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Wittmann, Angela Dorothea Anshi. "Spin currents in organic semiconductors." Thesis, University of Cambridge, 2019. https://www.repository.cam.ac.uk/handle/1810/290148.
Texte intégralRésumé :
Organic semiconductors have recently been found to have a comparably large spin diffusion time and length. This makes them ideal candidates for spintronic devices. However, spin injection, transport and detection properties in organic materials have yet to be fully understood. This work studies spin injection from ferromagnets into organic semiconductors via spin pumping. Furthermore, work towards thermal spin injection, and detection is presented and discussed. The first part of this thesis comprises the spin pumping experiments. Measuring linewidth broadening of the microwave absorption at ferromagnetic resonance due to increase in effective Gilbert damping by spin pumping from a ferromagnetic substrate into an adjacent non-magnetic semiconductor allows us to quantify the spin-mixing conductance. This technique is employed to demonstrate spin injection from a ferromagnetic metal, permalloy (Ni81Fe19), into organic small molecules and conjugated polymers as well as to quantify the spin injection efficiency. The results highlight the importance of structural properties of organic semiconductors at the interface to permalloy. Significant suppression of spin injection due to alkyl side-chains separating the core of the small molecules from the interface is exemplary for this finding. Furthermore, the spin-mixing conductance depends very sensitively on the charge carrier density within a certain range of doping level. This suggests a strong link between spin injection efficiency and spin concentration in the organic semiconductor at the interface to permalloy. The second part of the thesis aims to explore spin caloritronic effects. We study spin injection into organic semiconductors by probing the spin Seebeck effect by making use of the inverse spin Hall effect for spin-to-charge conversion. Moreover, we present experimental work towards observation of a novel effect, the inverse spin Nernst effect, for thermal spin detection.
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Díaz, Santiago Sebastián Alejandro. "Controlling Spin Interactions With Electric Currents." Tesis, Universidad de Chile, 2010. http://www.repositorio.uchile.cl/handle/2250/102410.
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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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Hahn, Christian. "Magnetization dynamics and pure spin currents in YIG/normal-metal systems." Thesis, Paris 6, 2014. http://www.theses.fr/2014PA066657.
Texte intégralRésumé :
Le domaine de recherche de la spintronique vise a concevoir des dispositifs électroniques misant sur le degré de libre de spin pour transporter de l'information. An d'intégrer ces courants de spin dans des dispositifs électroniques, il est particulièrement intéressant d'étudier l'inter-conversion d'un pur courant de spin en un courant de charge par l'effet Hall de spin, ainsi que le transfert de moment angulaire entre les électrons de conduction d'un métal normal (NM) et l'aimantation d'un ferromagnétique (FM) (couple de transfert de spin / pompage de spin). An de mieux comprendre ces différentes interaction, cette thèse se concentre sur l'étude du système hybride constitué de la juxtaposition d'un ferrimagnétique isolant, le grenat d'yttrium fer (YIG), et d'un métal normal _a fort couplage spin-orbite (Pt ou Ta), nécessaire pour bénéficier de la polarisation en spin de l'interface par un courant électrique dans le plan. Nous avons étudié le pompage de spin et la magnétorésistance produite par l'effet Hall de spin a l'interface entre des bicouches de YIG j Pt et YIG j Ta, et ceci sur des lms étendus de YIG de 200 nm d'épaisseur, produits par épitaxie en phase liquide. Nous observons que la tension électrique, produite par l'effet Hall de spin inverse, change de signe entre du Pt et du Ta confirmant ainsi l'inversion des signes de l'angle de Hall entre ces deux matériaux. En outre, en mesurant la variation de la tension de Hall inverse en fonction de l'épaisseur de la couche de Ta, nous avons réussi à borner la longueur de diffusion de spin dans le Ta. Tant le YIG j Pt et le YIG j Ta affiche une variation semblable de la magnétorésistance a effet Hall de spin en fonction de l'orientation du champ magnétique. Pour étudier l'inuence interfaciale du pompage de spin…<br>Spintronics aims at designing electronic devices which capitalize on the spin degree of freedom to transport information using spin currents. In order to incorporate spin currents intoelectronic devices, it is particularly interesting to study the interconversion from a spin current, the motion of spin angular momentum, to a charge current (Spin Hall Effect) as well as the transfer of spin angular momentum between the conduction electrons of a normal metal (NM) and the magnetization of a ferromagnet (FM) (Spin Transfer Torque/Spin Pumping). To investigate the interplay of those effects this thesis studies hybrid systems of the ferromagnetic insulator Yttrium Iron Garnet and normal metals with large spin-orbit coupling, a prerequisite for spin Hall e_ect. We study spin pumping and spin hall magnetoresistance in YIGjPt and YIGjTa bi-layers using extended _lms of 200 nm thick YIG, grown by liquid phase epitaxy. The inverse spin Hall voltages in Pt and Ta confirm the opposite signs of spin Hall angles in these two materials. Moreover, from the dependence of the inverse spin Hall voltage on the Ta thickness, we constrain the spin di_usion length in Ta. Both the YIGjPt and YIGjTa systems display a similar variation of resistance upon magnetic eld orientation, the spin Hall magnetoresistance. To study the inuence of interfacial spin pumping and a possible reverse e_ect, it is desirable to work with thin _lm thicknesses. A high quality 20 nm thick YIG _lm was grown by pulsed laser deposition, showing a damping similar to that of bulk YIG. We use nano-lithography to pattern series of YIG(20nm) and YIG(20nm)jPt(13nm) discs with diameters between 300 and 700 nm. The ferromagnetic resonance (FMR) spectra of the individual sub-micron sized samples are recorded through magnetic resonance force microscopy. . Passing dc-current through micron sized YIGjPt disks reveal a variation of the FMR linewidth consistent with the geometry and amplitude of the expected SHE transfer torque. In the absence of exciting microwave _elds, a variation in the magnetization is detected when the dc-current reaches the expected threshold for auto oscillations
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Savero, Torres Williams. "Interplay between pure spin currents and magnetic domain walls." Thesis, Grenoble, 2014. http://www.theses.fr/2014GRENY084.
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Ce manuscrit est basé sur l'étude de l'interaction entre des purs courants de spin et parois de domaines magnétiques. Cet étude a été divisée en quatre parties. Dans la première partie, nous avons donné une explication détaillée du transport de spin dans des nano structure métalliques en utilisant trois approches différentes. La deuxième partie est focalisée sur l'utilisation d'un pur courant de spin pour induire le mouvement d'un paroi de domaine. Dans la troisième et quatrième partie nous avons mis en évidence deux nouvelle techniques d'injection et détection de spin en utilisant des parois des domaines magnétiques<br>This thesis is based on the study of the interplay between pure spin currents and magnetic domains walls. This study has been divided in four chapters. In the first part, we provides a detailed explanation of the spin-transport in metallic structures by using three approaches. The second chapter concerns to the use of pure spin currents to induce DW motion in lateral spin valves. The third and four chapter, is mainly focused on the use of DWs for the efficient injection and detection of pure spin currents in lateral spin valves and cross shaped geometries
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Zhang, S., and A. Fert. "Conversion between spin and charge currents with topological insulators." AMER PHYSICAL SOC, 2016. http://hdl.handle.net/10150/622358.
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Injection of a spin current into the surface or interface states of a topological insulator (TI) induces a charge current (inverse Edelstein effect or IEE) and, inversely, a charge current flowing at the surface or interface states of a TI generates a nonzero spin density (Edelstein Effect or EE) from which a spin current can be ejected into an adjacent layer. The parameters characterizing the efficiency of these conversions between spin and charge currents have been derived in recent experiments. By using a spinor distribution function for a momentum-spin locked TI, we determine a number of spin transport properties of TI-based heterostructure and find that the spin to charge conversion in IEE is controlled by the relaxation of an out-of equilibrium distribution in the TI states while the charge to spin conversion in EE depends on the electron transmission rate at the interface of the TI.
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Stagraczyński, Stefan Piotr [Verfasser]. "Magnetic dynamics and spin currents in quantum spin systems strongly coupled to environment / Stefan Piotr Stagraczyński." Halle, 2017. http://d-nb.info/114951289X/34.
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Statuto, Nahuel. "Magnetic Excitations Induced by Surface Acoustic Waves and Spin-Polarized Currents." Doctoral thesis, Universitat de Barcelona, 2019. http://hdl.handle.net/10803/667710.
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The goal of this thesis is to explore and control the magnetization dynamics on magnetic multilayered thin films through two different techniques: the application of strain and spin- polarized currents, which represent lower-power consumption approaches to the control of magnetization dynamics compared with conventional techniques.
The ferromagnetic materials with nanometric thickness used in this thesis are magnetic materials widely used in research. Aside the purely scientific interest, these materials are potentially applicable in telecommunications or technologies for storing and transmitting information at high speeds.
