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Dissertations / Theses on the topic 'Spin wave'

Author: Grafiati

Published: 4 June 2021

Last updated: 27 April 2022

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Lassalle-Balier, Rémy. "Spin wave propagation and interferometry." Paris 6, 2011. http://www.theses.fr/2011PA066030.

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Ce travail a pour objectif l’observation d’interf´erence d’ondes de spin dans des structures magnétiques confinées. Le chemin jusqu’à cet objectif a mené à la conception un nouvel émetteur récepteur d’onde de spin qui permet l’observation du mode MsBVW qui est difficilement excitable. Ce transducteur a été modélisé en généralisant une théorie de transduction existante. L’utilisation d’un facteur démagnétisant constant a été identifiée comme la principale limite car cela ne permet pas de considérer proprement l’effet du confinement. Ensuite, l’émission et la réception d’onde de spin ont été caractérisées dans l’approche d’onde continue. Afin de compléter cette étude de propagation d’onde de spin dans des structures magnétiques confinées, une seconde expérience, dans l’espace temporel, a été utilisé pour observer les ondes de spin en mode pulsé. Ce ci a mené à la caractérisation de l’évolution du spectre d’onde de spin durant le régime transitoire. Enfin, deux types d’interférence ont été décrits, et deux types d’interféromtre ont été conçus. Les interférences par addition de champ ont été observées expérimentalement dans le cas des modes de surface. L’intégralité de ces travaux a été réalisée en utilisant du permalloy car il s’agit d’un alliage métallique ferromagnétique. Ce ci signifie qu’il est facilement déposable par pulvérisation cathodique ou par évaporation, qui sont deux techniques largement éprouvées dans l’industrie microélectronique. Même si ce matériaux présente un fort amortissement de la dynamique, il est un meilleur candidat pour l’intégration dans l’industrie que des matériaux à plus faible amortissement comme le YIG qui nécessite une lourde méthode
This work aims to observe spin wave interferences in confined magnetic structures. The way to this goal has led to the design of a new spin wave emitter and receiver that allows observation of MsBVW that are usually hard to excite. This transducer has been modeled by generalizing an existing spin wave transduction. The use of constant demagnetizing factor has been identified as its main limits as it does not consider properly confinement effect. Then, spin wave emission and reception has been characterized in continuous wave approach. To complete this study of propagating spin wave in confined magnetic structures, a second set-up, in time domain, has been used to observe spin wave in pulsed mode. This has led to characterization of spin wave spectrum evolution during transient. Finally, two kinds of spin wave interference have been described and two type of interferometer have been designed. Field addition interferences have been observed experimentally in the case of MsSW. All this work was done using only permalloy because it is a ferromagnetic metallic alloy. This means, it is easily deposited by sputtering or evaporation that are two methods widely used in microelectronic industry. Even if this material has a high damping, it would be more likely adopted by industry than low damping material such as YIG that requires heavy deposition technique, epitaxy

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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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Loutsenko, Igor. "Solitons in wave propagation and spin systems." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape9/PQDD_0013/NQ42468.pdf.

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Zheng, Liqiu. "Spin density wave phases in semiconductor superlattices." Connect to this title online, 2007. http://etd.lib.clemson.edu/documents/1202500635/.

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Li, Tian. "Spin wave propagation in ferromagnetic nano-structures." Doctoral thesis, Kyoto University, 2021. http://hdl.handle.net/2433/263500.

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Magnusson, Einar B. "High-spin impurities and surface acoustic waves in piezoelectric crystals for spin-lattice coupling." Thesis, University of Oxford, 2016. https://ora.ox.ac.uk/objects/uuid:09d23fb2-f501-4be2-a25f-b69ada0ce5b1.

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In this thesis we investigate various aspects of SAW devices and strain sensitive spin species in ZnO and LiNbO₃ for coupling surface acoustic waves to spin ensembles. Firstly, we performed a series of ESR experiments exploring the potential of Fe³⁺ impurities in ZnO for spin-lattice coupling. This spin system has already been identified as a high potential quantum technology component due to its long coherence time. We show that the system also has good properties for spin-lattice coupling experiments, with a strain-coupling parameter G₃₃ = 280 ± 5GHz/strain, which is about 16 times larger than the largest reported for NV centres in diamond. We found that the LEFE effect as well as the spin Hamiltonian parameter D have a linear temperature dependence. As the relative change in each coincide, this strongly supports the notion that the modification of D by an electric field is a multiplicative effect rather than an additive one, D = D₀(1 + κΕ). The LEFE coefficient we measured is several times larger for Fe³⁺:ZnO than for Mn²⁺:ZnO. Secondly, we have fabricated and characterised SAW devices on bulk ZnO crystals and Fe doped lithium niobate. We found that the nominally pure ZnO was conductive at room temperature due to n-type intrinsic doping, and electrical losses inhibited any transmission through a SAW delay line above T = 200K. The one-port resonator measured down to milli-Kelvin temperatures showed excellent quality factors of up to Q ≃ 1.5 x 10⁵ in its superconducting state. Finally, we performed a surface acoustic wave spin resonance (SAWSR) experiment using a one-port SAW resonator fabricated on Fe²⁺:LN. We observed a clear signal at T ≃ 25 K, at a field near the expected one for a Δm_s = 2 transition between the |â1⟩ and |+1⟩ states. We concluded it to be a transition induced by acoustic coupling since the signal intensity did not tend to zero when the magnetic field was parallel to the crystal anisotropy axis. Furthermore, this tells us that the coupling is due to a modulation of the E zero-field splitting parameter rather than D. We investigated the dependence on microwave power and found the saturation limit. We performed a measurement of Fe³⁺:LN as well to reassure ourselves that the resonance is not magnetically excited by the field around the IDT.

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Feiler, Laura [Verfasser]. "Nonlinear spin-wave excitation detected by the inverse spin-Hall effect / Laura Feiler." München : Verlag Dr. Hut, 2017. http://d-nb.info/1126296376/34.

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Mansfeld, Sebastian [Verfasser]. "Spin-Wave Optics: Refraction and Imaging / Sebastian Mansfeld." München : Verlag Dr. Hut, 2012. http://d-nb.info/1028785607/34.

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Tödt, Jan-Niklas [Verfasser]. "Control of spin-wave propagation / Jan-Niklas Tödt." München : Verlag Dr. Hut, 2017. http://d-nb.info/1126295949/34.

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Haidar, Mohammad. "Role of surfaces in magnetization dynamics and spin polarized transport : a spin wave study." Phd thesis, Université de Strasbourg, 2012. http://tel.archives-ouvertes.fr/tel-00869643.

