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Dissertations / Theses on the topic 'Spin valve'
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1
Huang, Biqin. "Optical spin valve effects." Access to citation, abstract and download form provided by ProQuest Information and Learning Company; downloadable PDF file, 57 p, 2007. http://proquest.umi.com/pqdweb?did=1338919421&sid=9&Fmt=2&clientId=8331&RQT=309&VName=PQD.
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Garzon, Samir Y. "Spin injection and detection in copper spin valve structures." College Park, Md. : University of Maryland, 2005. http://hdl.handle.net/1903/2192.
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Thesis (Ph. D.) -- University of Maryland, College Park, 2005.Thesis research directed by: Physics. Title from t.p. of PDF. Includes bibliographical references. Published by UMI Dissertation Services, Ann Arbor, Mich. Also available in paper.
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Hollingworth, Martin P. "Magnetostriction studies of spin valve components." Thesis, University of Sheffield, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.420790.
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Kuhlmann, Nils Felix [Verfasser]. "Lateral spin-valve devices operated by spin pumping / Nils Felix Kuhlmann." München : Verlag Dr. Hut, 2014. http://d-nb.info/1052375383/34.
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Hallan, André. "Material optimization for spin-thermo-electronic valve." Thesis, KTH, Tillämpad fysik, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-147355.
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Talanana, Mohand. "Spin transport from first-principles: metallic multilayers and a model spin-valve transistor." Enschede : University of Twente [Host], 2006. http://doc.utwente.nl/57129.
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Ozbay, Arif. "Noise and transport studies in spin valve structures." Access to citation, abstract and download form provided by ProQuest Information and Learning Company; downloadable PDF file, 165 p, 2009. http://proquest.umi.com/pqdweb?did=1892027511&sid=10&Fmt=2&clientId=8331&RQT=309&VName=PQD.
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Samad, Abdus. "Structural and magnetic properties of spin valve structures." Thesis, University of Cambridge, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.624580.
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Zocca, Andrea. "Produzione e funzionamento di un dispositivo spin valve." Bachelor's thesis, Alma Mater Studiorum - Università di Bologna, 2014. http://amslaurea.unibo.it/7699/.
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Il fenomeno della magnetoresistenza gigante (GMR) consiste nella marcata variazione della resistenza elettrica di una struttura in forma di film sottile, composta da un’alternanza di strati metallici ferromagnetici (FM) e non magnetici (NM), per effetto di un campo magnetico esterno. Esso è alla base di un gran numero di sensori e dispositivi magnetoelettronici (come ad esempio magnetiche ad accesso casuale, MRAM, ad alta densità) ed ulteriori innovazioni tecnologiche sono in via di elaborazione. Particolarmente rilevanti sono diventate le Spin Valve, dispositivi composti da due strati FM separati da uno spaziatore NM, metallico. Uno dei due film FM (free layer) è magneticamente più soffice rispetto all’altro (reference layer), la cui magnetizzazione è fissata mediante accoppiamento di scambio all’interfaccia con uno strato antiferromagnetico (AFM) adiacente. Tale accoppiamento causa l’insorgenza di una anisotropia magnetica unidirezionale (anisotropia di scambio) per lo strato FM, che si manifesta in uno shift orizzontale del ciclo di isteresi ad esso associato (effetto di exchange bias), solitamente accompagnato anche da un aumento del campo coercitivo.
Questo lavoro di tesi riporta la deposizione e la caratterizzazione magnetica e magnetoresistiva di due valvole spin, una a struttura top (SVT) composta da strati di Si/Cu[5 nm]/Py[5 nm]/Cu[5 nm]/Py[5 nm]/IrMn[10 nm], ed una a struttura bottom (SVB), di composizione Si/Cu[5 nm]/IrMn[10 nm]/Py[5 nm]/Cu[5 nm]/Py[5 nm], allo scopo di verificare il comportamento magnetoresistivo gigante del dispositivo per questa particolare scelta dei materiali. I campioni sono stati depositati mediante DC Magnetron sputtering, e caratterizzati magneticamente mediante magnetometro SQUID; la caratterizzazione resistiva è stata eseguita tramite metodo di van der Pawn.
Vengono infine presentati i risultati sperimentali, in cui si osserva una variazione di magnetoresistenza nei campioni nell’ordine del punto percentuale.
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Rokitowski, Jared David. "Magneto refractive effect in pseudo spin valve thin films." Diss., Online access via UMI:, 2006.
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Murphey, Mark Benjamin. "Spin-Valve Behavior in Aligned Arrays of Carbon Nanotubes." The Ohio State University, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=osu1267764111.
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Sampaio, Joao Miguel Ramos Melo. "Domain walls in spin-valve nanotracks : characterisation and applications." Thesis, Imperial College London, 2011. http://hdl.handle.net/10044/1/9053.
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Magnetic systems based on the manipulation of domain walls (DWs) in nanometre-scaled tracks have been shown to store data at high density, perform complex logic operations, and even mechanically manipulate magnetic beads. The magnetic nano-track has also been an indispensable model system to study fundamental magnetic and magneto-electronic phenomena, such as field induced DW propagation, spin-transfer torque, and other micromagnetic properties. Its value to fundamental research and the breath of potentially useful applications have made this class of systems the focus of wide research in the area of nanomagnetism and spintronics. This thesis focuses on DW manipulation and DW-based devices in spin-valve nanotracks. The spin-valve is a metallic multi-layered spintronic structure, wherein the electrical resistance varies greatly with the magnetisation of its layers. In comparison to monolayer tracks, the spin-valve track enables more sensitive and versatile measurements, as well as demonstrating electronic output of DW-based devices, an achievement of crucial interest to technological applications. However, these multi-layered tracks introduce new, potentially disruptive magnetic interactions, as well as fabrication challenges. In this thesis, the DW propagation in spin-valve nanotracks of different compositions was studied, and a system with DW propagation properties comparable to the state-of-the-art in monolayer tracks was demonstrated, down to an unprecedented lateral size of 33nm. Several DW logic devices of variable complexity were demonstrated and studied, namely a turn-counting DW spiral, a DW gate, multiple DW logic NOT gates, and a DW-DW interactor. It was found that, where the comparison was possible, the overall magnetic behaviour of these devices was analogous to that of monolayer structures, and the device performance, as defined by the range of field wherein they function desirably, was found to be comparable, albeit inferior, to that of their monolayer counterparts. The interaction between DWs in adjacent tracks was studied and new phenomena were observed and characterised, such as DW depinning induced by a static or travelling adjacent DW. The contribution of different physical mechanisms to electrical current induced depinning were quantified, and it was found that the Oersted field, typically negligible in monolayer tracks, was responsible for large variations in depinning field in SV tracks, and that the strength of spin-transfer effect was similar in magnitude to that reported in monolayer tracks. Finally, current induced ferromagnetic resonance was measured, and the domain uniform resonant mode was observed, in very good agreement to Kittel theory and simulations.
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Han, Shu-Jen. "CMOS integrated biosensor array based on spin valve devices /." May be available electronically:, 2007. http://proquest.umi.com/login?COPT=REJTPTU1MTUmSU5UPTAmVkVSPTI=&clientId=12498.
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Eggeling, Eike Moritz [Verfasser]. "Spin-torque induced high frequency excitations and switching in spin-valve nanocontacts / Eike Moritz Eggeling." Bielefeld : Universitätsbibliothek Bielefeld, Hochschulschriften, 2012. http://d-nb.info/1023863669/34.
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Morecroft, Deborah. "In-situ magnetoresistance measurements during patterning of spin valve devices." Thesis, University of Cambridge, 2003. https://www.repository.cam.ac.uk/handle/1810/34689.