1. Magnetization Dynamics Induced by the Application of Oscillating Strain
The first part of the thesis studies the magnetization dynamics induced by the application of dynamic strain on the magnetic material. The strain deforms the magnetic material and induces a change in the direction and intensity of the magnetic anisotropy. Therefore, the magnetic states are affected by this variation and align with the new direction of magnetic anisotropy inducing dynamics in the magnetization.
The main result of the first part of the thesis is the simultaneous time- and space-resolved observation of both the piezoelectric voltage wave associated to the SAW and the induced magnetization excitations on the ferromagnetic thin film of Nickel (Ni). We have found that manipulation of magnetization states in ferromagnetic thin films with SAWs is possible at the picosecond scale with efficiencies as high as for the static case. In Chapter 3 we have studied Ni nanostructures whose magnetization dynamics are governed by the intrinsic configuration of the magnetic domains and by their orientation with respect to the SAW- induced strain resulting in considerable delays between strain and magnetization. In Chapter 4 we have studied extended Ni thin film, on which SAWs induce spin waves that propagate millimeter distances and have a rotation amplitude of about 25 deg.
2. Magnetization Dynamics Induced by the Spin-Polarized Current
The second part of the thesis studies the magnetization dynamics induced by the application of spin-polarized current through the magnetic material that exchanges magnetic moment with the magnetic spins of the electrons in the current. The current density has to be high to induce dynamics on the magnetization (~106-107 A/cm2) and this results in a reduction of the diameter of the electrical contact 50-200 nm.
The main results of the second part of the thesis are related with the stability and the nucleation process of magnetic solitons. On the one hand, we have showed that magnetic solitons can exhibit multiple stable states, which are tunable with current or magnetic field. We also have correlated the existence of unstable states with an increment of low- frequency noise. Using simulations, we have identified the low-frequency spectra with the existence of drift resonances and we have observed that any asymmetry on the effective magnetic field suffered by the magnetic soliton can leads to drift resonances. On the other hand, we have experimentally observed that the processes of nucleation and annihilation of magnetic solitons have different intrinsic times, and using simulations we have identified a waiting time associated with the creation process, which make it a longer than annihilation. We also have studied, using micromagnetic simulations, the initial magnetization states that lead to the nucleation of topological and non-topological magnetic solitons.<br>La tesis gira en torno al estudio de la dinámica de la magnetización en capas y multicapas delgadas ferromagnéticas. Sin embargo, los sistemas estudiados son diversos y pueden clasificarse por la técnica utilizada para la excitación de la dinámica de la magnetización. Este hecho queda plasmado en la estructura de la tesis que consta de una introducción general, Capítulo 1, y luego de dos partes independientes y separadas, a su vez, en varios capítulos. El orden en la exposición de los resultados pretende seguir una linea lógica para su compresión. Como contrapartida, los resultados son presentados sin seguir un orden cronológico.
La primera parte de la tesis estudia la dinámica de la magnetización inducida por la aplicación de tensión dinámicamente sobre el material magnético, que al deformarlo induce en él un cambio en la dirección e intensidad de la anisotropía magnética. Por lo tanto, los estados magnéticos se ven afectados por esta variación y cambian para alinearse con la nueva dirección de anisotropía magnética induciendo dinámica en la magnetización.
La segunda parte de la tesis estudia la dinámica de la magnetización inducida por la aplicación de corriente polarizada a través del material magnético que intercambia momento magnético con los espines magnéticos de los electrones de la corriente. Para que esta transferencia de momento magnético sea efectiva la densidad de corriente ha de ser elevada (~106-107 A/cm2) y para conseguirla se reduce hasta los 50-200 nm el diámetro del contacto eléctrico.
Los materiales ferromagnéticos con grosor nanométrico usados en esta tesis son materiales magnéticos usados ampliamente en la investigación. Aparte del interés puramente científico, estos materiales son potencialmente aplicables en telecomunicaciones o tecnologías del almacenaje y transmisión de información a altas velocidades.
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Fransson, Jonas. "Non-Orthogonality and Electron Correlations in Nanotransport : Spin- and Time-Dependent Currents." Doctoral thesis, Uppsala University, Department of Physics, 2002. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-2687.
Texte intégralRésumé :
<p>The concept of the transfer Hamiltonian formalism has been reconsidered and generalized to include the non-orthogonality between the electron states in an interacting region, e.g. quantum dot (QD), and the states in the conduction bands in the attached contacts. The electron correlations in the QD are described by means of a diagram technique for Hubbard operator Green functions for non-equilibrium states. </p><p>It is shown that the non-orthogonality between the electrons states in the contacts and the QD is reflected in the anti-commutation relations for the field operators of the subsystems. The derived forumla for the current contains corrections from the overlap of the same order as the widely used conventional tunneling coefficients. </p><p>It is also shown that kinematic interactions between the QD states and the electrons in the contacts, renormalizes the QD energies in a spin-dependent fashion. The structure of the renormalization provides an opportunity to include a spin splitting of the QD levels by polarizing the conduction bands in the contacts and/or imposing different hybridizations between the states in the contacts and the QD for the two spin channels. This leads to a substantial amplification of the spin polarization in the current, suggesting applications in magnetic sensors and spin-filters.</p>
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Caruso, Laure. "Giant magnetoresistance based sensors for local magnetic detection of neuronal currents." Thesis, Paris 6, 2015. http://www.theses.fr/2015PA066272/document.
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L'étude de l'activité cérébrale nécessite des enregistrements simultanés à différentes échelles spatiales, d'une cellule unique aux aires corticales du cerveau. Ces mesures fournissent un aperçu sur la relation entre les structures, les fonctions et la dynamique des circuits neuronaux. Les techniques d'électrophysiologie apportent des informations cruciales sur l'activité électrique dans les neurones. Sonder localement la signature magnétique de cette activité donne des informations directes sur les courants neuronaux et la nature vectorielle d'une mesure magnétique renseigne sur la directionnalité du flux ionique neuronal sans le perturber. Le champ magnétique induit par les courants neuronaux est accessible par la magnetoencéphalographie (MEG), qui fournit la cartographie des champs neuromagnétiques à la surface du cerveau à l'aide des Superconducting Quantum Interference Devices (SQUIDs). Cependant, les mesures locales de courants neuronaux à l'échelle cellulaire nécessite des dispositifs miniaturisés et très sensibles. L'objectif de ce travail de thèse est de développer un nouvel outil pour la neurophysiologie, l'équivalent magnétique d'électrodes, nommé "magnetrodes", capable de détecter les courants neuronaux locaux par la détection magnétique. Les progrès récents de l'électronique de spin ont permis de donner naissance aux capteurs à magnétorésistance géante (GMR), qui offrent la possibilité d'être miniaturisé et suffisamment sensibles pour détecter des champs magnétiques très faibles, comme ceux émis par les neurones à l'échelle locale (de l'ordre du picotesla au nanotesla). Deux types de capteurs GMRs ont été développés au cours de ce travail, des sondes planes dédiées aux enregistrements en surface des tissues (tranche d'hippocampe, muscle ou cortex), les autres sont des sondes pointus, conçus pour pénétrer facilement les tissus et enregistrer localement les champs neuromagnétiques. Trois expériences ont été réalisées dont deux in vitro et une in vivo. Le premier potentiel d'action magnétique a été détecté in vitro à l'aide de sondes GMRs planes, résultant des courants axiaux dans un muscle de la souris. Le deuxième modèle analysé in vitro est la tranche d'hippocampe de cerveau de souris où les deux types de sondes ont été testés, montrant certains résultats préliminaires. Enfin, nous avons effectué les premiers enregistrements magnétiques in vivo sur le cortex visuel du chat, affichant des réponses corticales induites de l'ordre de 10-20 nTpp. Ces résultats ouvrent la voie à magnetophysiologie locale qui est une nouvelle approche d'exploration et d'interfaçage cerveau<br>Understanding brain activity requires simultaneous recordings across spatial scales, from single-cell to brain-wide network. Measurements provide insights about the relationship between structures, functions and dynamics in neuronal circuits and assemblies. Electrophysiological techniques carry crucial information about the electrical activity within neurons. Locally probing the magnetic signature of this activity gives direct information about neuronal currents and the vectorial nature of magnetic measurements provides the directionality of neuronal ionic flux without disturbing it. Noticeably, the magnetic signature induced by the neuronal currents is accessible through Magneto EncephaloGraphy (MEG), which provides neuromagnetic field mapping outside the head using Superconducting QUantum Interference Devices (SQUIDs). However, local measurements of neuronal currents at cellular scale requires small and very sensitive devices. The purpose of the present thesis work is to develop a novel tool for neurophysiology, the magnetic equivalent of electrodes, named “magnetrodes”, are able to detect the local neuronal currents through magnetic detection. Recent advances in spin electronics have given rise to Giant MagnetoResistance (GMR) based sensors, which offer the possibility to be miniaturized and sensitive enough to detect very weak magnetic fields like those emitted by neurons at local scale (in the picotesla to nanotesla range). Two kinds of GMR based sensors have been developed throughout this work, one of these are planar probes dedicated to surface measurements (hippocampus slice, muscle or cortex), the other kind are sharp probes, designed in a needle-shape to easily penetrate the tissues and locally record the neuromagnetic fields. Three experiments have been performed, either in vitro and in vivo. In the first experiment, an Action Potential has been detected magnetically in vitro by means of planar GMR sensors, resulting from axial currents within a mouse muscle. The second in vitro experiment analyzed the hippocampal mouse brain slices, where both planar and sharp probes were tested giving some preliminary results. Lastly we performed the first magnetic recordings in vivo on cat's cerebral cortex, displaying stimulus-induced cortical responses of 10-20 nT pp . These results pave the way for local magnetophysiology, a novel approach of brain exploration and interfacing
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Olbrich, Peter [Verfasser]. "THz radiation induced spin polarized currents in low dimensional semiconductor structures / Peter Olbrich." Regensburg : Univ.-Verl. Regensburg, 2010. http://d-nb.info/1007748214/34.
