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1
Serral, Gracià Rubèn. "Spin bosons and spin glasses". [S.l. : Amsterdam : s.n.] ; Universiteit van Amsterdam [Host], 2004. http://dare.uva.nl/document/76076.
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Perumal, Sathya Sai Ramakrishna Raj. "Spin-Orbit and Spin-Spin Coupling in the Triplet State". Doctoral thesis, KTH, Teoretisk kemi och biologi, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-95761.
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The underlying theory of “Spin” of an electron and its associated inter-actions causing internal fields and spectral shift to bulk-magnetism iswell established now. Our understanding of spin properties is significant andmore useful than ever before. In recent years there seems to be an enormousinterest towards application oriented materials that harness those spin prop-erties. Theoretical simulations remain in a position to “assist or pilot” theexperimental discovery of new materials.In this work, we have outlined available methodologies for spin coupling inmulti-reference and DFT techniques. We have benchmarked multi-referencespin-Hamiltonian computation in isoelectronic diradicals - Trimethylenemethane(TMM) and Oxyallyl. Also with DFT, parameters are predicted with anewly discovered TMM-like stable diradicals, reported to have large positiveexchange interactions. Excellent agreement were obtained and our findingsemphasize that the dipole-dipole interactions alone can predict the splittingof triplet states and that DFT spin procedures hold well in organic species.We have extended our spin-studies to a highly application oriented ma-terial - nanographene. Using our novel spin-parameter arguments we haveexplained the magnetism of graphene. Our studies highlight a few signifi-cant aspects - first there seems to be a size dependency with respect to thespin-Hamiltonian; second, there is a negligible contribution of spin-orbit cou-pling in these systems; third, we give a theoretical account of spin restrictedand unrestricted schemes for the DFT method and their consequences forthe spin and spatial symmetry of the molecules; and, finally, we highlightthe importance of impurities and defects for magnetism in graphene. Wepredict triplet-singlet transitions through linear response TDDFT for thetris(8-hydroxyquinoline) aluminium complex, an organic molecule shown tohave spintronics applications in recent experiments. Our spin studies werein line with those observations and could help to understand the role of thespin-coupling phenomena.QC 20120531
3
Perumal, Sathya S. R. R. "Spin-Spin and Spin-Orbit couplingstudies of small species andmagnetic system". Licentiate thesis, KTH, Theoretical Chemistry, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-12353.
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The spin of an electron often misleadingly interpreted as the classical rotationof a particle. The quantum spin distinguishes itself from classicalrotation by possessing quantized states and can be detected by its magneticmoment. The properties of spin and its collective behavior with otherfundamental properties are fascinating in basic sciences. In many aspectsit offers scope for designing new materials by manipulating the ensemblesof spin. In recent years attention towards high density storage devices hasdriven the attention to the fundamental level were quantum physics rules.To understand better design of molecule based storage materials, studies onspin degrees of freedom and their coupling properties can not be neglected.
To account for many body effect of two or more electrons consistent withrelativity, an approximation like the Breit Hamiltonian(BH) is used in modernquantum chemical calculations, which is successful in explaining the splitin the spectra and corresponding properties associated with it. Often differenttactics are involved for a specific level of computations. For example themulti-configurational practice is different from the functional based calculations,and it depends on the size of the system to choose between resourcesand accuracy. As the coupling terms offers extra burden of calculating theintegrals it is literally challenging.
One can readily employ approximations as it suits best for the applicationoriented device computations. The possible methods available in the literatureare presented in chapter 2. The theoretical implementations of couplingfor the multi-reference and density functional method are discussed in detail.The multi-reference method precedes the density functional methodin terms of accuracy and generalizations, however it is inefficient in dealingvery large systems involving many transition elements, which is vital formolecule based magnets as they often possess open shell manifolds. On theother hand existing density functional method exercise perturbations techniqueswhich is extremely specialized for a specific system - highly coupledspins.
The importance of spin-spin coupling(SSC) in organic radical-Oxyallyl(OXA)was systematically studied with different basis sets and compared with asimilar isoelectronic radical(TMM). The method of spin-spin coupling implementationsare also emphasized. Similar coupling studies were carriedivout for the species HCP and NCN along with spin-orbit coupling(SOC).The splitting of the triplet states are in good agreement with experiments
4
Mooser, Sebastian Thomas. "Spin injection, spin transport and spin-charge conversion in organic semiconductors". Thesis, University of Cambridge, 2013. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.608211.
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Batley, Joseph Thomas. "Spin transport in lateral spin valves". Thesis, University of Leeds, 2015. http://etheses.whiterose.ac.uk/12176/.
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This thesis outlines the construction of an ultra-high-vacuum angle-deposition system, developed specifically for the fabrication of lateral spin valves (LSVs). The thesis then proceeds to answer two important questions: what causes the loss of spin accumulation at low temperatures seen in LSVs? and how do spin currents interact in multi-terminal circuits? Through a double-dose electron beam lithography and angle-deposition technique, Cu/Py LSVs are fabricated and shown to have transparent contacts. By means of a DC injection method, the nonlocal voltage is measured as a function of injection current, magnetic field and temperature, enabling contributions from heat and spin currents to be isolated. The spin diffusion length is obtained from LSVs fabricated with Cu containing magnetic impurities $ < $1 ppm and $\sim$4 ppm. Temperature dependent charge and spin transport measurements provide evidence linking the presence of the Kondo effect in Cu to the suppression of the spin diffusion length below 30 K. The spin-flip probability for magnetic impurities is found to be 34\%, orders of magnitude larger than other scattering mechanisms. This is extended to explain similar observations in the spin accumulation. These measurements establish the dominant role of Kondo scattering in spin-relaxation, even in low concentrations of order 1 ppm. Finally, a new multi-terminal LSV (MTLSV) is fabricated and the interaction between two spin currents is investigated. Fan-out and fan-in measurements are performed, demonstrating that spin currents separate and combine at junctions in a circuit with magnitudes dictated by the spin resistance of the conduction channels. It is also shown that two spin currents of opposite polarity will cancel out. Whether Kirchhoff's law holds for spin currents is discussed and this chapter helps lay the ground work for spin current based circuits and computation.
6
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.
7
Perumal, Sathya S. R. R. "Spin-Spin and Spin-Orbit coupling studies of small species and magnetic system". Licentiate thesis, KTH, Teoretisk kemi (stängd 20110512), 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-12353.
Pełny tekst źródłaStreszczenie:
The spin of an electron often misleadingly interpreted as the classical rotationof a particle. The quantum spin distinguishes itself from classicalrotation by possessing quantized states and can be detected by its magneticmoment. The properties of spin and its collective behavior with otherfundamental properties are fascinating in basic sciences. In many aspectsit offers scope for designing new materials by manipulating the ensemblesof spin. In recent years attention towards high density storage devices hasdriven the attention to the fundamental level were quantum physics rules.To understand better design of molecule based storage materials, studies onspin degrees of freedom and their coupling properties can not be neglected. To account for many body effect of two or more electrons consistent withrelativity, an approximation like the Breit Hamiltonian(BH) is used in modernquantum chemical calculations, which is successful in explaining the splitin the spectra and corresponding properties associated with it. Often differenttactics are involved for a specific level of computations. For example themulti-configurational practice is different from the functional based calculations,and it depends on the size of the system to choose between resourcesand accuracy. As the coupling terms offers extra burden of calculating theintegrals it is literally challenging. One can readily employ approximations as it suits best for the applicationoriented device computations. The possible methods available in the literatureare presented in chapter 2. The theoretical implementations of couplingfor the multi-reference and density functional method are discussed in detail.The multi-reference method precedes the density functional methodin terms of accuracy and generalizations, however it is inefficient in dealingvery large systems involving many transition elements, which is vital formolecule based magnets as they often possess open shell manifolds. On theother hand existing density functional method exercise perturbations techniqueswhich is extremely specialized for a specific system - highly coupledspins. The importance of spin-spin coupling(SSC) in organic radical-Oxyallyl(OXA)was systematically studied with different basis sets and compared with asimilar isoelectronic radical(TMM). The method of spin-spin coupling implementationsare also emphasized. Similar coupling studies were carriedivout for the species HCP and NCN along with spin-orbit coupling(SOC).The splitting of the triplet states are in good agreement with experimentsQC 20110210
8
Sodickson, Daniel Kevin. "Spin-spin couplings in two limits : experimental, theoretical, and computational studies of dipole-coupled nuclear spins in solids". Thesis, Massachusetts Institute of Technology, 1994. http://hdl.handle.net/1721.1/32601.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Whitaker College of Health Sciences and Technology, 1994.Includes bibliographical references (leaves 193-200).
by Daniel Kevin Sodickson.
