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Silva, José Felix Estanislau da. "Shot Noise e corrente dependentes de spin: modelo quântico." Universidade de São Paulo, 2001. http://www.teses.usp.br/teses/disponiveis/76/76131/tde-08032017-091450/.
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Nesta dissertação, fazemos a primeira investigação sobre flutuações em corrente e corrente média dependentes de spin em potenciais duplo e simples da estrutura Zn1-xMnxSe. Consideramos efeitos de campos magnético e elétrico externos à temperatura nula. Na presença de um campo magnético, a interação dos íons de Mn com elétrons de condução e valência (interação de troca sp-d) origina potenciais dependentes de spin para o transporte em Zn1-xMnxSe. Aqui, flutuações em corrente (\"shot noise\") e a corrente média são calculados usando o modelo quântico de transporte através do potencial dependente de spin é descrito por uma matriz s de espalhamento. Os elementos da matriz de espalhamento, i.e., as amplitudes de transmissão e reflexão, são determinados pelo método da matriz transferência. Nossos resultados indicam que estruturas de potenciais simples e duplos Zn1-xMnxSe agem como se fossem \"filtros de spin\" para corrente. Em determinadas faixas de parâmetros do sistema, \"shot noise\" pode complementar informações obtidas da corrente médiaIn this dissertation we investigation for the first time spin dependent-current and its fluctuations in double and single barrier potentials of the Zn1-xMn xSe structure sandwiched between ZnSe layers. We consider effects of external magnetic field, the interaction of the Mn ions with thew conduction and valence electrons (sp-d exchange interation) give rises to spin-dependent potentials for transport across the Zn1-xMn xSe layer. Here, the average current and its fluctuations are calculated using the quantum transport model in which transport across the spin-dependent potential is described via scattering matrix s. The elements of the scattering matrix, i.e., the transmission and reflection amplitudes, are determined through the transfer-matrix method. Our results indicate date single and double potentials of the Zn1-xMn xSe structure act as \"spin filters\" for the current. Within some system parameter range, shot noise can supplement the information contained in the average current
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Sturma, Magali. "Modélisation par éléments finis des dispositifs pour la spintronique : couplage auto-cohérent des équations du micromagnétisme et du transport dépendant du spin." Thesis, Université Grenoble Alpes (ComUE), 2015. http://www.theses.fr/2015GREAY032/document.
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Cette thèse s'inscrit dans le contexte de l'électronique de spin et traite plus particulièrement de l'interaction réciproque entre un courant polarisé en spin et l'aimantation des structures magnétiques. Au cours de ce travail, les équations du transport diffusif dépendant du spin ont été couplées de façon auto-cohérente à l'équation de la dynamique d'aimantation dans l'approche micromagnétique au sein du code éléments finis. Cet outil numérique est appliqué à l'étude de la dynamique de parois de domaines dans différentes géométries sous l'action d'un courant polarisé. Il a permis de mettre en évidence plusieurs nouveaux phénomènes liés à l'interaction mutuelle entre l'aimantation et les spins des électrons. Pour des rubans à section rectangulaire, l'impact de cette interaction, habituellement négligée dans les modèles simplifiés, est quantifié via le calcul de la vitesse de déplacement de parois et du courant critique de Walker. Ces paramètres ont été étudiés en fonction de la largeur de paroi, du courant appliqué et des longueurs caractéristiques du transport polarisé en spin. L'augmentation du paramètre de non-adiabaticité du système, liée à l'augmentation du gradient d'aimantation ainsi qu'à une forte non-localité du modèle couplé, a été démontrée. Pour des fils à section circulaire et à diamètre modulable, une contribution supplémentaire à la non-adiabaticité du système liée, à la géométrie confinée, a été mise en évidence. Puis, les différents régimes dynamiques ainsi que les conditions de dépiégage de la paroi ont été caractérisés en fonction de la taille de constrictionsIn the context of spintronics this thesis studies the mutual interaction between a spin polarised current and the magnetization of magnetic structures. During this work, the diffusive spin transport equations were coupled in a self-consistent manner with the magnetization dynamics equations in the micromagnetic approach in our homemade finite element code. This numerical tool applied to the study of domain walls dynamics in different geometries under the action of spin polarized current highlighted several new phenomena related to the mutual interaction between the magnetization and the spins of electrons. For rectangular cross section stripes, the impact of this interaction, usually neglected in simplified models, is quantified by the computation of the domain wall velocity and the Walker critical current. These quantities were studied as a function of the domain wall width, the applied current, and the spin polarised transport characteristic lengths. Increasing the non-adiabatic parameter of the system related to the increase in the magnetization gradient and a strong non-locality of the coupled model was demonstrated. For circular cross section wires with a modulated diameter, an additional contribution to the non-adiabaticity of the system related to the confined geometry is highlighted. Then the different dynamic regimes and domain wall unpinning conditions are characterised according to the constriction size
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Sandschneider, Niko. "Strominduziertes Schalten der Magnetisierung." Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät I, 2009. http://dx.doi.org/10.18452/16035.
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Die vorliegende Arbeit beschäftigt sich mit der mikroskopischen Modellierung von strominduziertem Schalten der Magnetisierung in magnetischen Tunnelstrukturen. Die Tunnelstruktur besteht aus zwei durch einen nichtmagnetischen Isolator voneinander getrennten Ferromagneten und einem Paramagneten, der als Elektronenreservoir dient. Die Ferromagnete werden beide durch das Hubbard-Modell beschrieben. Durch Anlegen einer Spannung verschieben sich die chemischen Potentiale auf beiden Seiten des Isolators, wodurch ein endlicher Tunnelstrom entsteht. Dieser wird im Rahmen des Modells durch eine Hybridisierung zwischen benachbarten Schichten simuliert. Das Modell muss im Nichtgleichgewicht gelöst werden, da aufgrund der unterschiedlichen chemischen Potentiale thermodynamisches Gleichgewicht nicht angenommen werden darf. Daher wird zur analytischen Auswertung der Keldysh-Formalismus verwendet, der eine Erweiterung der Viel-Teilchen-Theorie ins Nichtgleichgewicht darstellt. Da es sich beim Hubbard-Modell um ein nicht exakt lösbares Viel-Teilchen-Modell handelt, wurde in der Arbeit eine approximative Lösung, der sogenannte Nichtgleichgewichtsspektraldichteansatz, entwickelt. Dieser beruht auf einer Hochenergieentwicklung der retardierten Greenfunktion mit Hilfe der exakt berechenbaren Spektralmomente. Die numerischen Resultate stimmen qualitativ mit dem Experiment überein. Insbesondere gelingt es, das Hystereseverhalten der Magnetisierung des freien Ferromagneten in Abhängigkeit der angelegten Spannung korrekt zu reproduzieren. Es kann somit allein durch Anlegen einer Spannung kontrolliert zwischen paralleler und antiparalleler Ausrichtung der Magnetisierungen geschaltet werden. Dieses Phänomen ist anhand der entsprechenden Quasiteilchenzustandsdichten erklärbar. Weiterhin wird das Verhalten der kritischen Spannung systematisch in Form von Phasendiagrammen dargestellt und diskutiert.This thesis is concerned with the microscopic modelling of current-induced switching of magnetization in magnetic tunnel junctions. The tunnel junction consists of two ferromagnets which are divided by a nonmagnetic insulator and a paramagnet, which acts as an electron reservoir. The ferromagnets are both described by the Hubbard model. By applying a voltage the chemical potentials on both sides of the insulator are shifted which results in a finite tunneling current. Within the model the current is simulated by a hybridization between neighbouring regions. The model has to be solved in non-equilibrium since thermal equilibrium requires a constant chemical potential for the whole system, which is not the case due to the voltage. Thus the Keldysh formalism will be used for evaluating the model. Since the Hubbard model is not exactly solvable one needs approximations. In this work a non-equilbrium spectral density approach is developed. It is based on a high-energy expansion of the retarded Green''s function and takes interactions beyond the mean field level into account. The numerical results of the theory are in qualitative agreement with experiments. It will be shown that it is possible to correctly get the hysterisis behaviour of the magnetization of the free ferromagnet in dependence on the applied voltage. Thus the relative alignment of the two magnetizations can be switched just by applying an electric field. This can be explained with the corresponding quasiparticle densities of state. Furthermore the behaviour of the critical voltage will be discussed systematically by calculating phase diagrams of the tunnel junction.
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Lee, Robert Frank. "Spin dependent transport in solids." Thesis, University of Cambridge, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.615695.
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Michel, Christoph. "Theoretical studies of spin dependent transport phenomena [transport in magnetic semiconductors ; spin dependent charge carrier recombination]." Göttingen Cuvillier, 2007.
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Dhandapani, Dhanalakshmi. "Spin Dependent Transport in Organic Materials." Thesis, University of Sheffield, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.522047.
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Jiang, Wenchao. "Spin dependent transport in ferromagnetic particles." Diss., Georgia Institute of Technology, 2014. http://hdl.handle.net/1853/52204.
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Spintronics is an emerging technology that arises from the interplay between spin of the charge carrier and the magnetic property of the materials. The miniaturization of spintronic devices requires a deep understanding of ferromagnetic materials at the nanometer scale. This thesis studies the properties of ferromagnetic particles (2-5nm in diameter) using electron transport measurements. A technique to fabricate nanoparticle devices and incorporate microwave in the electron tunneling measurement of the particles is presented. Repeated microwave pulses can directly excite the magnetization of the particles without heating the electrons. Results of the transport measurements on Co particles will be discussed, which demonstrate that electron tunneling through a ferromagnetic particle can induce magnetization excitations in that particle. A physical model regarding the mesoscopic fluctuations is presented to address the current driven magnetization noise. Numerical simulations based on that model are performed to explain the experimental data and validate the model. Electron transport measurements on Ni, Fe, and Ni??Fe?? are conducted. The hysteretic behaviors of the particles in presence of electron tunneling have strong material dependence, which is mainly due to the magnetic shape anisotropy. Electron tunneling is a main source of magnetization noise, while other sources still need to be identified. Some data we collected from literature will be included in this thesis as an appendix.