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This dissertation describes an experimental study on the patterning of thin films and spin valve devices. Initially the change in the magnetisation reversal of ferromagnetic Ni80Fe15Mo5 thin films was investigated as the shape anisotropy was increased using optical lithography to pattern wire arrays. These structures show a progressive increase in coercivity and a transition between single and two-stage reversal with increasing milling depth. A similar patterning technique was applied to unpinned (Ni80Fe20/Cu/Ni80Fe20) pseudo spin valve (PSV) structures in order to enhance the coercivity of one of the ferromagnetic layers. The increased coercivity induced by micropatterning changed the natural similarity of the magnetic layers and the structure exhibited a small spin valve response. These initial measurements were carried out with separate milling and electrical characterisation steps. However, it was decided that it would be ideal to design a technique to do in-situ magnetoresistance measurements during milling. This meant that the samples could be milled and characterised in the same step, leading to a much cleaner and more efficient process. In-situ magnetoresistance measurements were carried out during micropatterning of PSV devices, and the measurements showed the evolution in the electrical response as wire structures were gradually milled through the thickness. Contrary to what was expected, the structures showed a maximum spin valve response when fully milled through. The effect of further increasing the shape anisotropy by reducing the wire width, and changing the material properties in the PSV structure has also been investigated. MR measurements were taken as the temperature was increased from 291K to 493K, and the results show that the patterned PSV structures have a better thermal stability than exchange biased spin valves with an IrMn pinning layer. The experiment was extended to the nanoscale, and the results show that a significant increase in MR is not observed despite the fact that the magnetic configuration tends more towards single domain. This is thought to be due to an increase in the initial resistance of the structures. A small increase in MR was observed as the wire width was decreased from 730 to 470 nm, although the spin valve response is heavily dependent on the gallium dosage density during patterning in the Focused Ion Beam (FIB). Micromagnetic simulations were carried out, which agree with the experimental results and showed the change in the magnetisation reversal from rotation to switching as the dimensions were reduced on the nanoscale.
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Hossain, Md Iftekhar. "COHERENT SPIN TRANSPORT IN NANOWIRE SPIN VALVES AND NOVEL SPINTRONIC DEVICE POSSIBILITIES." VCU Scholars Compass, 2016. http://scholarscompass.vcu.edu/etd/4201.
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Coherent injection, detection and manipulation of spins in semiconductor nansotructures can herald a new genre of information processing devices that are extremely energy-efficient and non-volatile. For them to work reliably, spin coherence must be maintained across the device by suppressing spin relaxation. Suppression can be accomplished by structural engineering, such as by confining spin carriers to the lowest subband in a semiconductor quantum wire. Accordingly, we have fabricated 50-nm diameter InSb nanowire spin valves capped with Co and Ni nanocontacts in which a single conduction subband is occupied by electrons at room temperature. This extreme quantum confinement has led to a 10-fold increase in the spin relaxation time due to dramatic suppression of the D’yakonov -Perel’ (DP) spin relaxation mechanism. We have observed the spin-valve and Hanle effects at room temperature in these systems. Observing both effects allowed us to estimate the carrier mobility and the spin relaxation length/time and we found that the latter is ~10 times larger than the value reported in bulk InSb despite a four orders of magnitude decrease in the carrier mobility due to surface roughness scattering. We ascribe this dramatic increase in spin relaxation time to the suppression of the DP relaxation mode due to single subband occupancy.
Modulation of spin relaxation rate by an external agent can open new possibilities for spintronic devices. Any agent that can excite electrons from the lowest subband to higher subbands will dramatically increase the DP spin relaxation rate. We have shown that the spin relaxation rate in InSb nanowires can be modulated with infrared light. In the dark, almost all the electrons in the nanowires are in the lowest conduction subband, resulting in near-complete absence of DP relaxation and long spin coherence length. This results in a high resistance state in a spin valve whose ferromagnetic contacts have anti-parallel spin polarizations. Under infrared illumination, higher subbands get populated and the DP spin relaxation mechanism is revived, leading to a three-fold decrease in the spin relaxation length. As a result, injected spins flip in the spacer layer of the spin valve and this causes the spin valve resistance to drop. Therefore, this effect can be exploited to implement an infrared detector.
We also studied the transport behavior of a single nanowire (~50 nm diameter) captured between two non-magnetic contact pads. The wire was attached between the pads using dielectrophoresis. A giant (∼10,000,000%) negative magnetoresistance at 39 mT field was observed at room temperature in Cu nanowires contacted with Au contact pads. In these nanowires, potential barriers form at the two Cu/Au interfaces because of Cu oxidation that results in an ultrathin copper oxide layer forming between Cu and Au. Current flows when electrons tunnel through, and/or thermionically emit over these barriers. A magnetic field applied transverse to the direction of current flow along the wire deflects electrons toward one edge of the wire because of the Lorentz force, causing electron accumulation at that edge and depletion at the other. This makes the potential barrier at the accumulated edge shorter and at the depleted edge taller. The modulation of the potential barrier height with a magnetic field dramatically alters the tunneling and/or thermionic emission rate causing a giant magnetoresistance.
Currently, effort is underway to demonstrate strain sensitive anisotropic magnetoresistance (AMR) in a single Co-Cu-Co nanowire spin valve. AMR is caused by spin-orbit coupling effects which makes the resistance of a ferromagnet depend on the angle between the direction of current flow and the magnetization. The resistance maximizes when the angle is 00 or 1800 and minimizes when the angle is 900. When an external magnetic field is applied in a direction opposite to a ferromagnet’s magnetization, the latter begins to rotate in the direction of the field and hence its resistance continuously changes. This results in a trough in the magnetoresistance of a spin valve structure between the two fields when the magnetization starts to rotate and when the magnetization completes the rotation. We have observed a magnetoresistance peak (instead of trough) in the Co-Cu-Co spin valve, which is due to the normal spin valve effect that overshadows AMR. However, when an intense infrared light source is brought close to the sample, the peak gets overshadowed by a trough, showing that the AMR effect becomes dominant. We attribute this intriguing feature to the fact that the AMR effect is strongly influenced by strain. Heating by the light source generates strain in the Co contacts owing to unequal thermal expansion of Co and the underlying substrate. We also observed that the AMR effect becomes more pronounced as the light source is brought closer to the sample, resulting in increased heating and hence increased strain generation.
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Anaya, Armando Alonso. "Spin Valve Effect in Ferromagnet-Superconductor-Ferromagnet Single Electron Transistor." Diss., Georgia Institute of Technology, 2005. http://hdl.handle.net/1853/6864.
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This thesis describes a research of suppression of superconducting gap in a superconducting island of a Ferromagnetic-Superconducting-Ferromagnetic Single-Electron-Transistor due to the fringing magnetic fields produced by the ferromagnetic leads. The devices are working below the critical temperature of the superconducting gap. A model is proposed to explain how the fringing magnetic field produced by the leads is strong enough to suppress the superconducting gap. The peak of the fringing magnetic field produced by one lead reaches 5000 oe. It is observed an inverse tunneling magneto resistance during the suppression of the superconducting gap, obtaining a maximum absolute value 500 times greater than the TMR in the normal state where the efficiency of the spin injection is low.
It is concluded that the suppression of the superconducting gap is due to fringing magnetic field and not to the spin accumulation because the low efficiency of the spin injection. It is suggested a new geometry to reduce the effect of the fringing magnetic field so it can be obtained a suppression of the superconductivity due to the spin accumulation. It is described the qualitatively behavior of the IV characteristic when the suppression of the superconductivity is due to spin accumulation.
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Fujimoto, Tatsuo. "Magnetic and magnetoresistive properties of anisotropy-controlled spin-valve structures." Thesis, University of Cambridge, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.387613.
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Rortais, Fabien. "Etude de l'injection et détection de spin dans le silicium et germanium : d'une mesure locale de l'accumulation à la détection non locale du courant de spin." Thesis, Université Grenoble Alpes (ComUE), 2016. http://www.theses.fr/2016GREAY059/document.
