiltoniano efectivo.In the present thesis, magnetic and conducting properties of systems, one-dimensional chains of the family of so-called nanowires, have been studied computationally. These linear chains are supported by organic ligands surrounding the metal backbone where the number of binding sites determines the nuclearity of the chain. For these molecules, also called extended metal atom chains, magnetic coupling parameters have been calculated with the CASPT2 method. The use of standard Heisenberg Hamiltonian for systems M3(dpa)4Cl2 when two unpaired electrons are localized on each magnetic center has been examined by calculating the value of λ from DFT calculations. The different electrical conductivities observed in MMX chains [Ni2(dta)4I]∞ and [Pt2(dta)4I]∞ (dta = CH3CS2) and the charge ordering state have been analyzed with DFT periodic calculations and also through the comparison of extracted electronic structure parameters from ab initio calculations combined with the effective Hamiltonian theory.
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Tanveer, Muhammad [Verfasser]. "First-principles electronic theory of non-collinear magnetic order in transition-metal nanowires / Muhammad Tanveer." Kassel : Universitätsbibliothek Kassel, 2015. http://d-nb.info/1072321874/34.
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Saureu, Artesona Sergi. "From mononuclear to dinuclear : magnetic properties of transition metals complexes." Doctoral thesis, Universitat Rovira i Virgili, 2016. http://hdl.handle.net/10803/386451.
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En les darreres dècades, el món de la tecnologia i el desenvolupament de nous aparells electrònics s'han convertit en vitals per la nostra societat. Considerant la creixent demanda per la interpretació de resultats experimentals, la millora dels mètodes teòrics i el creixement dels recursos computacionals ens han permés un millor enteniment del comportament magnètic en sistemes amb metalls de transició. L'objectiu d'aquesta tesi és contribuir en aquest camp d'investigació amb l'estudi de materials magnètics utilitzant eines computacionals (DFT, TD-DFT, CASSCF, CASPT2, DDCI, etc.), i en alguns casos, combinant-ho amb resultats experimentals. La primera part (Capítols 3 i 4) inclou l'estudi dels estats electronics de complexes de spin-crossover de Fe(II) i Fe(III) combinant la teoria funcional de la densitat (DFT i TD-DFT) amb mètodes multiconfiguracionals (CASSCF, CASPT2). A més a més, utilitzant la mateixa combinació, hem descrit el fenomen LIESST en complexes de Fe(III). La segona part (Cap. 5 i 6) exposa l'estudi de les propietats magnètiques associades a l'acoblament magnètic utilitzant mètodes variacionals (DDCI, DDCI-2), en un complex de Fe(IV) i un complex bimetàl·lic [MnCr]-oxalat, y com els canvis estructurals afecten a aquest acoblament. Altrament, hem fet un rigurós anàlisi de l'estructura electrònica del complex de Fe(IV) per proporcionar més informació en la descripció més adequada del sistema.En las últimas décadas, el mundo de la tecnologia y el desarrollo de nuevos aparatos electrónicos se han convertido en vitales para nuestra sociedad. Considerando la creciente demanda para la interpretación de resultados experimentales, la mejora de los métodos teóricos y el crecimiento de los recursos computacionales nos han permitido un mejor entendimiento de los comportamientos magnéticos en los sistemas con metales de transición. El objetivo de esta tesis es contribuir a este campo de investigación con el estudio de materiales magnéticos usando herramientas computacionales (DFT, TD-DFT, CASSCF, CASPT2, DDCI, etc.), y en algunos casos, combinando con resultados experimentales. La primera parte (Capítulo 3 y 4) incluye el estudio de los estados electrónicos de los complejos de spin-crossover de Fe(II) y Fe(III) combinando la teoria funcional de la densidad (DFT y TD-DFT) con métodos multiconfiguracionales (CASSCF, CASPT2). Además, usando la misma combinación, hemos descrito el fenómeno LIESST en complejos de Fe(III). La segunda parte (Cap. 5 y 6) expone el estudio de las propiedades magnéticas asociadas al acoplamiento magnético utilizando metodos variacionales (DDCI, DDCI-2), en un complejo de Fe(IV) y un complejo bimetálico [MnCr]-oxalato, y como los cambios estructurales afectan a ese acoplamiento. Por otra parte, hemos hecho un riguroso analisis de la estructura electrónica del complejo de Fe(IV) para aportar la información para la descripción mas adecuada del sistema.