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Severac, Childerick Henri Louis. "Spin injection into high temperature superconductor." Thesis, University of Birmingham, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.369295.
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Cramer, Joel [Verfasser]. "Propagation, manipulation and detection of magnonic spin currents in magnetic oxides and metals / Joel Cramer." Mainz : Universitätsbibliothek Mainz, 2018. http://d-nb.info/1173005986/34.
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Terrade, Damien [Verfasser], and Walter [Akademischer Betreuer] Metzner. "Proximity effects and Josephson currents in ferromagnet : spin-triplet superconductors junctions / Damien Terrade. Betreuer: Walter Metzner." Stuttgart : Universitätsbibliothek der Universität Stuttgart, 2015. http://d-nb.info/1071843494/34.
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Czeschka, Franz Dominik [Verfasser], Rudolf [Akademischer Betreuer] Gross, and Martin S. [Akademischer Betreuer] Brandt. "Spin Currents in Metallic Nanostructures / Franz Dominik Czeschka. Gutachter: Rudolf Gross ; Martin S. Brandt. Betreuer: Rudolf Gross." München : Universitätsbibliothek der TU München, 2011. http://d-nb.info/1015627935/34.
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Loren, Eric Justin. "All optical injection and detection of ballistic charge and spin currents in gallium arsinide, germanium, and silicon." Diss., University of Iowa, 2011. https://ir.uiowa.edu/etd/2742.
Texte intégralRésumé :
Charge transport and spin transport (spintronics) over nanometer spatial scales are topics of fundamental scientific and technological interest. If the potential of nano-devices and spintronics is to be realized, ways must be developed to inject and control ballistic charge and spin currents, as well as to measure their motion. Here, using novel polarization and phase sensitive optical pump probe techniques, we not only inject ballistic charge and spin currents in GaAs, Ge, and Si but also follow the subsequent carrier motion with < 1 nm spatial and 200 fs temporal resolution. Unlike most free space measurements, the spatial resolution of these techniques is not limited by diffraction, and therefore these techniques provide a unique platform for studying ballistic transport in semiconductors and semiconductor structures.
The injection process relies on quantum interference between absorption pathways associated with two-photon absorption of a fundamental optical field and one-photon absorption of the corresponding second harmonic. By utilizing the phase, polarization, photon energy, and intensity of the optical fields we can control the type of current injection (spin current or charge current) and the direction and magnitude. In GaAs we present the first time resolved measurements of charge and spin currents injected by this process and also show the ballistic direct and inverse Spin Hall Effect. These techniques are extended to the more technologically relevant group IV semiconductors Si and Ge. The charge currents injected in these materials show similar qualitative behavior. The electrons and holes are injected with oppositely directed average ballistic velocities that move apart and return to a common position on sub-picosecond time scales. The spin currents however, are very different. The spin up and spin down carrier profiles move apart and remain apart until their spin profiles decay. In GaAs the profile decay on picosecond time scales however, in Ge they decay on femtosecond time scales since the electrons quickly scatter to the side valleys. Unlike GaAs and Ge, the spin orbit coupling in Si is much too small to produce measurable spin currents.
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Stanley, Daniel C. "MAGNETIC DAMPING IN FE3O4 THROUGH THE VERWEY TRANSITION FOR VARIABLE AG THICKNESSES." Miami University / OhioLINK, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=miami1376500586.
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Schlitz, Richard [Verfasser], Sebastian T. B. [Gutachter] Goennenwein, and Felix [Gutachter] Casanova. "Topological Transport Effects and Pure Spin Currents in Nanostructures / Richard Schlitz ; Gutachter: Sebastian T. B. Goennenwein, Felix Casanova." Dresden : Technische Universität Dresden, 2020. http://d-nb.info/1227201397/34.
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Saygun, Turab. "Magnetic State Detection in Magnetic Molecules Using Electrical Currents." Thesis, Uppsala universitet, Materialteori, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-257094.
Texte intégralRésumé :
A system with two magnetic molecules embedded in a junction between non-magnetic leads was studied. In this system electrons tunnel from the localized energy level in region one to the localized energy level in region two generating a flow of electric charge through the quantum dot system. The current density and thus the conductance changes depending on the molecular spin moment. In this work we studied molecules with either spin "up" or spin "down" and with symmetric coupling strengths. The results indicate that the coupling strength between energy level and molecule together with the tunneling rate through the insulating layer play a major role when switching from parallel to anti-parallel molecular spin, for a specific combination of the coupling strength and tunneling rate we could observe a decrease in the current by 99.7% in the non-gated system and 99.4% in the gated system.
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Remy, Quentin. "Ultrafast spin dynamics and transport in magnetic metallic heterostructures." Electronic Thesis or Diss., Université de Lorraine, 2021. http://www.theses.fr/2021LORR0191.
Texte intégralRésumé :
Le contrôle de l'aimantation, et donc du spin, aux échelles de temps ultra courtes, est un sujet d'importance fondamentale pour l'élaboration de systèmes qui peuvent stocker de l'information beaucoup plus rapidement. La possibilité d'écrire de l'information avec des pulses laser femtoseconde sur des métaux magnétiques tels que GdFeCo ou MnRuGa en quelques picosecondes fut une étape conséquente pour pouvoir réaliser ce progrès technologique. Cependant, le renversement de l'aimantation observé dans ces matériaux après les avoir irradié avec un unique pulse laser, appelé retournement tout optique indépendant de l'hélicité (AO-HIS pour {All Optical Helicity Independent Switching} en anglais), est toujours limité à une petite catégorie de matériaux ferrimagnétiques et sa description physique n'est toujours pas entièrement comprise. Dans cette thèse, nous étudions l'AO-HIS dans des films minces composés d'une ou deux couches d'alliages de GdFeCo de différentes compositions. Nous montrons que ces couches génèrent des courants de spin qui peuvent modifier l'AO-HIS de ces matériaux. En particulier, nous montrons qu'il est possible d'utiliser ces courants de spin pour renverser l'aimantation des différentes multicouches ferromagnétiques, avec un seul pulse laser femtoseconde, qui ne subiraient qu'une désaimantation et ne se retourneraient donc pas autrement. En changeant la composition de l'alliage de GdFeCo et la température de Curie du matériau ferromagnétique, nous pouvons modifier l'énergie nécessaire pour engendrer le renversement magnétique de la multicouche ferromagnétique avec un pulse de lumière. De plus, nous montrons que l'AO-HIS de l'alliage de GdFeCo n'est en réalité pas nécessaire ainsi que l'illumination directe de la couche ferromagnétique par la lumière laser. Il est donc possible de retourner l'aimantation d'un matériau ferromagnétique en utilisant uniquement des courants ultra courts de chaleur et de spin qui sont créés par la désaimantation ultra rapide partielle de l'alliage de GdFeCo et transportés jusqu'à la couche ferromagnétique via une couche de cuivre. Ces expériences sont comprises grâce à un modèle de transport semi classique dans un système contenant des électrons, des phonons et des spins quantiques et qui est basé sur l'échange de moment cinétique entre des spins localisés et itinérants. Enfin, nous avons mesuré la dynamique du renversement de l'aimantation de ce système ferromagnétique. Nous montrons que ce retournement se passe en moins d'une picoseconde, ce qui est le retournement d'aimantation le plus rapide jamais observé. Nous montrons que le courant de spin provenant de l'alliage de GdFeCo à un pouvoir réfrigérant sur l'aimantation, déjà visible en moins d'une picoseconde, et qui peut augmenter l'aimantation transitoire du système jusqu'à trente pourcents. Ces résultats sont également compris dans le cadre de notre modèle de transport de chaleur et de moment cinétique<br>The control of magnetization, and thus spin, at the shortest timescale, is a fundamental subject for the development of faster data storage devices. The capability to encode information with femtosecond laser pulses on magnetic metals such as GdFeCo or MnRuGa within a few picoseconds was a significant step towards the realization of such a technology. However, the reversal of magnetization observed in these materials upon a single laser pulse irradiation, called All Optical Helicity Independent Switching (AO-HIS), is still limited to a small class of ferrimagnetic materials and its physical mechanism is not completely understood.In this work, we study AO-HIS in magnetic thin films composed of a single or two GdFeCo layers with different alloy compositions. We show that these layers generate spin currents that can affect the AO-HIS of these materials. In particular, we can use such spin currents to reverse the magnetization of various ferromagnetic multilayers, with a single femtosecond laser pulse, which would otherwise only demagnetize and never switch. Playing with the GdFeCo alloy concentration and the ferromagnetic multilayer Curie temperature, we can tune the energy required to observe single shot reversal of the ferromagnet. In addition, we show that neither AO-HIS of the GdFeCo layer is actually required nor direct light illumination of the ferromagnetic multilayer. It is then possible to reverse the magnetization of ferromagnets using only ultrashort heat and spin currents which are generated by the partial ultrafast demagnetization of GdFeCo and transported via a thick metallic copper spacer. These experimental results were successfully understood using semiclassical transport equations for electrons, phonons and quantum spins based on exchange of angular momentum between localized and itinerant spins.Finally, we were able to measure the dynamics of the ferromagnetic multilayer magnetization reversal which is shown to happen in less than a picosecond, being the fastest magnetization reversal ever observed. The action of the external spin current is shown to have an ultrafast cooling effect on the spin which is visible at the sub-picosecond timescale and which can enhance the transient magnetization by up to thirty percent. These results are also understood using our model of heat and angular momentum transport
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Souza, Marcos Vinicios de. "Estudo da reorientação de spin nos compostos RX2 (R = terra rara; X: Al, Ni)." Pós-Graduação em Física, 2013. https://ri.ufs.br/handle/riufs/5290.