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Depuis la découverte de la magnétorésistance (MR) géante en 1988 par le groupe d'Albert Fert (prix Nobel de physique en 2007), le domaine de l'électronique de spin a connu un essor sans précédent, justifié par toutes les applications qu'elle permet d'envisager en électronique.Depuis une vingtaine d'années, il est question d'utiliser le degré de liberté de spin directement dans les matériaux semi-conducteurs avec le gros avantage par rapport aux métaux de pouvoir manipuler électriquement le spin des porteurs. L'électronique de spin dans les matériaux semi-conducteurs utilise pour coder l'information non seulement la charge des porteurs (électrons et trous), mais aussi leur spin. En associant charge et spin, on ajoute de nouvelles fonctionnalités aux dispositifs de micro-électronique traditionnels.Le premier challenge consiste à contrôler l’injection et la détection d’une population de porteurs polarisés en spin dans les semi-conducteurs traditionnels (Si, Ge).Pour cela, nous avons étudié des dispositifs hybrides de type MIS: Métal ferromagnétique/Isolant/Semi-conducteur qui nous permettent d'injecter et de détecter électriquement un courant de spin. La première partie de cette thèse concerne les dispositifs à 3 terminaux sur différents substrats qui utilisent une unique électrode ferromagnétique pour injecter et détecter par effet Hanle l’accumulation de spin dans les semi-conducteurs. Une amplification des signaux de spin extraits expérimentalement par rapport aux valeurs théoriques du modèle diffusif est à l’origine d’une controverse importante. Nous avons alors démontré que l’origine du signal de MR ou de l’amplification ne peut être expliquée par la présence de défauts dans la barrière tunnel. A l’inverse, nous prouvons la présence d’états d’interface qui peuvent expliquer l’amplification du signal de spin. De plus, la réduction de la densité d’états d’interface par une préparation de surface montre des changements significatifs comme la diminution du signal de spin.La deuxième partie de ces travaux concerne la transition vers les vannes de spin latérales sur semi-conducteurs. Dans ces dispositifs utilisant deux électrodes FM, le découplage entre l’injection et la détection de spin permet de s’affranchir des effets de magnétorésistance parasites car seul un pur courant de spin est détecté dans le semi-conducteur. Par une croissance d’une jonction tunnel ferromagnétique épitaxiée, nous avons démontré l’injection de spin dans des substrats de silicium et germanium sur isolant. En particulier nous observons un fort signal de spin jusqu’à température ambiante dans le germanium.Finalement, les prémices de la manipulation de spin par l’étude du couplage spin-orbite ont été étudiées dans les substrats d’arséniure de gallium et de germanium. En effet, nous avons induit par effet Hall de spin (une conséquence du couplage spin-orbite) une accumulation de spin qui a été sondée en utilisant la spectroscopie de muon. On démontre alors, à basse température, la présence de l’accumulation grâce au couplage entre les spins électroniques accumulés et les noyaux de l’arséniure de galliumSince the discovery of the giant magnetoresistance in 1988 by the group of Albert Fert (Nobel Prize in 2007), the field of spintronics has been growing very fast due to its potential applications in micro-electronics.For almost 20 years, it has been proposed to introduce the spin degree of freedom directly in the semiconducting materials. Spintronics aims at using not only the charge of carriers (electrons and holes) but also their intrinsic spin degree of freedom. In that case, spins might be manipulated with electric fields. By using both charge and spin, one might add new functionalities to traditional micro-electronic devices.Indeed, the first challenge of semiconductor spintronics is to create and detect a spin polarized carrier population in traditional semiconductors like Si and Ge to further manipulate them.For this purpose, we have used hybrid ferromagnetic metal/insulator/semiconductor devices which allow us to perform electrical spin injection and detection. The first part of this thesis deals with 3 terminal devices grown on different substrates and in which a single ferromagnetic electrode is used to inject and detect spin polarized electrons using the Hanle effect. A spin signal amplification is measured experimentally as compared to the value from the theoretical diffusive model, this raised a controversy concerning 3 terminal measurements. We demonstrate that localized defects in the tunnel barrier cannot be at the origin of the measured MR signal and spin signal amplification. Instead, we show that the presence of interface states is the origin of the spin signal amplification in all the substrates. By using a proper surface preparation and the MBE growth of the magnetic tunnel junctions, we reduce the density of interface states and show a significant modification of the spin signals.In a second part, we present the transition from 3 terminal measurements to lateral spin valves on semiconductors. In the last configuration by using two ferromagnetic electrodes, charge and spin currents are decoupled in order to avoid any spurious magnetoresistance artefacts. Using epitaxially grown magnetic tunnel junctions we can prove the spin injection in silicon and germanium. Especially, we are able to measure non local spin signals in germanium up to room temperature.Finally, we study the spin Hall effect in gallium arsenide and germanium substrates. For this propose we induce spin accumulation using the spin Hall effect (i.e spin-orbit coupling) and probe it using muon spectroscopy. We demonstrate, at low temperature the presence of spin accumulation by the coupling between nuclear spins and the electron spin accumulation
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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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Lindebaum, Stephan [Verfasser], Jürgen [Akademischer Betreuer] König, and Wolfgang [Akademischer Betreuer] Belzig. "Spin-Polarized Transport in Single-Electron Spin-Valve Transistors / Stephan Lindebaum. Gutachter: Wolfgang Belzig. Betreuer: Jürgen König." Duisburg, 2012. http://d-nb.info/1036115887/34.
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Gökcan, Hüseyin. "Magnetotransport of hot electrons and holes in the spin-valve transistor." Enschede : University of Twente [Host], 2006. http://doc.utwente.nl/57119.
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Wurft, Tobias [Verfasser]. "Investigation of the Magnetic Vortex State for Spin-Valve Sensors / Tobias Wurft." Bielefeld : Universitätsbibliothek Bielefeld, 2018. http://d-nb.info/1169057802/34.
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Colin, Irénée A. (Irénée Anthelme). "Field and current induced magnetization reversal in patterned Pseudo Spin Valve devices." Thesis, Massachusetts Institute of Technology, 2007. http://hdl.handle.net/1721.1/39546.
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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2007.Includes bibliographical references.
The field and current induced magnetization switchings of Pseudo-Spin-Valve (PSV) devices are described in this dissertation. An aligned sequence of three (one optical and two electron-beam) lithographies was used to define the devices and their electrical contacts. The PSV stack comprised a layer of soft ferromagnetic material Ni80oFe20 (NiFe or Py), a non-magnetic spacer layer of Cu, a hard ferromagnetic layer of Co and a capping layer of Au. The current flowed in plane (CIP) and the devices displayed giant magnetoresistance (GMR). Three different shapes were investigated: notched bars, elliptical rings and rhomboidal rings. In the bars, the notches provided strong pinning potential wells for transverse domain walls in the NiFe layer, which, upon cycling an external field, reversed in a step-like fashion, with domain walls nucleating from both ends of the bars, due to strong magnetostatic coupling between both magnetic layers. Additional important magnetostatic coupling effects were measured and micromagnetic simulations confirmed the ubiquity of such coupling. Current induced magnetic switching (CIMS) experiments were conducted, and threshold densities of the order of 1011 A/m2 were used to switch the magnetization under an external bias field, and the critical current decreased with increasing bias.
(cont.) Simulations showed that the Oersted field generated by the current was sufficiently strong to switch the magnetization in the soft NiFe layer, without taking into account spin-transfer torque effects. Ring shaped devices allowed for a diversity of responses depending on the contact configurations used which may be divided into two categories: the classical configurations and the Wheatstone bridge configurations. The latter allowed for large effective GMR ratios up to 200 %, with low switching fields down to a few Oersted. Both types of contact configuration along with micromagnetic simulations enabled a deep understanding of the field-induced reversal of both elliptical and rhomboidal rings. Magnetostatic coupling effects were also found to play a key role. CIMS experiments were conducted, and the rhomboidal ring device successfully switched, in the Wheatstone bridge configuration, under zero bias with a threshold current density of the order of 1011 A/m2. The density and length of current pulses was found to change the critical current density, which suggested that the spin structure of the domain walls in the NiFe layer was modified by the current.
by Irénée A. Colin.
S.M.