Over the last decades the world of technology and the development of new devices have become vital for our society. Considering the growing demand for interpretation of experimental observations, the improvement of theoretical methods and the increasing of the computational resources has allowed us to deepen the understanding of magnetic beahvior of metal transitions architectures. The aim of this thesis is to contribute to this research field with the study of magnetic materials by using computational tools (DFT, TD-DFT, CASSCF, CASPT2, DDCI, etc.), and in some cases combining it with experimental results. The first part (Chapters 3 and 4) includes the study of the electronic states of Fe(II) and Fe(III) spin-crossover complexes combining the density functional theory (DFT and TD-DFT) with multiconfigurational methodologies (CASSCF, CASPT2). In addition, we have described the LIESST phenomenon in Fe(III) using the same combination. The second part (Chapters 5 and 6) exposes the study of the magnetic properties related to the magnetic coupling using variational methods (DDCI, DDCI-2) of a Fe(IV) complex and bimetallic [MnCr] oxalate-based complexes and how changes can influence to the coupling. Moreover, a rigorous analysis of the electronic structure of the Fe(IV) system has been performed to provide more information about the most adequate description of the system in terms of intuitive chemical concepts.
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Leppert, Linn [Verfasser], and Stephan [Akademischer Betreuer] Kümmel. "Structural and electronic properties of transition metal nanoalloys and magnetic compounds / Linn Leppert. Betreuer: Stephan Kümmel." Bayreuth : Universität Bayreuth, 2013. http://d-nb.info/1059352869/34.
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Kasperkiewicz, Karolina. "Structure, magnetic and electronic properties of new 1111-type and 42622-type transition metal-based oxyarsenides." Thesis, University of Edinburgh, 2014. http://hdl.handle.net/1842/9667.
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Discovery of high-temperature superconductors aroused a great interest in studies on these materials. In 1987 an yttrium-based compound YBCO (Yttrium-Barium- Copper-Oxide) was synthesised with Tc at 93 K. It was immediately evident that the BCS theory does not explain the pairing mechanism in these oxide-based superconductors, which predicted that a maximum Tc of about 30 K could be achieved. Layered copper oxides were for a long time the most studied high-Tc superconductors. With the discovery, at the beginning of 2008, by Kamihara of a new non-cuprate high-Tc superconductor a different path of studies had opened. This family of quaternary oxyarsenides LaO1-xFxFeAs was surprising due to the presence of Fe, which should lead to long-range magnetic order suppressing superconductivity. Although the parent compound LaFeAsO is not superconducting, electron doping (by partial substitution of O2- with F-) leads to superconductivity with Tc of 26 K. Since these discoveries there has been extensive research on the family of rare-earth quaternary oxypnictides with general formula REFaAsO (RE = La, Sm, Ce, Nd, Pr, Gd, Tb, Dy) and with Tc reaching 55 K for electron doped SmFeAsO. A study of new NdFeAsO family with Sr doping on Nd site was conducted. Synthesis of Nd1-xSrxFeAsO compounds and their further characterisation revealed that hole doping in these materials is a successful route to achieve superconductivity. Partial substitution of Nd3+ by Sr2+ with small doping level (x = 0.05) shows semiconducting type behaviour, while increasing doping level leads to the emergence of metallic conductivity and with level of doping 20% obtaining superconductivity at Tc = 13.5 K. These materials adopt a simple tetragonal crystal structure (space group P4/nmm), which undergoes a structural phase transition on cooling to orthorhombic symmetry (space group Cmma). The changes of structural, electronic and magnetic properties with doping level show very different behaviour – non-symmetric to the electron doped side of the phase diagram. The family of Fe-As based superconductors has expanded further by the discoveries of A1-xA’xFe2As2 (A = Alkaline Earth, A’ = Alkali metal), LiFeAs and NaFeAs phases, Sr3Sc2Fe2As2O5. A series of iron-based oxyarsenides with general formula Sr4M12O6M2 2As2 (M1 = Sc, Cr, V; M2 = Fe, Co, Ni) was synthesised and their structure was studied using powder X-ray and neutron diffraction. These materials adopt tetragonal crystal structure (space group P4/nmm) in analogy with REFeAsO systems. The Fe-As planes are sandwiched between perovskite K2NiF4-type oxide layers of Sr4M2O6 (MI = Sc, Cr, V), the large size of which creates a large distance between Fe-As planes. In spite of structural analogy with REFeAsO these new materials show a different behaviour from REFeAsO, which is absence of a structural phase transition on cooling. Both Sr4V2O6Fe2As2 and Sr4Sc2O6Ni2As2 compounds are superconducting without doping with Tc at 28 K and 2.5 K respectively. Neither Sr4Sc2O6Fe2As2 nor Sr4Cr2O6Fe2As2 show these properties, but are good parent compounds for doping, which may lead to producing compounds that achieve superconductivity. Further research was made with synthesising doped Sr4Cr2O6Fe2As2 with doping on Fe site with Co. The structure and magnetic and electrical properties of these compounds were studied and proved to show superconducting behaviour with Tc up to 17.5 K for 5% Co doping.