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In this thesis, the interplay between electron transport and magnetization dynamics is explored in order to access to fundamental properties of ferromag- netic metal thin films. With the aim of extracting the influence of the electron surface scattering on the spin-dependent resistivities, thickness series of permal-loy (Ni80Fe20) films were grown and studied. In addition to standard electrical and magnetic measurements, a detailed study of the propagation of spin waves along these films was performed. Resorting to the current-induced spin-wave Doppler shift technique, the degree of spin-polarization of the electrical current was extracted. This degree of spin-polarization was found to decrease when the film thickness decreases, which suggests that the film surfaces contribute to the spin dependent resistivities and tend to depolarize the electrical current.

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Eklund, Anders. "Microwave Frequency Stability and Spin Wave Mode Structure in Nano-Contact Spin Torque Oscillators." Doctoral thesis, KTH, Integrerade komponenter och kretsar, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-188546.

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The nano-contact spin torque oscillator (NC-STO) is an emerging device for highly tunable microwave frequency generation in the range from 0.1 GHz to above 65 GHz with an on-chip footprint on the scale of a few μm. The frequency is inherent to the magnetic material of the NC-STO and is excited by an electrical DC current by means of the spin torque transfer effect. Although the general operation is well understood, more detailed aspects such as a generally nonlinear frequency versus current relationship, mode-jumping and high device-to-device variability represent open questions. Further application-oriented questions are related to increasing the electrical output power through synchronization of multiple NC-STOs and integration with CMOS integrated circuits. This thesis consists of an experimental part and a simulation part. Experimentally, for the frequency stability it is found that the slow but strong 1/f-type frequency fluctuations are related to the degree of nonlinearity and the presence of perturbing, unexcited modes. It is also found that the NC-STO can exhibit up to three propagating spin wave oscillation modes with different frequencies and can randomly jump between them. These findings were made possible through the development of a specialized microwave time-domain measurement circuit. Another instrumental achievement was made with synchrotron X-rays, where we image dynamically the magnetic internals of an operating NC-STO device and reveal a spin wave mode structure with a complexity significantly higher than the one predicted by the present theory. In the simulations, we are able to reproduce the nonlinear current dependence by including spin wave-reflecting barriers in the nm-thick metallic, magnetic free layer. A physical model for the barriers is introduced in the form of metal grain boundaries with reduced magnetic exchange coupling. Using the experimentally measured average grain size of 30 nm, the spin wave mode structure resulting from the grain model is able to reproduce the experimentally found device nonlinearity and high device-to-device variability. In conclusion, the results point out microscopic material grains in the metallic free layer as the reason behind the nonlinear frequency versus current behavior and multiple propagating spin wave modes and thereby as a source of device-to-device variability and frequency instability.
Dagens snabba utveckling inom informationsteknik drivs på av ständigt växande informationsmängder och deras samhällsanvändning inom allt från resursoptimering till underhållning. Utvecklingen möjliggörs till stor del hårdvarumässigt av miniatyrisering och integrering av elektroniska komponenter samt trådlös kommunikation med allt större bandbredd och högre överföringshastighet. Det senare uppnås främst genom utnyttjande av högre radiofrekvenser i teknologiskt tidigare oåtkomliga delar av spektrumet. Frekvensutnyttjandet har det senaste årtiondet ökat markant i mikrovågsområdet med typiska frekvenser runt 2.4 GHz och 5.2-5.8 GHz. I den spinntroniska oscillatorn (STO:n) möjliggörs frekvensgenerering i det breda området från 0.1 GHz upp till över 65 GHz av en komponent med mikrometerstorlek som kan integreras direkt i CMOS-mikrochip. Till skillnad från i konventionella radiokretsar med oscillatorer konstruerade av integrerade transistorer och spolar, genereras mikrovågsfrekvensen direkt i STO:ns magnetiska material och omvandlas därefter till en elektrisk signal genom komponentens magnetoresistans. Dessa materialegenskaper möjliggör ett tillgängligt frekvensband med extrem bredd i en och samma STO, som därtill kan frekvensmoduleras direkt genom sin styrström och på så sätt förenklar konstruktionen av sändarsystem. STO:ns icke-linjära egenskaper kan potentiellt också användas för att i en och samma komponent blanda ned mottagna mikrovågssignaler och på så sätt förenkla konstruktionen även av mikrovågsmottagare. STO:ns signalegenskaper bestäms av det magnetiska materialets fysik i form av magnetiseringsdynamik driven av elektriskt genererade spinnströmmar. I denna avhandling studeras denna dynamik experimentellt med särskilt fokus på frekvensstabiliteten i den hittills mest stabila STO-typen; nanokontakts-STO:n. Genom mätningar i tidsdomän av STO:ns elektriska signaler runt 25 GHz har frekvensstabiliteten funnits hänga samman med den typ av icke-linjärt beteende som också funnits vara utmärkande för tillverkningsvariationen i komponenterna. Mikroskopiska undersökningar av materialet visar att en trolig källa till denna variation är den magnetiska metallens uppbyggnad i form av korn i storleksordningen 30 nm, och datorsimuleringar av en sådan materialstruktur har visats kunna reproducera de experimentella resultaten. Därtill har en metod utvecklats för att med röntgenstrålning direkt mäta de små, magnetiska mikrovågsrörelserna i materialet. Denna röntgenteknik möjliggör detaljerade experimentella studier av magnetiseringsdynamiken och kan användas för att verifiera och vidareutveckla den existerande teorin för mikrovågsspinntronik. Sammantaget förs STO-teknologin genom denna studie ett steg närmare sina tänkbara samhällsbreda tillämpningar inom snabb, trådlös kommunikation för massproducerade produkter med integrerad sensor- och datorfunktionalitet.

QC 20160620

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Dennis, Mark Richard. "Topological singularities in wave fields." Thesis, University of Bristol, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.391183.

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Balhorn, Felix [Verfasser]. "Three-Dimensional Tubular Spin-Wave Resonator Systems / Felix Balhorn." München : Verlag Dr. Hut, 2013. http://d-nb.info/1042878242/34.

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Gates, Michael Richard. "Surface acoustic wave investigations of spin and pseudospin systems." Thesis, University of Nottingham, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.247121.

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Schmool, David Simon. "Structural and spin wave resonance studies in magnetic multilayers." Thesis, University of York, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.359228.

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Watts, Richard. "Spin wave resonance studies of compositionally tailored magnetic films." Thesis, University of York, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.241113.

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Bharadwaj, Sripoorna Paniyadi Krishna. "Theoretical Study of Spin-wave Effects in Quantum Ferromagnets." Thesis, University of Oregon, 2017. http://hdl.handle.net/1794/22640.