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Drögeler, Marc [Verfasser], Christoph [Akademischer Betreuer] Stampfer, and Thomas [Akademischer Betreuer] Schäpers. "Spin transport in graphene-hBN heterostructures in inverted non-local spin valve devices / Marc Drögeler ; Christoph Stampfer, Thomas Schäpers." Aachen : Universitätsbibliothek der RWTH Aachen, 2017. http://d-nb.info/1162499591/34.
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Xiao, Jiang. "Spin-transfer Torque in Magnetic Nanostructures." Diss., Georgia Institute of Technology, 2006. http://hdl.handle.net/1853/11513.
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This thesis consists of three distinct components: (1) a test of Slocnzewski's theory of spin-transfer torque using the Boltzmann equation, (2) a comparison of macrospin models of spin-transfer dynamics in spin valves with experimental data, and (3) a study of spin-transfer torque in continuously variable
magnetization.
Slonczewski developed a simple circuit theory for spin-transfer torque in spin valves with thin spacer layer. We developed a numerical method to calculate the spin-transfer torque in a spin valve using Boltzmann equation. In almost all realistic cases, the circuit theory predictions agree well with the Boltzmann equation results.
To gain a better understanding of experimental results for spin valve systems, current-induced magnetization dynamics for a spin valve are studied using a single-domain approximation and a generalized Landau-Lifshitz-Gilbert equation. Many features of the experiment were reproduced by the simulations. However, there are two significant discrepancies: the current dependence of the magnetization precession frequency, and the presence and/or absence of a microwave quiet magnetic phase with a distinct magnetoresistance signature.
Spin-transfer effects in systems with continuously varying magnetization also have attracted much attention. One key question is under what condition is the spin current adiabatic, i.e., aligned to the local magnetization. Both quantum and semi-classical calculations of the spin current and spin-transfer torque are done in a free-electron Stoner model. The calculation shows that, in the adiabatic limit, the spin current aligns to the local magnetization while the spin density does not. The reason is found in an effective field produced by the gradient of the magnetization in the wall. Non-adiabatic effects arise for short domain walls, but their magnitude decreases exponentially as the wall width increases.
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Проценко, Сергій Іванович, Сергей Иванович Проценко, Serhii Ivanovych Protsenko, Максим Геннадійович Демиденко, Максим Геннадьевич Демиденко, Maksym Hennadiiovych Demydenko, Олена Вікторівна Федченко, Елена Викторовна Федченко, Olena Viktorivna Fedchenko, and P. Wegierek. "Magneto-optical Properties of Spin-Valve Systems on the Basis of Au/Fe/Au/Co/Si." Thesis, Sumy State University, 2012. http://essuir.sumdu.edu.ua/handle/123456789/35104.
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This paper presents the results of investigation of magneto-optical Kerr effect in pseudo spin-valve systems
on the basis of Fe, Co and Au. The significant dependence of coercetivity on such parameters as relative
position of ferromagnetic layers, their thicknesses and surface morphology was shown. The investigation
was carried out with AFM and TEM methods. Coercitivity value is greater for
Au(3)/Fe(3)/Au(6)/Co(20)/SiO2/Si system. This is explained with different transitional metals growth mechanisms
on the substrate and on non-magnetic layer and with more varied surface morphology of films with
thickness about 3 nm because of three-dimensional islands in Stranski - Krastanov growth mode.
When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/35104
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Sambricio, Garcia Jose Luis. "Graphene-hybrid devices for spintronics." Thesis, University of Manchester, 2017. https://www.research.manchester.ac.uk/portal/en/theses/graphenehybrid-devices-for-spintronics(e552a341-6af9-45fb-ba16-d9c43c3412c8).html.
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This thesis explores the use of 2D materials (graphene and hBN) for spintronics. Interest on these materials in spintronics arose from theoretical predictions of high spin filtering in out-of-plane transport through graphene and hBN sandwiched by ferromagnets. Similarly, 5-layer graphene was forecast to be a perfect spin filter. In the case of in-plane spin transport, graphene was expected to be an excellent material due to its low spin-orbit coupling and low number of defects. Although there already exist experimental works that attempted to explore the aforementioned predictions, they have failed so far to comply with the expected results. Earlier experimental works in graphene and hBN out-of-plane spin transport achieved low spin filtering on the order of a few percent; while spin relaxation parameters in graphene for in-plane spin transport remained one or two orders of magnitude below the predicted values. In the case of vertical devices, the failure to meet the theoretical expectations was attributed to the oxidation of the ferromagnets and the lack of an epitaxial interface between the later and the graphene or hBN. Similarly, the exact mechanisms that lead to high spin relaxation for in-plane spin transport in graphene are not completely understood, in part due to the low-quality of the explored devices. In this thesis we analyze new architectures and procedures that allowed us to fabricate ultraclean and oxidation-free interfaces between ferromagnets and graphene or hBN. In these devices we encountered negative and reversible magnetoresistance, that could not be explained with the previous theoretical models. We propose a new model based on a thorough characterization of the devices and well-known properties of graphene that were not taken into account in the previous model. We also employed a novel type of contact to graphene (1D-contacts) and applied it for the first time to achieve spin-injection in graphene. The main advantage of this type of contact is the full encapsulation of graphene with hBN, which leads to high quality graphene spintronic devices.
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Vistoli, Lorenzo. "Charge and spin transport in memristive La0.7Sr0.3Mno3/SrTiO3/Co devices." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2015. http://amslaurea.unibo.it/9325/.
Full textAbstract:
Il lavoro svolto si concentra sul trasporto di carica e spin in dispositivi trilayer
La0.7Sr0.3MnO3/SrTiO3/Co multifunzionali. Questi dispositivi mostrano sia magnetoresistenza
che resistive switching, con un'interessante interazione fra i due effetti. Le
giunzioni SrTiO3 sono state scelte per questo lavoro sia per via dei precedenti studi
su SrTiO3 come barriera in dispositivi spintronici (cioè dispositivi con magnetoresistenza),
sia perché sono promettenti come materiale base per costruire memristor
(cioè dispositivi con resistive switching). Il lavoro di tesi è stato svolto all'Istituto per
lo studio dei materiali nanostrutturati (ISMN-CNR) a Bologna.
Nella prima parte di questa tesi illustrerò la fisica dietro al resistive switching e alla
magnetoresistenza di dispositivi trilayer, mostrando anche risultati di studi su dispositivi
simili a quelli da me studiati. Nella seconda parte mostrerò la complessa fisica
degli ossidi utilizzati nei nostri dispositivi e i possibili meccanismi di trasporto attraverso
essi.
Nell'ultima parte descriverò i risultati ottenuti. I dispositivi La0.7Sr0.3MnO3/SrTiO3/Co
sono stati studiati tramite caratterizzazione elettrica, di magnetotrasporto e con spettroscopia
di impedenza. Le misure ottenute hanno mostrato una fisica molto ricca
dietro al trasporto di spin e carica in questi dispositivi, e la mutua interazione fra
fenomeni spintronici e di resistive switching rappresenta una chiave per comprendere
la fisica di questi fenomeni. Analisi dati della dipendenza della resistenza della temperature
e caratteristiche corrente-tensioni saranno usati per quantificare e descrivere
il trasporto in questi dispositivi.
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Jayathilaka, Priyanga Buddhika. "Spin Dependent Transport in Novel Magnetic Heterostructures." Scholar Commons, 2013. http://scholarcommons.usf.edu/etd/4513.
Full textAbstract:
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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Zhou, Yun. "Spin-dependent electron transport in nanomagnetic thin film devices." Thesis, University of Plymouth, 2011. http://hdl.handle.net/10026.1/556.
Full textAbstract:
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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Chalastaras, Athanasios. "Giant magnetoresistance in magnetic multilayers using a new embossed surface." ScholarWorks@UNO, 2004. http://louisdl.louislibraries.org/u?/NOD,137.
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Thesis (M.S.)--University of New Orleans, 2004.Title from electronic submission form. "A thesis ... in partial fulfillment of the requirements for the degree of Master of Science in the Department of Physics."--Thesis t.p. Vita. Includes bibliographical references.