Texte intégralRésumé :
In this work, our initial efforts have been directed to study the behavior of the magnetization as a function of temperature, calculated according to the approximate method of the anisotropy constants and the resolution of a Hamiltonian (that includes the crystal field) as exemplified for the DyAl2 compound. Furthermore, we investigated the magneto-thermal characteristics of some members of the RX2 series (R: rare earth, X: Al, Ni), including spin reorientation (SR), by using a model Hamiltonian, that consists of localized magnetic moments interacting via exchange and crystal field interaction, in the molecular-field approximation. We studied how the SR depends on the direction of the application of magnetic field, the intensity of this field and temperature. For the magnetic calculations, the problem of self-consistency was solved by using a computational routine developed in the Fortran 90 programming language. We emphasize that special attention was directed to the crystal field, because of its high relevance to the anisotropic characteristics of the RX2 studied compounds. Thus, in our attempts to study the peculiarities of the rare earth elements, due to crystal field effects, we have not only considered the intensity change, but the direction change of the applied field. In the cases of both Er+3 and Tb+3 compounds, we obtained second-order or continuous magnetization behavior along the polar angle axis. We stressed that the crystal field terms plays an important role in the first order spin reorientation for Dy+3 and Ho+3 compounds. First, it can be revealed by the discontinuity in the Cartesian components of the magnetization vector as a function of the polar angle. Second, the discontinuity is of great importance in the calculation of latent heat associated to the spin reorientation in the case where the first order transitions were observed. Finally, we were able to separate the first and second order contributions of the anisotropic magnetic entropy change, which is the main result of this work.<br>Neste trabalho, nossos esforços iniciais foram direcionados a estudar o comportamento da magnetização em função da temperatura, calculado segundo o método aproximativo das constantes de anisotropia e da resolução de um hamiltoniano (que inclui o campo cristalino) como exemplificado para o composto DyAl2. Além disto, investigamos as características magneto-térmicas de alguns integrantes da série RX2 (R: Terra rara; X: Al, Ni), incluindo a reorientação de spin (RS), usando um hamiltoniano modelo que consiste de momentos magnéticos localizados interagentes via interações de troca e de campo cristalino, na aproximação do campo molecular. Estudamos como a RS depende da direção de aplicação do campo magnético, da sua intensidade e da temperatura. Para os cálculos magnéticos, o problema da auto consistência foi solucionado utilizando uma rotina, computacional desenvolvida na linguagem computacional Fortran 90. Ressaltamos que, uma atenção especial foi direcionada ao campo cristalino, por conta da sua alta relevância sobre as características anisotrópicas dos compostos RX2 estudados. Portanto, em nossas tentativas para estudar as peculiaridades dos elementos terras raras, devido aos efeitos do campo cristalino, não consideramos somente a mudança na intensidade, mas a variação na direção do campo aplicado. No caso dos compostos Er+3 e Tb+3, obteve-se um comportamento da magnetização de segunda ordem ou contínuo face à mudança do ângulo polar. Salientamos que os termos de campo cristalino desempenham um papel fundamental na reorientação de spin de primeira ordem para Dy+3 e Ho+3. Primeiro, tal transição pode ser revelada por uma descontinuidade nas componentes cartesianas do vetor de magnetização em função do ângulo polar. Segundo, a descontinuidade é de grande importância para o cálculo do calor latente associado à reorientação spin nos casos em que foram observadas as transições de primeira ordem. Finalmente, foi possível separar as contribuições de primeira e segunda ordem da variação de entropia magnética anisotrópica, o qual é o principal resultado deste trabalho.
22
Hau, Wing Yu. "Electrical current converted from optically excited spin current /." View abstract or full-text, 2008. http://library.ust.hk/cgi/db/thesis.pl?PHYS%202008%20HAU.
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Денисов, Станіслав Іванович, Станислав Иванович Денисов, Stanislav Ivanovych Denysov, and 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.
Texte intégralRésumé :
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.
24
He, Jiexuan. "Effects of spin current in ferromagnets." Diss., Columbia, Mo. : University of Missouri-Columbia, 2008. http://hdl.handle.net/10355/6060.
Texte intégralRésumé :
Thesis (Ph. D.)--University of Missouri-Columbia, 2008.<br>The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file (viewed on August 4, 2009) Vita. Includes bibliographical references.
25
Ivanov, V. I., V. K. Dugaev, E. Y. Sherman, and J. Barnas. "Spin current in (110)-oriented GaAs quantum wells." Thesis, Sumy State University, 2011. http://essuir.sumdu.edu.ua/handle/123456789/20556.
Texte intégralRésumé :
We consider a possibility of generation of the stationary spin current in (110) –
oriented GaAs-basedsymmetric quantum well due to the nonlinear response to externalperiodic
electric field. The model includes the Dresselhaus spin-orbit interaction and
the random Rashbaspin-orbit coupling.
When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/20556
26
Mazzoni, Michele. "Generalized hydrodynamics of a (1+1)-dimensional integrable scattering theory with roaming trajectories." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2021. http://amslaurea.unibo.it/23209/.
Texte intégralRésumé :
The emergence of hydrodynamic features in off-equilibrium (1 + 1)-dimensional integrable quantum systems has been the object of increasing attention in recent years. In
this Master Thesis, we combine Thermodynamic Bethe Ansatz (TBA) techniques for
finite-temperature quantum field theories with the Generalized Hydrodynamics (GHD)
picture to provide a theoretical and numerical analysis of Zamolodchikov’s staircase
model both at thermal equilibrium and in inhomogeneous generalized Gibbs ensembles.
The staircase model is a diagonal (1 + 1)-dimensional integrable scattering theory with
the remarkable property of roaming between infinitely many critical points when moving
along a renormalization group trajectory. Namely, the finite-temperature dimensionless
ground-state energy of the system approaches the central charges of all the minimal unitary conformal field theories (CFTs) M_p as the temperature varies. Within the GHD
framework we develop a detailed study of the staircase model’s hydrodynamics and compare its quite surprising features to those displayed by a class of non-diagonal massless
models flowing between adjacent points in the M_p series. Finally, employing both TBA
and GHD techniques, we generalize to higher-spin local and quasi-local conserved charges
the results obtained by B. Doyon and D. Bernard [1] for the steady-state energy current
in off-equilibrium conformal field theories.
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Pattinson, Neil. "Spin-current induced torques in nanoscale ferromagnets." Thesis, Lancaster University, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.420539.
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Fördös, Tibor. "Coherent light sources with spin-polarized current." Thesis, Université Paris-Saclay (ComUE), 2018. http://www.theses.fr/2018SACLX043/document.