Ph.D.
9
Rodríguez-Arias, Inés. "Collective behaviours in interacting spin systems". Thesis, Université Paris-Saclay (ComUE), 2018. http://www.theses.fr/2018SACLS332/document.
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La polarisation dynamique nucléaire (DNP pour son acronyme en anglais) est une des techniques les plus prometteuses d’amélioration de l’IRM. En pratique, on voudrait utiliser la résonance magnétique nucléaire (RMN) sur d’autres noyaux que ceux d’hydrogène, par exemple le carbone. Pour pouvoir détecter le carbone, sa polarisation de spin doit être augmentée. À l’équilibre thermodynamique — à basse température et forts champs magnétiques — les électrons sont bien plus polarisés que tout système de spin nucléaires, ce qui est dû à leur plus petite masse. La technique de DNP consiste à amener le système hors d’équilibre avec une irradiation par des microondes. Cette irradiation va induire le transfer de polarisation des spins électroniques vers les spins nucléaires. Pendant ma thèse, j’ai étudié, par des méthodes analytiques et numériques, la compétition entre les interactions dipolaires présentes entre les spins électroniques (qui peuvent se régler expérimentalement) et le désordre naturellement présent dans l’échantillon. Pour ce faire, j’ai proposé deux modèles : une chaîne de spins d’Heisenberg et un système de fermions libres dans le modèle d’Anderson. J’ai trouvé l’existence de deux régimes : Pour le régime de fortes interactions, l’état stationnaire a des traces d’un comportement thermodynamique, étant caractérisé par une température effective. Dans le régime de faibles interactions, il n’est pas possible de définir une température effective, et l'on peut le relier à une phase de many-body localization (ou localisation d'Anderson). Mes recherches portent sur l’étude des propriétés deux phases en relation avec la performance de la DNP et j’ai trouvé qu’elle est optimale à la transition entre les deux phases. Ce résultat intéressant a récemment été confirmé par des expériences menées à l’École Normale Supérieure de ParisDynamic nuclear polarization (DNP) is one of the most promising techniques towards a new generation of Magnetic Resonance Imaging (MRI). The idea is to use the Nuclear Magnetic Resonance (NMR) in other nuclei rather than the traditional hydrogen, such as carbon. For the carbon signal to be detected, one needs to enhance its spin polarization. In thermal equilibrium — at low temperature and high magnetic field — electron spins are far more polarized than any system of nuclear spins, which is due to their smaller mass. With the DNP technique we bring the system out-of-equilibrium irradiating it with microwaves. This triggers polarization transfer from the electron spins to the nuclear ones. During my Ph.D, I have studied both analytically and numerically the competition between the dipolar interactions among electron spins (which can be tuned experimentally) and the disorder naturally present in the sample. I proposed two models to study DNP: a Heisenberg spin-chain and a system free-fermions in the Anderson model. Two different regimes were found : For strongly interacting electron spins, the out-of-equilibrium steady state displays an effective thermodynamic behavior characterised by a very low spin temperature. In the weakly interacting regime, it is not possible to define a spin temperature, and it is associated to a many-body localized phase (or an Anderson-localized phase). My research was focused on the properties of the two phases with respect to the performance of DNP, and I found it to be optimal at the transition between the two. This is a very important result that has been verified by recent experiments carried in École Normale Supérieure de Paris
10
Konovalenko, Alexander. "Spin transfer torques and spin dynamics in point contacts and spin-flop tunnel junctions". Doctoral thesis, Stockholm : Department of Physics, Royal Institute of Technology, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-4805.
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Evers, Martin [Verfasser]. "Two antagonizing aspects of spin transport : spin-wave localization and spin superfluidity / Martin Evers". Konstanz : KOPS Universität Konstanz, 2019. http://d-nb.info/1230323309/34.
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Notbohm, Susanne. "Spin dynamics of quantum spin-ladders and chains". Thesis, St Andrews, 2007. http://hdl.handle.net/10023/403.
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Woo, Seonghoon. "Manipulation of spin textures by unconventional spin torques". Thesis, Massachusetts Institute of Technology, 2015. http://hdl.handle.net/1721.1/98577.
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Thesis: Ph. D., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2015.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references.
Dynamically controlling magnetism at the nanoscale is the foundation for realizing high-performance, low-power solid-state spintronic devices. The manipulation of nonuniform magnetization textures such as domain walls and skyrmions provide both a means to control magnetism in devices, and to gain new fundamental insights into spin-charge and spin-orbital interactions in magnetic materials. In this thesis, we examine novel mechanisms for the evolution and control of nonuniform magnetization textures. We first show that magnonic spin currents due to spin wave propagation can couple to and drive magnetic domain walls in nanowires mainly with experiments, supported by micromagnetic simulations. This work highlights a route towards integrating domain walls and spin waves for enhanced functionality in spintronics applications. We then focus on pure spin currents generated at the interface between a metallic ferromagnet and a heavy metal due to the spin Hall effect induced by strong spin orbit interaction. We demonstrate that the spin Hall effect can efficiently amplify or attenuate spin waves in an adjacent ferromagnet, and the efficiency of spin current generation can also be dramatically enhanced by optimizing the ferromagnet/heavy-metal interfaces. Moreover, we describe the microscopic mechanisms by which the spin Hall effect leads to magnetization switching, in the presence of chiral exchange interactions due to interfacial Dzyaloshinskii-Moriya interaction. This work shows the essential role that Dzyaloshinskii-Moriya interaction plays in magnetization switching. Finally, by harnessing this effect in carefully engineered materials, we show for the first time that the Dzyaloshinskii-Moriya interaction can stabilize topologically-protected skyrmions, whose statics and dynamics we have imaged for the first time in transition-metal ferromagnets at room temperature without any static external bias field. This finding provides not only experimental evidence of recent predictions but also opens the door to room-temperature skyrmion spintronics in robust thin-film heterostructures
by Seonghoon Woo.
Ph. D.
14
Qureshi, Tariq. "Spin chemistry". Thesis, University of Oxford, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.365292.
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Jackson, Stephen Siegel Robert. "Spin Cycle". [Greenville, N.C.] : East Carolina University, 2009. http://hdl.handle.net/10342/2236.
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Kalappattil, Vijaysankar. "Spin Seebeck effect and related phenomena in functional magnetic oxides". Scholar Commons, 2018. https://scholarcommons.usf.edu/etd/7632.
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In recent years, Spin Seebeck effect (SSE) emerges as one of the efficient and easiest ways to generate pure spin current for spintronics devices. In this dissertation, we have systematically studied the SSE and related phenomena like spin Hall magneto-resistance (SMR), anomalous Nernst effect (ANE) in functional magnetic oxides for both fundamental understanding of their origins and practical ways to apply into technological devices. The research has been performed on three different systems of topical interest: (i) Y3Fe5O12 (YIG)/Pt and YIG/C60/Pt, (ii) CoFe2O4 (CFO)/Pt and CFO/C60/Pt, and (iii) Nd0.6Sr0.4MnO3 (NSMO).