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Blundell, Stephen John. "Spin-dependent transport in artificial structures." Thesis, University of Cambridge, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.309331.
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Yi, Ji. "Spin-dependent transport through point-contacts." Available to US Hopkins community, 2003. http://wwwlib.umi.com/dissertations/dlnow/3080691.
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Gul, Y. "Spin dependent transport in semiconductor nanostructures." Thesis, University College London (University of London), 2018. http://discovery.ucl.ac.uk/10050201/.
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This project investigates transport properties of electrons and holes con- fined into one-dimensional regions using lithographically patterned surface gates in In0.75Ga0.25As and p-type Ge quantum wells respectively. A series of transport experiments was conducted to investigate many body effects in electrons and holes in one dimension. The experimental results provided here show important advances in both In0.75Ga0.25As and p-type Ge quan- tum wires and lays the ground work for future experiments for spintronics research using these materials. The first experiments reported here (chapter 4) describes the experiments carried out to optimise fabrication methods and determine the ideal length scales of split gates to observe clear ballistic transport features in high mobility In0.75Ga0.25As wafers. The following chapter (chapter 5) summarises the one dimensional trans- port measurements carried out on narrow split gates fabricated on the high mobility In0.75 Ga0.25 As quantum wells. It explores how Rashba spin or- bit coupling effects the transport properties. In In0.75Ga0.25As a weaker backscattering due to the time-reversal asymmetry in the one-dimensional channel results in enhanced ballistic transport characteristics with clear quantised conductance plateaus up to 6(2e2/h). We investigate the con- ductance data when a d.c. voltage is applied to the source and the drain contacts and a method for obtaining the effective g factor is described. Chapter 6 introduces p-type Ge, and summarises one dimensional transport properties of these devices. We demonstrate quantised conductance up to 10 (2e2/h). Applied source-drain voltages and symmetric gating of the channel has uncovered plateau at half integer values as well as ballistic structure down to 0.25(2e2/h). These systems also show a ballistic plateau at 0.25 (2e2/h), when the carrier density is reduced using a top gate electrode. The last experimental chapter (chapter 7) analyses the many-body effects observed in one-dimensional transport measurements in p-Ge and analysis of anomalous 0.25 (2e2/h) plateau is provided with possible explanations for it. We have also shown that we can alter the confining potential using lateral gate voltages to create a row formation as the ground state effectively creates a Wigner lattice.
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Lin, Ran. "Organic spintronic devices utilizing spin-injection, spin-tunneling and spin-dependent transport." Diss., University of Iowa, 2013. https://ir.uiowa.edu/etd/5015.
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Spintronics, also known as spin electronics, or magnetoelectronics, refers to the study of the role that electron and (less frequently) nuclear spins play in solid state physics, and a group of devices that specifically exploit both the intrinsic spin of the electron and its associated magnetic moment, in addition to its fundamental electronic charge. As a principal type of spintronic device, a spin-valve is a device that uses ferromagnetic electrodes to polarize and analyze the electronic spins. The electrical resistance of the device depends sensitively on the relative magnetization of its two ferromagnetic electrodes, a phenomenon referred to as Giant Magnetoresistance (GMR). Having been successfully applied in the field of data storage, GMR also shows potential for future logic devices. Organic semiconductors possess many advantages in electronic device applications. Therefore, using organic semiconductors in spintronics is very interesting and promising, in part, because of their exceptionally long spin-decoherence times.
This thesis concerns itself with the scientific study of magnetic field and spin effects in organic spin valves (OSV) and organic light emitting diodes (OLED). Three projects were finished, achieving a better understanding of the transportation of charge and spin carriers inside organic films, and paving the way to enhancing the spin diffusion length and the organic magnetoresistance (OMAR) effect.
Firstly, C60 films were used as the spin-transport layer of OSV devices, because of its low hyperfine coupling and high mobility, which prior work suggested to be beneficial. Subsequently we studied the spin injection and transport properties by measuring the devices' magnetoresistance (MR) response at various biasing voltages, V, temperatures, T and different C60 film thickness. But we do not observe a significantly increased spin-diffusion length compared to OSV devices based on other organic semiconductors. We propose conductivity mismatch as a likely cause of the loss of spin-valve signal with increasing C60 layer thickness.
There exists some disagreement in the scientific literature regarding whether OSV operate in the so-called tunneling regime or the so-called injection regime. To shed light on this question, we fabricated spin-valve devices made of organic semiconductor thin films of rubrene sandwiched between ferromagnetic cobalt and iron electrodes. Current-voltage (I-V) characteristics in Co/AlOx/rubrene/Fe junctions with a rubrene layer thickness, d, ranging from 5-50 nm, were measured, and we found two different modes of conductivity. The first mode, tunneling, occurs in relatively thin junctions, d < 15 nm, and decays exponentially with increasing rubrene thickness. We determined the tunneling decay length to be 1 nm. The tunneling mode is also characterized by a weak temperature dependence and a nearly parabolic differential conductance. The second mode, injection followed by hopping, occurs in relatively thick devices, d ≥ 15 nm, and can be identified by strongly temperature dependent, highly non-linear I-V traces that are similar to those commonly measured in organic injection devices such as OLEDs. We observed MR in devices with a rubrene thickness of 5 nm and 10 nm. Those devices are clearly in the tunneling regime. For the 15 nm device, for which the tunneling current is just barely measurable we could not observe MR.
In the third project, we show that the performance of both OMAR and OSV devices very sensitively depends on whether the metallic layers are deposited by thermal evaporation or electron-beam evaporation. A strongly reduced spin diffusion length and an enhanced OMAR response can be achieved in devices fabricated by electron-beam
evaporation. Then we showed that the difference must be attributed to the generation of traps resulting from the exposure of the organic layer to X-ray bremsstrahlung that is generated during the e-beam evaporation process. We also used the thermally stimulated current technique (TSC) to characterize these traps.
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Bergeson, Jeremy D. "Spin-dependent transport phenomena in organic semiconductors." Columbus, Ohio : Ohio State University, 2007. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1167674229.
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Jayathilaka, Priyanga Buddhika. "Spin Dependent Transport in Novel Magnetic Heterostructures." Scholar Commons, 2013. http://scholarcommons.usf.edu/etd/4513.
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Magnetic oxides have become of interest source for spin transport devices due to their high spin polarization. But the real applications of these oxides remains unsatisfactory up to date, mostly due to the change of properties as a result of nano structuring. Magnetite (Fe3O4) is one such a material. High Curie temperature and the half metallicity of Fe3O4 make it a good potential candidate for spin transport devices. Studies have shown that the nano structuring Fe3O4 changes most of it's important properties. This includes high saturation magnetization and drop of conductivity by a few orders of magnitude in Fe3O4 thin films.
In this study, we have successfully grown Fe3O4 by reactive sputtering and studied the effect of transition metal buffer layers on structural, transport, and magnetic properties of Fe3O4. It is shown that the lattice strain created by different buffer layers has major impacts on the properties of Fe3O4 thin films. Also for the first time the magnetic force microscopic measurements were carried out in Fe3O4 thin films through Verwey transition. MFM data with the magnetization data have confirmed that the magnetization of Fe3O4 thin films rotate slightly out of the plane below the Verwey transition.
Fe3O4 thin films were also successfully used in fabricating spin valve structures with Chromium and Permalloy. Here, the Fe3O4 was used to generated the spin polarized electrons through reflection instead of direct spin injection. This is a novel method that can be used to inject spins into materials with different conductivities, where the traditional direct spin injection fails. Also the effect of growth field on Fe3O4 and Fe3O4/Cr/Py spin valves were investigated. In Fe3O4 the growth field induced an uni-axial anisotropy while it creates a well defined parallel and anti-parallel states in spin valves.
Magneto thermal phenomenon including spin dependent Seebeck effect, Planar Nernst effect, and Anomalous Nernst effect were measured in ferromagnetic thin films and spin valves. Spin dependent Seebeck effect and planar Nernst effect were directly
compared with the charge counterpart anisotropic magneto resistance. All the effects exhibited similar behavior indicating the same origin, namely spin dependent scattering.
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Wei, Yaguang. "Spin-dependent electron transport in nanoscale samples." Diss., Atlanta, Ga. : Georgia Institute of Technology, 2007. http://hdl.handle.net/1853/26498.
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Thesis (Ph.D)--Physics, Georgia Institute of Technology, 2008.Committee Chair: Dragomir Davidovic; Committee Member: Alexei Marchenkov; Committee Member: David Citrin; Committee Member: Elisa Riedo; Committee Member: Walter A. de Heer. Part of the SMARTech Electronic Thesis and Dissertation Collection.
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Galceran, Vercher Regina. "Spin-dependent transport in oxide-based tunnel junctions." Doctoral thesis, Universitat Autònoma de Barcelona, 2015. http://hdl.handle.net/10803/287903.