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Mishra, Snigdharaj K. "Mean-field and density-functional studies of charge ordering and magnetic transitions in lanthanum manganites /." free to MU campus, to others for purchase, 1997. http://wwwlib.umi.com/cr/mo/fullcit?p9841176.
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Denawi, Hassan. "Electronic and magnetic properties of polymer chains exploiting the reactivity of zwitterionic quinone with transition metal atoms." Electronic Thesis or Diss., Aix-Marseille, 2019. http://theses.univ-amu.fr.lama.univ-amu.fr/191010_DENAWI_493r256nufumz934umq262qn_TH.pdf.
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En utilisant le code VASP, plusieurs calculs de premier principe ont été effectués pour étudier les monocouches métallo-organiques sans et avec substrats métalliques, ces calculs reposent sur la théorie de la fonctionnelle de la densité polarisée en spin (DFT) avec l’approximation en gradient généralisée (SGGA) résolue en spin pour le potentiel d’échange et de corrélation et les pseudo-potentiels d’onde plane augmentée (PAW). En raison des problèmes bien connus de la DFT standard dans la description de systèmes fortement corrélés, nous utilisons SGGA + U avec un traitement explicite de la corrélation d’électrons forts dans la couche d incomplètement remplie des métaux de transition. Nous étudions les polymères de métaux de transition (TM) avec des molécules de quinone zwitterionique (ZQ) sous forme de chaînes unidimensionnelles (1D), d’arrangements bidimensionnels (2D) ou adsorbés sur des substrats métalliques. A partir des calculs ab-initio, nous prévoyons que les chaînes de polymères Fe-ZQ sont des composés à jonction de spin unidimensionnels. Les calculs déterminent les positions atomiques, les couplages magnétiques et la structure électronique. Nous étudions la structure électronique et magnétique d'un arrangement bidimensionnel (2D) récemment synthétisé de chaînes de polymères basées sur des atomes de Fe et des quinones zwitterioniques sur différents substrats métalliques (Au(110), Ag(111), Cu(110) et Cu(111)). De plus, toutes les séries de chaînes 3d TM-ZQ ont été étudiées, ainsi que de nombreuses 4d et 5d TM, une chaîne de ZQ avec Fe et V qui s’alternent montrent également des propriétés prometteusesUsing the VASP code (Vienna Ab initio Simulation Package) several first principle calculations have been performed to study metal-organic monolayers as free-standing layers and on metallic substrates. The first principles calculations are based on spin-polarized density functional theory (DFT) with the spin polarized gradient approximation with Hubbard term U (SGGA+U) with explicit treatment of the strong electron correlation in the incompletely filled d-shell of the transition metal ions. We study polymers of transition metals (TM) with zwitterionic quinone (ZQ) molecules as one dimensional (1D) chains, two-dimensional (2D) arrangements, or adsorbed on metallic substrates. From the ab-initio calculations we predict the Fe-ZQ zwitterionic quinoidal polymer chains to be one-dimensional spin cross-over compounds. The calculations determine the atomic positions, the magnetic couplings and the electronic structure. We investigate the electronic and magnetic structure of a recently synthesized two-dimensional (2D) arrangement of polymer chains based on Fe atoms and zwitterionic quinone on different metallic substrates (Au(110), Ag(111), Cu(110) and Cu(111)). The adsorption of the Fe atoms and zwitterionic quinone on the surfaces was studied via SGGA+U and the free-standing isolated polymer chain, the 2D arrangement and the adsorbed polymers have been calculated. Furthermore, all the series of 3d TM-ZQ chains has been studied, as well as many 4d and 5d TM. Promising properties show also alternating chains of FeV-ZQ
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Heyrendt, Laurent. "Études des actions des forces magnétiques volumiques créées par un champ magnétique intense sur des fluides à seuil - possibilités de transition solide-gel." Phd thesis, Université de Lorraine, 2012. http://tel.archives-ouvertes.fr/tel-00799586.