In case of the YIG/Pt structure, we have achieved a new consensus regarding the temperature dependence of the longitudinal SSE (LSSE). For the first time, we have demonstrated the temperature dependence of LSSE in association with the magnetocrystalline anisotropy (HK) and surface perpendicular magnetic anisotropy field (HKS) of YIG in the same YIG/Pt system. We show that on lowering temperature, the sharp drop in LSSE signal (VLSSE) and the sudden increases in HK and HKS at ~175 K are associated with the spin reorientation due to single ion anisotropy of Fe2+ ions. The VLSSE peak at ~75 K is attributed to the HKS and MS (saturation magnetization) whose peaks also occur at the same temperature. The effects of surface and bulk magnetic anisotropies are corroborated with those of thermally excited magnon number and magnon propagation length to satisfactorily explain the temperature dependence of LSSE in the Pt/YIG system.
As a new way to reduce conductivity mismatch, promote spin transport, and tune the spin mixing conductance (G) at the YIG/Pt interface, we have deposited an organic semiconductor (OSC), C60, between ferrimagnetic material (FM) and Pt. Transverse susceptibility study on YIG/C60/Pt has shown that the deposition of C60 has reduced HKS at the surface of YIG significantly, due to the hybridization between the dz2 orbital in Fe and C atoms, leading to the overall increase in spin moments and G and consequently the LSSE. Upon lowering temperature from 300 K, we have observed an exponential increase in LSSE at low temperature (a ~800% increment at 150 K) in this system, which is attributed to the exponential increase in the spin diffusion length of C60 at low temperature. On the other hand, similar experiments on CoFe2O4 (CFO)/C60/Pt show a reduction in the LSSE signal at room temperature, due to the hybridization between the dz2 orbital in Co and C atoms that results in the increased magnetic anisotropy. Upon decreasing the temperature below 150 K, we have interestingly observed that LSSE signal from CFO/C60/Pt exceeds that of CFO/Pt and increases remarkably with temperature. This finding confirms the important role played by the spin diffusion length of C60 in enhancing the LSSE.
A systematic study of SMR, SSE, and HKS on the YIG/Pt system using the same YIG single crystal has revealed a low-temperature peak at the same temperature (~75 K) for all the phenomena. Given the distinct origins of the SSE and SMR, our observation points to the difference in spin states between the bulk and surface of YIG as the main reason for such a low-temperature peak, and suggests that the ‘magnon phonon drag’ theory developed to explain the temperature-dependent SSE behavior should be adjusted to include this important effect.
SSE and ANE studies on NSMO films have revealed the dominance of ANE over SSE in this class of perovskite-structured materials. The substrate-dependent study of the films shows that compressive strain developed due to the large lattice mismatch from LAO gives rise to the enhanced ANE signal. On the same substrate, ANE signal strength increases as the thickness increases. A sign change in ANE has been observed at a particular temperature, which explains that the Anomalous Hall effect (AHE) and ANE in these systems arise due to intrinsic scattering mechanisms.
Overall, we have performed the SSE and related studies on the three important classes of functional magnetic oxide materials. We demonstrate the important role of magnetic anisotropy in manipulating the SSE in these systems. With this knowledge, we have been able to design the novel YIG/C60/Pt and CFO/C60/Pt heterostructures that exhibit the giant SSEs. The organic semiconductor C60 has been explored for the first time as a means of controlling pure spin current in inorganic magnetic oxide/metal heterostructures, paying the way for future spintronic materials and devices.
17
Belkhir, Mohamed Akli. "Structure de bandes à spin polarisé par la méthode des fonctions localisées : application à MnO et NiO". Metz, 1988. http://docnum.univ-lorraine.fr/public/UPV-M/Theses/1988/Belkhir.Mohamed_Akli.SMZ8812.pdf.
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Un calcul de bandes spin polarisé basé sur une méthode de fonctions localisées a été effectué sur MnO et NiO dans leur configuration antiferromagnétique. Lorsque l'échange intra-atomique est assez fort comme dans MnO, il apparaît une bande interdite entre les bandes d majoritaires et minoritaires qui suffit à expliquer les propriétés isolantes de cet oxyde. De plus nous avons montré qu'il existe une séparation systématique à l'intérieur de chaque bande majoritaire et minoritaire due essentiellement à la structure D5(3d). La présence d'une telle bande minoritaire interdite dans le NiO est responsable de ses propriétés semiconductrices. Ainsi l'hybridation p-d qui empêchait la formation d'une bande interdite dans la structure NaCl, conduit à une issue favorable lorsqu'on prend en compte l'arrangement magnétiqueA spin polarized band calculation based on a localized function method has been performed on MnO and NiO in their antiferromagnetic configuration. When the intra-atomic exchange is strong enough like in MnO, a gap appears between the majority and minority d bands which suffices to explain the insulating behaviour of that oxide. Further it has been show that a gap is systematically opened in each majority and minority band due in NiO is responsible for its semiconducting properties. Thus the p-d hybridization which prevents the gap formation in the NaCl structure leads to a satisfactory issue only when the magnetic ordering is taken into account
18
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.
19
Graf, Tobias. "Spin-spin interactions of localized electronic states in semiconductors". [S.l. : s.n.], 2003. http://deposit.ddb.de/cgi-bin/dokserv?idn=970274157.
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Li, Jian. "Spin transport in mesoscopic systems with spin-orbit coupling". Click to view the E-thesis via HKUTO, 2008. http://sunzi.lib.hku.hk/hkuto/record/B39794015.
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Kamenskyi, Dmytro. "Electron spin resonance studies of frustrated quantum spin systems". Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2013. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-108777.
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Since the last few decades frustrated spin systems have attracted much interest. These studies are motivated by the rich variety of their unusual magnetic properties and potential applications. In this thesis, excitation spectra of the weakly coupled dimer system Ba3Cr2O8, the spin-1/2 chain material with distorted diamond structure Cu3(CO3)2(OH)2 (natural mineral azurite), and the quasi-twodimensional antiferromagnet with triangle spin structure Cs2CuBr4 have been studied by means of high-field electron spin resonance. Two pairs of gapped modes corresponding to transitions from a spin-singlet ground state to the first excited triplet state with zero-field energy gaps, of 19.1 and 27 K were observed in Ba3Cr2O8.
The observation of ground-state excitations clearly indicates the presence of a non-secular term allowing these transitions. Our findings are of crucial importance for the interpretation of the field-induced transitions in this material (with critical fields Hc1 = 12.5 T and Hc2 = 23.6 T) in terms of the magnon Bose-Einstein condensation. The natural mineral azurite, Cu3(CO3)2(OH)2, has been studied in magnetic fields up to 50 T, revealing several modes not observed previously. Based on the obtained data, all three critical fields were identified.
A substantial zero-field energy gap, Δ = 9.6 K, has been observed in Cs2CuBr4 above the ordering temperature. It is argued that contrary to the case for the isostructural Cs2CuCl4, the size of the gap can not be explained solely by the uniform Dzyaloshinskii-Moriya interaction, but it is rather the result of the geometrical frustration stabilizing the spin-disordered state in Cs2CuBr4 in the close vicinity of the quantum phase transition between a spiral magnetically ordered state and a 2D quantum spin liquid.
22
Leontiadou, Marina A. "Spin dynamics and spin control in narrow gap semiconductors". Thesis, University of Surrey, 2012. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.580626.