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Aquesta tesi estudia les propietats de magnetotransport en unions túnel on un dels elèctrodes és l’òxid ferromagnètic La0.7Sr0.3MnO3 (LSMO). En concret, ens interessem per dos fenòmens diferents: (i) magnetoresistència (MR) en unions túnel amb un sol elèctrode magnètic i (ii) filtratge d’espí en unions túnel magnètiques. L’efecte túnel és extremadament dependent de les interfícies i una bona qualitat de les heteroestructures resulta crucial per a obtenir un bon rendiment dels dispositius. És per aquest motiu que bona part d’aquesta tesi es dedica al creixement (per polvorització catòdica) i caracterització de capes primes, a l’estudi de les interfícies de les heterostructures i a la fabricació de les unions.
Pel que fa a les unions amb un únic elèctrode magnètic, ens centrem en l’estudi del transport túnel en funció de la temperatura i del camp magnètic aplicat en unions de Pt/LaAlO3/LSMO. En el nostre treball hem identificat diferents mecanismes físics que juguen un paper important en la MR d’aquest sistema: la magnetoresistència túnel anisòtropa (TAMR), de l’ordre de 4 % a baixa temperatura, i una altra contribució a la magnetoresistència, de l’ordre de 17%. A més, TAMR a baix camp magnètic s’atribueix a la rotació de dominis magnètics.
En el cas d’unions amb dos elèctrodes magnètics, també cal tenir en compte l’orientació relativa entre les magnetitzacions d’aquests. El sistema que estudiem és Fe/MgO/LSMO, en el qual s’espera un valor de magnetoresistència túnel (TMR) gran degut a la combinació del filtratge d’espín per part del Fe/MgO i la semimetal·licitat del LSMO. Com a conseqüència de la formació de FeOX en la interfície Fe/MgO, obtenim diferent signe de TMR per a diferents unions: una TMR negativa de 4% a baixes temperatures s’atribueix a un FeOX magnèticament desordenat i una TMR positiva de 25% a 70 K s’atribueix a la ordenació magnètica del FeOX a la intercara amb el MgO, que dóna lloc a filtratge d’espín. Quan el gruix de la barrera d’MgO es redueix a 1.2 nm, aquesta capa ordenada de FeOX s’acobla antiferromagnèticament amb la de LSMO donant lloc a un comportament molt interessant de la MR especialment quan es mesura aplicant el camp magnètic fora del pla de la capa. La formació de FeOX en aquesta estructura no s’ha aconseguit eliminar ni amb creixement in-situ ni amb recuits, i se suggereix que la barrera d’MgO és permeable a l’oxigen de la manganita, fet que duria a l’oxidació del Fe.
Per altra banda, amb l’objectiu de fabricar unions amb una barrera túnel magnètica que actuï com a filtre d’espín, hem estudiat la possibilitat d’utilitzar capes primes de La2CoMnO6 (LCMO) com a barrera. Aquest material és ferromagnètic, aïllant i amb estructura de doble perovskita, però hi ha pocs treballs sobre la seva preparació en capes primes. A més a més, en aquests les capes estan crescudes per depòsit de làser pulsat i els gruixos són superiors a 100 nm, i per tant no aptes per actuar com barreres aïllants en filtres d’espí. L’objectiu principal s’ha orientat cap a un estudi detallat del creixement, optimització i caracterització de les propietats de capes primes de LCMO. En aquest sentit, s’han aconseguit capes (de 20 a 5 nm) epitaxials, aïllants i ferromagnètiques amb temperatures de Curie prop del 230 K i anisotropia magnètica perpendicular. S’han crescut heterostructures epitaxials de LCMO/LSMO, les propietats magnetoresistives de les quals es preveuen aprofundir en futurs treballs.This thesis studies the magnetotransport properties of tunnel junctions in which one of the electrodes is the ferromagnetic oxide La0.7Sr0.3MnO3 (LSMO). In particular, we focus on two different phenomena: (i) magnetoresistance (MR) in tunnel junctions with a single magnetic electrode and (ii) spin filtering in magnetic tunnel junctions. The tunneling effect is extremely sensitive to the interfaces and good quality of the heterostructures is crucial toward the optimal performance of the devices. For this reason, much of the thesis is dedicated to the growth (by sputtering) and characterization of thin films, to the study of interfaces in heterostructures and to the fabrication of junctions. With respect to the junctions with a single magnetic electrode, we concentrate on the tunnelling transport as a function of temperature and magnetic field applied in Pt/LaAlO3/LSMO junctions. In our work, we have identified the different physical mechanisms which play a relevant role on the MR of this system: tunnelling anisotropic magnetoresistance (TAMR), of the order of 4 % at low temperature, and another contribution to the MR, of the order of 17 %. Furthermore, TAMR at low magnetic field is attributed to rotation of magnetic domains. In the case of junctions with two magnetic electrodes, we must also take into account the relative orientation between their magnetizations. The studied system is Fe/MgO/LSMO, in which a large tunnel magnetoresistance (TMR) is expected due to the combination of spin filtering from the Fe/MgO and the half-metallicity of LSMO. As a consequence of the formation of FeOX at the Fe/MgO interface, we obtain different sign of the TMR for different junctions: a negative TMR of 4 % at low temperatures is ascribed to a magnetically disordered FeOX and a positive TMR of 25 % at 70 K is attributed to magnetic ordering of the FeOX at the interface with MgO, which results in spin filtering. When the MgO barrier thickness is reduced to 1.2 nm, this ordered FeOX coupled antiferromagnetically to the LSMO layer gives rise to an interesting magnetoresistive behaviour, especially when measured with the magnetic field applied out-of-plane. We have not been able to avoid the formation of FeOX in this heterostructure, even for in-situ growth or annealings, and we suggest that the MgO barrier is permeable to the oxygen from the manganites, which would be responsible for the oxidation of the Fe. On the other hand, aiming at the fabrication of junctions with magnetic tunnel barrier which acts as spin filter, we have studied the possibility of using La2CoMnO6 (LCMO) thin films as barrier. This material is ferromagnetic, insulating and possesses perovskite structure, but there are only a few works on its thin film growth. What is more, such works are performed with pulsed laser deposition and thicknesses are above 100 nm, thus not suitable as insulating barriers in spin filters. We have performed a detailed study of the growth, optimization and characterization of LCMO thin films. In this regard, we have achieved epitaxial, insulating, ferromagnetic thin films (from 20 to 5 nm), with Curie temperatures around 230 K and perpendicular magnetic anisotropy. LCMO/LSMO heterostructures, whose magnetoresistive properties remain to be studied in future work, have also been grown.
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Jeong, Taehee. "Spin-dependent heat transport and thermal boundary resistance." Research Showcase @ CMU, 2011. http://repository.cmu.edu/dissertations/66.
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Spin-dependent heat transport is a new research area and can create many future applications. The Giant Magnetoresistance (GMR) effect, which was discovered in 1988, is significant change in electric resistance due to spin-dependent electron scattering. The GMR effect has greatly impacted on techniques of data storage and magnetic sensors. For example, the areal density of hard disk drive was increased 100 times using the GMR effect. Likewise, spin-dependent heat transport, which is also called the Giant Magnetothermal Resistance (GMTR) effect, is expected to create a wealth of new applications, for example nanoscale heat or temperature detectors and spin thermoelectrics. In addition, the technique developed for this study will help with heat management in micro/nano electronics including data storage devices and heat/energy assisted magnetic recording.
In this thesis, thermal conductivity change depending on the magnetic configurations has been studied. In order to make different magnetic configurations, we developed a spin valve structure, which has high MR ratio and low saturation field. The high MR ratio was achieved using Co/Cu multilayer and 21Å or 34Å thick Cu layer. The low saturation field was obtained by implementing different coercivities of the successive ferromagnetic layers. For this purpose, Co/Cu/Cu tri-layered structure was used with the thicknesses of the Co layers; 15 Å and 30 Å. For the thermal conductivity measurement, a three-omega method was employed with a thermally isolated microscale rod. We fabricated the microscale rod using optical lithography and MEMS process. Then the rod was wire-bonded to a chip-carrier for further electrical measurement. For the thermal conductivity measurement, we built the three-omega measurement system using two lock-in amplifiers and two differential amplifiers. A custom-made electromagnet was added to the system to investigate the impact of magnetic field.
We observed titanic thermal conductivity change depending on the magnetic configurations of the Co/Cu/Co multilayer. The thermal conductivity change was closely correlated with that of the electric conductivity in terms of the spin orientation, but the thermal conductivity was much more sensitive than that of the electric conductivity. The relative thermal conductivity change was 50% meanwhile that of electric resistivity change was 8.0%. The difference between the two ratios suggests that the scattering mechanism for charge and heat transport in the Co/Cu/Co multilayer is different. The Lorentz number in Weidemann-Franz law is also spin-dependent. The application of this significant thermal conductivity change is remained for future work.
Thermal boundary resistance between metal and dielectrics was also studied in this thesis. The thermal boundary resistance becomes critical for heat transport in a nanoscale because the thermal boundary resistance can potentially determine overall heat transport in thin film structures. A transient thermoreflectance (TTR) technique can be used for measuring the thermal conductivity of thin films in cross-sectional direction. In this study, a pump-probe scheme was employed for the TTR technique. We built an optical pump-probe system by using a nanosecond pulse laser for pumping and a continuous-wave laser for probing. A short-time heating event occured at the surface of a sample by shining a laser pulse on the surface. Then the time-resolved thermoreflectance signals were detected using a photodetector and an oscilloscope. The increased temperature decreases slowly and its thermal decay depends on the thermal properties of a sample. Since the reflectivity is linearly proportional to the temperature, the time-resolved thermoreflectance signals have the information of the thermal properties of a sample. In order to extract the thermal properties of a sample, a thermal analysis was performed by fitting the experimental data with thermal models. We developed 2-layered and 3-layered thermal models using the analogies between thermal conduction and electric conduction and a transmission-line concept.