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Kameš, Jaroslav. "Studium magnetických nanostruktur pro spintroniku." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2009. http://www.nusl.cz/ntk/nusl-228666.
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The Cu/NiFe/Cu/Co/(CoOx) spin-valves have been prepared by the ion-beam sputtering method. Their GMR ratio and the time stability have been investigated by the magnetoresistance and the MOKE measurements at room temperature. The reproducibility of the preparation of the samples have been studied as well, i.e. two identically configurations of the layers should have the same magnetotransport properties.
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Пазуха, Ірина Михайлівна, Ирина Михайловна Пазуха, Iryna Mykhailivna Pazukha, and K. S. Levchenko. "Magnetoresistive Properties of Py/Ag/Co Pseudo Spin-valves." Thesis, Sumy State University, 2018. http://essuir.sumdu.edu.ua/handle/123456789/67956.
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The pseudo spin-valve (PSV) structures based on soft magnetic permalloy Ni80Fe20 (Py) and hard magnetic Co, separated by a layer of nonmagnetic material (Ag) belong to the pseudo spin-valve structures, in which independent magnetization reversal of magnetic layers is gained by diverse coercive forces of magnetic layers.
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Miguel, Ochoa de Zuazola Ruben. "Dynamique de l'aimantation dans des oscillateurs à vortex." Thesis, Paris 11, 2013. http://www.theses.fr/2013PA112129.
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Cette thèse décrit le comportement dynamique des vortex magnétiques dans une structure comprenant un nanocontact sur une multicouche magnétique dans la configuration vanne de spin. Notre approche a couvert des aspects expérimentaux principalement basés sur des mesures électriques cryogéniques micro-ondes, et des aspects théoriques analytiques basés sur le formalisme de Thiele ainsi que des aspects théoriques numériques par le biais de simulations micromagnétiques. La première partie du travail a été consacrée à la compréhension de la dynamique hyperfréquence d'un vortex situé dans la couche ferromagnétique libre, lorsque le couple de transfert de spin met le vortex en mouvement gyrotropique permanent autour du nanocontact. La seconde partie du travail a été consacrée à la compréhension du processus de nucléation du vortex telle qu'induite par la combinaison du champ Ampérien et du transfert de spin. La dépendance de la nucléation envers température et indirectement envers en champ d'anisotropie d'échange a été étudiée, et modélisé en validant l'hypothèse de la création d'un paire vortex-antivortex dans la couche piégée de la vanne de spinThis thesis describes the dynamical behavior of a magnetic vortex structure occuring in a system comprising a nano-contact on a magnetic multilayer which is in the spin valve configuration. Our approach covered experimental aspects mainly based on cryogenic microwave measurements, together with analytical theory based on the formalism of Thiele and numerical modeling through micromagnetic simulations. The first part of the work was devoted to the understanding of the microwave dynamics of a vortex located in the ferromagnetic free layer, when the spin transfer torque puts the vortex in permanent gyrotropic motion about the nanocontact. The second part of the work was devoted to the understanding of the process of the nucleation of a vortex, as induced by the combination of Ampére field and spin transfer torques. In the pinned layer, the dependence of the nucleation on the temperature and indirectly on the exchange bias field has been studied. It has been modelled by the creation of a vortex-antivortex pair in the pinned layer of the spin valve
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Limeira, Vinicius Pena Coto. "Estudos das propriedades magnéticas e magnetorresistivas em válvulas de spin do tipo NiFe/Cu/NiFe/IrMn." Universidade de São Paulo, 2017. http://www.teses.usp.br/teses/disponiveis/43/43134/tde-23012018-101058/.
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Válvulas de Spin têm sido utilizadas na fabricação de sensores magnéticos e memórias de acesso randômico, sendo muito importantes do ponto de vista tecnológico. Neste trabalho, foram exploradas as análises das curvas de reversão de primeira ordem da magnetorresistência (MR-FORC), bem como ajustes das curvas de histereses da magnetização e magnetorresistência, para estudar o fenômeno de exchange-bias, anisotropia magnética e propriedades magnetorresistivas. As válvulas de spin estudadas foram do tipo NiFe/Cu/NiFe/IrMn, tendo camadas semente e de cobertura de Ta, preparadas por sputtering. Um modelo fenomenológico de parede de domínios no material antiferromagnético (AFM) foi utilizado, levando em conta as anisotropias magnéticas e interações entre as camadas. Também foram consideradas certas dispersões da anisotropia dos grãos ferromagnéticos (FM) e antiferromagnéticos (com distribuições Gaussianas) em torno dos respectivos eixos de anisotropia uniaxiais. Para o ajuste da magnetização para algumas amostras, foi necessário utilizar uma rotação no plano de um ângulo nos eixos de anisotropia uniaxiais do FM e AFM, em relação à direção do campo magnético aplicado durante a deposição dos filmes. Bons ajustes das curvas de histereses das magnetizações foram obtidos nas direções medidas do campo magnético aplicado. Um método baseado em medidas de variações angulares da magnetorresistência em campos constantes foi proposto para extrair este ângulo para cada amostra. Foram obtidas razoáveis concordâncias entre estes ângulos e os correspondentes extraídos dos ajustes das curvas de magnetização. Através da análise dos diagramas da MR-FORC e de simulações indicados dos resultados dos ajustes das histereses da magnetização, foi encontrada uma relação direta entre os campos de interação (e suas incertezas) com os campos de exchange-bias (HEB) dos grãos da distribuição (extraídos das simulações, usando a largura da distribuição obtida do ajuste). Resumindo, esta análise mostrou que esta técnica permite extrair informações comparativas sobre a dispersão dos eixos de anisotropia dos grãos FM e AFM em torno do eixo de anisotropia uniaxial, o que pode ser importante na caracterização dos sensores magnetorresistivos. Além disso, análise dos diagramas MR-FORC indicaram início da presença de descontinuidade na camada de NiFe presa em 27, com um aumento acentuado (acima do previsto) para a amostra com 25. Este aumento acima do previsto corrobora com nossa hipótese. As simulações das curvas de histerese da magnetorresistência não foram muito bons, indicando que melhorias devem ser introduzidas no modelo utilizado para a simulação da histerese da magnetorresistência, obtidos a partir dos ângulos das camadas ferromagnéticas livre e presa. A questão referente a presença em algumas das amostras de um desalinhamento entre os eixos fácéis do FM e do AFM ainda é uma questão em aberta, mas neste trabalho foi encontrado que este ângulo é igual a 2.Spin Valves have been employed as magnetic sensors and used in random access memories, showing they are very important in terms of technological point of view. In this work, analyses of the magnetoresistance first order reversal curves (MR-FORC) have been used, as well as fittings of the magnetization and magnetoresistance hysteresis, to study the exchange-bias phenomena, magnetic anisotropies and magnetoresistance in spin valves. Sputtering has been used to the deposition of NiFe/Cu/NiFe/IrMn, and Ta has been deposited as seed and buffer layers. A domain wall model (in the antiferromagnetic layer) taking into account the magnetic anisotropies and the interactions between the layers has been employed to fit the magnetization hysteresis. Some textures have been also introduced to take into account the ferromagnetic (FM) and antiferromagnetic (AFM) grains dispersion (with Gaussian distributions) centered around the respective uniaxial anisotropy axes. However, to obtain good fits for some samples, it has been necessary to include an in-plane rotation of an angle of the both FM and AFM easy axes in relation to the field direction applied during the growing of the films. Good fits of the magnetization hysteresis have been obtained for all measured directions of the applied field. A new method based on the angular variation of the magnetoresistance to constant fields has been proposed to extract directly these angles. Reasonable agreements have been obtained between these angles and the corresponding ones extracted from the fits of the magnetization loops. Through the analyses of the MR-FORC and from the simulations indicated by the parameters (obtained from the fittings of magnetization loops), a direct relation between the interaction fields (and its uncertainties) and the exchange-bias fields of the grains of the distribution (extracted from the simulations, using the width of the distribution obtained from the magnetization fittings) has been identified. In summary, this analysis has showed that this technique allows to extract comparative information about the dispersion of the anisotropy axes of the FM and AFM grains around the uniaxial axis, which can be very import to the characterization of spin-valve based sensors. Besides, MR-FORC analyses have also indicated the presence of a threshold of discontinuity of the pinned NiFe layer at 27, showing a huge increase (above of the expected) to the sample at 25, and this unexpected increasing has corroborated with our hypothese. Simulations of the magnetoresistance loops have not been good, indicating that improvements should be included in the model employed to simulate these curves, obtained from the pinned and free angles of the NiFe layers. Concerning the case of the presence of misalignments of FM and AFM for some samples, it is still an open question, but in this work, we have found that this angle () is equal to 2.