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Les fluides à seuil ont des propriétés mécaniques étonnantes : en dessous d'une certaine contrainte, appelée contrainte seuil, le fluide se comporte comme un solide. Au-delà de la contrainte seuil, ils s'écoulent comme un gel. Ce mémoire porte sur l'étude des actions des forces magnétiques volumiques sur ces fluides. Nous étudions la possibilité de réaliser la transition solide--gel à partir des forces magnétiques volumiques créées par différents dispositifs magnétiques. Ces fluides n'ont pas de propriétés magnétiques particulières. Il est donc nécessaire de créer des champs magnétiques intenses pour agir sans contact sur ces fluides. Nous étudions différentes configurations magnétiques capables de dépasser la contrainte seuil au sein du fluide. L'influence des différents paramètres des configurations magnétiques est explorée, notamment à l'aide d'études paramétriques. Notre travail mêle des équations de magnétostatique et de mécanique des fluides non-newtoniens. Les calculs de magnétostatique sont menés de façon analytique alors que la partie mécanique et le couplage magnéto-mécanique sont traités par un logiciel de simulation numérique par la méthode des éléments finis. Les conditions magnétiques et mécaniques nécessaires à la transition solide--gel et à la modification d'écoulements de fluides à seuil sont discutées, notamment à l'aide de simulations numériques et de nombres adimensionnels.
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Woollacott, Claire. "Electronic and plasmonic properties of real and artificial Dirac materials." Thesis, University of Exeter, 2015. http://hdl.handle.net/10871/18227.
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Inspired by graphene, I investigate the properties of several different real and artificial Dirac materials. Firstly, I consider a two-dimensional honeycomb lattice of metallic nanoparticles, each supporting localised surface plasmons, and study the quantum properties of the collective plasmons resulting from the near field dipolar interaction between the nanoparticles. I analytically investigate the dispersion, the effective Hamiltonian and the eigenstates of the collective plasmons for an arbitrary orientation of the individual dipole moments. When the polarisation points close to normal to the plane the spectrum presents Dirac cones, similar to those present in the electronic band structure of graphene. I derive the effective Dirac Hamiltonian for the collective plasmons and show that the corresponding spinor eigenstates represent chiral Dirac-like massless bosonic excitations that present similar effects to those of electrons in graphene, such as a non-trivial Berry phase and the absence of backscattering from smooth inhomogeneities. I further discuss how one can manipulate the Dirac points in the Brillouin zone and open a gap in the collective plasmon dispersion by modifying the polarisation of the localized surface plasmons, paving the way for a fully tunable plasmonic analogue of graphene. I present a phase diagram of gapless and gapped phases in the collective plasmon dispersion depending on the dipole orientation. When the inversion symmetry of the honeycomb structure is broken, the collective plasmons become gapped chiral Dirac modes with an energy-dependent Berry phase. I show that this concept can be generalised to describe many real and artificial graphene-like systems, labeling them Dirac materials with a linear gapped spectrum. I also show that biased bilayer graphene is another Dirac material with an energy dependent Berry phase, but with a parabolic gapped spectrum. I analyse the relativistic phenomenon of Klein Tunneling in both types of system. The Klein paradox is one of the most counter-intuitive results from quantum electrodynamics but it has been seen experimentally to occur in both monolayer and bilayer graphene, due to the chiral nature of the Dirac quasiparticles in these materials. The non-trivial Berry phase of pi in monolayer graphene leads to remarkable effects in transmission through potential barriers, whereas there is always zero transmission at normal incidence in unbiased bilayer graphene in the npn regime. These, and many other 2D materials have attracted attention due to their possible usefulness for the next generation of nano-electronic devices, but some of their Klein tunneling results may be a hindrance to this application. I will highlight how breaking the inversion symmetry of the system allows for results that are not possible in these system's inversion symmetrical counterparts.