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We report a spin dynamic investigation with the use of the optical polarisation pump-probe technique in bulk and quantum well narrow gap semiconductors (NGSs) of the Ill-V and IV-VI families. By taking advantage of their zinc-blende (Ill-Vs) and rock-salt (IV-VIs) crystal symmetries, their direct energy band-gap, small effective mass, high electron effective g-value, strong relativistic effects, and with the use of the Surrey Ultrafast Laser system and the Free Electron Laser system (FELIX) for interband excitation process we prove that they are attractive for high speed electronic and new proposed spintronic concepts. The electron spin relaxation times have been measured in InSb and InAs epilayers in Faraday and Voigt configurations. A strong and opposite field dependence of the spin lifetime has been observed. We report the existence of a new spin relaxation process, which was theoretically predicted but not observed before. We demonstrate that for these NGSs, and specifically for the Ill-Vs, the electron spin lifetime can be modified by more than one order of magnitude simply by changing the direction of a moderate, externally applied magnetic field. We used circular two-photon absorption (CTPA) and investigated the "allowed- forbidden" and "allowed-allowed" transitions in n-InSb, the theory of which has not been investigated experimentally until now. The detailed CTPA spectrum presented here shows that the sign of photo-excited spin polarisation can in principle be controlled by the excitation wavelength in the two-photon absorption processes. We report the analysis of optical measurement of the spin dynamics at elevated temperatures and in zero magnetic field, for degenerately n-doped InSb/lnAISb QWs, one asymmetric and one symmetric. For the asymmetric QW, by making use of directly determined experimental parameters, we have made a direct measurement of the zero field spin splitting without the influence of the large Zeeman effect. The extracted Rashba parameter is more than an order of magnitude larger than that measured earlier for GaAs QW s. Pump-pump photoconductivity experiments have been performed and we successfully measured the recombination time in InSb-based devices of different geometries, allowing new investigation methods of low dimensional structures and manipulation of samples of weak transmittance signals. We investigated the dependence of spin lifetime on controlled asymmetry in IV- VI Multi-QWs. We show for the first time experimentally that lead-cha1cogenide semiconductor heterostructures can exhibit long spin lifetimes by virtue of their centro-symmetric crystal structure, and a tuning of the lifetime of over one order of magnitude after appropriate structure control corresponding to a large zero field spin splitting. The results imply that this system can be the material' of choice for certain , semiconductor spintronic applications requiring control of spins. We report a significant temperature dependence of the transverse electron g*- factor in symmetric IV-VI Multi-QWs. A second oscillation frequency has been observed, suggesting a possible method for distinguishing the actual excited states and the activation of an electron-hole mechanism. Although temperature tuning of lead salt laser emission wavelengths has been the method of choice in these systems for many years, we demonstrate that temperature can also be used to modulate g*, and hence the spin lifetime in lead salt QW spintronic devices.
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Charnock, Gareth Trevor Patrick. "Computational spin dynamics and visualisation of large spin systems". Thesis, University of Oxford, 2012. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.601126.
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The thesis commences with a detailed review of the background theory of spin dynamics simulations. State space rest riction is introduced via a "top-down" approach. Common terms that make up the spin Hamiltonian are reviewed, and it is noted that the mathemat ical forms of these terms can be categorised in one of three ways. The review of the background theory complete, w::counts are given of the following four areas of research: 1. Formal conditions are established for the validity of state space restriction via spin order pruning, based on tracking the density matrix norm through spin order subspaces. The primary predictor for success is seen t o be the ratio of the largest eigenvalue to the relaxation rate. The lower this ratio; the fewer spin orders are required. 2. Software based around the Spin XML format , suitable for constructing and visualising large spin systems, is presented. Both a functional specification and a discussion of the internals are given. 3. A potential applicat ion of state space restriction, called "direct structure fitting" , (DSF) is explored. In DSF, a candidate chemical structure is optimised directly by minimising the difference between its predicted spectrum and an experimental spectrum. The following examples of successful fits are provided: cyanomethyl, propargyl, and tyrosyl radicals, in the liquid state, and, tyrosyl embedded in two ribonuclease reductase proteins in the powder state. 4. A new model of the pseudocontact shift, which assumes a delocalised electron, is presented. Mathematical subtleties are resolved that would otherwise lead to the failure of numerical evaluation if left untreated. Techniques to improve efficiency are discussed , and the resulting program runs comfortably on workstation-grade hardware on protein sized datasets. E. Coli DNA Polymerase III is investigated as an example, and evidence is presented that suggests that the new model would predict significant differences in structures if used in conjunction with molecular dynamics based structural refinement
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Li, Jian, i 李牮. "Spin transport in mesoscopic systems with spin-orbit coupling". Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2008. http://hub.hku.hk/bib/B39794015.
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Child, Abigail. "Spin diffusion and spin rotation in '3He-'4He solutions". Thesis, University of Nottingham, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.357967.
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Steinmüller, Stephan Jan. "Optical studies of electron spin transport and spin dynamics". Thesis, University of Cambridge, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.616269.
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Patrakov, Alexander. "Topologische Analysen von NMR-Spin-Spin-Kopplungspfaden über Realraumfunktionen". kostenfrei, 2008. http://www.opus-bayern.de/uni-wuerzburg/volltexte/2008/2850/.
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Göpfert, Alois. "Classical description of dynamical many-body systems with central forces, spin-orbit forces and spin-spin forces". Bordeaux 1, 1994. http://www.theses.fr/1994BOR10551.
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Cette these presente un nouveau modele et les techniques necessaires afin de decrire un systeme a n corps dependant en temps qui interagit par des forces centrales, des forces spin-orbite et des forces spin-spin. Il fournit un cadre pour l'analyse de l'echange d'energie et de moment angulaire entre le sous-systeme spin-spin et le mouvement orbital. Les interactions internes entre les charges et les moments magnetiques des particules sont bien decrites par un couplage electromagnetique. En effet, compare a des calculs conventionnels en dynamique moleculaire des clusters de type van der waals, qui n'ont pas de degres de liberte avec un couplage non trivial. Le modele a ete utilise avec succes pour des simulations dynamiques de differents systemes de clusters saturant par des forces de type van der waals
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Recher, Patrik. "Correlated spin transport in nanostructures: entanglement creation and spin filtering". Basel : Universität Basel, 2003. http://www.unibas.ch/diss/2003/DissB_6688.htm.
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Bühler, Alexander. "High temperature series expansions for spin and spin phonon systems". [S.l. : s.n.], 2003. http://deposit.ddb.de/cgi-bin/dokserv?idn=969818203.
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Arango, Yulieth Cristina. "Electron spin resonance (ESR) spectroscopy of low-dimensional spin systems". Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2011. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-69811.
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The research in low-dimensional (low-D) quantum spin systems has become an arduous challenge for the condensed matter physics community during the last years. In systems with low dimensional magnetic interactions the exchange coupling is restricted to dimensions lower than the full three-D exhibited by the bulk real material. The remarkable interest in this field is fueled by a continuous stream of striking discoveries like superconductivity, quantum liquid and spin gap states, chiral phases, etc, derived from the strong effect of quantum fluctuations on the macroscopic properties of the system and the competition between electronic and magnetic degrees of freedom. The main goal of the current studies is to reach a broad understanding of the mechanisms that participate in the formation of those novel ground states as well as the characteristic dependence with respect to relevant physical parameters. In this thesis we present the results of an Electron Spin Resonance (ESR)-based study on different quasi-1D spin systems, exemplifying the realization of 1D-magnetic spin-chains typically containing transition metal oxides such as Cu2+ or V4+.
The local sensitivity of the ESR technique has been considered useful in exploring magnetic excitation energies, dominant mechanisms of exchange interactions, spin fluctuations and the dimensionality of the electron spin system, among others. Aside from ESR other experimental results, e.g., magnetization and nuclear magnetic resonance besides some theoretical approaches were especially helpful in achieving a proper understanding and modeling of those low-D spin systems.
This thesis is organized into two parts: The first three chapters are devoted to the basic knowledge of the subject. The first chapter is about magnetic exchange interactions between spin moments and the effect of the crystal field potential and the external magnetic field. The second chapter is a short introduction on exchange interactions in a 1D-spin chain, and the third chapter is devoted to ESR basics and the elucidation of dynamic magnetic properties from the absorption spectrum parameters.