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In this dissertation, we examine quantum ferromagnets and determine various effects of the magnetic Goldstone modes or "magnons'' in these systems. Firstly, we calculate the magnon contribution to the transport relaxation rate of conduction electrons in metallic ferromagnets and find that at asymptotically low temperatures, the contribution behaves as T^2 exp(-T_0/T) and not as T^2 predicted previously. To perform these calculations, we derive and use a very general effective theory for metallic ferromagnets. This activation barrier-like behavior is due to the fact that spin waves only couple electrons from different Stoner subbands that arise from the splitting of the conduction band in presence of a nonzero magnetization. The T^2 behavior is found to be valid only in a pre-asymptotic temperature window. The temperature scale T_0 is the energy of the least energetic ferromagnon that couples electrons of different spins. Second, we discuss magnon-induced long-range correlation functions in quantum magnets. In the ordered phases of both classical ferromagnets and antiferromagnets, the long-range correlations induced by the magnons lead to a singular wavenumber dependence of the longitudinal order-parameter susceptibility in spatial dimensions 2

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Zhang, Chi. "Spin-orbit torque damping control and auto-oscillations of dipole field-localized spin wave modes." The Ohio State University, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=osu1515079497750423.

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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.

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Hoq, Qazi Enamul. "Quantization Of Spin Direction For Solitary Waves in a Uniform Magnetic Field." Thesis, University of North Texas, 2003. https://digital.library.unt.edu/ark:/67531/metadc4210/.

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It is known that there are nonlinear wave equations with localized solitary wave solutions. Some of these solitary waves are stable (with respect to a small perturbation of initial data)and have nonzero spin (nonzero intrinsic angular momentum in the centre of momentum frame). In this paper we consider vector-valued solitary wave solutions to a nonlinear Klein-Gordon equation and investigate the behavior of these spinning solitary waves under the inﬂuence of an externally imposed uniform magnetic ﬁeld. We ﬁnd that the only stationary spinning solitary wave solutions have spin parallel or antiparallel to the magnetic ﬁeld direction.

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Wainwright, C. L. "The effects of spin-orbit coupling on gravitational wave uncertainties." Pomona College, 2007. http://ccdl.libraries.claremont.edu/u?/stc,20.

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Paper discusses the expected uncertainty of orbital parameters of binary stars as measured by the space-based gravitational wave observatory LISA (Laser Interferometer Space Antenna) and how the inclusion of spin in the model of the binary stars affects the uncertainty. The uncertainties are found by calculating the received gravitational wave from a binary pair and then performing a linear least-squares parameter estimation. The case of a 1500 solar mass black hole that is 20 years from coalescing with a 1000 solar mass black hole--both of which are 50 x 10^6 light years away--is analyzed, and the results show that the inclusion of spin has a negligible effect upon the angular resolution of LISA but can increase the accuracy in mass and distance measurements by factors of 15 and 65, respectively.

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Waby, Neil Anthony. "Nonlinear magnetostatic spin wave pulses in ferromagnetic and antiferromagnetic films." Thesis, University of Salford, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.308262.

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Roe, Austin R. "RESONANT ACOUSTIC WAVE ASSISTED SPIN-TRANSFER-TORQUE SWITCHING OF NANOMAGNETS." VCU Scholars Compass, 2019. https://scholarscompass.vcu.edu/etd/6029.

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We studied the possibility of achieving an order of magnitude reduction in the energy dissipation needed to write bits in perpendicular magnetic tunnel junctions (p-MTJs) by simulating the magnetization dynamics under a combination of resonant surface acoustic waves (r-SAW) and spin-transfer-torque (STT). The magnetization dynamics were simulated using the Landau-Lifshitz-Gilbert equation under macrospin assumption with the inclusion of thermal noise. We studied such r-SAW assisted STT switching of nanomagnets for both in-plane elliptical and circular perpendicular magnetic anisotropy (PMA) nanomagnets and show that while thermal noise affects switching probability in in-plane nanomagnets, the PMA nanomagnets are relatively robust to the effect of thermal noise. In PMA nanomagnets, the resonant magnetization dynamics builds over few 10s of cycles of SAW application that drives the magnetization to precess in a cone with a deflection of ~45⁰ from the perpendicular direction. This reduces the STT current density required to switch the magnetization direction without increasing the STT application time or degrading the switching probability in the presence of room temperature thermal noise. This could lead to a pathway to achieve energy efficient switching of spin-transfer-torque random access memory (STT-RAM) based on p-MTJs whose lateral dimensions can be scaled aggressively despite using materials with low magnetostriction by employing resonant excitation to drive the magnetization away from the easy axis before applying spin torque to achieve a complete reversal.

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Gladii, Olga. "Spin wave propagation and its modification by an electrical current in Py/Al2O3, Py/Pt and Fe/MgO films." Thesis, Strasbourg, 2016. http://www.theses.fr/2016STRAE038/document.

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Des mesures d’ondes de spin propagatives ont été réalisées pour caractériser deux effets de l’interaction spin-orbite ainsi que le transport électrique dépendant du spin. Les effets du couplage spin-orbite ont été étudiés dans des bicouches nickel-fer/platine. Dans ces films, les fréquences de deux ondes de spin contre-propageantes ne sont pas les mêmes, ce qui est attribué à l’effet combiné d’une interaction magnétique chirale appelée interaction Dzyaloshinskii-Moriya et d’une asymétrie dans l’épaisseur du film magnétique. En appliquant le courant électrique dans ce système nous avons observé une modification du taux de relaxation de l’onde de spin qui est attribuée au transfert de spin induit par effet Hall de spin. D’autre part, les études de propagation d’ondes de spin dans une couche mince de fer épitaxié à température ambiante ont montré une polarisation en spin du courant électrique de 83%, ce qui est attribué à une forte asymétrie du couplage électron-phonon
Propagating spin wave measurements were realised to characterize two spin-orbit related phenomena, as well as spin dependent electrical transport. The effects of spin-orbit coupling have been studied in nickel-iron/platinum bilayers. It has been shown that in these films the frequencies of two counter-propagating spin waves are not the same, which is attributed to the combined effects of a chiral magnetic interaction named Dzyaloshinskii-Moriya interaction and an asymmetry of the magnetic properties across the film thickness. By applying an electrical current in such system we have observed a modification of the spin wave relaxation rate due to the spin transfer torque induced by spin Hall effect. On the other hand, from the study of spin wave propagation in thin epitaxial iron films at room temperature, a degree of spin polarization of the electrical current of 83% was extracted, which is attributed to a significant spin-asymmetry of the electron-phonon coupling

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Hussain, A. A. "Spin wave and ferromagnetic resonance studies on single crystal nickel films." Thesis, University of York, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.354383.

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Sigurdsson, Ari. "Micromagnetic study of spin Hall nano-oscillator arrays and their synchronization dynamics." Thesis, KTH, Skolan för elektroteknik och datavetenskap (EECS), 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-285562.