We used two sets of sample structures: Au/SiNx/Si substrate and Au/CoFe/SiNx/Si substrate with various thickness of SiNx layer. Using the pump-probe system, we measured the time-resolved thermoreflectance signals for each sample. Then, the thermal conductivity and thermal boundary resistance were obtained by fitting the experimental data with the thermal models. The thermal conductivity of SiNx films was measured to be 2.0 W/mK for both structures. In the case of the thermal boundary resistance, it was 0.81´10-8 m2K/W at the Au/SiNx interface and 0.54´10-8 m2K/W at the CoFe/SiNx interface, respectively. The difference of the thermal boundary resistance between Au/SiNx and CoFe/SiNx might be came from the different phonon dispersion of Au and CoFe. The thermal conductivity did not depend on the thickness of SiNx films in the thickness range of 50-200nm. However, the thermal boundary resistance at metal/SiNx interfaces will impact overall thermal conduction when the thickness of SiNx thin films is in a nanometer order. For example, apparent thermal conductivity of SiNx film becomes half of the intrinsic thermal conductivity when the thickness decreases to 16nm. Therefore, it is advised that the thermal boundary resistance between metal and dielectrics should be counted in nano-scale electronic devices.
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Lee, Kiyoung. "Spin dependent transport in semiconductor and semimetal materials." Thesis, University of Cambridge, 2012. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.610139.
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Merodio, Camara Pablo. "Spin dependent transport in antiferro and ferrimagnetic nanostructures." Thesis, Grenoble, 2014. http://www.theses.fr/2014GRENY072/document.
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En électronique de spin, le couple de transfert de spin (STT) et la magnétorésistance tunnel (TMR) dans les jonctions tunnel magnétiques à électrodes ferromagnétiques (F) sont deux phénomènes physiques essentiels. Dans cette thèse, nous présentons une étude théorique du STT dans des jonctions tunnel antiferromagnétiques (AF), où deux électrodes non-plus F mais AF sont séparées par une barrière isolante non-magnétique. Plus concrètement, les comportements du STT et de la TMR sont étudiés dans des jonctions tunnel AF cristallines, et ce, à l´aide de calculs de liaisons fortes dans le cadre du formalisme de Keldysh. Nous avons observé une distribution spatiale de la composante perpendiculaire du STT régulière et de signe alternatif, ce qui est similaire au comportement de la composante parallèle. Ces variations spatiales de la composante perpendiculaire sont cependant spécifiques à l'utilisation d'une barrière tunnel et contrastent avec les effets observés par le passé pour le cas de couches séparatrices métalliques. De plus, contrairement aux jonctions tunnel F conventionnelles, nous avons montré que la TMR peut augmenter avec la tension appliquée et atteindre des valeurs du même ordre de grandeur que pour des vannes de spin usuelles : tout-métallique et à électrodes F.L´analyse effectuée pour des AF est ensuite étendue aux matériaux ferrimagnétiques (FI), pour lesquels les AF constituent, somme toute, des cas limites. La complexité magnétique additionnelle inhérente aux FI se traduit par un comportement spatial du STT beaucoup plus riche dans les jonctions tunnel FI. Nous observons notamment que les paramètres électroniques tels que les largeurs et les décalages de bandes ont une très forte influence sur le STT. Plus particulièrement, la différence entre les couplages d'échange inter-spin locaux des deux sous-réseaux du FI donne lieu à une distribution spatiale du STT ondulatoire qui est modulée par la densité locale de spin. Il est possible d'ajuster cet effet en jouant sur la tension appliquée aux bornes de la jonction tunnel FI. Nous trouvons de plus que la différence entre les couplages d'échange inter-spin locaux constitue un paramètre fondamental pour la quantification des longueurs caractéristiques du STT dans les FIs. Ce paramètre peut être considéré comme un champ d´échange effectif, par similitude avec le cas usuel des Fs qui présentent un champ d´échange homogène.Pour finir, nous avons sondé expérimentalement les longueurs caractéristiques du STT dans des AFs. Pour de l'Ir20Mn80 et du Fe50Mn50, nous avons déterminé les longueurs de pénétration de spin et les mécanismes d'absorption de courants de spin à température ambiante en utilisant la résonance F et le pompage de spin. Plus précisément, nous avons associé les profondeurs de pénétration critiques à deux mécanismes d'absorption distincts: du déphasage pour l´Ir20Mn80 et du retournement de spin pour le Fe50Mn50Spin transfer torque (STT) and tunnelling magnetoresistance (TMR) in magnetic tunnel junctions with ferromagnetic (F) leads are two essential underlying phenomena of modern spintronics. We present here a theoretical study of STT in antiferromagnet (AF) based tunnel junctions, where two AF metal electrodes are separated by a thin nonmagnetic insulating barrier. In particular, the behaviour of STT and TMR in epitaxial AF-based tunnel junctions is investigated using tight binding calculations in the framework of the Keldysh formalism. The spatial distribution of the STT out-of-plane component is found to be staggered, similar to the in-plane component. This behaviour is specific to the use of a tunnel barrier and significantly differs from the out-of-plane torques reported in previous works using a metallic spacer. Additionally, we show that unlike conventional ferromagnetic-based tunnel junctions, the TMR can increase with applied bias and reach values comparable to typical magnetoresistances found for usual spin valves.Next, the analysis carried out for AFs is extended to ferrimagnets (FI), for which AFs constitute simpler limiting cases. The additional magnetic complexity inherent to FI materials yields to a richer physics concerning the STT spatial behaviour in FI based tunnel junctions.Electronic structure parameters such as band widths and exchange splittings of the FI are shown to have a strong influence on STT. In particular, the STT spatial distribution within the leads exhibits a striking spin-modulated wave-like behaviour resulting from the interplay between the exchange splittings of the two FI sublattices. This wave-like behaviour can also be tuned via the applied voltage across the junction. Furthermore, the fundamental intrinsic parameter for quantifying STT characteristic lengths in FI metals is identified. This fundamental parameter can be considered as an effective exchange field in FIs, similar to the homogeneous exchange field in the F case.Finally, the STT characteristic lengths in AF materials are investigated experimentally. Here, room temperature critical depths and absorption mechanisms of spin currents in Ir20Mn80 and Fe50Mn50 are determined by F-resonance and spin pumping. In particular, room temperature critical depths are observed to be originated from different absorption mechanisms: dephasing for Ir20Mn80 and spin flipping for Fe50Mn50
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Johansson, Jan. "Single Charge and Spin Transport in Nanostructures." Doctoral thesis, KTH, Physics, 2003. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3685.
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Zhou, Yun. "Spin-dependent electron transport in nanomagnetic thin film devices." Thesis, University of Plymouth, 2011. http://hdl.handle.net/10026.1/556.
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Spin-dependent electron transport in submicron/nano sized magnetic thin film devices fabricated using the optical lithography, e-beam lithography and focused ion beam (FIB) was investigated with the primary aim to find the ballistic magnetoresistance (BMR) in thin film nanoconstrictions. All experimental results were analysed in combination with micromagnetic simulations. The magnetisation reversal processes were investigated in a submicron half-pinned NiFe stripe with a microconstriction. An asymmetric MR curve was observed, and micromagnetic simulations verified it was due to the exchange-bias on the left side, which changed the magnetic switching mechanism. The effects of different pinning sites on the magnetisation switching and domain wall displacement were studied in NiFe film and spin-valve based nanodevices. A sign of domain wall MR was seen on the transversal MR curve of the NiFe nanodevice due to the domain wall induced electron scattering. The size effect on the magnetisation switching and interlayer magnetostatic coupling was demonstrated and characterised in synthetic antiferromagnet (SAF)-pinned spin-valve nanorings. It has been clarified by micromagnetic simulations that these nanorings exhibit a double or single magnetisation switching process, which is determined by the magnetostatic coupling as a function of the ring diameter. The interlayer magnetostatic coupling was efficiently reduced in large SAF-pinned nanorings, resulting in a small shift of the minor MR curve, which is beneficial to the magnetic memory applications. In-situ MR measurements and the investigation of domain wall properties have been carried out in FIB patterned NiFe film nanoconstrictions. Spin-valve like sharp transitions were observed on the MR curves in the 80 nm/130 nm wide nanoconstriction devices. However, our analysis of the results by micromagnetic simulations and domain observations with scanning electron microscopy with polarisation analysis (SEMPA) concluded that these sharp MR transitions originated from the anisotropic magnetoresistance (AMR) effect, due to the fast magnetisation rotation in the nanoconstriction, and not from BMR. The numerical investigation has proved that a further reduction of the constriction width/length is necessary for large MR values.
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Platt, Christopher L. "Magnetic and transport properties of spin-dependent tunnel junctions /." Diss., Connect to a 24 p. preview or request complete full text in PDF format. Access restricted to UC IP addresses, 1999. http://wwwlib.umi.com/cr/ucsd/fullcit?p9952654.
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Zhang, Zhaohui. "Spin-dependent electrical and thermal transport in magnetic tunnel junctions." APS, 2012. http://hdl.handle.net/1993/31947.
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Thermoelectricity can directly convert a temperature difference into a voltage or charge current. Recently, the development of spin caloritronics has introduced spin as another degree of freedom in traditional thermoelectrics. This discovery bodes a new generation of magnetic random access memories (MRAMs), where thermal spin-transfer torque (TSTT) rather than voltage driven spin-transfer torque (STT) is used to switch the magnetization in magnetic tunnel junctions (MTJs). To advance the rising trend of spin caloritronics, the coupling of charge, spin, and heat flow during electron transport in MTJs was systematically studied in this thesis.