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Read, Daniel Edward. "Electrical and magnetic properties of n-Cd(_1-x)Mn(_x) Te close to the metal-insulator transition." Thesis, Durham University, 2001. http://etheses.dur.ac.uk/3783/.
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Electrical transport and magnetic measurements have been made on n-Cd(_1-x)Mn(_x) Te (0.047 < X < 0.197) for samples doped with hi or In,Al. Results are presented for measurements made as a function of temperature (40 mK < T < 300 K), applied magnetic field (0 T < B < 6 T) and photogenerated carrier density. Low field magnetic susceptibility measurements have identified a transition from a paramagnetic phase to a spin glass phase at low temperatures. The measured temperature dependence of the magnetic susceptibility is consistent with a cluster glass model. Measurements of the spin glass freezing temperature have been carried out on four samples having different Mn fractions The results obtained are in agreement with the limited number of previous measurements on nominally undoped samples. At low temperatures photo-induced changes in magnetism have been measured in both the paramagnetic and the spin glass phase. The change in magnetisation on illumination is due to an increased number of bound magnetic polarons formed around quasi localised s-spins. High temperature susceptibility measurements have been used to examine the parameters characterising the paramagnetic phase, and their variation with Mn fraction. Electrical transport measurements at very low temperatures (T < 800 mK) have shown a strong temperature dependent electron localisation. This has resulted in the confirmation of insulating behaviour in a sample (x = 0.047) having n. At low temperatures and in zero field an activated form of the conductivity is observed. In applied magnetic fields (B > 50 mT) Efros-Shklovskii variable range hopping is observed in the insulating phase. These results are attributed to the formation of a hard gap in the density of states, having a magnetic origin. At higher fields an insulator-metal phase transition occurs. In the metallic phase the conductivity can be described by a quantum correction to the zero temperature conductivity due to the effect of electron-electron interactions. Results obtained before and after illumination are consistent with scaling theory of electron localisation, having a critical exponent close to unity, indicative of the importance of electron-electron interactions. A reduction in the value of the critical field is seen after increasing the carrier density (B(_c) = 2.0 and 1.3 T for n = 3.3 xl0(^17)cm(^-3) and 3.8 x10(^17) cm(^-3) respectively).At low temperatures an anisotropy in the resistivity has been measured for samples in the spin glass phase. Magnetoresistance measurements have shown results consistent with previous measurements, in addition to a large, low field component that is attributed to the effect of magnetic field on electrons in the variable range hopping regime.
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Woodruff, Daniel. "Organometallic and metal-amide precursors for transition metal and lanthanide cluster complexes with interesting electronic an magnetic properties." Thesis, University of Manchester, 2012. https://www.research.manchester.ac.uk/portal/en/theses/organometallic-and-metalamide-precursors-for-transition-metal-and-lanthanide-cluster-complexes-with-interesting-electronic-an-magnetic-properties(d35cea40-6e84-4d19-ba6a-7a7fe1e4a135).html.