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Spintronics is the study of electron spins and their utilization in electronic devices. Within this field, spin-based oscillators have shown promise for mi- crowave signal generation as they can operate at high frequencies, are small in scale and are compatible with modern fabrication techniques. Among these oscillators are the spin Hall nano-oscillators (SHNOs). They are nanoscale thin-film structures driven by pure spin-current injection from a primary con- ductor into a ferromagnetic material. This process can be used to generate microwave signals through oscillations in the material’s magnetization. By constraining the current flow in the device to individual constrictions, an ar- ray arrangement of multiple oscillators can be realized. These oscillators can then be coupled together via their internal interactions to achieve mutual syn- chronization and improve their characteristics.In this work, a versatile micromagnetic modelling procedure for simulating constriction-based SHNOs and their synchronization dynamics in different ar- ray arrangements is presented. A case study of various 2x2 array geometries is conducted along with an exploration of higher-order networks of 4x4, 6x6 and 8x8 oscillators. A perturbative optimization algorithm is developed to improve excitation conditions and drive geometries into a synchronized regime. Lastly, a comparison to nonlinear auto-oscillator theory is presented to illustrate the dependence of generated signals on constriction sizes and the spacing between oscillators. Mutual synchronization between multiple oscillators is achieved and favourable geometry and excitation conditions are defined. The conducted simulations show good agreement with experimental results and illustrate the potential for future studies of SHNO characteristics through micromagnetic modelling.
Spinntronik är ett forskningsområde, som handlar om hur elektronens s.k. spinn kan användas i elektroniska komponenter. Inom detta område har spinnbaserade oscillatorer visat sig ha lovande egenskaper för generering av mikrovågssignaler, eftersom de har höga arbetsfrekvenser, liten storlek och är kompatibla med moderna tillverkningstekniker. En typ av dessa oscillatorer kallas spinn-Hall nano-oscillatorer (SHNO). De är nanometerstora tunnfilms- strukturer, vilka drivs av en ren spinnström, som injiceras från en (metallisk) ledare till en ett ferromagnetiskt material. Denna mekanism kan användas för att skapa mikrovågssignaler genom oscillationer i materialets magnetisering. Genom att begränsa strömflödet i komponenten till enskilda gap kan man skapa en matris med ett stort antal oscillatorer. Dessa oscillatorer kan sedan kopplas till varandra genom interna utbytesmekanismer och på så sätt uppnår man en ömsesidig koppling och förbättrade egenskaper.I detta arbete presenteras ett mångsidigt mikromagnetiskt modelleringsflö- de, för att simulera SHNO:er, baserade på nano-gap, och deras synkronisering i olika matriskonfigurationer. En fallstudie som inkluderar olika 2x2 matris- geometrier har genomförts tillsammans med explorativ utforskning av högre ordnings nätverk, såsom 4x4, 6x6 och 8x8 oscillatorer. En störnings-baserad optimerings-algoritm har utvecklats för att förbättra exciterings-parametrarna och för att tvinga geometrierna in i en synkroniserad regim. Som en avslutning presenteras en jämförelse med icke-linjär auto-oscillatorteori för att visa den genererade signalens beroende på gapens storlek och avståndet mellan dem. Ömsesidig synkronisering mellan flera oscillatorer kunde uppnås och en för- delaktig geometri samt lämpliga värden på exciterings-parametrarna kunde definieras. Simuleringarna i studien hade bra överensstämmelse med experi- mentella resultat och visar på potentialen för vidare studier av SHNO egen- skaper med hjälp av mikromagnetisk modellering.

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Wyngaardt, Shaun Metzler. "Relativistic plane wave description of spin transfer observables for proton knockout reactions." Thesis, Stellenbosch : Stellenbosch University, 2001. http://hdl.handle.net/10019.1/52429.

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Thesis (PhD)--Stellenbosch University, 2001.
ENGLISH ABSTRACT: In this dissertation we set out to develop the first relativistic model for calculating complete sets of (p, 2p) spin transfer observables. In addition to this a new technique has been developed which allows us to evaluate the transition amplitude, which is used to calculate the scattering observables for the reaction directly. The influence of various modiuin-modificd parameters ()1I the scattered wave functions anr] NN interact ion lH-IVC' })('('11 invest igatcd DlIC t,C) (I,llIlJigllitic's surrounding the nNN coupling we have included both pseudosoalar and pseudovector coupling into the nucleon-nucleon interaction model. Furthermore we have included two different kinematic prescriptions to obtain the effective NN laboratory kinetic energy and center of mass scattering angle, which are used to obtain the NN scattering amplitudes. The aim of this study is to investigate the effects of the various model parameters on complete sets of scattering observables. Our investigation has shown that although the analyzing power is not very sensitive to nuclear medium effects, and the various other spin transfer observables such as Dnn should provide valuable insight. Further refinements of the model would be to include nuclear distortions as well as the IA2 model of the NN interaction.
AFRIKAANSE OPSOMMING: In hierdie tesis ontwikkel ons die eerste relatiwistiese model vir die berekening van 'n volledige stel (p, 2p) spin waarneembares. Verder word 'n nuwe tegniek ingevoer wat ons toelaat om die oorgangsamplitude, wat gebruik word in berekening van die verstrooings waarneembares vir die reaksie, direk te evalueer. Die invloed van verskeie medium-gemodifiseerde parameters op die verstrooide golffunksies en die NN wisselwerking word bestudeer. As gevolg van onsekerhede betreffende die лNN koppeling word beide die pseudoskalaar en pseudovektor koppeling in die nukleon-nukleon interaksie model ingesluit. Ons sluit ook twee verskillende kinematiese preskripsies in om die effektiewe NN laboratorium kinetiese energie en die massa middelpunt verstrooiings hoek, wat gebruik word vir die berekening van die NN verstrooiings amplitude, te bereken. Die doel van hierdie studie is om die effek van verskeie model parameters op 'n volledige stel spin waarneembares te ondersoek. Die studie toon dat alhoewel die analiseervermoë nie baie sensitief is vir medium effekte nie, die ander spin waarneembares soos byvoorbeeld Dnn waardevolle insig lewer. Daar word voorgestel dat die model verfyn word deur kerndistorsies as ook die meer algemele IA2 model vir die NN interaksie in te sluit.

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Sanches, Piaia Monica. "Femtosecond magneto-optical four-wave mixing in Garnet films." Thesis, Strasbourg, 2014. http://www.theses.fr/2014STRAE024/document.