To begin with, the static transport properties of MTJs were studied by observing current dependent tunnel magnetic resistance (TMR). The observed decrease of TMR with a biased current is attributed to the change in spin polarization of the free ferromagnetic layer. A phenomenological model has been built based on the current dependent polarization, which agrees with our experimental results. Next, the Seebeck rectification effect in MTJs was studied. By applying microwave currents to MTJs, an intrinsic thermoelectric coupling effect in the linear response regime of MTJs was discovered. This intrinsic thermoelectric coupling contributes a nonlinear correction to Ohm's law. In addition, this effect can be controlled magnetically since the Seebeck coefficient is related to magnetization configuration. Finally, TSTT in MTJs was systematically studied. A laser heating technique was employed to apply a temperature difference across the tunnel barrier and ferromagnetic resonance (FMR) spectra were measured electrically through spin rectification. By analyzing the FMR spectra, TSTT in MTJs was observed and the angular dependence of TSTT was found to be different from dc-biased STT. By solving the Landau-Lifshitz-Gilbert equation including STT, the experimental observations were well explained.
The discovery of Seebeck rectification refines the previous understanding of magneto-transport and microwave rectification in MTJs and provides a new possibility for utilizing spin caloritronics in high-frequency applications. The study of TSTT in MTJs shows clear experimental evidence of TSTT in MTJs. Further optimization of the design of MTJs may succeed in decreasing the necessary switching fields strength or even achieve a switching by only TSTT in MTJs.February 2017
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Hankinson, John H. "Spin dependent current injection into epitaxial graphene nanoribbons." Diss., Georgia Institute of Technology, 2015. http://hdl.handle.net/1853/53884.
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Over the past decade there has been a great deal of interest in graphene, a 2-dimensional allotrope of carbon with exceptional mechanical and electrical properties. Its outstanding mobility, minimal size, and mechanical stability make it an appealing material for use in next generation electronic devices. Epitaxial graphene growth on silicon carbide is a reliable, scalable method for the production of high quality graphene films. Recent work has shown that the SiC can be patterned prior to graphitization, in order to selectively grow graphene nanostructures. Graphene nanoribbons grown using this technique do not suffer from the rough edges caused by lithographic patterning, and recent measurements have revealed extraordinary transport properties. In this thesis the magnetic properties of these nanoribbons are investigated through spin polarized current injection. The sensitivity of these nanoribbons to spin polarized current is interesting from a fundamental physics standpoint, and may find applications in future spintronic devices.
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Li, Juerong. "Spin dependent electron transport in nanoscale InSb quantum well devices." Thesis, University of Surrey, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.543919.
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Cole, Alexander Alan. "Studies of spin dependent transport in magnetic thin film heterostructures." Thesis, University of Leeds, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.414159.
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Bundesmann, Jan [Verfasser], and Klaus [Akademischer Betreuer] Richter. "Spin-dependent transport in graphene nanostructures / Jan Bundesmann. Betreuer: Klaus Richter." Regensburg : Universitätsbibliothek Regensburg, 2014. http://d-nb.info/106088934X/34.
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Martin, Kevin Norman. "Magnetization switching and spin-dependent transport in REFe2 exchange spring multilayers." Thesis, University of Southampton, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.500733.
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Wang, Weigang. "Spin-dependent transport in magnetic tunnel junctions and diluted magnetic semiconductors." Access to citation, abstract and download form provided by ProQuest Information and Learning Company; downloadable PDF file, 184 p, 2009. http://proquest.umi.com/pqdweb?did=1654494821&sid=3&Fmt=2&clientId=8331&RQT=309&VName=PQD.
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Kurebayashi, Hidekazu. "Spin-dependent non-equilibrium electron transport in epitaxial Fe/GaAs interfaces." Thesis, University of Cambridge, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.611645.
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Cadiz, Fabian. "Spin dependent electron transport in semiconductors due to the Pauli principle." Palaiseau, Ecole polytechnique, 2015. https://theses.hal.science/tel-01174645/document.
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Ce travail de thèse est consacré à l'étude du transport des électrons minoritaires dans des semi-conducteurs dopés, en fonction de la densité et de la température du gaz électronique. Dans des couches minces de p-GaAs, le transport de la charge et du spin est étudié par un approche à la fois théorique et expérimental en utilisant une technique de microscopie originale permettant d'imager en régime stationnaire le profil de charge et de spin en fonction de la distance r par rapport à la tache d'excitation lumineuse. L'étude de ces profils a faible concentration et sous l'application d'un champ électrique montre que la mobilité des électrons minoritaires est déterminée principalement par la température des électrons et non pas par la statistique des trous majoritaires, ce qui invite a reformuler les modèles théoriques concernant les processus de diffusion des porteurs minoritaires dans les semi-conducteurs. Notre technique expérimentale a aussi permis d'explorer un nouveau mécanisme de couplage charge-spin lorsque la densité électronique est élevée. En effet, sous l'effet de la dégénérescence du gaz électronique (forte concentration, basse température), une diminution de la polarisation de spin à l'endroit d'excitation apparaît, avec un maximum de polarisation visible à environ r=2 µm. Ce résultat contra intuitif révèle le fait que, à cause du principe de Pauli, la diffusion des photo-électrons dépend du spin, car la raideur de spin devient une fonction de la concentration dans le régime dégénéré. Un nouveau mécanisme de filtre à spin en découle, mais qui ne fait pas intervenir une interface entre deux matériaux. D'autres effets pouvant modifier le transport de spin dans le régime dégénéré sont les courants thermoélectriques de spin (courants de Soret) et le couplage ambipolaire avec les trous. Une comparaison entre les profils expérimentaux et une solution numérique des équations de diffusion couplées montre que le couplage ambipolaire augmente la concentration de photo-électrons dans le régime stationnaire, et donc l'amplitude des effets liées à la dégénérescence, tandis que les courants de Soret de spin sont négligleables. Des effets tels que la renormalisation du gap et le couplage Coulombien entre électrons de spin opposés sont aussi négligeables à cause de l'écrantage des intéractions électron-électron induit par le gaz électronique. On s'attend à que l'effet de la dégénérescence augmente dans des systèmes confinés, tels que les puits quantiques, où la raideur de spin et la mobilité peuvent avoir des dépendances en spin encore plus fortesThis thesis is concerned with transport of photoinjected minority spin-polarized electrons in doped semiconductors, as a function of both the density and the temperature of the injected electron gas. In p-GaAs thin films, charge and spin transport is investigated theoretically and experimentally by using a novel polarized microphotoluminescence (µPL) technique which consists in imaging the spatially-resolved PL intensity and polarization under a tightly-focused circularly-polarized CW laser excitation. Study of the experimental profiles at low concentration and under an applied electric field shows that the minority electron mobility is mainly determined by the electron temperature instead of the majority hole statistics, introducing a puzzling piece to the current understanding of scattering processes in semiconductors. At higher densities, this experimental technique has allowed us to explore a novel charge-spin coupling mechanism which modifies electron transport. Under degeneracy of the electron gas (high concentration, low temperature), a dip at the centre of the spin polarization profile appears with a polarization maximum at a distance of about r= 2 µm from the excitation. This counterintuitive result reveals that photoelectron diffusion depends on spin, as a direct consequence of the Pauli principle which causes in general a concentration dependence of the spin stiffness. This results in a novel spin filter effect in an homogeneous material. The other effects which may modify spin transport in a degenerate electron gas are thermoelectric spin currrents (spin Soret currents) and ambipolar coupling with holes. A comparison of the data with a numerical solution of the coupled diffusion equations reveals that ambipolar diffusion increases the steady-state photo-electron density at the centre and therefore the amplitude of the degeneracy-induced spin-dependent diffusion, while the contribution of the spin Soret current is negligible. Coulomb spin drag and bandgap renormalization are negligible due to electrostatic screening by the hole gas. It is expected for degeneracy to have larger effects in confined systems, such as quantum wells, where both the spin stiffness and the mobility can have a much strong spin dependence
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Pu, Yong. "Spin-dependent transport properties of Ga₁₋[subscript]xMn[subscript]xAs ferromagnetic semiconductors." Diss., UC access only, 2009. http://proquest.umi.com/pqdweb?index=142&did=1874094571&SrchMode=1&sid=1&Fmt=7&retrieveGroup=0&VType=PQD&VInst=PROD&RQT=309&VName=PQD&TS=1270493990&clientId=48051.
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Thesis (Ph. D.)--University of California, Riverside, 2009.Includes abstract. Includes bibliographical references (leaves 122-126). Issued in print and online. Available via ProQuest Digital Dissertations.
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Loraine, Duncan. "The growth of silicon on iron and the implications for spin dependent transport in spin electronic devices." Thesis, University of York, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.325642.
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Rincon, Garcia Nicolas. "Freight transport, routing software and time-dependent vehicle routing models." Thesis, University of Southampton, 2016. https://eprints.soton.ac.uk/397141/.