The second part deals with the experimental results. In the fourth chapter we start with the magnetization results from the zero-dimensional endohedral fullerene Dy3N@C80. This system is seemingly ESR “silent” at the frequency of X-band experiments. The fifth chapter shows an unexpected temperature dependence of the anisotropy in the homometallic ferrimagnet Na2Cu5Si4O14 containing alternating dimer-trimer units in the zig-zag Cu-O chains. In the sixth chapter different magnetic species in the layer structure of vanadium oxide nanotubes (VOx-NT) have been identified, confirming earlier magnetization measurements. Moreover the superparamagnetic-like nature of the Li-doped VOx-NT samples was found to justify its ferromagnetic character at particular Li concentration on the room temperature scale. In the seventh chapter the Li2ZrCuO4 system is presented as a unique model to study the influence of additional interactions on frustrated magnetism. The eighth chapter highlights the magnetic properties of the pyrocompound Cu2As2O7. The results suggest significant spin fluctuations below TN.
The thesis closes with the summary and the list of references.
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Ozerov, Mykhaylo. "High-field electron spin resonance in low-dimensional spin systems". Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2011. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-69892.
Pełny tekst źródłaStreszczenie:
Due to recent progress in theory and the growing number of physical realizations, low-dimensional quantum magnets continue to receive a considerable amount of attention. They serve as model systems for investigating numerous physical phenomena in spin systems with cooperative ground states, including the field-induced evolution of the ground-state properties and the corresponding rearrangement of their low-energy excitation spectra. This work is devoted to systematic studies of recently synthesized low-dimensional quantum spin systems by means of multi-frequency high-field electron spin resonance (ESR) investigations. In the spin- 1/2 chain compound (C6H9N2)CuCl3 [known as (6MAP)CuCl3] the striking incompatibility with a simple uniform S = 1/2 Heisenberg chain model employed previously is revealed. The observed ESR mode is explained in terms of a recently developed theory, revealing the important role of the alternation and next-nearest-neighbor interactions in this compound. The excitations spectrum in copper pyrimidine dinitrate [PM·Cu(NO3)2(H2O)2]n, an S = 1/2 antiferromagnetic chain material with alternating g-tensor and Dzyaloshinskii-Moriya interaction, is probed in magnetic fields up to 63 T. To study the high field behavior of the field-induced energy gap in this material, a multi-frequency pulsed-field ESR spectrometer is built. Pronounced changes in the frequency-field dependence of the magnetic excitations are observed in the vicinity of the saturation field, B ∼ Bs = 48.5 T. ESR results clearly indicate a transition from the soliton-breather to a spin-polarized state with magnons as elementary excitations. Experimental data are compared with results of density matrix renormalization group calculations; excellent agreement is found. ESR studies of the spin-ladder material (C5H12N)2CuBr4 (known as BPCB) completes the determination of the full spin Hamiltonian of this compound. ESR results provide a direct evidence for a pronounced anisotropy in this compound, that is in contrast to fully isotropic spin-ladder model employed previously for BPCB. Our observations can be of particular importance for describing the rich temperature-field phase diagram of this material. The frequency-field diagram of magnetic excitations in the quasi-two dimensional S = 1/2 compound [Cu(C4H4N2)2(HF2)]PF6 in the AFM-ordered state is studied. The AFM gap is observed directly. Using high-field magnetization and ESR results, parameters of the effective spin-Hamiltonian (exchange interaction, anisotropy and g-factor) are obtained and compared with those estimated from thermodynamic properties of this compound.
33
Chang, Ming-Shien. "Coherent Spin Dynamics of a Spin-1 Bose-Einstein Condensate". Diss., Georgia Institute of Technology, 2006. http://hdl.handle.net/1853/10547.
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Bose-Einstein condensation (BEC) is a phenomenon in which identical bosons occupy the same quantum state below a certain critical temperature. A hallmark of BEC is the coherence between particles every particle shares the same quantum wavefunction and phase. This coherence has been demonstrated for the external (motional) degrees of freedom of the atomic condensates by interfering two condensates. In this thesis, the coherence is shown to extend to the internal spin degrees of freedom of a spin-1 Bose gas evidenced by the observed coherent and reversible spin-changing collisions. The observed coherent dynamics are analogous to Josephson oscillations in weakly connected superconductors and represent a type of matter-wave four-wave mixing. Control of the coherent evolution of the system using magnetic fields is also demonstrated. The studies on spinor condensates begin by creating spinor condensates directly using all-optical approaches that were first developed in our laboratory. All-optical formation of Bose-Einstein condensates (BEC) in 1D optical lattice and single focus trap geometries are developed and presented. These techniques offer considerable flexibility and speed compared to magnetic trap approaches, and the trapping potential can be essentially spin-independent and are ideally suited for studying spinor condensates. Using condensates with well-defined initial non-equilibrium spin configuration, spin mixing of F = 1 and F = 2 spinor condensates of rubidium-87 atoms confined in an optical trap is observed. The equilibrium spin configuration in the F = 1 manifold confirms that 87Rb is ferromagnetic. The coherent spinor dynamics are demonstrated by initiating spin mixing deterministically with a non-stationary spin population configuration. Finally, the interplay between the coherent spin mixing and spatial dynamics in spin-1 condensates with ferromagnetic interactions is investigated.
34
Mohseni, Armaki Seyed Majid. "Spin valves and spin-torque oscillators with perpendicualr magnetic anisotropy". Doctoral thesis, KTH, Materialfysik, MF, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-105223.
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Researches in spintronics, especially those remarkably classified in the current induced spin-transfer torque (STT) framework, circumvent challenges with different materials and geometries. Perpendicular magnetic anisotropy (PMA) materials are showing capability of holding promise to be employed in STT based spintronics elements, e.g. spin-torque oscillators (STOs), STT-magnetoresistive random access memories (STT-MRAMs) and current induced domain wall motion elements. This dissertation presents experimental investigations into developing sputter deposited Co/Ni multilayers (MLs) with PMA and employs these materials in nano-contact STOs (NC-STOs) based on giant magnetoresistance (GMR) effect and in pseudo-spin-valve (PSV) structures. The magnetostatic stray field coupling plays an important role in perpendicular PSVs. The temperature dependent coupling mechanism recommends that this coupling can be tailored, by i) the saturation magnetization and coercivity of the individual layers, ii) the coercivity difference in layers, and iii) the GMR spacer thickness, to get a well decoupled and distinguishable switching response. Moreover, this thesis focused on the implementation and detailed characterization of NC-STOs with strong PMA Co/Ni ML free layers and in-plane Co reference layers as orthogonal (Ortho) magnetic geometry in so-called Ortho-NC-STOs. The primary target of reaching record high STO frequencies, 12 GHz, at close to zero field, 0.02 Tesla, was achieved. However, in large external fields, >0.4 Tesla, an entirely new magnetodynamic object, a “magnetic droplet”, theoretically predicted in 1977, was discovered experimentally. Detailed experiments, combined with micromagnetic simulations, demonstrate the formation of a magnetic droplet with a partially reversed magnetization direction underneath the NC, and a zone of large amplitude precession in a region bounding the reversed magnetization. The magnetic droplet exhibits a very rich dynamics, including i) auto-modulation as a combine of droplet frequency with a slow time evolution (few GHz) of un-centering the droplet mode under the NC, ii) droplet breathing as reversible deformation of droplet mode with ½ droplet frequency. All observation of droplet opens a new mechanism of excitation for future fundamental studies as well as experiments especially for domain wall electronics and nano-scopic magnetism.QC 20121119
35
Rhensius, Jan [Verfasser]. "Spin Dynamics and Spin Configuration in Nanopatterned Elements / Jan Rhensius". Konstanz : Bibliothek der Universität Konstanz, 2011. http://d-nb.info/1017360499/34.