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Un des objectifs du Femtomagnetisme est de contrôler l’aimantation des matériaux avec des impulsions laser femtoseconde. Il a été démontré qu’une réponse magnéto-optique (MO) cohérente a lieu avant la thermalisation des populations de spins dans une configuration pompe-sonde MOKE. Elle résulte du couplage cohérent spin-photon dû à l’interaction spin-orbite. Une description simplifiée de cet effet a été faite en tenant compte d’un système à huit niveaux couplés au champ laser. La cohérence MO est définie par le temps de déphasage dépendent du champ T2MO. Dans ce travail, il est montré que la réponse MO cohérente d’un grenat dopé au bismuth peut être mesurée directement avec différentes configurations de mélange à quatre ondes MO. L’importance de connaître la phase spectrale de l’impulsion pour obtenir T2MO a été étudié. Avec des impulsions de 10fs dans le proche infra-rouge, une mesure de T2MO donne (2.8+/-1)fs, c. à d., du même ordre de grandeur que le temps de déphasage des charges
One of the goals of Femtomagnetism is to manipulate the magnetization of materials using femtosecond optical pulses. It has been shown in ferromagnetic films that a magneto-optical (MO) coherent response takes place before the thermalization of the spins populations in a pump and probe MOKE experiment. It results from the coherent spin-photon coupling mediated by the spin-orbit interaction. A simplified description of this effect has been made by considering an eight-level system coupled with the laser field. The MO coherence can be defined by the magnetic field dependent dephasing time T2MO. In the present work, it is shown that the coherent MO response of a bismuth-doped garnet can be directly measured in different degenerated MO four-wave mixing configurations. The importance of well-knowing the spectral phase of the pulse to measure T2MO was studied. Using 10fs near infra-red pulses, T2MO was shown to be (2.8+/-1)fs that is of the same order of the charges dephasing time

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Skubic, Björn. "Spin Dynamics and Magnetic Multilayers." Doctoral thesis, Uppsala University, Department of Physics, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-8168.

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Theoretical studies based on first-principles theory are presented for a number of different magnetic systems. The first part of the thesis concerns spin dynamics and the second part concerns properties of magnetic multilayers. The theoretical treatment is based on electronic structure calculations performed by means of density functional theory.

A method is developed for simulating atomistic spin dynamics at finite temperatures, which is based on solving the equations of motion for the atomic spins by means of Langevin dynamics. The method relies on a mapping of the interatomic exchange interactions from density functional theory to a Heisenberg Hamiltonian. Simulations are performed for various magnetic systems and processes beyond the reach of conventional micromagnetism. As an example, magnetization dynamics in the limit of large magnetic and anisotropy fields is explored. Moreover, the method is applied to studying the dynamics of systems with complex atomic order such as the diluted magnetic semiconductor MnGaAs and the spin glass alloy CuMn. The method is also applied to a Fe thin film and a Fe/Cr/Fe trilayer system, where the limits of ultrafast switching are explored. Current induced magnetization dynamics is investigated by calculating the current induced spin-transfer torque by means of density functional theory combined with the relaxation time approximation and semi-classical Boltzmann theory. The current induced torque is calculated for the helical spin-density waves in Er and fcc Fe, where the current is found to promote a rigid rotation of the magnetic order.

Properties of magnetic multilayers composed of magnetic and nonmagnetic layers are investigated by means of the Korringa-Kohn-Rostocker interface Green's function method. Multilayer properties such as magnetic moments, interlayer exchange coupling and ordering temperatures are calculated and compared with experiments, with focus on understanding the influence of interface quality. Moreover, the influence on the interlayer exchange coupling of alloying the nonmagnetic spacer layers with small amounts of a magnetic impurity is investigated.

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Davies, M. "The observation and interpretation of S.W.R. in thin films." Thesis, University of Nottingham, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.374809.

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Morgan, T. "Theoretical study of high energy collective excitations in ferromagnetic nickel and iron." Thesis, University of Reading, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.376651.

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Silva, Wanêssa Façanha da. "Ondas de spin em redes decoradas." reponame:Repositório Institucional da UFC, 2014. http://www.repositorio.ufc.br/handle/riufc/13700.

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SILVA, Wanêssa Façanha. Ondas de spin em redes decoradas. 2014. 62 f. Dissertação (Mestrado em Física) - Programa de Pós-Graduação em Física, Departamento de Física, Centro de Ciências, Universidade Federal do Ceará, Fortaleza, 2014.
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Low-dimensional systems have attracted much attention lately due to systems such as graphene and carbon nanotubes. Such systems have great potential for technological applications. In particular the creation of electronic devices due to their specific electronic properties. In this sense , the study of other systems in low dimension becomes urgent. More specifically , the study of magnetic properties of materials at low dimensionality also brings great new features in the behavior of ferromagnetic systems . The behavior of spin waves in such systems may be important to the study of spintronic and the development of new devices and magnetic memories . Thus in this work we aim to study the behavior of ferromagnetic spin waves in two-dimensional systems . For two-dimensional systems we consider here two-dimensional networks decorated . The decorations are introduced to generate networks with more than one basic atom in the unit cell of the system to study the richness of the spectrum of spin waves due to these changes . At first deal with a superimposition of square networks where the displacement of these networks depends on the control parameters alpha and beta . We also use the superposition of a square on a hexagonal network.
Sistema de baixa dimensionalidade têm atraído uma grande atenção ultimamente devido a sistemas como grafeno e nanotubos de carbono. Tais sistemas têm grandes possibilidades de aplicações tecnológicas, em particular na criação de dispositivos eletrônicos, devido às suas propriedades eletrônicas específicas. Nesse sentido, o estudos de outros sistemas em baixa dimensão se torna urgente. Mais especificamente, o estudo de propriedades magnéticas de materiais de materiais em baixa dimensionalidade também trás grandes novidades no comportamento de sistemas ferromagnéticos. O comportamento de ondas de spin em tais sistemas pode ser para o estudo da spintrônica e o desenvolvimento de novos aparelhos e memórias magnéticas. Dessa forma temos como objetivo nesse trabalho estudar o comportamento de ondas de spin em sistemas bidimensionais ferromagnéticos. Por sistemas bidimensionais consideramos aqui redes bidimensionais decoradas. As decorações são introduzidas para gerar redes com mais de um átomo na base da célula unitária da rede para estudarmos a riqueza do espectro das ondas de spin devido a essas modificações. A princípio tratamos com uma superposição de redes quadradas onde o deslocamento dessas redes depende dos parâmetros de controle α e β. Também usamos a superposição de um rede quadrada sobre um hexagonal.

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Redjai, Sani Sohrab. "Fabrication and Characterization of Nanocontact Spin-Torque Oscillators." Doctoral thesis, KTH, Materialfysik, MF (Stängd 20120101), 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-122292.