Texte intégralRésumé :
Les spin-lasers sont des dispositifs semi-conducteurs dans lesquels les processus de recombinaison radiative impliquant des porteurs polarisés en spin résultent en une émission de photons polarisés circulairement. Néanmoins, des anisotropies linéaires supplémentaires dans la cavité conduisent généralement à une émission laser préférentiellement polarisée linéairement et à un éventuel couplage entre modes. Dans cette thèse, une méthode générale pour la modélisation de lasers à semi-conducteurs tels que laser à surface verticale (externe) à cavité et contenant des puits quantiques multiples et impliquant des anisotropies pouvant révéler (i) une biréfringence linéaire locale due au champ de déformation à la surface ou (ii) une biréfringence dans les puits quantiques due au couplage d'amplitude de phase provenant de la réduction du D2d biaxial au groupe de symétrie C2v aux interfaces semiconductrices ternaires III-V. Une nouvelle méthode récursive à matrice S de diffusion est mise en œuvre en utilisant un tenseur de gain dérivé analytiquement des équations de Maxwell-Bloch. Il permet de modéliser les propriétés de l'émission (seuil, polarisation, dédoublement de mode) du laser avec plusieurs zones actives à puits quantiques en recherchant les modes propres résonnants de la cavité. La méthode est démontrée sur des structures laser réelles et est utilisée pour l'extraction de tenseurs de permittivité optique de déformation de surface et de puits quantiques en accord avec des expériences. La méthode est généralisée pour trouver les modes propres au laser dans le cas le plus général des pompes polarisées circulaires (déséquilibre entre les canaux de spin-up et de spin-down) et le dichroïsme à gain linéaire. De plus, la mesure de la matrice de Mueller 4x4 complète pour des angles d'incidence multiples et des angles azimutaux dans le plan a été utilisée pour l'extraction de tenseurs de permittivité optique de couches contraintes superficielles et de puits quantiques. Une telle dépendance spectrale des éléments tensoriels optiques est cruciale pour la modélisation des modes propres du laser de spin, les conditions de résonance, et aussi pour la compréhension des sources d'anisotropies de structure<br>Spin-lasers are semiconductor devices in which the radiative recombination processes involving spin-polarized carriers result in an emission of circularly polarized photons. Nevertheless, additional linear in-plane anisotropies in the cavity generally lead in preferential linearly-polarized laser emission and to possible coupling between modes. In this thesis, a general method for the modeling of semiconductor laser such as vertical-(external)-cavity surface-emitting laser containing multiple quantum wells and involving anisotropies that may reveal i) a local linear birefringence due to the strain field at the surface or ii) a birefringence in quantum wells (QWs) due to phase amplitude coupling originating from the reduction of the biaxial D2d to the C2v symmetry group at the III-V ternary semiconductor interfaces. A novel scattering S-matrix recursive method is implemented using a gain tensor derived analytically from the Maxwell-Bloch equations. It enables to model the properties of the emission (threshold, polarization, mode splitting) from the laser with multiple quantum well active zones by searching for the resonant eigenmodes of the cavity. The method is demonstrated on real laser structures and is used for the extraction of optical permittivity tensors of surface strain and quantum wells in agreement with experiments. The method is generalized to find the laser eigenmodes in the most general case of circular polarized pumps (unbalance between the spin-up and spin-down channels) and linear gain dichroism. In addition, the measurement of full 4x4 Mueller matrix for multiple angles of incidence and in-plane azimuthal angles has been used for extraction of optical permittivity tensors of surface strained layers and quantum wells. Such spectral dependence of optical tensor elements are crucial for modeling of spin-laser eigenmodes, resonance conditions, and also for understanding of sources of structure anisotropies
29
Bansal, Rajni. "Enhancing spin current efficiency using novel materials." Thesis, IIT Delhi, 2019. http://eprint.iitd.ac.in:80//handle/2074/8134.
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Eriksson, Oscar, and Kaj Dahl. "Magnetic Monopole Current in Artificial Square Spin Ice." Thesis, KTH, Skolan för teknikvetenskap (SCI), 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-154229.
Texte intégralRésumé :
Recent theoretical and experimental results have revealed the existence of magnetic monopoles, in the form of quasi particles, in both condensed matter known as spin ice, as well as in two-dimensional artificial versions of the same material. In this report a two-dimensional Ising model is first examined, then an artificial square spin ice model using a dipole approximation, only taking into account nearest and next nearest neighbors. The Metropolis algorithm is used to obtain the internal energy, specific heat capacity and entropy as functions of temperature. In the latter model the magnetic monopole concentration and monopole current is also simulated. The two models show similar quantitative behavior in the above mentioned physical quantities, and in comparison to previously published results. In the artificial square spin ice model, under the influence of a magnetic field, a rapidly decreasing monopole current is observed, which decreases faster for higher temperatures. The magnitude of the magnetic field plays a significant role in the generation of the monopole current, and no direct effect of the phase transitionis observed.<br>Nya teoretiska och experimentella resultat har uppvisat förekomsten av magnetiska monopoler, i form av kvasi-partiklar, både i kondenserade material kallade spinn-is, och i tvådimensionella artificiella versioner av samma material. I den här rapporten undersöks först en tvådimensionell Isingmodell, därefter en artificiell kvadratisk spinn-is-modell med hjälpav en dipolapproximation, där hänsyn endast tas till närmaste och näst närmaste grannar. Metropolis-algoritmen används för beräkna energi, specifika värmekapaciteten och entropinsom funktioner av temperatur. I den senare modellen simuleras även monopolskoncentrationen och monopolsströmmen. De två modellerna uppvisar snarlikt kvantitativt beteende med avseende på ovan nämnda fysikaliska storheter, jämfört med varandra och tidigare publicerade resultat. Under inverkan av ett magnetfält observeras en snabbt avtagande monopolsström, i den artificiella kvadratiska spinn-is-modellen, som avtar snabbare med högre temperaturer. Storleken på det pålagda magnetfältet har markant betydelse för alstrande av monopolsströmmen, och ingen direkt effekt av fasövergången observeras.
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Hankinson, John H. "Spin dependent current injection into epitaxial graphene nanoribbons." Diss., Georgia Institute of Technology, 2015. http://hdl.handle.net/1853/53884.
Texte intégralRésumé :
Over the past decade there has been a great deal of interest in graphene, a 2-dimensional allotrope of carbon with exceptional mechanical and electrical properties. Its outstanding mobility, minimal size, and mechanical stability make it an appealing material for use in next generation electronic devices. Epitaxial graphene growth on silicon carbide is a reliable, scalable method for the production of high quality graphene films. Recent work has shown that the SiC can be patterned prior to graphitization, in order to selectively grow graphene nanostructures. Graphene nanoribbons grown using this technique do not suffer from the rough edges caused by lithographic patterning, and recent measurements have revealed extraordinary transport properties. In this thesis the magnetic properties of these nanoribbons are investigated through spin polarized current injection. The sensitivity of these nanoribbons to spin polarized current is interesting from a fundamental physics standpoint, and may find applications in future spintronic devices.
32
Abdullah, Ranjdar M. "Spin current amplification by a geometrical ratchet effect." Thesis, University of York, 2015. http://etheses.whiterose.ac.uk/8866/.
Texte intégralRésumé :
A lateral spin-valve (LSV) is a structure to achieve non-local spin accumulation in future spintronic devices. Although numerous studies have been performed and have demonstrated highly efficient and reliable non-local accumulation, the use of a LSV is still hampered by the small magnitude of spin-current signals. Therefore, this study focused on the amplification of the pure spin-current signals by controlling the geometry of the non-magnetic nanowire in the LSV for the first time. A two-dimensional model was developed based on a diffusion equation and was used for a series of Cu nanowires with different shapes implemented at their centre to identify their geometrical ratchet effect (GRE) upon the spin-polarised electron transport. Asymmetric shapes, such as obtuse- and right-angle triangles, were found to induce the GRE, leading to the spin-current amplification in both time-dependent and steady states. The geometries have then been optimised for the maximum amplification. Before the experimental validation of the GRE, Py and Cu bars and conventional Py/Cu/Py LSVs were fabricated and characterised to optimise the fabrication and transport-measurement processes. The spin-current amplification was then investigated in LSVs with right-angle triangles maintaining the same base (100nm) but varying their height (0 ≤ h ≤ 60nm). The non-local signals were measured by a direct current (DC)-reversal technique. The spin-current signals were measured to be significantly amplified by a factor of more than 7 for h = 60nm as compared with the conventional LSV (h = 0 nm). These results were compared with the steady-state calculations using measured device dimensions, showing a good qualitative agreement. The measurements were also carried out with a DC setup, which revealed the junction spin polarisation (~1% in this study) allowed both up- and down-spin currents with similar amplitudes to flow. Further improvement in the junction spin polarisation should increase the GRE, leading to future device implementation.
33
Pfeiffer, Alexander [Verfasser]. "Pure spin current transport and magnetic state manipulation in lateral spin valves / Alexander Pfeiffer." Mainz : Universitätsbibliothek Mainz, 2020. http://d-nb.info/1203414412/34.
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Lee, Soobeom. "Study on Electrical Generation and Manipulation of Spin Current in n-type Si Spin MOSFET." Doctoral thesis, Kyoto University, 2021. http://hdl.handle.net/2433/263671.
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Giles, Brandon L. "Opto-thermal measurements of thermally generated spin current in Yttrium Iron Garnet." The Ohio State University, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=osu1503024951599588.
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Sirisathitkul, C. "Studies of transport phenomena at ferromagnet/semiconductor interfaces." Thesis, University of Oxford, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.325445.