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Frougier, Julien. "Toward Spin-LED and Spin-VECSEL operations at magnetic remanence". Thesis, Paris 11, 2014. http://www.theses.fr/2014PA112175/document.
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Cette thèse de doctorat propose d'explorer un nouveau paradigme de propagation de l'information de spin sur de très longues distances après encodage sur la polarisation de lumière cohérente. L'objectif principal de ce manuscrit est de fournir une étude détaillée de l'injection de spin dans des composants optoélectroniques III-V à géométrie verticale. Pour atteindre cet objectif, nous nous concentrons sur l'étude de l'injection optique et électrique de spin dans des structures « Light Emitting Diodes » (LEDs) et des structures « Vertical External Cavity Surface Emitting Lasers » (VECSELs) à base de semiconducteurs III-V. Nos investigations et résultats sont présentés suivant trois axes majeurs.La première partie regroupe un état de l'art sur l'injection de spin dans les composants optoélectroniques III-V et se concentre sur les phénomènes physiques engagés dans la conversion d'une accumulation de spin en information de polarisation lumineuse. Une discussion sur l'injection et le transport de spin dans des structures semi-conductrices est suivie par une analyse orientée-composant sur l'injection de spin dans les LEDs et les VCSELs.La deuxième axe s'articule autour de notre travail expérimental sur le développement et l'optimisation sur LEDs III-V d'un injecteur de spin MgO/CoFeB/Ta ultra-fin présentant une aimantation perpendiculaire à la rémanence magnétique. Nous nous focalisons en premier lieu sur l'optimisation de la barrière tunnel MgO pour maximiser l'injection de porteurs polarisés en spin et détaillons par la suite le développement et la caractérisation d’un injecteur de spin possédant une aimantation perpendiculaire à la rémanence magnétique.La troisième partie contient le travail principal de cette thèse de doctorat. Elle est entièrement consacrée à notre recherche expérimentale sur l'injection de spin dans les structures « Vertical External Cavity Surface Emitting Lasers ». Nous commençons par introduire un model vectoriel permettant la compréhension théorique de la sélection de polarisation dans les structures VECSELs injectées en spin. Nous rapportons ensuite la mesure de biréfringence d'une structure VECSEL designée pour le pompage optique en utilisant une technique expérimentale originale basée sur la mesure du décalage en fréquence entre les deux modes de polarisation orthogonaux TE et TM. Ultérieurement, nos observations et résultats sur l'injection optique de spin dans les VECSELs sont détaillés, analysés et commentés. L'étude est étendue à l'estimation des temps de vie caractéristiques du système par mesures de Photoluminescence résolues en temps afin d'évaluer l'efficacité de conversion de l'information de spin. Pour finir, les résultats préliminaires sur l'injection électrique de spin dans les VECSELs sont présentésThis Ph.D Thesis proposes to explore a new paradigm of spin-information propagation over very long distances after encoding on coherent light polarization. The main objective of this manuscript is to provide a detailed study of spin-injection into III-V semiconductor based opto-electronic devices with vertical geometries. To achieve this goal, we focus on the study of optical and electrical spin-injection in III-V semiconductor based Light Emitting Diodes (LEDs) and Vertical External Cavity Surface Emitting Lasers (VECSELs). Our investigations and results are presented on three axes.The first part regroups a state-of-the-art of spin-injection into semiconductors optoelectronic devices and focuses on the physical phenomena engaged in the conversion of a spin accumulation into light polarization information. A discussion on spin-injection and spin-transport into III-V semiconductor structures is followed by a more device-oriented review on spin-injection in LEDs and VCSELs.The second axis is articulated around our experimental work on the development and the optimization on III-V semiconductors LEDs of an ultra-thin MgO/CoFeB/Ta spin-injector with perpendicular magnetization at magnetic remanence. We focus on the MgO tunnel barrier optimization for maximizing the spin-injection efficiency and further detailed the development and the characterization of the spin-injector with perpendicular magnetization at remanence.Finally, the third part contains the main work of this Ph.D thesis. It is fully dedicated to our experimental research on spin-injection in Vertical External Cavity Surface Emitting Laser structures. A vectorial model allowing the theoretical understanding of polarization selection in spin-injected VECSELs is first introduced. Next, we report the birefringence measurement of a VECSEL designed for optical pumping using an original frequency detuning measurement between the two orthogonal TE- and TM-modes. Afterward, our observations and results on optical spin-injection in VECSELs are displayed, analyzed and commented. The study is farther extended to the measurement of the system's characteristic lifetimes using Time Resolved Photo-Luminescence in order to evaluate the spin-information conversion efficiency. Finally the preliminary results on electrical spin-injection experiment are presented
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Skinner, Timothy. "Electrical control of spin dynamics in spin-orbit coupled ferromagnets". Thesis, University of Cambridge, 2015. https://www.repository.cam.ac.uk/handle/1810/247392.
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This thesis describes the control of magnetisation dynamics using electricity. Direct electrical control of magnetisation is desirable for the development of efficient scalable magnetic memories. In materials with broken inversion symmetry and spin-orbit coupling, electrical current can exert a torque on a local magnetisation. In the studies presented here, a microwave current-induced ferromagnetic resonance (spin-orbit FMR) technique is used to characterise the dynamical magnetic properties and to determine the symmetries of the spin-orbit torques of ferromagnetic layers with broken inversion symmetry. Ultra-thin ferromagnetic/heavy metal bilayers have recently become an important area of study in spintronics. Magnetic torques originating from the spin-Hall effect and a Rashba spin-orbit field have both been reported in these materials. These spin-orbit torques may allow commercialisation of magnetic random access memories with higher efficiency than previous technologies. However, the exact origin of the torques is still not well understood. In the first study of this thesis, dynamic pumping of spin current induced by an external waveguide is used to investigate the dependence of the inverse spin-Hall effect in Co/Pt on the magnet thickness. An enhancement of the inverse-spin Hall effect is seen in devices with the thinnest cobalt layers which can not be explained by a conventional understanding of the spin-Hall effect. In the second study, spin-orbit FMR is used to identify the symmetries of the current-induced torques in the same Co/Pt layers. Anti-damping and field-like torque symmetries are identified, consistent in thicker cobalt layers with origins from the spin-Hall effect and an Oersted field respectively. In thinner cobalt layers, an additional field-like torque opposing the Oersted torque appears, consistent with a Rashba origin. (Ga,Mn)As is a dilute magnetic semiconductor with a record highest Curie temperature of around 180 K. At low temperatures, large spin-orbit torques with a Dresselhaus symmetry are known to exist in the material. In the final study of the thesis, spin-orbit FMR measurements demonstrate that the broken symmetry of unannealed Ga(0.03)Mn(0.97)As can generate torques with the same Dresselhaus symmetry in an adjacent iron layer at room temperature. This enables the spin-orbit torque to be distinguished from the torque due to the spin-Hall effect by symmetry.
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Hamley, Christopher David. "Spin-nematic squeezing in a spin-1 Bose-Einstein condensate". Diss., Georgia Institute of Technology, 2012. http://hdl.handle.net/1853/47523.
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The primary study of this thesis is spin-nematic squeezing in a spin-1 condensate.
The measurement of spin-nematic squeezing builds on the success of previous experiments of spin-mixing together with advances in low noise atom counting.
The major contributions of this thesis are linking theoretical models to experimental results and the development of the intuition and tools to address the squeezed subspaces.
Understanding how spin-nematic squeezing is generated and how to measure it has required a review of several theoretical models of spin-mixing as well as extending these existing models. This extension reveals that the squeezing is between quadratures of a spin moment and a nematic (quadrapole) moment in abstract subspaces of the SU(3) symmetry group of the spin-1 system.