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The manufacturing of nanocontact-based spin-torque oscillators (NC-STOs)has opened the door for spintronic devices to play a part as active microwaveelements. The NC-STO has the capability of converting a direct current intoa microwave signal, and vice versa, by utilizing the spin transfer torque (STT)in ferromagnetic multilayer systems. However, the high-frequency operation ofNC-STOs typically requires high magnetic fields and the microwave power theygenerate is rather limited. As a result, NC-STOs are not yet commercially used,and they require improvements in both material systems and device geometriesbefore they can find actual use in microwave applications. In order to improve and advance this technology, NC-STOs are requiredwith both different nanocontact (NC) sizes and geometries, and using differ- ent stacks of magnetic materials. This dissertation presents experimental in- vestigations into the manufacturing of such devices using different fabrication techniques and a number of different magnetic material stacks. Currently, the fabrication of NC-STOs is limited to advanced laboratories, because NC fabri- cation requires high-resolution lithography tools. In the present work, we have developed an alternative method of fabrication, which does not require such tools and has the capability of fabricating NC-STOs having one to hundreds of NCs in a variety of sizes, possibly down to 20 nm. Devices fabricated with this method have shown mutual synchronization of three parallel-connected NCs, and pairwise synchronization in devices with four and five NCs. Furthermore, the present work demonstrates low-field operation (down to0.02 Tesla) of NC-STOs at a record high frequency of 12 GHz. This wasachieved by implementing multilayers with a perpendicular magnetic anisotropy(PMA) material in the free layer of the NC-STO. In addition, the fabricateddevices revealed an unexpected dynamic regime under large external appliedfield (above 0.4 Tesla). The new dynamic regime was found to be due to anentirely novel nanomagnetic dynamic object â a so-called magnetic droplet soliton,predicted theoretically in 1977 but not experimentally observed until now.Detailed experiments and micromagnetic simulations show that the droplet hasvery rich dynamics. Finally, spin-torque-induced transverse spin wave instabilities have beenstudied. A NC-STO with a material stack consisting of a single ferromag- netic metal sandwiched between two non-ferromagnetic metals was fabricated. Prior to this work, evidence of spin wave instabilities was reported as resis- tance switching in nanopillar- and mechanical point contact based STOs. In the present work, the fabricated NC-STOs showed actual microwave signals up to 3 GHz under zero applied field with strong current hysteresis. All the fabricated NC-STOs open up new means of studying STT in different environ- ments, in order to resolve their current drawbacks for industrial applications.

QC 20130527

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Smith, Kevin James. "Optical control of ultrafast spin -wave relaxation by magnetic anisotropy in a ferromagnet." W&M ScholarWorks, 2010. https://scholarworks.wm.edu/etd/1539623568.

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This thesis presents an investigation of the damping of spin waves in ferromagnetic Au(3 nm)/Ni(10 nm)/MgO(001) thin films using the time-resolved Magneto-optical Kerr Effect (TR-MOKE) and ferromagnetic resonance (FMR) techniques. In the optical measurements, a 150 fs, 800 nm laser beam pulse is split into pump and probe components. The pump pulse, containing most of the beam energy, thermally excites coherent spin precession. The weaker probe pulse, time-delayed by a variable beam path, captures the magnetization dynamics via the polar MOKE effect, and oscillations are observed as a function of external field amplitude and direction. The extracted precession frequency is consistent in both the optical and resonance techniques; however, additional damping is observed in the TR-MOKE measurements that is strongly correlated to the orientation of the magnetization with respect to the magnetic anisotropy. The damping is identical in TR-MOKE and FMR only when the external field is applied near the easy axis of magnetization. The enhanced damping in TR-MOKE is shown to be a consequence of pump-induced inhomogeneous broadening in the presence of magnetic anisotropy, a result of differing temperature recovery profiles for the magnetization and magnetic anisotropy. Finally, a simple model is developed which explains the anisotropic damping: mode broadening occurs in regions where the magnetization changes rapidly with respect to changes in the external field, as determined by the curvature of the magnetic free energy. We thus introduce a novel damping effect in TR-MOKE: pump-induced anisotropic damping (PIAD).

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Gaw, Stephen Michael. "Cooperative spin excitations in quantum materials studied by neutron spectroscopy." Thesis, University of Oxford, 2014. http://ora.ox.ac.uk/objects/uuid:c20676e1-b927-4ee5-a3fe-97f0f80cb141.

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This thesis describes the experimental investigation of three different strongly correlated transition-metal oxide systems. The magnetic behaviour of each has been probed using inelastic neutron spectroscopy. A distinctive hour-glass excitation spectrum has been observed in the layered cobaltate La_1.75Sr_0.25CoO₄. This spectrum is similar to that measured in a related cobaltate La_1.67Sr_0.33CoO₄, although it appears broader. The spectrum has been reproduced using a spin wave model derived from a disordered cluster spin glass ground state. Signatures of spin glass behaviour have also been observed in bulk magnetisation measurements of La_1.75Sr_0.25CoO₄. These findings, once more, demonstrate the emergence of an hour-glass spectrum from a ground state that combines quasi-one dimensional magnetic correlations and disorder. Additionally, this study shows that charge and magnetic stripe order persists to lower dopings in La_2-xSr_xCoO₄ than previously thought. The complete magnetic excitation spectrum of the multiferroic compound CuO has been measured for the first time. A high energy, one-dimensional magnetic spectrum is observed and modelled using the Muller ansatz derived for the S=1/2 Heisenberg antiferromagnetic chain. At lower energies, a three-dimension spectrum is observed. The measured spectrum is inconsistent with all previous theoretical estimates of the dominant inter-chain exchange interactions in CuO. The inter-chain dispersion is successfully described by a phenomenological model based on linear spin wave theory. The third material investigated, LuFe₂O₄ demonstrates complex charge and magnetic order, the precise nature of which is still under debate. The full spectrum of in-plane excitations in LuFe₂O₄ has been measured and a complicated dispersion consistent with six magnetic modes is observed. These findings are compatible with structures described by a magnetic unit cell containing six spins. The dispersion can be described by a spin wave model derived from a bilayer structure comprised of charge-rich and charge-poor monolayers. This structure is consistent with the original site-specific model for the 3D magnetic ordering in LuFe₂O₄.

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Sietsema, Glade Robert. "Properties and dynamics of spin waves in one and two dimensional magnonic crystals." Diss., University of Iowa, 2016. https://ir.uiowa.edu/etd/2141.