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Mohamad, Haidar Jawad. "Ultrafast optical measurements of spin-polarized electron dynamics in nanostructured magnetic materials." Thesis, University of Exeter, 2015. http://hdl.handle.net/10871/18425.
Texte intégralRésumé :
At present, electronic devices depend upon electric charge to transfer and record information. However, such devices are approaching a scaling limit due to Joule heating. Spintronics offers a solution by exploiting the spin rather than the charge of the electron, since the propagation of spin current can in principle occur without dissipation. Immediate applications lie in magnetic random access memory and novel media for hard disk recording. Within this thesis, the Magneto-optical Kerr effect (MOKE) has been used to measure the static and dynamic magnetic properties of a number of different thin film samples that are of interest for spintronic applications. A femtosecond laser has been used to perform time-resolved MOKE (TRMOKE) and time resolved reflectivity (TRR) measurements simultaneously, which probe the spin and charge dynamics respectively. Measurements have been performed upon a continuous thin film of CrO2 that is known to be half-metallic in bulk form, and a series of YIG/Cu/Ni81Fe19 based structures that are expected to exhibit the spin Seebeck effect (SSE). Chemical vapour deposition (CVD) was used to fabricate the continuous CrO2 thin film on a (100)-oriented TiO2 substrate. Precessional magnetisation dynamics were studied by means of the TRMOKE technique. The dependence of the precession frequency and the effective damping parameter upon the static applied magnetic field were investigated. The precession frequency exhibited a minimum at the hard axis saturation field as expected. However precession was also observed for fields greater than the hard axis saturation value, perhaps suggesting the presence of a twisted magnetic state within the film. TRMOKE and TRR measurements were performed upon the YIG/Cu/Ni81Fe19 based structures for different values of the pump fluence and applied magnetic field. For fixed pump fluence and varying applied field, the frequency of precession is well described by a numerical solution of the Landau-Lifshitz equation for the Ni81Fe19 (permalloy, Py) layer. The frequency, amplitude, damping, phase and chirp of the precessional oscillations was extracted from measurements made with a field of 3 kOe applied at 2.8° from the normal to the sample plane, in a configuration designed to maximise any spin transfer torque (STT) generated by the SSE. The oscillation parameters extracted for trilayer samples and a Py reference sample were found to be very similar. Features indicative of STT predicted by simulations were not observed. This suggests that either the YIG/Cu interface was unable to efficiently transmit spin current within the samples studied here, or else that the STT generated by means of the SSE is too small to be of practical use.
38
Edblom, Christin. "Current control of localized spins." Thesis, Uppsala University, Materials Theory, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-126606.
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Rohra, Stefan Bruno. "Exact exchange Kohn-Sham spin current density functional theory." [S.l.] : [s.n.], 2006. http://deposit.ddb.de/cgi-bin/dokserv?idn=98054078X.
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Wei, Jiaqi. "Magnetization manipulation induced by spin current and ultrafast laser." Electronic Thesis or Diss., Université de Lorraine, 2021. http://www.theses.fr/2021LORR0121.
Texte intégralRésumé :
La manipulation de l’aimantation est un des sujets de recherche les plus étudiés dans le domaine de l’électronique de spin. Différentes méthodes de manipulations peuvent exciter les propriétés dynamiques de l’aimantation à différentes échelles de temps. Parmi les phénomènes dynamiques, la précession de l’aimantation et la désaimantation ultrarapide ont suscité un intérêt particulier. La fréquence de précession de l’aimantation est de l’ordre du GHz et correspond à une période de centaines de picosecondes. Cette précession est le mécanisme à l’œuvre dans les nano-oscillateurs à transfert de spin (NOTS), un nouveau type de dispositif microonde présentant des avantages sur l’oscillateur commandé en tension (OCT) conventionnel en termes de taille, de consommation d’énergie et d’adaptabilité de la fréquence. La désaimantation ultrarapide a été observé pour la première fois dans du nickel en quelques centaines de femtosecondes. Le renversement tout optique (RTO), nécessitant la désaimantation ultrarapide, a ensuite été démontré expérimentalement. Le RTO est bien plus rapide que tout autre retournement de l’aimantation par couple et est donc prometteur pour construire des mémoires magnétiques ultrarapides. Bien que de nombreuses études sur ces deux phénomènes existent, plusieurs problèmes se doivent d’être résolus avant de pouvoir passer à l’étape de production industrielle. Les NOTS sont censés être utilisés pour la modulation par déplacement d’amplitude (MDA) ou la modulation par déplacement de fréquence (MDF), mais les conditions optimales pour ces deux types de modulation microondes n’ont pas encore été assez investiguées. Quant au RTO, l’influence des paramètres du laser tels que la fluence ou la durée de l’impulsion et des propriétés du matériau tels que le composition et l’épaisseur n’a pas fait l’objet d’études systématique. Dans ce manuscrit, ces deux types de manipulation de l’aimantation sont étudiés en détail. En ce qui concerne la précession de l’aimantation, nous démontrons qu’un champ magnétique accru permet d’obtenir une plus large plage de fréquence possible alors qu’un champ magnétique plus faible résulte en une plage d’amplitude possible élargie. Ainsi ces deux scenarii sont applicables au MDF et MDA, respectivement, et posent les bases d’une utilisation des NOTS en modulation microonde. Dans la deuxième étude, nous démontrons que le RTO dépends fortement des caractéristiques de l’impulsion laser. Pour cela nous avons construit un diagramme d’état pour le GdFeCo et le Co/Pt, deux matériaux typiques respectivement du retournement tout optique indépendant de l’hélicité (RTO-IH) et du retournement tout optique dépendant de l’hélicité (RTO-DH). Ces résultats permettent une meilleure compréhension du mécanisme fondamental régissant la dynamique de l’aimantation induite par exposition à un laser<br>Magnetization manipulation is one of the most actively researched topics in the field of spintronics. Different ways of manipulation can trigger magnetization dynamics on different time scales. Among these dynamics, magnetization precession and ultrafast demagnetization have attracted substantial interests. The frequency of magnetization precession is normally in the GHz range corresponding to a period of hundreds of ps, which is the basic mechanism of spin torque nano-oscillators (STNO), a new type of microwave devices which show advantages over conventional voltage-controlled oscillator (VCO) in terms of size, energy consumption and tunable frequency. Ultrafast demagnetization was first observed in Ni which takes places in hundreds of femtoseconds. Triggered by this, All-Optical Switching (AOS) was then demonstrated which is much faster than any torque induced switching, promising for application in the high-speed magnetic memory. Although many studies on these two phenomena have been reported, several issues need to be addressed before they move toward application. STNOs are supposed to be used for amplitude shift keying (ASK) or frequency shift keying (FSK), but the optimal conditions for these two types of microwave modulation are still not well explored. As for AOS, the influence of the laser parameters such as fluence and pulse duration and the material properties such as the composition and the thickness has not been systematically investigated. In this thesis, these two types of magnetization manipulation are studied in detail. Concerning magnetization precession, we demonstrate that a stronger magnetic field allows a wider frequency tuning range while a smaller magnetic field results in a wider amplitude tuning range. Thus, these two scenarios are applicable to FSK and ASK, respectively, providing guidelines for STNO in microwave modulation. In the second study, we demonstrate that AOS depends strongly on pulse characteristic. This was shown by building a magnetization state diagram for GdFeCo and Co/Pt which are two typical materials showing All-Optical Helicity-Independent Switching (AO-HIS) and All-Optical Helicity-Dependent Switching (AO-HDS), respectively. These results allow a better understanding of the fundamental mechanism behind laser-induced magnetization dynamics
41
Fang, Zhou. "Current-induced torques in ferromagnets at room temperature." Thesis, University of Cambridge, 2017. https://www.repository.cam.ac.uk/handle/1810/268099.
Texte intégralRésumé :
This thesis uses ferromagnetic resonance to explore the current-induced torques (CITs) in two different systems, namely YIG/heavy metal bilayers and bulk NiMnSb, at room temperature. We apply a microwave current to the sample while sweeping the external magnetic field, and measure the longitudinal DC voltage. From a symmetry analysis of the ferromagnetic resonance lineshape, the amplitudes and directions of the CITs parameterised by an effective magnetic field are accurately estimated. In Chapter 4, YIG samples of different thickness, capped by either Pt or Ta, are studied. The resonance is driven by both spin-transfer torque and Oersted field, and the DC voltage is attributed to both spin rectification and spin pumping. The CITs can be well analysed from the lineshape of the voltage and its dependence on YIG thickness, from which we deduce that the Oersted field dominates over the spin-transfer torque in driving magnetization dynamics. In Chapter 5, we characterise the CITs in bulk NiMnSb induced by the relativistic spin-orbit coupling effect. Both field-like and antidamping-like spin-orbit torques are observed and analysed in detail. At the end of this chapter, we study the spin-wave resonance driven by the CITs, from which the exchange stiffness of NiMnSb is determined. In Chapter 6, we extrapolate a new form of magnetoresistance in NiMnSb: unidirectional spin-orbit magnetoresistance (USOMR). USOMR scales linearly with the current and has opposite sign when the magnetization is reversed. Similar to the giant magnetoresistance in magnetic multilayers, USOMR can be used to distinguish between two opposite magnetization directions directly in the bulk of the ferromagnet.