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This project exploited the Brönsted basicity of the organometallic/metal-amide compounds,MnCp2 and Ln[N(SiMe3)2]3·LiCl(THF)3 (Ln = Gd, Tb and Dy) in attempts to synthesizepolymetallic cluster compounds via deprotonation of X-H (X = N or S) bond containing proligands.The chemical, electronic and magnetic properties of the resulting compounds werestudied with a variety of methods.The reaction of Ln[N(SiMe3)2]3·LiCl(THF)3 (Ln = Gd, Tb and Dy) with EtSH yieldsa series of [{Ln(N(SiMe3)2)(μ2-SEt)2}4(μ3-SEt)][Li(THF)4] “Ln4” squares in which theterbium and dysprosium analogues show SMM behaviour in zero field, with the dysprosiumanalogue displaying a fast relaxation process which can be “switched off” by the applicationof a 2000 Oe external field.Reactions of MnCp2 with Me3SiNP(NHR)3 (R = nPr, Cy, tBu) afforded a series ofcompounds; [CpMn{Me3SiN=P(NHnPr)2(μ-NnPr)}]2, [Mn{Me3SiN=P(NHCy)2(NCy)}2]and [CpMn{Me3SiN=P(NHtBu)2(NtBu)}]. Q-band EPR studies of these complexes revealthat altering the R group attached to the ligand causes a variation in coordination geometryaround the manganese centers and as such alters the electronic properties of the manganesecentres present in each complex.In order to avoid the synthesis of potentially unstable organometallic/metal-amideprecursors, one pot synthetic methodologies were developed to allow the isolation a series ofμ8-oxo centred Li7M cubes [MLi7(μ8-O)(μ-hpp)6]+ (M = Co, Mn and Zn). Addition ofstiochiometric amounts of water to the initial reaction mixture produced the Li7M cubes inhigh yields.Extension of the one pot synthetic strategy to the use of DyCl3 and YbCl3 inreactions with Li-TMP (TMP = 2,2,6,6-tetramethylpipiridine) afforded the lanthanidedimers [Ln(TMP)2(μ-OEt)]2 (Ln = Dy and Yb) in which the EtO- ligands were formed via insitu ether cleavage and the dysprosium analogue shows SMM behaviour under a 7000Oeapplied field.
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Wei, Haoming, Jose Luis Barzola-Quiquia, Chang Yang, Christian Patzig, Thomas Höche, Pablo Esquinazi, Marius Grundmann, and Michael Lorenz. "Charge transfer-induced magnetic exchange bias and electron localization in (111)- and (001)-oriented LaNiO3/LaMnO3 superlattices." American Institute of Physics, 2017. https://ul.qucosa.de/id/qucosa%3A23554.
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High-quality lattice-matched LaNiO3/LaMnO3 superlattices with monolayer terrace structure have
been grown on both (111)- and (001)-oriented SrTiO3 substrates by pulsed laser deposition. In contrast
to the previously reported experiments, a magnetic exchange bias is observed that reproducibly
occurs in both (111)- and (001)-oriented superlattices with the thin single layers of 5 and 7 unit cells,
respectively. The exchange bias is theoretically explained by charge transfer-induced magnetic
moments at Ni atoms. Furthermore, magnetization data at low temperature suggest two magnetic
phases in the superlattices, with Néel temperature around 10 K. Electrical transport measurements
reveal a metal-insulator transition with strong localization of electrons in the superlattices with the
thin LaNiO3 layers of 4 unit cells, in which the electrical transport is dominated by two-dimensional
variable range hopping.
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Richard, Laura Amanda. "A study of the crystallographic, magnetic and electronic properties of selected ZrM2-H systems." Thesis, University of Oxford, 2011. http://ora.ox.ac.uk/objects/uuid:276c59fe-cf45-42d2-a5a0-8c534c8b46bd.