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Spintronics is a newly emerging field in physics, aimed at using the spin of electrons to carry information. One of the primary ways in which this could be done is through the use of spin waves. In order to do this, it will be necessary to have a complete understanding of spin waves and how they behave in various materials and structures. In this dissertation, we aim to create a thorough model of spin waves in both one-dimensional and two-dimensional magnonic crystals in an effort to understand and control their dispersion properties and propagation patterns. Using the Landau-Lifshitz-Gilbert equation, we have derived a model for spin waves in magnonic crystals that allowed us to calculate their dispersion and propagation properties. In the first part of this work we considered two-dimensional magnonic crystals consisting of magnetic cylinders arrange in a lattice and embedded in a second magnetic material. The dispersion relations were found to be heavily dependent on the magnetic properties of the two materials, with band gaps appearing more readily when the magnetization was larger in the cylinders than in the host. It was also found that the dipolar field reduced the symmetry of the results, with reflection symmetry not appearing in the dispersion relations even when it was present in the physical lattice. For the propagation of spin waves in two-dimensional magnonic crystals, we found that their directionality was highly dependent on changes in frequency. Propagation patterns varied from roughly isotropic for spin waves in the middle of a band level, to highly directional propagation along the x and y axes for a frequency near the edge of a band. The absence of propagation was also found for frequencies in a band gap. For spin waves in one-dimensional magnonic crystals, we investigated the effects of applying an electric field to the system. When a uniform electric field was applied to a magnonic crystal consisting of a periodic variation in magnetic materials, the band levels were found to shift downward in frequency, with the magnitude of the shift being dependent on the strength of the electric field. While this method could move existing band gaps, it was not capable of creating a band gap in the dispersion relations. Creation of band gaps was found to occur when a periodically varying electric field was applied to a uniform magnetic material. This effect could be used to create a magnonic device where the dispersion properties can be dynamically controlled with an electric field.

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Karenowska, Alexy Davison. "Some magnetic reflections on wave dynamics." Thesis, University of Oxford, 2011. http://ora.ox.ac.uk/objects/uuid:d31bd222-a948-45f8-9617-40507f4f96c6.

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Mei, Zhongtao. "Wave Functions of Integrable Models." University of Cincinnati / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1530880774625297.

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Johansson, Petter. "Contribution from Spin-Orbit Coupling to the Langmuir Wave Dispersion Relation in Magnetized Plasmas." Thesis, Umeå universitet, Institutionen för fysik, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-46820.

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This thesis analyses the effect spin-orbit coupling has on the dispersion of Langmuir waves in magnetized plasmas, using recently developed kinetic theories of plasmas including quantummechanical and relativistic effects. Two new wave modes appearclose to the resonance $\Delta \omega_{c}$ = ( g/2 − 1) $\omega_{c}$ , where $\omega_{c}$ is the cyclotron frequency and g is the electron gyromagnetic ratio. Forconsidered long wave lengths the deviation from this resonanceis very small. The wave modes are also very weakly damped.

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Silva, WanÃssa FaÃanha da. "Ondas de spin em redes decoradas." Universidade Federal do CearÃ, 2014. http://www.teses.ufc.br/tde_busca/arquivo.php?codArquivo=12439.

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Sistema de baixa dimensionalidade tÃm atraÃdo uma grande atenÃÃo ultimamente devido a sistemas como grafeno e nanotubos de carbono. Tais sistemas tÃm grandes possibilidades de aplicaÃÃes tecnolÃgicas, em particular na criaÃÃo de dispositivos eletrÃnicos, devido Ãs suas propriedades eletrÃnicas especÃficas. Nesse sentido, o estudos de outros sistemas em baixa dimensÃo se torna urgente. Mais especificamente, o estudo de propriedades magnÃticas de materiais de materiais em baixa dimensionalidade tambÃm trÃs grandes novidades no comportamento de sistemas ferromagnÃticos. O comportamento de ondas de spin em tais sistemas pode ser para o estudo da spintrÃnica e o desenvolvimento de novos aparelhos e memÃrias magnÃticas. Dessa forma temos como objetivo nesse trabalho estudar o comportamento de ondas de spin em sistemas bidimensionais ferromagnÃticos. Por sistemas bidimensionais consideramos aqui redes bidimensionais decoradas. As decoraÃÃes sÃo introduzidas para gerar redes com mais de um Ãtomo na base da cÃlula unitÃria da rede para estudarmos a riqueza do espectro das ondas de spin devido a essas modificaÃÃes. A princÃpio tratamos com uma superposiÃÃo de redes quadradas onde o deslocamento dessas redes depende dos parÃmetros de controle α e β. TambÃm usamos a superposiÃÃo de um rede quadrada sobre um hexagonal
Low-dimensional systems have attracted much attention lately due to systems such as graphene and carbon nanotubes. Such systems have great potential for technological applications. In particular the creation of electronic devices due to their specific electronic properties. In this sense , the study of other systems in low dimension becomes urgent. More specifically , the study of magnetic properties of materials at low dimensionality also brings great new features in the behavior of ferromagnetic systems . The behavior of spin waves in such systems may be important to the study of spintronic and the development of new devices and magnetic memories . Thus in this work we aim to study the behavior of ferromagnetic spin waves in two-dimensional systems . For two-dimensional systems we consider here two-dimensional networks decorated . The decorations are introduced to generate networks with more than one basic atom in the unit cell of the system to study the richness of the spectrum of spin waves due to these changes . At first deal with a superimposition of square networks where the displacement of these networks depends on the control parameters alpha and beta . We also use the superposition of a square on a hexagonal network.

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Merdan, Mohammad Ghanim Merdan. "Study of the excited states of the quantum antiferromagnets." Thesis, University of Manchester, 2013. https://www.research.manchester.ac.uk/portal/en/theses/study-of-the-excited-states-of-the-quantum-antiferromagnets(dfd01ec6-806c-464a-9b68-910217679c3c).html.

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We investigate the quantum dynamics of the spins on different Heisenberg antiferromagnetic spin lattice systems. Firstly, we applied the coupled-cluster method to the spin-1/2 antiferromagnetic XXZ model on a square lattice by employing an approximation which contains two-body long-range correlations and high-order four-body local correlations. Improvement is found for the ground-state energy, sublattice magnetization, and the critical anisotropy when comparing with the approximation including the two-body correlations alone. We also obtain the full excitation spectrum which is in good agreement with the quantum Monte Carlo results and the high-order spin-wave theory. Secondly, we study the longitudinal excitations of quantum antiferromagnets on a triangular lattice by a recently proposed microscopic many-body approach based on magnon-density waves. We calculate the full longitudinal excitation spectra of the antiferromagnetic Heisenberg model for a general spin quantum number in the isotropic limit. Similar to the square lattice model, we find that, at the center of the first hexagonal Brillouin zone Γ(q=0) and at the magnetic ordering wavevectors ±[Q= (4π/3,0)], the excitation spectra become gapless in the thermodynamic limit, due to the slow, logarithmic divergence of the structure factor. However, these longitudinal modes on two-dimensional models may be considered as quasi-gapped, as any finite-size effect or small anisotropy will induce a large energy gap, when compared with the counterpart of the transverse spin-wave excitations. We have also investigated the excited states of the quasi-one-dimensional quantum antiferromagnets on hexagonal lattices, including the longitudinal modes based on the magnon-density waves. A model Hamiltonian with a uniaxial single-ion anisotropy is first studied by a spin-wave theory based on the one-boson method; the ground state thus obtained is employed for the study of the longitudinal modes. The full energy spectra of both the transverse modes (i.e., magnons) and the longitudinal modes are obtained as functions of the nearest-neighbor coupling and the anisotropy constants. We have found two longitudinal modes due to the non-collinear nature of the triangular antiferromagnetic order, similar to that of the phenomenological field theory approach by Affleck. The excitation energy gaps due to the anisotropy and the energy gaps of the longitudinal modes without anisotropy are then investigated. We then compares our results for the longitudinal energy gaps at the magnetic wavevectors with the experimental results for several antiferromagnetic compounds with both integer and non-integer spin quantum numbers, and we find good agreements after the higher-order contributions are included in our calculations.