42
Spicer, Timothy Michael. "Excitation of picosecond magnetisation dynamics by spin transfer torque." Thesis, University of Exeter, 2018. http://hdl.handle.net/10871/34684.
Texte intégralRésumé :
This thesis presents the results from investigations of ultrafast magnetisation dynamics driven by pure spin currents. Spin orbit coupling in heavy metal layers - such as tungsten, tantalum or platinum - allows for the generation of pure spin currents, whereby spin up and spin down electrons move in opposite directions. Hence, a flow of angular momentum can be controlled through the manipulation of charge current through a heavy metal layer. When a spin current is injected into a ferromagnet, a torque is exerted on its magnetisation, with the potential to induce a wide variety of ultrafast dynamics. The experimental investigation of these phenomena employed a variety of high-frequency electrical techniques and time-resolved scanning Kerr microscopy (TRSKM) methods. In addition, various simulative and analytical approaches were used to gain insight into the underlying mechanisms. Spin Hall nano-oscillators (SHNOs) have recently been shown to support a tunable GHz spin wave `bullet’ under injection of direct current (DC), making it an exciting candidate for microwave communication applications. This thesis will show how TRKSM can be used to measure the torques within these devices, revealing that radio frequency (RF) current does not possess the same distribution as the DC. The competition between self-inductance and focusing within the device geometry results in a modified distribution of spin current. Further TRSKM measurements show the modified torque landscape to promote the mobility of the `bullet' within the magnetic layer. Devices that exploit spin currents for magnetisation reversal have received interest from academia and industry for their potential use as memory elements. The perpendicular magnetic anisotropy present in Ta/CoFeB/MgO leads to lower write currents and higher thermal stability. However, ultrafast processes have not been previously observed in such devices. TRSKM measurements of Hall bar devices were compared with a macrospin model to understand the underlying torques, and to investigate the conditions required to promote switching. Square elements built from the same stack structure exhibited contrasting static and dynamic behaviour. Pulsed currents drove differing dynamics at the edge and center of the device, while enabling the realignment of magnetic domains. The domains themselves could be driven directly by the spin current leading to domain wall dynamics. Measurements with a bipolar electrical pulse demonstrated that meta-stable switching can be achieved in micron-scale elements.
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She, Diana. "Molecular beam epitaxy growth of the BiSb/MnGa heterosrtuctures for the charge current to spin current conversion study." Electronic Thesis or Diss., université Paris-Saclay, 2024. http://www.theses.fr/2024UPASP003.
Texte intégralRésumé :
Récemment, les isolants topologiques (TI) ont attiré beaucoup d'attention en raison de leurs propriétés prometteuses potentiellement utiles pour les technologies émergentes, telles que la mémoire MRAM. En effet, les systèmes TI/ferromagnétiques (FM) peuvent réduire considérablement le courant d'écriture en utilisant le renversement par couple spin-orbite (SOT) comme méthode d'écriture. Cet avantage découle de l'utilisation des états de surface topologiques polarisés en spin des TI. Dans ce travail, notre objectif était de faire croître des hétérostructures TI/FM par épitaxie par jets moléculaires (MBE), de réaliser une caractérisation complète des propriétés structurelles, magnétiques et électroniques, et d'étudier leurs propriétés de conversion spin-charge. Nous avons développé une hétérostructure Bi ₁₋ ₓSbₓ (TI)/ Mnₓ Ga₁₋ₓ (FM)//GaAs(001) de haute qualité par MBE, malgré la différence de symétrie cristalline. Les films minces FM de MnxGa1-x présentent une anisotropie magnétique perpendiculaire, un champ coercitif faible, une température de Curie élevée, un cycle d'hystérésis carré et une résistivité suffisamment élevée. Cela garantit que la majorité du courant circule à travers la couche Bi ₁₋ ₓSbₓ pendant les expériences SOT. Les mesures SOT suggèrent que les états de volume de Bi ₁₋ ₓSbₓ contribuent principalement aux propriétés de transport. Cependant, nous avons démontré la présence d'états de surface topologiques par ARPES. Ainsi, les états de volume et de surface peuvent coexister. De plus, les résultats préliminaires de la spectroscopie terahertz ont montré une conversion efficace du spin en charge dans la bicouche étudiée, démontrant un potentiel prometteur. En conséquence, nos résultats indiquent que Bi ₁₋ ₓSbₓ présente un potentiel significatif pour les dispositifs spintroniques<br>Recently, topological insulators (TI) have attracted much attention with their promising prop-erties potentially useful for the emerging memory technologies, as magnetic random access memory (MRAM). Indeed, TI/ferromagnetic (FM) systems may drastically reduce the writing current using the spin-orbit torque (SOT) switching as a writing method. This advantage stems from the utilization of the spin-polarized topological surface states of the TIs. In this work, we were aiming to grow TI/FM bilayer heterostructures by molecular beam epitaxy (MBE), to perfrom comprehensive structural, magnetic and electronic characterization, and to study their charge-to-spin interconversion properties.We developped a high-quality Bi ₁₋ ₓSbₓ (TI)/ Mnₓ Ga₁₋ₓ (FM)//GaAs(001) bilayer heterostrucure by MBE, despite the difference in crystal symmetries. The FM Mnₓ Ga₁₋ₓ thin films exhibit perpendicular magnetic anisotropy, low coercive field, high Curie temperature, square hysteresis cycle, and sufficiently high resistivity. This ensured that a major portion of the electrical current flows through the Bi ₁₋ ₓSbₓ layer during the SOT experiments. The SOT measurements suggest that bulk states of Bi ₁₋ ₓSbₓ predominantly contributed to the transport properties. However, we demostrated the presence of topological surface states with ARPES. So the bulk and surface states may coexist. Additionally, the preliminary results of terahertz spectroscopy showed the efficient spin-to-charge conversion in the studied bilayer, showing promising potential. Consequently, our findings indicate that Bi ₁₋ ₓSbₓ holds significant promise for spintronic devices
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Silva, José Felix Estanislau da. "Shot Noise e corrente dependentes de spin: modelo quântico." Universidade de São Paulo, 2001. http://www.teses.usp.br/teses/disponiveis/76/76131/tde-08032017-091450/.
Texte intégralRésumé :
Nesta dissertação, fazemos a primeira investigação sobre flutuações em corrente e corrente média dependentes de spin em potenciais duplo e simples da estrutura Zn1-xMnxSe. Consideramos efeitos de campos magnético e elétrico externos à temperatura nula. Na presença de um campo magnético, a interação dos íons de Mn com elétrons de condução e valência (interação de troca sp-d) origina potenciais dependentes de spin para o transporte em Zn1-xMnxSe. Aqui, flutuações em corrente (\"shot noise\") e a corrente média são calculados usando o modelo quântico de transporte através do potencial dependente de spin é descrito por uma matriz s de espalhamento. Os elementos da matriz de espalhamento, i.e., as amplitudes de transmissão e reflexão, são determinados pelo método da matriz transferência. Nossos resultados indicam que estruturas de potenciais simples e duplos Zn1-xMnxSe agem como se fossem \"filtros de spin\" para corrente. Em determinadas faixas de parâmetros do sistema, \"shot noise\" pode complementar informações obtidas da corrente média<br>In this dissertation we investigation for the first time spin dependent-current and its fluctuations in double and single barrier potentials of the Zn1-xMn xSe structure sandwiched between ZnSe layers. We consider effects of external magnetic field, the interaction of the Mn ions with thew conduction and valence electrons (sp-d exchange interation) give rises to spin-dependent potentials for transport across the Zn1-xMn xSe layer. Here, the average current and its fluctuations are calculated using the quantum transport model in which transport across the spin-dependent potential is described via scattering matrix s. The elements of the scattering matrix, i.e., the transmission and reflection amplitudes, are determined through the transfer-matrix method. Our results indicate date single and double potentials of the Zn1-xMn xSe structure act as \"spin filters\" for the current. Within some system parameter range, shot noise can supplement the information contained in the average current
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Ghosh, Abhijit. "Pompage de spin et absorption de spin dans des hétérostructures magnétiques." Phd thesis, Université de Grenoble, 2012. http://tel.archives-ouvertes.fr/tel-00846031.