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Manzke, Yori. "Non-local, local, and extraction spin valves based on ferromagnetic metal/GaAs hybrid structures." Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät, 2015. http://dx.doi.org/10.18452/17230.
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Im Gebiet der Spin-Elektronik wird der Spin des Elektrons zusätzlich zu seiner Ladung für Bauelementkonzepte ausgenutzt. Hierbei ist die effiziente elektrische Erzeugung einer Spinakkumulation in einem halbleitenden Material von großer Bedeutung. Die Erzeugung der Spinakkumulation kann mithilfe eines ferromagnetischen Metall-Kontaktes erfolgen. Wird eine elektrische Spannung an die Grenzfläche zwischen dem ferromagnetischen Metall und dem Halbleiter so angelegt, dass spinpolarisierte Elektronen vom Metall in den Halbleiter fließen, spricht man von elektrischer Spininjektion. Bei einer Umkehrung der Spannung werden bevorzugt Elektronen der entgegengesetzten Spinorientierung aus dem halbleitenden Material entfernt. Dieser Prozess wird als Spinextraktion bezeichnet. In dieser Arbeit wird die elektrische Erzeugung einer Spinakkumulation in lateral strukturierten, epitaktischen Hybridstrukturen bestehend aus ferromagnetischen Metallkontakten auf n-dotiertem GaAs untersucht. Allgemein ist neben der Spinpolarisation im Ferromagneten auch die spinunabhängige elektrische Charakteristik eines Kontaktes von zentraler Bedeutung für die effiziente Spinerzeugung. Hier wird gezeigt, dass die gewöhnlichen Strom-Spannungs-Kennlinien die Spininjektionseigenschaften dominieren können. Außerdem wird ein neuartiges Bauelementkonzept vorgestellt und experimentell untersucht. Hierbei handelt es sich um ein lokales Spin-Ventil, welches Spinextraktion statt Spininjektion als Spinerzeugungsprozess verwendet. Im Gegensatz zum gewöhnlichen lokalen Spin-Ventil kann ein solches Extraktions-Spin-Ventil als Baustein eines erweiterten Bauelements angesehen werden, welches auf mehreren, aufeinanderfolgenden Extraktionsprozessen beruht. Die Eigenschaften des Extraktions-Spin-Ventils werden diskutiert und es wird gezeigt, wie seine Funktionalität beispielsweise für das Auslesen der Daten in magnetischen Speichern angewendet werden kann.The efficient electrical generation of a spin accumulation inside a semiconductor (SC) utilizing the interface with a ferromagnetic metal (FM) is essential for the realization of many spintronic device concepts, in which the spin of the electron is exploited in addition to its charge for computational and memory purposes. At FM/n-type SC hybrid contacts, the application of a reverse bias leads to the injection of spin-polarized electrons into the SC. Alternatively, an applied forward bias can be used to generate a spin accumulation of opposite sign due to the extraction of electrons with a particular spin orientation. In this work, the electrical generation and detection of a spin accumulation is studied using epitaxial and laterally structured ferromagnetic metal/n-type GaAs hybrid systems in various measurement geometries. To achieve a high spin generation efficiency, the spinindependent electrical properties of the contact have to be considered in addition to the choice of the injector material with respect to its degree of spin polarization. Here, it is shown that the current-voltage characteristics can even constitute the dominating design parameter with respect to the spin injection properties. In addition, a novel device concept is presented and studied experimentally. This approach essentially relies on spin extraction as the spin generation process in a local spin valve geometry. In contrast to local spin valves based on spin injection, the presented extraction spin valve can be regarded as a building block of an extended device comprising multiple extraction events along the lateral spin transport channel. It is shown how such multiple extraction spin valves allow for an intriguing functionality, which can be used, for example, for the read-out of data in magnetic memory applications.
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Mundinar, Simon [Verfasser], and Jürgen [Akademischer Betreuer] König. "Summation of Path Integrals for Resonant Transport through an Interacting Quantum-Dot Spin Valve / Simon Mundinar ; Betreuer: Jürgen König." Duisburg, 2020. http://d-nb.info/1222908794/34.
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Chikara, Shalinee. "A SYSTEMATIC STUDY OF THERMODYNAMIC AND TRANSPORT PROPERTIES OF LAYERED 4D AND 5D CORRELATED ELECTRON SYSTEMS." UKnowledge, 2011. http://uknowledge.uky.edu/gradschool_diss/843.
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Correlated electron materials have been at the forefront of condensed matter research in the past couple of decades. Correlation in materials, especially, with open d and f electronic shells often lead to very exciting and intriguing phenomenon like high temperature superconductivity, Mott metal-insulator transition, colossal magnetoresistance (CMR). This thesis focuses on triple-layered Sr4Ru3O10, Sr substituted double layered (Ca1-- xAx)3Ru2O7 (A = Ba, Sr) and 5d system Sr2IrO4 and Sr3Ir2O7. Triple-layered Sr4Ru3O10 displays interesting phenomena ranging from quantum oscillations, tunneling magnetoresistance, unusual low temperature specific heat, strong spin-lattice coupling to switching behavior. The central feature, however, is the unique borderline magnetism: along the c-axis. Sr4Ru3O10 shows spontaneous ferromagnetism, indicating a strong Coulomb exchange interaction, U and a large density of states at the Fermi surface, g(EF ), hence Ug(EF ) ≥ 1 (Stoner criterion). But within the ab-plane it features a pronounced peak in magnetization and a first-order metamagnetic transition. The coexistence of the interlayer ferromagnetism and the intralayer metamagnetism makes Sr4Ru3O10 a really unique system. Also, in this thesis the spin-valve behavior exhibited by impurity doping at the Ca site by Ba and Sr in the double layered Ca3Ru2O7 is reported. Spin valve effect is a phenomenon only realized in multilayer thin films. Here, spin valve is observed in bulk single crystals of impurity dopedCa3Ru2O7, Ca3(Ru1-xCrx)2O7 and (Ca1- xAx)3Ru2O7 (A = Ba, Sr). 5d Iridates are expected to be more metallic and less magnetic than their 3d and 4f counterparts because of the extended 5d orbitals. In marked contrast, many iridates are magnetic insulators with exotic properties. The focus in this thesis is on Sr2IrO4 which diplays a novel Jeff = 1/2 Mott state. Magnetic, electrical, and thermal measurements on single-crystals of Sr2IrO4, reveal a novel giant magneto-electric effect (GME) arising from a frustrated magnetic/ferroelectric state. The GME and electric polarization hinge on a spin-orbit gapping of 5d-bands, rather than the magnitude and spatial dependence of magnetization, as traditionally accepted.
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Riegler, Andreas [Verfasser], and Laurens Wigbolt [Akademischer Betreuer] Molenkamp. "Ferromagnetic resonance study of the Half-Heusler alloy NiMnSb : The benefit of using NiMnSb as a ferromagnetic layer in pseudo-spin-valve based spin-torque oscillators / Andreas Riegler. Betreuer: Laurens Wigbolt Molenkamp." Würzburg : Universitätsbibliothek der Universität Würzburg, 2011. http://d-nb.info/101816328X/34.