The identification of the subspaces within the SU(3) symmetry allowed the development of techniques using RF and microwave oscillating magnetic fields to manipulate the phase space in order to measure the spin-nematic squeezing. Spin-mixing from a classically meta-stable state, the phase space manipulation, and low noise atom counting form the core of the experiment to measure spin-nematic squeezing. Spin-nematic squeezing is also compared to its quantum optics analogue, two-mode squeezing generated by four-wave mixing.
The other experimental study in this thesis is performing spin-dependent photo-association spectroscopy. Spin-mixing is known to depend on the difference of the strengths of the scattering channels of the atoms. Optical Feshbach resonances have been shown to be able to alter these scattering lengths but with prohibitive losses of atoms near the resonance. The possibility of using multiple nearby resonances from different scattering channels has been proposed to overcome this limitation. However there was no spectroscopy in the literature which analyzes for the different scattering channels of atoms for the same initial states. Through analysis of the initial atomic states, this thesis studies how the spin state of the atoms affects what photo-association resonances are available to the colliding atoms based on their scattering channel and how this affects the optical Feshbach resonances. From this analysis a prediction is made for the extent of alteration of spin-mixing achievable as well as the impact on the atom loss rate.
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Wulfhorst, Jeannette [Verfasser]. "Nonlocal spin currents in mesoscopic metallic spin valves / Jeannette Wulfhorst". München : Verlag Dr. Hut, 2012. http://d-nb.info/1028783183/34.
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Cunningham, Elizabeth Sarah. "The effect of spin-spin interactions on nucleon-nucleus scattering". Thesis, University of Surrey, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.527010.
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Ozerov, Mykhaylo. "High-field electron spin resonance in low-dimensional spin systems". Doctoral thesis, Helmholtz-Zentrum Dresden-Rossendorf, 2010. https://tud.qucosa.de/id/qucosa%3A25598.
Pełny tekst źródłaStreszczenie:
Due to recent progress in theory and the growing number of physical realizations, low-dimensional quantum magnets continue to receive a considerable amount of attention. They serve as model systems for investigating numerous physical phenomena in spin systems with cooperative ground states, including the field-induced evolution of the ground-state properties and the corresponding rearrangement of their low-energy excitation spectra. This work is devoted to systematic studies of recently synthesized low-dimensional quantum spin systems by means of multi-frequency high-field electron spin resonance (ESR) investigations. In the spin- 1/2 chain compound (C6H9N2)CuCl3 [known as (6MAP)CuCl3] the striking incompatibility with a simple uniform S = 1/2 Heisenberg chain model employed previously is revealed. The observed ESR mode is explained in terms of a recently developed theory, revealing the important role of the alternation and next-nearest-neighbor interactions in this compound. The excitations spectrum in copper pyrimidine dinitrate [PM·Cu(NO3)2(H2O)2]n, an S = 1/2 antiferromagnetic chain material with alternating g-tensor and Dzyaloshinskii-Moriya interaction, is probed in magnetic fields up to 63 T. To study the high field behavior of the field-induced energy gap in this material, a multi-frequency pulsed-field ESR spectrometer is built. Pronounced changes in the frequency-field dependence of the magnetic excitations are observed in the vicinity of the saturation field, B ∼ Bs = 48.5 T. ESR results clearly indicate a transition from the soliton-breather to a spin-polarized state with magnons as elementary excitations. Experimental data are compared with results of density matrix renormalization group calculations; excellent agreement is found. ESR studies of the spin-ladder material (C5H12N)2CuBr4 (known as BPCB) completes the determination of the full spin Hamiltonian of this compound. ESR results provide a direct evidence for a pronounced anisotropy in this compound, that is in contrast to fully isotropic spin-ladder model employed previously for BPCB. Our observations can be of particular importance for describing the rich temperature-field phase diagram of this material. The frequency-field diagram of magnetic excitations in the quasi-two dimensional S = 1/2 compound [Cu(C4H4N2)2(HF2)]PF6 in the AFM-ordered state is studied. The AFM gap is observed directly. Using high-field magnetization and ESR results, parameters of the effective spin-Hamiltonian (exchange interaction, anisotropy and g-factor) are obtained and compared with those estimated from thermodynamic properties of this compound.
42
Huang, Meng-Zi. "Spin squeezing and spin dynamics in a trapped-atom clock". Thesis, Sorbonne université, 2019. http://www.theses.fr/2019SORUS134.
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Les capteurs atomiques sont un outil de référence pour les mesures de précision du temps, des champs électriques et magnétiques et des forces d'inertie. Cependant, en absence d’une corrélation quantique entre atomes, le bruit de projection quantique constitue une limite fondamentale pour ces capteurs, appelée la limite quantique standard (SQL). Les meilleures horloges actuelles ont déjà atteint cette limite. Cependant, elle peut être surmonté en utilisant l’intrication quantique, dans un état comprimé de spin notamment. Ce dernier peut être crée par mesure quantique non-destructive (QND), en particulier dans le cadre de l’électrodynamique quantique en cavité (cQED). Dans cette thèse, je présente la deuxième génération de l'horloge à atomes piégés sur puce TACC, dans laquelle nous combinons une horloge atomique compacte avec une plateforme cQED miniature pour tester les protocoles de métrologie quantique à un niveau de précision métrologique. Dans une mesure Ramsey standard, nous mesurons une stabilité de 6E-13 à 1 s. Nous démontrons la compression de spin par mesure QND, atteignant 8(1) dB pour 1.7E4 atomes, limitée actuellement par la décohérence due au bruit technique. Les collisions entre atomes froids jouent un rôle important à ce niveau de précision, donnant lieu à une riche dynamique de spin. Nous constatons que l’interaction entre mesures par la cavité et dynamique collisionnelle de spin se manifeste dans un effet d'amplification du signal de la cavité. Un modèle simple est proposé et confirmé par des mesures préliminaires. De nouvelles expériences sont proposés pour éclairer davantage la physique à N corps surprenante dans ce système d'atomes froidsAtomic sensors are among the best devices for precision measurements of time, electric and magnetic fields, and inertial forces. However, all atomic sensors that utilise uncorrelated particles are ultimately limited by quantum projection noise, as is already the case for state-of-the-art atomic clocks. This so-called standard quantum limit (SQL) can be overcome by employing entanglement, a prime example being the spin-squeezed states. Spin squeezing can be produced in a quantum non-demolition (QND) measurement of the collective spin, particularly with cavity quantum electrodynamical (cQED) interactions. In this thesis, I present the second-generation trapped-atom clock on a chip (TACC) experiment, where we combine a metrology-grade compact clock with a miniature cQED platform to test quantum metrology protocols at a metrologically-relevant precision level. In a standard Ramsey spectroscopy, the stability of the apparatus is confirmed by a fractional frequency Allan deviation of 6E-13 at 1 s. We demonstrate spin squeezing by QND measurement, reaching 8(1) dB for 1.7E4 atoms, currently limited by decoherence due to technical noise. Cold collisions between atoms play an important role at this level of precision, leading to rich spin dynamics. Here we find that the interplay between cavity measurements and collisional spin dynamics manifests itself in a quantum amplification effect of the cavity measurement. A simple model is proposed, and is confirmed by initial measurements. New experiments in this direction may shed light on the surprising many-body physics in this sytem of interacting cold atoms
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Денисов, Станіслав Іванович, Станислав Иванович Денисов, Stanislav Ivanovych Denysov i V. V. Shchotkin. "Influence of Spin-polarized Current on Spin Waves in Ferromagnets". Thesis, Sumy State University, 2018. http://essuir.sumdu.edu.ua/handle/123456789/67944.
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It has been recently established that spin-polarized current can have a direct influence on the magnetization dynamics in conducting ferromagnets. This effect has quantum origin and is of great interest from both fundamental and applied viewpoints. In particular, it can be useful for developing magnetoresistance random access memory, magnetic logic elements and microwave devices, to name a few.