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Freamat, Mario Vadim. "NORMAL AND SPIN POLARIZED TRANSPORT IN HIGH-TEMPERATURE SUPERCONDUCTOR TUNNELING JUNCTIONS." UKnowledge, 2004. http://uknowledge.uky.edu/gradschool_diss/426.

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One of the challenges facing condensed matter physics nowadays is to understand the electronic structure of high temperature superconductors. This dissertation compiles our contribution to the experimental information concerning this subject. Tunneling conductance spectroscopy a technique capable of probing the electronic density of states in hybrid structures was used to study the current and spin transport properties across junctions between metallic counterelectrodes and Bi2Sr2CaCu2O8- (BSCCO) crystals. Since in these structures the transport is mediated by transmission channels depending on superconductive characteristics, the energy resolved density of states is a signature of the mechanism of superconductivity. For instance, one can observe the superconductive energy gap and the behavior of subgap bound states due to phase sensitive Andreev reflections at the junction interface. In particular, tunneling spectroscopy makes possible the observation of the LOFF state characterized by the coexistence of superconductivity and magnetism. Cuprates like BSCCO are highly anisotropic materials and their superconductivity is almost two dimensional, being confined in the CuO2 planes. Therefore, our junctions combine monocrystals of underdoped samples of BSCCO with various thin film counterelectrodes normal metal (Ag), conventional superconductor (Pb) and ferromagnetic metal (Fe) deposited perpendicular onto the cuprate ab-plane (CuO2 plane). We performed measurements on Ag/BSCCO junctions for two current injection directions into the same crystal. We observed that, near the 110 crystal surface, the conductance spectra show a high zero bias peak (ZBCP) which is a manifestation of zero energy Andreev bound states due to an anisotropic superconductive order parameter. Near the 100 surface, the ZBCP is largely suppressed. This is consistent with a predominantly 2 2 x y d - -wave pairing symmetry. In some cases, the ZBCP splits or decreases in amplitude at low temperatures. This is consistent with the existence of a subdominant s-wave (or xy d ) resulting in a mixed d is + state which breaks time reversal symmetry (BTRS). Since we observe this phenomenon in the underdoped case, we do not confirm the possibility of a quantum critical point close to the optimal doping. Our Pb/BSCCO spectra contradict the theory explaining the BTRS by proximity effect. The Fe/BSCCO junctions measure the effect of spin polarization. We explain the recorded 4-peak asymmetric structure by the combined effect of a spin independent BTRS state and a spin filtering exchange energy in the barrier responsible for a large ZBCP splitting. The LOFF state was observed in the proximity region induced on the ferromagnetic side of multilayered-Fe/Ag/BSCCO structures. As expected for the LOFF order parameter, the spectra develops coherent damped oscillations with the Fe layer thickness probing different regions. The magnitude and sign of the oscillation depends on the energy. The conductances at energy zero or equal to the superconductive gap are modulated in antiphase proving that the order parameters takes successively positive and negative values. Changing the junction orientation with 4 p , results in an opposite behavior for the same distance. The maximal amplitudes in one direction is replaced by minima, showing that, besides space, the LOFF state modulation depends on the phase of the high temperature order parameter inducing the proximity

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Lake, Alysia C. I. "Neutron scattering studies of alternating chain antiferromagnets." Thesis, University of Oxford, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.360395.

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Niesert, Manfred [Verfasser]. "Ab initio calculations of spin-wave excitation spectra from time-dependent density-functional theory / Manfred Niesert." Aachen : Hochschulbibliothek der Rheinisch-Westfälischen Technischen Hochschule Aachen, 2012. http://d-nb.info/102156754X/34.

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Kreisel, Andreas [Verfasser], Peter [Akademischer Betreuer] Kopietz, and Sebastian [Akademischer Betreuer] Eggert. "Spin-wave calculations for Heisenberg magnets with reduced symmetry / Andreas Kreisel. Gutachter: Peter Kopietz ; Sebastian Eggert." Frankfurt am Main : Univ.-Bibliothek Frankfurt am Main, 2011. http://d-nb.info/1044195223/34.

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Waizner, Johannes [Verfasser], Markus [Gutachter] Garst, and Achim [Gutachter] Rosch. "Spin wave excitations in magnetic helices and skyrmion lattices / Johannes Waizner ; Gutachter: Markus Garst, Achim Rosch." Köln : Universitäts- und Stadtbibliothek Köln, 2017. http://d-nb.info/1149794127/34.

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Ruane, William Terrence. "Controllable Spin Wave Generation with Spatially Dependent Magnetic Fields and Their Detection Using Ferromagnetic Resonance Force Microscopy." The Ohio State University, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=osu1524171463673634.

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Heimbach, Florian [Verfasser], Dirk [Akademischer Betreuer] [Gutachter] Grundler, and Martin S. [Gutachter] Brandt. "Current-Controlled Spin-Wave Interference in Magnonic Waveguides and Magnetization Dynamics in Artificial Spin Ice and Ferromagnetic Nanotubes / Florian Heimbach. Betreuer: Dirk Grundler. Gutachter: Dirk Grundler ; Martin S. Brandt." München : Universitätsbibliothek der TU München, 2016. http://d-nb.info/1103658298/34.

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Grechnyev, Oleksiy. "Theoretical Studies of Two-Dimensional Magnetism and Chemical Bonding." Doctoral thesis, Uppsala : Acta Universitatis Upsaliensis : Univ.-bibl. [distributör], 2005. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-4815.

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Gerlach, Max Henner [Verfasser], Simon [Gutachter] Trebst, and Achim [Gutachter] Rosch. "Quantum Monte Carlo studies of a metallic spin-density wave transition / Max Henner Gerlach ; Gutachter: Simon Trebst, Achim Rosch." Köln : Universitäts- und Stadtbibliothek Köln, 2017. http://d-nb.info/112720002X/34.

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