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Protsenko, Ivan Yukhymovych, Иван Ефимович Проценко, Іван Юхимович Проценко, Iryna Volodymyrivna Cheshko, Ирина Владимировна Чешко, Ірина Володимирівна Чешко, and Є. Майкова. "Структурні перетворення в плівках кобальту для спін-вентильних систем." Thesis, Видавництво СумДУ, 2008. http://essuir.sumdu.edu.ua/handle/123456789/4278.
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Шуляренко, Д. О. "Дослідження магнітоопору у системах спін-вентильного типу на основі CoNi та Cu." Thesis, Сумський державний університет, 2016. http://essuir.sumdu.edu.ua/handle/123456789/45832.
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Ефект гігантського магнітоопору, виявлений у магнітних багатошарових структурах, відрізняється за своєю величиною та природою від класичного магніторезистивного ефекту і може бути пояснений на основі квантових уявлень про рух електронів провідності з різною поляризацією їх спінів через мультишари.
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Colis, Silviu-Mihail. "Magnétisme, transport et structure des systèmes de type "spin-valve" utilisant comme couche magnétique dure un sandwich couplé antiferromagnétiquement à base d'iridium." Université Louis Pasteur (Strasbourg) (1971-2008), 2001. http://www.theses.fr/2001STR13103.
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Le, Quang Tuan. "Magnetodynamics in Spin Valves and Magnetic Tunnel Junctions with Perpendicular and Tilted Anisotropies." Doctoral thesis, KTH, Materialfysik, MF, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-191176.
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Spin-torque transfer (STT) effects have brought spintronics ever closer to practical electronic applications, such as MRAM and active broadband microwave spin-torque oscillator (STO), and have emerged as an increasingly attractive field of research in spin dynamics. Utilizing materials with perpendicular magnetic anisotropy (PMA) in such applications offers several great advantages such as low-current, low-field operation combined with high thermal stability. The exchange coupling that a PMA thin film exerts on an adjacent in-plane magnetic anisotropy (IMA) layer can tilt the IMA magnetization direction out of plane, thus creating a stack with an effective tilted magnetic anisotropy. The tilt angle can be engineered via both intrinsic material parameters, such as the PMA and the saturation magnetization, and extrinsic parameters, such as the layer thicknesses. STOs can be fabricated in one of a number of forms—as a nanocontact opening on a mesa from a deposited pseudospin-valve (PSV) structure, or as a nanopillar etching from magnetic tunneling junction (MTJ)—composed of highly reproducible PMA or predetermined tilted magnetic anisotropy layers. All-perpendicular CoFeB MTJ STOs showed high-frequency microwave generation with extremely high current tunability, all achieved at low applied biases. Spin-torque ferromagnetic resonance (ST-FMR) measurements and analysis revealed the bias dependence of spin-torque components, thus promise great potential for direct gate-voltage controlled STOs. In all-perpendicular PSV STOs, magnetic droplets were observed underneath the nanocontact area at a low drive current and low applied field. Furthermore, preliminary results for microwave auto-oscillation and droplet solitons were obtained from tilted-polarizer PSV STOs. These are promising and would be worth investigating in further studies of STT driven spin dynamics.Effekter av spinnvridmoment (STT) har fört spinntroniken allt närmare praktiska elektroniska tillämpningar, såsom MRAM och den spinntroniska mikrovågsoscillatorn (STO), och har blivit ett allt mer attraktivt forskningsområde inom spinndynamik. Användning av material med vinkelrät magnetisk anisotropi (PMA) i sådana tillämpningar erbjuder flera stora fördelar, såsom låg strömförbrukning och funktion vid låga fält i kombination med hög termisk stabilitet. Den utbyteskoppling (”exchange bias”) en PMA-tunnfilm utövar på ett intilliggande skikt med magnetisk anisotropi i planet (IMA) kan få IMA-magnetiseringsriktningen att vridas ut ur planet, vilket ger en materialstack med en effektivt sett lutande magnetisk anisotropi. Lutningsvinkeln kan manipuleras med både inre materialparametrar, såsom PMA och mättningsmagnetisering, och yttre parametrar, såsom skikttjocklekarna. STO:er kan tillverkas som flera olika typer - som en nanokontaktsöppning på en s.k. mesa av en deponerad pseudospinnventilstruktur (PSV) eller som en nanotråd etsad ur en magnetisk tunnlingsövergång (MTJ) –och bestå av mycket reproducerbar PMA eller av skikt med på förhand bestämt lutning av dess magnetiska anisotropi. MTJ-STO:er av CoFeB med helt vinkelrät anisotropi visar högfrekvent mikrovågsgenerering med extremt stort frekvensomfång hos strömstyrningen, detta vid låg biasering. Mätning och analys av spinnvridmoments-ferromagnetisk resonans (ST-FMR) avslöjade ett biasberoende hos spinnvridmomentskomponenter, vilket indikerar en stor potential för direkt gate-spänningsstyrda STO:er. I helt vinkelräta PSV-STO:er observerades magnetiska droppar under nanokontaktområdet vid låg drivström och lågt pålagt fält. Dessutom erhölls preliminära resultat av mikrovågssjälvsvängning och av s.k. ”droplet solitons” hos PSV-STO:er med lutande polarisator. Dessa är lovande och skulle vara värda att undersökas i ytterligare studier av STT-driven spinndynamik.
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Duarte, Celso de Araujo. ""Propriedades magnéticas e de spin em semicondutores do grupo III-V"." Universidade de São Paulo, 2006. http://www.teses.usp.br/teses/disponiveis/43/43134/tde-06092006-101017/.
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Neste trabalho, apresentamos o resultado de nossas investigações em amostras de poços quânticos parabólicos (PQW) de AlGaAs crescidas em substratos de GaAs por MBE (Molecular Beam Epitaxy). Nossos estudos se concentram nas implicações da variação do fator g de Landé ao longo da estrutura dos PQW, a qual ocorre em virtude da dependência dessa grandeza com respeito ao conteúdo de Al na liga AlGaAs. Essas implicações são analisadas através de medidas de transporte eletrônico (medidas de Hall e do efeito Shubnikov-de Haas). As medidas de Subnikov-de Haas a temperaturas da ordem de dezenas a centenas de milikelvin com variação do ângulo de inclinação se mostram um eficiente método para a determinação do fator g. Distinguimos não só o fator g determinado pelas propriedades da liga, como também uma contribuição oriunda de efeitos de muitos corpos (contribuição de troca). Por outro lado, as medidas de Hall nos revelam um comportamento anômalo, que mostramos não ter origem no conhecido "efeito Hall anômalo" presente em materiais ferromagnéticos, nem em efeitos de ocupação de múltiplas sub-bandas. Atribuímos o fenômeno a um efeito "válvula de spin", conseqüente da variação espacial do fator g. Nossas observações nos permitem a idealização de um transistor "válvula de spin", prescindindo do emprego de materiais magnéticos.We present the results of our investigations concerning MBE grown AlGaAs/GaAs parabolic quantum well (PQW) samples. We focused on the variation of the Landé g factor along the structure of the PQWs, which occur as a consquence of its dependence on the Al content on the alloy AlGaAs. The implications are studied by Hall and Shubnikov-de Haas measurements. Shubnikov-de Haas measurements at temperatures of the order of tenths to hundreds of milikelvin with variation of the tilt angle are shown to be an efficient method for the determination of the g factor. We could distinguish not only the alloy g factor, but its many body contribution (exchange contribution). On the other hand, Hall measurements exhibit an unusual behavior, which we prooved it has no relation neither to the well known "anomalous Hall effect", a characteristic of ferromagnetic materials, nor to a multi subband occupation effect. We atribute such behavior to a "spin valve effect", caused by the spatial variation of the g factor. Our observations allow us to idealize a "spin valve" transistor, without any ferromagnetic material in its structure.
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Vigroux, Julien [Verfasser], and Günther [Akademischer Betreuer] Bayreuther. "Fabrication and characterization of a magnetic tunnel transistor with an epitaxial spin valve by the shadow mask technique / Julien Vigroux. Betreuer: Günther Bayreuther." Regensburg : Universitätsbibliothek Regensburg, 2010. http://d-nb.info/1022820435/34.