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Shaikh, Yasin Shadi. "Electron spin resonance in low-dimensional spin chains and metals". [S.l. : s.n.], 2008. http://nbn-resolving.de/urn:nbn:de:bsz:93-opus-38273.
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Liu, Yi. "Dynamics, Synchronization and Spin Squeezing in a Two-Spin Model". Thesis, Paris 11, 2013. http://www.theses.fr/2013PA112216.
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Cette thèse se concentre sur la dynamique d'un système atomique froid qui se composede deux états internes d'atomes piégés dans un potentiel magnétique . La motivation decette thèse est une série d'expériences sur ce système réalisées en 2010, où un grandtemps de cohérence surprenante entre les deux états internes ont été observés. Cephénomène a été expliqué par la théorie cinétique qui a utilisé une approche de champmoyen. Dans cette thèse, nous essayons d'utiliser une approche différente et étudier leseffets de corrélations quantiques dans la dynamique du système. De plus, nous sommeségalement intéressés au phénomène de compression de spin qui est la redistribution desfluctuations quantiques dans le système de spin. Afin d'étudier les effets des corrélationsquantiques, nous proposons un modèle simplifié qui divise les atomes froids en deuxgroupes en fonction de leurs énergies de mouvement orbital dans le potentiel de piégeageet traitons chaque groupe comme un macro-spin. Les principaux ingrédients de ce modèlesont l'inhomogénéité du champ externe qui déphase les deux macro-spins et l'interactiond'échange entre les deux macro-spins, qui imite l'effet de rotation des spins identiques(ISRE), avec la condition initiale que les deux spins sont parallèle dans le plan transversaldu champ externe. Ensuite, nous étudions la dynamique du système classique où ladynamique ne dépendent pas de la taille des spins et une transition de synchronisation esttrouvée lorsque l'interaction d'échange est plus grande que le seuil , la moitié de l'inhomogénéité du champ externe. Une analyse de l'espace de phase révèle que cettetransition de synchronisation est liée à une transition de bifurcation et de la conditioninitiale. Ensuite, la dynamique quantique est étudiée où la taille de spin joue un rôleimportant dans la dynamique. Il n'y a pas de transition de synchronisation dans lessystèmes quantiques et du comportement dynamique très riche est trouvée. Dans ladynamique quantique , plusieurs échelles de temps caractéristiques apparaissent commela taille de spin augmente, ce qui est d'origine quantique. Ces échelles de temps dépendde la taille de spin et tous deviennent infinies lorsque la taille de spin est infinie. De cettefaçon, la limite classique est récupéré. Basé sur l’intensité de l'interaction d'échange ,deux modèles effectifs sont proposés pour calculer les échelles du temps quantiques lesplus petites, ce qui coïncide bien avec les résultats numériques. La compression de spinest également étudié avec ces modèles effectifsThis thesis focuses on the dynamics of a cold atomic system which consists of two internalstates of atoms trapped in a magnetic trapping potential. The motivation of this thesis is aseries of experiments on such system carried out in 2010, where a surprising longcoherence time between the two internal states were observed. This phenomenon wasexplained by the kinetic theory which has used a mean-field approach. In this thesis, wetry to use a different approach and study the effects of quantum correlations in thedynamics of the system. In addition to that, we are also interested in the phenomenon ofspin squeezing which is the redistribution of quantum fluctuations in the spin system. Inorder to study the effects of the quantum correlations, we propose a simplified which splitsthe cold atoms into two groups based on their orbital movement energies in the trappingpotential and treat each group as a macro-spin. The main ingredients in this model are theinhomogeneity of the external field which dephases the two macro-spins and theexchange interaction between the two macro-spins, which mimics the identical spinrotation effect (ISRE), with the initial condition that the two spins lie parallel in thetransverse plane of the external field. Then we study the classical dynamics of the systemwhere the dynamics do not depend on the size of the spins and a synchronizationtransition is found when the exchange interaction is larger than the threshold, the half ofthe inhomogeneity of the external field. A phase space analysis reveals that thissynchronization transition is related to a bifurcation transition and the initial condition. Thenthe quantum dynamics is studied where the spin size plays an important role in thedynamics. There is no synchronization transition in the quantum systems and very richdynamical behavior is found. In the quantum dynamics, many characteristic time scalesemerge as the size of spin is increased, which are of quantum origin. These time scales isdependent of the spin size and all become infinite when the size of spin is infinite. In theway, the classical limit is recovered. Based on the strength of the exchange interaction,two effective models are proposed to calculate the smallest quantum characteristic timescales, which give very good agreement with the numerical results. Spin squeezing is alsostudied with these effective models
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Bailleul, Matthieu. "Propagation et confinement d'ondes de spin dans les microstructures magnétiques". Phd thesis, Ecole Polytechnique X, 2002. http://tel.archives-ouvertes.fr/tel-00001976.
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Ce travail a porté sur les propriétés d'éléments minces de métaux ferromagnétiques étudiées à petite échelle (µm) et àhaute fréquence (GHz). Dans ce but, un spectromètre hyperfréquence à antennes micrométriques a été mis au point. Cet
instrument a été utilisé pour explorer deux problématiques différentes. Pour un film continu, d'abord, nous avons réalisé des
expériences d'émission-réception d'ondes de spin. Ces résultats nous ont permis de caractériser les processus de
transduction et de relaxation d'ondes magnétostatiques progressives. Nous avons également étudié des rubans de largeur
micrométrique, pour lesquels l'équilibre lui-même est inhomogène. Nous avons interprété leur réponse hyperfréquence en
termes de transitions de phase micromagnétiques et en termes de confinement d'ondes de spin.
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Rennie, Adam Charles. "Noncommutative spin geometry". Title page, contents and introduction only, 2001. http://web4.library.adelaide.edu.au/theses/09PH/09phr4163.pdf.
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Mantke, Wolfgang. "Spin and gravity". Thesis, Georgia Institute of Technology, 1989. http://hdl.handle.net/1853/27605.
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Hijano, Cubelos Eliot. "Higher spin gravity". Thesis, McGill University, 2012. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=110694.
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In this thesis we study higher spin theories in three dimensional gravity with a negative cosmological constant based on the gauge group SL(N,R)xSL(N,R). First we introduce the topic of semi-classical gravity in three dimensional anti de Sitter space andits conjectured duality with a two dimensional conformal field theory. We study black hole solutions for the case of N=3 characterized by their holonomies around the non-contractible cycles of space-time. The black hole solutions are shown to be gauge equivalent to a BTZ black hole which is charged under a set of U(1) Chern-Simons fields. Nevertheless, depending on the choice of embedding of the gravitational gauge group, the space-time geometry may be non-trivial. We also investigate in detail the physical sensibility of non principal embeddings of the gravitational SL(2,R) in SL(N,R) and we conclude that theonly embedding with a positive definite spectrum is the principal one.Cette thèse s'intéresse aux théories gravitationnelles couplées à des spins entiers avec une constante cosmologiquenégative, dont l'origine provient de l'étude du groupe de jauge sl_N. La gravitation dans l'espace tridimensionnel anti de Sitter est d'abord décrite de manière semi-classique et la dualité avec la théorie conforme de champs en deux dimensions est ensuite présentée. L'exposition des solutions de la théorie N=3 permet la caractérisation des trous noirs par les propriétés des holonomies autour de boucles non-contractiles. L'invariance de jauge rapproche alors ces solutions aux trous noirs BTZ avec une charge d'un champ Chern-Simons. Néanmoins, la géometrie de l'espace-temps dépend du plongement des symétries gravitationnelles SL(2,R) dans le groupe de jauge SL(N,R). Le spectre des solutions est calculé pour tous ces plongements, et la condition de positivité exclut alors tous les cas sauf le plongement principal.
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Lewis, C. "Spin(7) instantons". Thesis, University of Oxford, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.301867.
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