Texte intégralRésumé :
L'interaction entre électrons de conduction itinérants et électrons localisés dans les hétérostructures magnétiques est à l'origine d'effets tels que le transfert de moment de spin, le pompage de spin ou l'effet Hall de spin. Cette thèse est centrée sur le phénomène de pompage de spin : une couche ferromagnétique (FM) en précession injecte un courant de spin pur dans les couches adjacentes. Ce courant de spin peut être partiellement ou totalement absorbé par une couche, dite réservoir de spin, placée directement en contact avec le matériau ferromagnétique ou séparée par une couche d'espacement. L'absorption de la composante transverse du courant de spin induit une augmentation de l'amortissement de la précession ferromagnétique de la couche libre. Cet effet à été mesuré par des expériences de résonance ferromagnétique avec, pour la couche en précession FM, trois matériaux ferromagnétiques différents (NiFe, CoFeB et Co), et pour la couche de réservoir de spin, différents matériaux paramagnétiques (Pt, Pd, Ru), ferromagnétiques et antiferromagnétiques. Dans un premier temps, nous avons vérifié que le facteur d'amortissement non-local généré est de type amortissement de Gilbert, et qu'il est inversement proportionnel à l'épaisseur de la couche en précession FM. L'analyse de l'augmentation de l'amortissement a été réalisée dans le cadre du modèle de pompage de spin adiabatique proposé par Tserkovnyak et al.. Dans un second temps et suivant ce modèle, nous avons extrait les paramètres de conductance avec mélange de spin à l'interface g↑↓ pour différentes interfaces, ces paramètres déterminent le transport du courant de spin à travers des interfaces ferromagnétique/métal non-magnétique. Un troisième résultat important de cette thèse porte sur la longueur d'absorption du courant de spin dans des matériaux ferromagnétiques et paramagnétiques. Celle-ci varie considérablement d'un matériau à l'autre. Pour les matériaux ferromagnétiques, la longueur d'absorption du courant de spin est linéaire par rapport à l'épaisseur de la couche réservoir de spin, avec pour longueur caractéristique ~ 1 nm. Ce résultat est en cohérence avec les théories antérieures et avec les valeurs de longueur de déphasage de spin pour le transfert de moment de spin dans les matériaux ferromagnétiques. Dans les paramagnétiques tels que Pt, Pd, Ru, la longueur d'absorption est soit linéaire soit exponentielle selon que le réservoir paramagnétique est directement en contact avec la couche en précession ou bien séparé par une couche mince d'espacement en Cu. La longueur caractéristique correspondante est inférieure à la longueur de diffusion de spin. Des mesures complémentaires de dichroïsme circulaire magnétique par rayons X ont révélé une induction de moments magnétiques dans les matériaux paramagnétiques comme Pd, Pt, lorsque couplé directement ou indirectement avec une couche FM. Ce résultat fournit une explication de la dépendance en épaisseur linéaire observée dans les hétérostructures en contact direct. Etant donné que le pompage de spin et le couple de transfert de spin (STT) sont des processus réciproques, les résultats de cette thèse sur la conductance avec mélange de spin, la longueur d'absorption de spin et les moments de spin induits sont également d'un grand intérêt pour les études de transfert de moment de spin, ainsi que d'effet Hall de spin, direct et inverse. L'avantage des études présentées ici réside dans le fait qu'elles sont effectuées sur des couches minces continues, sans aucune étape de nanofabrication.
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Shigematsu, Ei. "Study on transport and conversion of ac and dc spin current generated by magnetization dynamics." Doctoral thesis, Kyoto University, 2020. http://hdl.handle.net/2433/245846.
Texte intégralRésumé :
京都大学<br>0048<br>新制・課程博士<br>博士(工学)<br>甲第22161号<br>工博第4665号<br>新制||工||1728(附属図書館)<br>京都大学大学院工学研究科電子工学専攻<br>(主査)教授 白石 誠司, 教授 藤田 静雄, 准教授 掛谷 一弘<br>学位規則第4条第1項該当<br>Doctor of Philosophy (Engineering)<br>Kyoto University<br>DGAM
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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.
Texte intégralRésumé :
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<br>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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Inoue, Jun-ichiro, Gerrit E. W. Bauer, and Laurens W. Molenkamp. "Suppression of the persistent spin Hall current by defect scattering." The American Physical Society, 2004. http://hdl.handle.net/2237/7121.
Texte intégral
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Lin, Weiwei, Kai Chen, Shufeng Zhang, and C. L. Chien. "Enhancement of Thermally Injected Spin Current through an Antiferromagnetic Insulator." AMER PHYSICAL SOC, 2016. http://hdl.handle.net/10150/614754.
Texte intégralRésumé :
We report a large enhancement of thermally injected spin current in normal metal (NM)/antiferromagnet (AF)/yttrium iron garnet (YIG), where a thin AF insulating layer of NiO or CoO can enhance the spin current from YIG to a NM by up to a factor of 10. The spin current enhancement in NM/AF/YIG, with a pronounced maximum near the Neel temperature of the thin AF layer, has been found to scale linearly with the spin-mixing conductance at the NM/YIG interface for NM = 3d, 4d, and 5d metals. Calculations of spin current enhancement and spin mixing conductance are qualitatively consistent with the experimental results.
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Haltz, Eloi. "Domain wall dynamics driven by spin-current in ferrimagnetic alloys." Thesis, Université Paris-Saclay (ComUE), 2019. http://www.theses.fr/2019SACLS607.
Texte intégralRésumé :
Malgré les grands succès de la spintronique de ces dernières années, plusieurs questions demeurent quant à l'efficacité et la rapidité de la manipulation électrique de l’aimantation. Ces problèmes semblent pouvoir être résolus en considérant des nouveaux matériaux plus exotiques mélangeant différents sous-réseaux magnétiques. Les alliages ferrimagnétiques de type terres rares-métaux de transitions sont composés de deux populations magnétiques couplées antiferromagnétiquement. Dans ces matériaux, deux configurations particulièrement intéressantes se distinguent : les points de compensation magnétique et angulaire auxquels l'aimantation ou le moment angulaire totale de l'alliage s’annulent. Dans ces configurations, ces matériaux ferrimagnétiques présentent de nouvelles propriétés très intéressantes tant sur le plan fondamental que technologique. Dans cette thèse, la dynamique d’aimantation dans ces matériaux a été étudié expérimentalement et théoriquement à travers la dynamique de paroi de domaine magnétique par application de courants de spin.Les alliages ferrimagnétiques (comme le TbFeCo ou le GdFeCo) ont été déposés en couche mince par co-évaporation et étudiés en combinant plusieurs méthodes : magnétiques, électriques et optiques ce qui révéla leur grand intérêt spintronic. Des techniques d'imagerie ont montré une organisation en domaines magnétiques, séparés par des parois facilement manipulables. Cette étude des propriétés statiques a également montré l’existence d’un gradient chimique en épaisseur induisant des effets habituellement surfaciques dans la zone centrale de films comme le DMI.La dynamique de paroi sous courant de spin (par couple de transfert de spin et spin-orbite) a été étudiée dans deux études qui ont mis en évidence l'efficacité et la rapidité du contrôle électrique de l’aimantation. L’une d’elles a également révélé une dynamique particulière qui est la signature directe d’un retournement magnétique sans précession à la compensation angulaire.Enfin, un modèle théorique effectif des propriétés statique et dynamique des alliages ferrimagnétiques a été développé et a révélé de nouveaux modes de propagation de paroi comme le retournement sans précession ou la disparition des régimes transitoires<br>Despite the large success of spintronics, several questions remain concerning the improvement of efficiency and speed of the magnetization manipulation by electrical current. Those issues can be addressed through the study of new exotic materials that mix different magnetic sub-lattices. Rare earth-transition metal ferrimagnetic alloys are composed of two different magnetic sub-lattices that are antiferromagneticaly coupled. Specifically, two interesting configurations can emerge called the magnetic and the angular compensation points at which the alloy’s net magnetization or net angular momentum independently vanishes. In these configurations, ferrimagnets seem to present new and very convenient properties which makes them promising for both fundamental and technological point of view. In this thesis, these materials were experimentally and theoretically studied through the prism of magnetic domain wall dynamics driven by spin-currents.Ferrimagnetic alloys (such as TbFeCo or GdFeCo) were grown in thin films by co-evaporation. Their structural and magnetic properties were studied by combining magnetization, electrical and optical methods which have revealed their spintronic value. Imaging techniques showed a perpendicularly magnetized domain organization separated by easily handled domain walls. These statics properties studies also showed a chemical depth gradient which induces surface-like effects in the bulk region of films such as DMI à définir.The domain wall dynamics driven by spin current were investigated in two studies revealing very high efficiency and speed of their electrical manipulation. First, the efficiency of the current manipulation via spin-transfer torque was measured by studying the domain wall motion under combined effects of field and current in the creep regime. Secondly, the domain wall dynamics driven by spin-orbit torque was fully characterized using in-plane fields. This measurement revealed a singular dynamic of the domain wall at the angular compensation point which is the direct signature of the precession-free reversal of the magnetization.Finally, an effective theoretical model of both the static and dynamic properties of ferrimagnets was developed. It allows the description of all the observed experimental results. Using this formalism, we analytically and numerically studied the domain wall dynamics driven by field or spin-currents thus revealing new propagation regimes such as precession-free dynamics or the vanishing of transient motions