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Routing and scheduling software is part of the Information and Technology systems available to support the transport industry, and uses complex algorithms along with geographical representations of the road network to allow better planning of daily collection and delivery schedules. This research reviews the evolution of routing and scheduling software, the algorithms used along with reported barriers to wider take-up and potential industry driven improvements that could be made. A survey of transport companies in the United Kingdom was conducted in order to validate and prioritize the software capabilities that require the most development according to the new challenges that the industry is facing. Responses suggested that companies required improved route optimization to tackle congestion based on time-dependent data and models, and greater accuracy in the representation of the road network. Not considering congestion leads to the underestimation of travel times and the production of inaccurate schedules. Literature shows that operational research techniques are available to solve problems that represent real world conditions, but research into the relative merits of using time-dependent models needs to be undertaken. Although exact methods have been developed to solve the Vehicle Routing Problem, they cannot cope with large instances and rich variants that are required by the industry. Therefore, metaheuristic algorithms are usually implemented in routing software. A reported barrier in metaheuristic algorithms is the lack of accuracy (the difference between optimal or best-known values and the result of the proposed algorithm). In this research an algorithm was developed using elements of Large Neighbourhood Search that is capable to substantially improve the state of the art for the time-dependent Vehicle Routing Problem. Comparison of results with available test instances shows that the proposed algorithm is capable of obtaining a reduction in the number of vehicles (4.15%), travel distance (10.88%) and travel time (12.00%) compared to previous implementations in reasonable time. A variant that considers the Rules on Drivers’ hours required in the scheduling of vehicles over 3.5 tons in the European Union and the UK is also introduced. Analysis of results show result improvements in number of vehicles (19.0%), travel distance (17.7%) and route duration (4.4%) compared to previous implementations.
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Kaidatzis, Andreas. "Spin-dependent hot electron transport and manoscale magnetic imaging of metal/Si structures." Paris 11, 2008. http://www.theses.fr/2008PA112232.
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Nous étudions expérimentalement le transport dépendant du spin d’électrons chauds dans des multicouches (MC) magnétiques, qui contiennent des couches uniques magnétiques, ou des tricouches de type « vannes de spin » (VS). Pour cela, nous avons mis en œuvre la microscopie à émission d’électrons balistiques (BEEM), une extension à trois contacts de la microscopie à effet tunnel sur des structures métal/semiconducteur. La méthode mise au point pour satisfaire les nombreuses contraintes imposées par le BEEM sur les échantillons est décrite en détail. La transmission des électrons chauds dans des MC a été systématiquement mesurée dans la gamme d’énergie 1-2 eV au dessus du niveau de Fermi. De l’étude en fonction des épaisseurs des couches magnétiques nous avons déduit les longueurs d’atténuation des électrons chauds en fonction du spin et de l’énergie. Ces mesures, sur le cobalt et l’alliage doux NiFe, sont comparées à des calculs et résultats expérimentaux de la littérature. Pour des épaisseurs inférieures à la monocouche atomique, une organisation spatialement hétérogène a été observée, avec un effet très important sur la transmission BEEM, variant sur une échelle sub-nanométrique. En mode imagerie, nous avons étudié les configurations magnétiques de VS, en particulier des parois à 360° dans des couches de cobalt. Les effets de l’intensité et la direction du champ appliqué sur la structure de ces parois ont été observés. Ces résultats ont été comparés quantitativement à des calculs micromagnétiques, avec un accord excellent. Ceci a permis de montrer que la résolution magnétique de BEEM est meilleure que 50 nmIn this work, we experimentally study spin-dependent hot electron transport through metallic multilayers (ML), containing single magnetic layers or “spin-valve” (SV) trilayers. For this purpose, we have set up a ballistic electron emission microscope (BEEM), a three terminal extension of scanning tunnelling microscopy on metal/semiconductor structures. The implementation of the BEEM requirements into the sample fabrication is described in detail. Using BEEM, the hot electron transmission through the ML’s was systematically measured in the energy range 1-2 eV above the Fermi level. By varying the magnetic layer thickness, the spin-dependent hot electron attenuation lengths were deduced. For the materials studied (Co and NiFe), they were compared to calculations and other determinations in the literature. For sub-monolayer thickness, a non uniform morphology was observed, with large transmission variations over sub-nanometric distances. This effect is not yet fully understood. In the imaging mode, the magnetic configurations of SV’s were studied under field, focussing on 360° domain walls in Co layers. The effects of the applied field intensity and direction on the DW structure were studied. The results were compared quantitatively to micromagnetic calculations, with an excellent agreement. From this, it can be shown that the BEEM magnetic resolution is better than 50 mn
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Zwolak, Michael Philip. "DNA Electronics." Thesis, Virginia Tech, 2003. http://hdl.handle.net/10919/78135.
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DNA is a potential component in molecular electronics. To explore this end, there has been an incredible amount of research on how well DNA conducts and by what mechanism. There has also been a tremendous amount of research to find new uses for it in nanoscale electronics. DNA's self-assembly and recognition properties have found a unique place in this area. We predict, using a tight-binding model, that spin-dependent transport can be observed in short DNA molecules sandwiched between ferromagnetic contacts. In particular, we show that a DNA spin-valve can be realized with magnetoresistance values of as much as 26% for Ni and 16% for Fe contacts. Spin-dependent transport can broaden the possible applications of DNA as a component in molecular electronics and shed new light into the transport properties of this important biological molecule.Master of Science
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Weber, Peter. "Spin dependent transport and magnetic ordering in rare earth metals infrared spectroscopy on holmium /." [S.l. : s.n.], 2004. http://www.bsz-bw.de/cgi-bin/xvms.cgi?SWB11293366.
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Inyang, Oto-Obong Andrew. "Magnetic proximity effect and interfacial spin dependent transport in ferromagnet/heavy metal thin films." Thesis, Durham University, 2018. http://etheses.dur.ac.uk/12795/.
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Platinum (Pt) has widely been used for interface driven spintronics applications due to its strong spin-orbit interaction. Pt has been reported to experience spin polarisation when placed in close proximity to a ferromagnetic (FM) material thereby influencing many spintronic phenomena. Consequently, the effect of proximity induced magnetization (PIM) in Pt is studied in this thesis with a detailed investigation of the mechanism and the implications of PIM on magnetoresistance measurements. In this work, CoFeTaB (CFTB) is the FM material investigated. Structural and magnetic characterisation of CFTB/Pt, Pt/CFTB and Pt/CFTB/Pt samples were made in order to investigate PIM at the interface. X-ray reflectivity (XRR) and x-ray diffraction (XRD) were performed on these samples, where asymmetry in the Pt density and the crystalline texture were observed at the top and bottom interfaces. XRD measurements show the Pt crystalline texture depends on the CFTB thickness for the CFTB/Pt interface, but no significant thickness dependence was observed for the Pt/CFTB interface. The magnetic depth profile of the CFTB layer was obtained with polarised neutron reflectivity (PNR), which shows magnetisation grading. An asymmetry in Pt magnetisation was found between the two interfaces using x-ray resonant magnetic reflectivity (XRMR) with a higher moment at the top interface and lower at the buffer interface, giving a similar CFTB thickness dependence as the XRD results. This indicated that the Pt magnetisation depends slightly on Pt texture at the interface. No PIM was found in a YIG/Pt bilayer and the Pt XRD texture was poor, supporting a possible link of Pt polarisation to crystalline the morphology at the interface. Magnetoresistance investigations in three geometries performed on Pt/CFTB and CFTB/Pt bilayers were used to decouple the magnetoresistance contributions as a result of the anisotropy of the sample, spin Hall effect and other processes. The spin Hall MR ratio obtained was ~0.2 %, with an additional contribution with a cos θ dependence of ~0.1 %, which is a result of the impact of PIM generated spin current. No evidence of the Rashba effect was found in the symmetric CFTB/Pt/CFTB sample. Also, residual plots indicated the presence of higher harmonics that are dependent on the magnetisation direction. Temperature dependent proximity induced magnetism in Pt in contact with CFTB was presented, with PNR providing the magnetic sensitivity to the FM layer while the XRMR provide sensitivity to Pt magnetisation. PIM scales linearly with CFTB magnetisation which is inconsistent with the Pauli susceptibility. Significantly, a threshold CFTB magnetization is required for PIM to occur. Therefore the asymmetry in PIM at Pt/CFTB and CFTB/Pt interface is attributed to different magnetic susceptibilities at these interfaces.
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Kuzmanović, Marko. "Spin and out-of-equilibrium transport in mesoscopic superconductors Evidence for spin-dependent energy transport in a superconductor Nonadiabatic dynamics in strongly driven diffusive Josephson junctions." Thesis, université Paris-Saclay, 2020. https://tel.archives-ouvertes.fr/tel-02890643.