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Dissolution of hydrogen into intermetallic compounds characteristically occurs at interstitial sites, causing little alteration to the base metal substructure but often bringing about substantial electronic and magnetic changes to the material. These hydrogen-induced alterations in the intermetallic hydrides are of interest both on a fundamental research level and in terms of technological applications; however, there exists no general theory as to how and why these alterations arise. The objective of this research is to elucidate to general effect of hydrogen on intermetallic compounds through the study of crystallographic, magnetic and electronic properties. An investigation has been carried out on the properties of three intermetallic compound - hydrogen systems of general formula ZrM₂, where M = V, Cr, Mn. All three compounds reversibly absorbed hydrogen with no change in crystal symmetry: powder diffraction studies showed that hydrogen was accommodated in interstitial sites of the existing metal sublattice via lattice expansion. The measurement of the magnetic properties of these systems was combined with the determination of conductivity and dielectric properties in order to describe the electronic e¤ects of hydrogen absorption. Despite the lack of signi
cant structural alteration in these systems, electron transfer between the metal sublattice and hydrogen may occur, as manifested in the appearance/disappearance of magnetic phenomena and the increase/decrease of electrical conductivity. Whilst the hydrogen addition in ZrM₂-H occurs simply via an expansion of the crystal structure, hydrogen does not act purely as null dilutant - there exist subtle electronic changes connected with the hydriding process as well.
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Klironomos, Alexios. "Structural transitions of the vortex lattice in anisotropic superconductors and fingering instability of electron droplets in an inhomogeneous magnetic field." [Gainesville, Fla.] : University of Florida, 2003. http://purl.fcla.edu/fcla/etd/UFE0000723.
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Ramanathan, Sivakumar. "Optical and electrical properties of compound and transition metal doped compound semiconductor nanowires." VCU Scholars Compass, 2009. http://scholarscompass.vcu.edu/etd/1667.
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Nanotechnology is the science and engineering of creating functional materials by precise control of matter at nanometer (nm) length scale and exploring novel properties at that scale. It is vital to understand the quantum mechanical phenomena manifested at nanometer scale dimensions since that will enable us to precisely engineer quantum mechanical properties to realize novel device functionalities. This dissertation investigates optical and electronic properties of compound and transition metal doped compound semiconductor nanowires with a view to exploiting them for a wide range of applications in semiconductor electronic and optical devices. In this dissertation work, basic concepts of optical and electronic properties at low dimensional structures will be discussed in chapter 1. Chapter 2 discusses the nanofabrication technique employed to fabricate highly ordered nanowires. Using this method, which is based on electrochemical self-assembly techniques, we can fabricate highly ordered and size controlled nanowires and quantum dots of different materials. In Chapter 3, we report size dependent fluorescence spectroscopy of ZnSe and Mn doped ZnSe nanowires fabricated by the above method. The nanowires exhibit blue shift in the emission spectrum due to quantum confinement effect, which increases the effective bandgap of the semiconductor. We found that the fluorescence spectrum of Mn doped ZnSe nanowires shows high luminescence efficiency, which seems to increase with increasing Mn concentration. These results are highly encouraging for applications in multi spectral displays. Chapter 4 investigates field emission results of highly ordered 50 nm tapered ZnO nanowires that were also fabricated by electrochemical self-assembly. Subsequent to fabrication, the nanowires tips are exposed by chemical etching which renders the tips conical in shape. This tapered shape concentrates the electric field lines at the tip of the wires, and that, in turn, increases the emission current density while lowering the threshold field for the onset of field emission. Measurement of the Fowler-Nordheim tunneling current carried out in partial vacuum indicates that the threshold electric field for field emission in 50-nm diameter ZnO nanowires is 15 V/µm. In this study we identified the key constraint that can increase the threshold field and reduce emission current density. In Chapter 5 we report optical and magnetic measurement of Mn-doped ZnO nanowires. Hysterisis measurements carried out at various temperatures show a ferromagnetic behavior with a Curie temperature of ~ 200 K. We also studied Mn-doping of the ZnO nanowires. The room temperature fluorescence spectroscopy of Mn-doped ZnO nanowires shows a red-shift in the spectra compared to the undoped ZnO nanowires possibly due to strain introduced by the dopants in the nanowires. Finally, in Chapter 6, we report our study of the ensemble averaged transverse spin relaxation time (T2*) in InSb thin films and nanowires using electron spin resonance (ESR) measurement. Unfortunately, the nanowires contained too few spins to produce a detectable signal in our apparatus, but the thin films contained enough spins (> 109/cm2) to produce a measurable ESR signal. We found that the T2* decreases rapidly with increasing temperature between 3.5 K and 20 K, which indicates that spin-dephasing is primarily caused by spin-phonon interactions.