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Tietjen, Detlev. "Kopplungen und Riesenmagnetowiderstand (GMR) in Mehrlagensystemen für die Magnetosensorik." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2004. http://nbn-resolving.de/urn:nbn:de:swb:14-1086786498875-45169.
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Die Messung magnetischer Felder ist in der Sensorik von großem Interesse. Benötigt werden dazu physikalische Effekte, die magnetische Größen in elektrische Größen umsetzen. Ein interessanter Vertreter ist dabei der Riesenmagnetowiderstand (GMR). Systeme, die den GMR zeigen, sind Thema dieser Arbeit. Die untersuchten Systeme lassen sich in zwei Typen einteilen: Multilagen bestehen aus einer großen Zahl (30-40) nominell identischer Doppellagen aus abwechselnd ferromagnetischem und nichtmagnetischem Metall. Diese Systeme zeigen eine Widerstandsänderung mit der Stärke des externen Magnetfeldes. Untersucht wurden Schichten Co/Cu und NiFe/Cu. Es konnten Schichten mit einer Sensitivität von 3.2%/mT präpariert werden. Für den Rückgang der Signalstärke bei erhöhten Temperaturen sind, abhängig von der Cu-Dicke, zwei unterschiedliche Mechanismen verantwortlich. Diese werden diskutiert. Spin Valves bestehen aus Einzellagen unterschiedlicher Materialien (antiferro-, ferro- und paramagnetisch), meist Metalle, die eine Widerstandsänderung mit der Richtung des externen Magnetfeldes zeigen. Untersucht wurden Systeme, die auf NiO, FeMn und IrMn basieren. Die Temperaturabhängigkeit dieser Systeme zeigt Eigenschaften, die für die kommerzielle Nutzung wichtig sein können. Die mikroskopischen Ursachen werden diskutiert. Ein neu entwickeltes, leistungsfähiges Modell kann das sensorische Verhalten dieser Systeme sehr gut nachbilden und erlaubt so einen Einblick in die internen Vorgänge.
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Ayllon, Edgar Fernando Aliaga. "O transistor válvula de spin de AlGaAs/GaAs e outros semicondutores: dirigido a novos dispositivos spintrônicos." Universidade de São Paulo, 2013. http://www.teses.usp.br/teses/disponiveis/43/43134/tde-20102014-164755/.
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Neste trabalho, apresentamos estudos de magnetotransporte em um sistema quase tridimensional de elétrons produzido em amostras contendo poços quânticos parabólicos (PQW, Parabolic Quantum Well ) formados em heteroestruturas de AlGaAs crescidos sobre substratos de GaAs pela técnica de epitaxia por feixe molecular (MBE). Na primeira parte do nosso trabalho realizamos medidas de magnetoresistência, efeito Hall e efeito Shubnikov-de Haas em PQWs com larguras de 1000 Å a fim de investigar as propriedades eletronicas tais como a concentração e a mobilidade dos elétrons nas amostras. Através de cálculos autoconsistentes determinou-se os perfis de potencial, os níveis de energia e as concentrações de cada uma das sub-bandas ocupadas no poço. Uma análise através da transformada de Fourier também permitiu determinar as concentrações eletrônicas nas sub-bandas. Em uma segunda parte estudou-se a influência da aplicação de potenciais externos através de uma porta metálica com barreira em uma amostra contendo um PQW de largura 3000 Å na presença de campos magnéticos perpendicular e paralelo à superfície da amostra. Encontrou-se que para uma tensão de porta de Vg = 0, 55V forma-se uma barreira de potencial ainda sem ter depleção de cargas no poço. Apresenta-se a idealização do dispositivo transistor válvula de spin, a partir do fato que aplicando uma tensão de porta é possível deslocar espacialmente os elétrons e mudar a sua orientaçãp de spin.Results from magnetic transport studies made on quasi-three-dimensional electron systems are presented in this work. AlGaAs heterostructures grown on GaAs subtrates through molecular beam epitaxy (MBE) enable the existence of this type of systems by means of parabolic quantum wells (PQW) formation. This work was developed in two main parts. First, we studied magnetoresistence phenomena, such as Hall effect and Shubnikov-de Haas, on 1000 Å width PQWs. This permits to know the electronic concentration and mobility values of this type of samples, among other electrical properties. Then, self-consistent calculations gave an outline of the size and shape of the potentials, and gave the values for the energy levels and the electronic concentration on each occupied sub-band of the quantum well. Through Fourier transform analysis was also possible to obtain and confirm the electronic concentrations of the occupied sub-bands. In the second part of the work, we studied the effects of applying an external potential through a barrier gate to a 3000 Å width PQW sample in the presence of magnetic fields parallel and perpendicular to the sample surface. For a V g = 0, 55 V gate voltage, it was found that a potential barrier was formed even without charge depletion in the well. An idealization for the spin valve transistor device, based on the fact that applying a gate potential spatially dislocates the electrons and changes their spin orientation, is presented.
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Durairaj, Vinobalan. "A SYSTEMATIC STUDY OF THERMODYNAMIC AND TRANSPORT PROPERTIES OF LAYERED Can+1(Ru1-xCrx)nO3n+1." UKnowledge, 2008. http://uknowledge.uky.edu/gradschool_diss/661.
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Orbital degrees of freedom play vital role in prompting novel phenomena in ruthenium based Ruddlesden-Popper compounds through coupling of orbits to spin and lattice. Physical properties are then particularly susceptible to small perturbations by external magnetic fields and/or slight structural changes. Current study pertains to the impact when a more-extended 4d Ruthenium ion is replaced by a less-extended 3d Chromium ion.
Perovskite CaRuO3 (n=∞) is characterized by borderline magnetism and non- Fermi liquid behavior – common occurrences in quantum critical compounds. Remarkably, Cr substitution as low as x=0.05 abruptly drives CaRu1−xCrxO3 from a paramagnetic state to an itinerant ferromagnetic state (MS~0.4μB/f.u.), where TC=123K for x=0.22. The Cr-driven magnetism is highly anisotropic suggesting an important role of spin-orbit coupling. Unlike other chemical substitutions in the compound, Cr does not induce any Metal-Insulator transition that is expected to accompany the magnetic transition. The results indicate a coupling of Ru-4d and Cr-3d electrons that is unexpectedly favorable for itinerant ferromagnetism, which often exists delicately in the ruthenates.
Bilayered Ca3Ru2O7 (n=2), an abode of huge anisotropy, exhibits a wide range of physical properties – Colossal Magnetoresistance occurring only when the spin polarized state is avoided, Antiferromagnetic-Metallic (AFM-M) state, Quantum Oscillations (periodic in 1/B and in B) that are highly angular dependent, to mention a few. Experimental results obtained so far provide a coherent picture illustrating that orbital order and its coupling to lattice and spin degrees of freedom drive the exotic electronic and magnetic properties in this Mott-like system. Transport and thermodynamic studies on Ca3(Ru1-xCrx)2O7 (0 ≤ x ≤ 0.20) reveal that AFM-M region is broadened with x that ultimately reaches 70K for x=0.20 (~8K for x=0). In this region, electron transport is enhanced and inhibited when B is applied along crystal’s respective axes, confirming an intrinsic half-metallic behavior. Moreover, the difference in coercivities of Ru and Cr magnetic ions pave way for the first-ever observation of a strong spin-valve effect in bulk material, a quantum phenomenon so far realized only in multilayer thin films or heterostructures. This discovery opens new avenues to understand the underlying physics of spin-valves and fully realize its potential in practical devices.
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Шабельник, Юрій Михайлович, Юрий Михайлович Шабельник, Yurii Mykhailovych Shabelnyk, Ірина Володимирівна Чешко, Ирина Владимировна Чешко, and Iryna Volodymyrivna Cheshko. "Фізичні процеси у плівковому спін-клапані." Thesis, Вид-во СумДУ, 2009. http://essuir.sumdu.edu.ua/handle/123456789/3961.
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