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Dans un dispositif supraconducteur de taille mésoscopique la faible interaction entre quasi-particuleset le faible taux de relaxation de spin à basse température permet de préserver la cohérence de phasesur la taille de l’échantillon et de modifier artificiellement les fonctions de distribution, pour lesporter loin de l’équilibre. Ainsi un supraconducteur peut devenir magnétique ou un métal normalsupraconducteur. Pour opérer de telles transformations nous avons réalisé des dispositifs hybridesoù le supraconducteur est en contact avec des métaux normaux ou sous champ magnétique Zeeman.Nous avons utilisé la lithographie électronique et le dépôt en couche minces pour préparer dedispositifs hybrides métalliques et nous avons étudié le transport de charge, spin et énergie dans dessupraconducteurs diffusifs par le biais des propriétés spectrales et des fonctions de distributions. Ace fin nous avons réalisé trois expériences.1. Spectroscopie des quasi-particules hors-équilibre. Grâce au splitting Zeeman de la densité d’étatssupraconductrice de l’Aluminium, il est possible d’injecter un courant de quasi-particules polariséesen spin. L’Aluminium acquière ainsi une aimantation hors-équilibre. Par la mesure de lacaractéristique non-linéaire courant-tension de détecteurs positionnés à différentes distances dupoint d’injection, nous réalisons une mesure résolue en énergie et sensible au spin du nombre dequasi-particules de basse énergie injectées. Si le détecteur est situé à une distance inférieure à lalongueur de relaxation de spin-flip et de relaxation de l’énergie du point d'injection, nous observonsque la fonction de distribution des quasi-particules dépend du spin et ne sont pas Fermi-Dirac. Nousmontrons ainsi que le flux d’énergie associé au courant d’injection est aussi dépendant du spin.Comme attendu théoriquement, le splitting Zeeman brise la dégénerescence de spin du mode hors-équilibre d’énergie.2. Emission Josephson hors-équilibre. Dans une jonction superconductor–normal metal–superconductor,le métal normal devient supraconducteur par effet de proximité avec le supraconducteur et les étatsliés d’Andreev dans le métal normal transportent le supercourant. En mesurant l’émissionJosephson-ac autour de la fréquence de 6 GHz, on accède au contenu harmonique de la relationcourant-phase (CPR). Nous avons expérimentalement identifié un régime non adiabatique danslequel la CPR est modifiée par irradiation micro-ondes à haute fréquence. Cette observations’explique par l’excitation de quasi-particules dans le métal normal induite par le champélectromagnétique haute fréquence. La distorsion du CPR provient de la fonction de distributionhors équilibre dans le métal normal qui dépend de la différence de phase à travers la jonction etmodifie le courant spectral. Pour une différence de phase qui s’approche de π, les transitions àtravers le mini-gap sont favorisées de manière dynamique, ce qui conduit à une réduction dusupercourant. Cette constatation est corroborée par une comparaison avec la théorie quasi-classiquede la supraconductivitéIn a mesoscopic superconducting device, weak quasiparticle-quasiparticle interactions and slow spinrelaxation at low temperatures makes it possible to preserve phase coherence over the whole sampleand artificially modify distribution functions, driving them far from equilibrium. Partly because ofthis, superconductors can become magnetic or a normal metals superconducting. To induce thesetransformations we fabricated hybrid devices where the superconductor is in contact with normalmetals or experiences a Zeeman magnetic field, using e-beam lithography and thin film deposition.We studied charge, spin and energy transport in diffusive superconductors through their spectralproperties and distribution functions in three different experiments.1. Spectroscopy of out-of-equilibrium quasiparticles. The Zeeman splitting of their density of states insuperconducting aluminium makes the injection of spin-polarised quasiparticles possible. Aluminumthus acquires a non-equilibrium magnetization. By measuring non-linear current-voltagecharacteristics of detectors placed at different distances from the injection point, we obtain energy-resolved and spin-sensitive information on the number of low-energy quasiparticles. If the detectoris located at a distance less than the spin-flip relaxation and injection site energy relaxation time, weobserve that the quasiparticle distribution function depends on the spin and is non-Fermi-Dirac. Weshow that the energy flow associated with the injection current is also spin-dependent. Astheoretically expected, the Zeeman splitting breaks the spin degeneracy of the energy excitationmode.2. Out-of-equilibrium Josephson emission. A normal metal in contact with two superconductors becomessuperconducting through the proximity effect; Andreev bound states carry supercurrents throughthe normal metal. By measuring the AC Josephson emission around 6 GHz, we probe higher orderFourier components of the current-phase relation (CPR). We have experimentally identified a non-adiabatic regime in which the CPR is modified by high-frequency microwave radiation. Thisobservation is explained by the excitation of quasiparticles in the normal metal by the high-frequency electromagnetic field. The CPR distortion results from the non-equilibrium quasiparticledistribution functions in the normal metal, which depend on the phase difference across thejunction and modifies the spectral current. For a phase difference close to π, transitions across themini-gap are dynamically preferred, which leads to a reduction of the supercurrent. Our results agreewell with the quasiclassical theory of superconductivity
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Machon, Peter [Verfasser]. "Electronic Transport Theory of the Spin-Dependent Proximity Effect in Superconductor-Ferromagnet Heterostructures / Peter Machon." Aachen : Shaker, 2017. http://d-nb.info/1138179272/34.
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Baumard, Julie. "Transport and spectral properties of low-dimensional superconductors in the presence of spin-dependent fields." Thesis, Bordeaux, 2019. http://www.theses.fr/2019BORD0357.
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Lorsqu’un supraconducteur est soumis à des champs dépendant du spin, on observe l'émergence de nouveaux phénomènes comme l’augmentation du champ magnétique critique, des effets magnétoélectriques ou encore l’apparition d’états de bord de Yu-Shiba-Rusinov autour d’impuretés magnétiques. Dans cette thèse, on s’intéresse à ces effets dans des systèmes de basse dimension.Tout d’abord, on démontre que la combinaison d’un champ Zeeman avec un couplage spin-orbite dans des systèmes supraconducteurs unidimensionnels induit une phase inhomogène à faible champ magnétique et haute température critiques. On montre que l’état fondamental correspond à un état de courant nul, où le courant induit par le couplage spin-orbite, nommé courant de charges anomal, est exactement compensé par le courant venant du vecteur d’onde du paramètre d’ordre supraconducteur. On discute également la possibilité de prédire l’apparition du courant anomal à partir d’arguments de symétrie basés sur le formalisme covariant SU(2).Dans un second temps, on considère une couche mince supraconductrice de type II en contact avec un skyrmion de Néel. Ce dernier induit des courants spontanés dans la couche supraconductrice, pouvant conduire à l’émergence d’un vortex supraconducteur en l’absence de champ magnétique extérieur. Les distributions de champ magnétique et de courant sont calculées dans le supraconducteur en présence du skyrmion de Néel.La dernière partie de cette thèse est consacrée à l’étude de l’apparition d’états de Yu-Shiba-Rusinov dans le cristal beta-Bi2Pd. On propose des modèles effectifs pour expliquer les récents résultats expérimentaux montrant une double oscillation spatiale de la densité d’états locale à l’énergie de Shiba. On démontre que la condition minimale pour reproduire cette double oscillation correspond à la présence de deux canaux supraconducteurs connectés via un terme de saut ou via une impureté magnétique. Ces modèles effectifs peuvent facilement être généralisés pour décrire le spectre de supraconducteurs multi-bandes en présence d’impuretés magnétiquesThe interplay between superconductivity and spin-dependent fields is known to lead to striking phenomena, like critical field enhancement, magnetoelectric effects and the appearance of Yu-Shiba-Rusinov bound states at magnetic impurities. In this thesis, we investigate these effects in low dimensional systems.We first demonstrate that the combination of both spin-orbit and Zeeman fields in superconducting one-dimensional systems leads to the appearance of an inhomogeneous phase at low magnetic field and high critical temperature. We show that the ground state corresponds to a zero-current state where the current stemming from spin-orbit coupling, called anomalous charge current, is exactly compensated by the current coming from the wave-vector of the superconducting order parameter. We also discuss how it is possible to predict the appearance of the anomalous current from symmetry arguments based on the SU(2)-covariant formalism.In a second part, we consider a type-II superconducting thin film in contact with a Néel skyrmion. The skyrmion induces spontaneous currents in the superconducting layer, which under the right condition generate a superconducting vortex in the absence of external magnetic fields. We compute the magnetic field and current distributions in the superconducting layer in the presence of the Néel skyrmion.In the last part of this thesis, we focus on the appearance of Yu-Shiba-Rusinov states in the superconducting crystal beta-Bi2Pd. We propose effective models in order to explain recent experimental results showing a double spatial oscillation of the local density of states at Shiba energy. We demonstrate that the minimal condition to reproduce this double oscillation is the presence of two superconducting channels connected via a hopping term or via a magnetic impurity. These effective models can be easily generalized to describe the spectrum of multiband superconductors with magnetic impurities
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Olbrant, Edgar [Verfasser]. "Models and numerical methods for time- and energy-dependent particle transport / Edgar Olbrant." Aachen : Hochschulbibliothek der Rheinisch-Westfälischen Technischen Hochschule Aachen, 2012. http://d-nb.info/1023980002/34.
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Fransson, Jonas. "Non-Orthogonality and Electron Correlations in Nanotransport : Spin- and Time-Dependent Currents." Doctoral thesis, Uppsala University, Department of Physics, 2002. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-2687.
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The concept of the transfer Hamiltonian formalism has been reconsidered and generalized to include the non-orthogonality between the electron states in an interacting region, e.g. quantum dot (QD), and the states in the conduction bands in the attached contacts. The electron correlations in the QD are described by means of a diagram technique for Hubbard operator Green functions for non-equilibrium states.
It is shown that the non-orthogonality between the electrons states in the contacts and the QD is reflected in the anti-commutation relations for the field operators of the subsystems. The derived forumla for the current contains corrections from the overlap of the same order as the widely used conventional tunneling coefficients.
It is also shown that kinematic interactions between the QD states and the electrons in the contacts, renormalizes the QD energies in a spin-dependent fashion. The structure of the renormalization provides an opportunity to include a spin splitting of the QD levels by polarizing the conduction bands in the contacts and/or imposing different hybridizations between the states in the contacts and the QD for the two spin channels. This leads to a substantial amplification of the spin polarization in the current, suggesting applications in magnetic sensors and spin-filters.
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Behrends, Jan [Verfasser]. "Spin-dependent transport and recombination in solar cells studied by pulsed electrically detected magnetic resonance / Jan Behrends." Berlin : Freie Universität Berlin, 2010. http://d-nb.info/1024541339/34.
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Yasin, Ula [Verfasser]. "Paramagnetic States in Organic and Perovskite Solar Cells : From Chemical Doping to Spin-Dependent Transport / Ula Yasin." Berlin : Freie Universität Berlin, 2019. http://d-nb.info/1201346649/34.
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Yasin, Ula Mehsen Hummadi [Verfasser]. "Paramagnetic States in Organic and Perovskite Solar Cells : From Chemical Doping to Spin-Dependent Transport / Ula Yasin." Berlin : Freie Universität Berlin, 2019. http://d-nb.info/1201346649/34.
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Hamilton, Steven. "A Time-Dependent Slice Balance Method for High-Fidelity Radiation Transport Computations." Thesis, Georgia Institute of Technology, 2007. http://hdl.handle.net/1853/14608.
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A general finite difference discretization of the time-dependent radiation transport equation is developed around the framework of an existing steady-state three dimensional radiation transport solver based on the slice-balance approach. Three related algorithms are outlined within the general finite difference scheme: an explicit, an implicit, and a semi-implicit approach. The three algorithms are analyzed with respect to the discretizations of each element of the phase space in the transport solver. The explicit method, despite its small computational cost per time step, is found to be unsuitable for many purposes due to its inability to accurately handle rapidly varying solutions. The semi-implicit method is shown to produce results nearly as reliable as the fully implicit solver, while requiring significantly less computational effort.
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Zöllner, Martin Sebastian [Verfasser], and Carmen [Akademischer Betreuer] Herrmann. "First-Principles Investigation of Puzzling Spin-Dependent Transport Phenomena in Molecular and Nanostructured Systems / Martin Sebastian Zöllner ; Betreuer: Carmen Herrmann." Hamburg : Staats- und Universitätsbibliothek Hamburg, 2020. http://d-nb.info/1208394843/34.
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Peters, John Archibald. "Ballistic Magnetotransport and Spin-Orbit Interaction InSb and InAs Quantum Wells." Ohio University / OhioLINK, 2006. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1143487911.
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Frangou, Lamprini. "Injection, transmission et détection de spin dans les matériaux antiferromagnétiques." Thesis, Université Grenoble Alpes (ComUE), 2017. http://www.theses.fr/2017GREAY079/document.
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La spintronique antiferromagnétique est un domaine de recherche émergent dans le secteur des technologies de l'information. Ce domaine exploite la combinaison unique de propriétés dans les matériaux antiferromagnétiques. Leur grande fréquence d'excitation, leur robustesse face à des champs extérieurs, une aimantation totale nulle et la possibilité de générer de forts effets de magnéto-transport les rendent particulièrement intéressants. Le transfert de spin, le couplage spin-orbite et les effets caloritroniques constituent les phénomènes qui ont façonné une grande partie de la recherche et des développements récents en spintronique. Dans cette thèse, nous avons étudié les effets de transfert et de pompage de spin dans des antiferromagnétiques métalliques et isolants au moyen de la technique de résonance ferromagnétique, dans des tricouches du type injecteur de spin ferromagnétique - NiFe, CoFeB / (conducteur de spin - Cu / absorbeur de spin antiferromagnétique - IrMn, NiFeOx, NiO. Les mesures de la dépendance en température de la relaxation ferromagnétique ont révélé un nouvel effet de pompage de spin associé aux fluctuations linéaires lors de la transition de phase magnétique de l'antiferromagnétique, quel que soit l'état électronique et la nature du transport de spin. Cela ouvre de nouvelles voies pour un pompage de spin plus efficace, tout en fournissant une méthode polyvalente pour mesurer la température critique des films ultra-minces à aimantation totale nulle. Dans le but de mesurer à la fois les fluctuations de spin linéaires et non linéaires dans l'antiferromagnétique, nous avons effectué des mesures électriques dans une configuration de mesure du type ‘spin Hall’. Une dépendance en température non-monotone inédite de la tension dc transverse a parfois été observée. Elle est principalement associée aux propriétés d’un ferromagnétique spécifique: le Permalloy, sans rapport avec les effets de rectification de spin. Ces résultats s'ajoutent à une littérature croissante sur l'absorption d’un courant de spin, soulignant la capacité des ferromagnétiques à agir comme détecteurs de courant de spin émis à la suite de phénomènes impliquant une dynamique d’aimantation. Finalement, nous avons utilisé le couplage d'échange pour étudier et ensuite façonner les propriétés magnétiques et électriques de plusieurs antiferromagnétiques destinés à diverses applications spintroniques, y compris la lecture par magnétorésistance tunnel anisotropeAntiferromagnetic spintronics is an emerging research field in the area of information technology that exploits the unique combination of properties of antiferromagnets. It is their high excitation frequency, robustness against external fields, zero net magnetization and possibility of generating large magneto-transport effects that makes them so interesting. Spin transfer, spin-orbit coupling and spin caloritronics constitute the phenomena that have shaped much of the recent research and development towards pure antiferromagnetic spintronics. Here we investigate spin transfer torque and spin pumping in both metallic and insulating antiferromagnets by means of ferromagnetic resonance technique, in ferromagnetic spin injector – NiFe, CoFeB / (spin conductor – Cu) / antiferromagnetic spin sink – IrMn, NiFeOx, NiO trilayers. Temperature dependence measurements of the ferromagnetic relaxation revealed a novel spin pumping effect associated to the linear fluctuations at the magnetic phase transition of the antiferromagnet, regardless its electronic state and the nature of the spin transport. This opens new ways towards more efficient spin pumping, while providing at the same time a versatile method to probe the critical temperature of ultrathin films with zero net magnetization. Next, in an effort to probe linear as well as non-linear fluctuations in the antiferromagnet we conducted electrical measurements in spin Hall geometry. A novel non-monotonous temperature dependence of transverse dc voltage was sometimes observed, mostly associated to the properties of a specific ferromagnet: Permalloy, unrelated to spin rectification effects. These findings add to a growing body of literature on spin current absorption, highlighting the ability of ferromagnets to act as spin current detectors, in phenomena involving magnetization dynamics. Finally, we used exchange bias to investigate and subsequently engineer the magnetic and electric properties of various antiferromagnets intended for diverse spintronic applications including reading via tunneling anisotropic magnetoresistance
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Nandi, Riya. "Non-equilibrium dynamics in three-dimensional magnetic spin models and molecular motor-inspired one-dimensional exclusion processes." Diss., Virginia Tech, 2021. http://hdl.handle.net/10919/102652.
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We investigate the relaxation dynamics of two distinct non-equilibrium processes: relaxation of three-dimensional antiferromagnetic lattice spin models with Heisenberg interaction following a critical quench, and a one-dimensional exclusion process inspired by the gear-like motion of molecular motors.
In a system of three-dimensional Heisenberg antiferromagnets the non-conserved staggered magnetization components couple non-trivially to the conserved magnetization densities inducing fully reversible terms that enter the Langevin dynamic equation. We simulate the exact microscopic dynamics of such a system of antiferromagnets by employing a hybrid simulation algorithm that combines the reversible spin precession implemented by the fourth-order Runge-Kutta integration method with the standard relaxational dynamics at finite temperatures using Monte Carlo updates. We characterize the dynamic universality class of this system by probing the early temporal window where the system exhibits aging scaling properties. We also verify an earlier renormalization group prediction that the temporal decay exponent in the two-time spin autocorrelation function exhibits non-universality, specifically it depends on the width of the initial spin orientation distribution. We employ a similar numerical technique to study the critical dynamics of an anisotropic Heisenberg antiferromagnet in the presence of an external field. The phase diagram of this system exhibits two critical lines that meet at a bicritical point. We study the aging scaling dynamics for the model C critical line, probe the model F critical line by investigating the system size dependence of the characteristic spin-wave frequencies near criticality, and measure the dynamic critical exponents for the order parameter including its aging scaling at the bicritical point.
We introduce a one-dimensional non-equilibrium lattice gas model representing the processive motion of dynein molecular motors over the microtubule. We study both dynamical and stationary state properties for the model consisting of hardcore particles hopping on the lattice with variable step sizes. We find that the stationary state gap-distribution exhibits striking peaks around gap sizes that are multiples of the maximum step size, for both open and periodic boundary conditions, and verify this using a mean-field calculation. For open boundary conditions, we observe intriguing damped oscillator-like distribution of particles over the lattice with a periodicity equal to the maximum step size. To characterize transient dynamics, we measure the mean square displacement that shows weak superdiffusive growth with exponent γ≈ 1.34 for periodic boundary and ballistic growth ( γ≈ 2) for open boundary conditions at early times. We also study the effect of Langmuir dynamics on the density profile.Doctor of Philosophy
Most systems found in nature are out of equilibrium. In this dissertation we investigate the relaxation dynamics of two such non-equilibrium systems: 1. We investigate a three-dimensional antiferromagnetic system relaxing towards equilibrium from an initial state that is driven far away from equilibrium at the point in the parameter space where the system undergoes a second-order phase transition. We devise a novel simulation method that captures emerging dynamic universal features and scaling features at these points of continuous phase transition in the early times of relaxation when the system is still far away from equilibrium. 2. Cytoplasmic dyneins are one of three kinds of motor proteins that move on tubular structures called microtubules carrying and transporting cellular cargo inside the cells. Unlike the other molecular motors that move forward with fixed step sizes, the dyneins have been experimentally observed to vary their step size depending on the amount of cargo they are carrying. We model an exclusion process in a one-dimensional lattice inspired by the motion of the dynein molecular motors where the motors can hop from one to four steps depending on their internal states. We study the effect of this variable step size on the dynamics of a collection of dyneins. We observe intriguing oscillating density profiles and discrete peaks in the distribution of empty sites. Our results suggest self-organization among the motors and the empty sites.