京都大学 / 0048 / 新制・課程博士 / 博士(理学) / 甲第22270号 / 理博第4584号 / 新制||理||1658(附属図書館) / 京都大学大学院理学研究科化学専攻 / (主査)教授 小野 輝男, 教授 吉村 一良, 教授 島川 祐一 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DGAM

With the aggressive scaling of complementary metal-oxide semiconductor (CMOS) nearing an inevitable physical limit and its well-known power crisis, the quest for an alternative/augmenting technology that surpasses the current semiconductor electronics is needed for further technological progress. Spintronic devices emerge as prime candidates for Beyond CMOS era by utilizing the electron spin as an extra degree of freedom to decrease the power consumption and overcome the velocity limit connected with the charge. By using the nonvolatility nature of magnetization along with its direction to represent a bit of information and then manipulating it by spin-polarized currents, routes are opened for combined memory and logic. This would not have been possible without the recent discoveries in the physics of nanomagnetism such as spin-transfer torque (STT) whereby a spin-polarized current can excite magnetization dynamics through the transfer of spin angular momentum. STT have expanded the available means of switching the magnetization of magnetic layers beyond old classical techniques, promising to fulfill the need for a new generation of dense, fast, and nonvolatile logic and storage devices. All-spin logic (ASL) is among the most promising spintronic logic switches due to its low power consumption, logic-in-memory structure, and operation on pure spin currents. The device is based on a lateral nonlocal spin valve and STT switching. It utilizes two nanomagnets (whereby information is stored) that communicate with pure spin currents through a spin-coherent nonmagnetic channel. By using the well-known spin physics and the recently proposed four-component spin circuit formalism, ASL can be thoroughly studied and simulated. Previous attempts to model ASL in the linear and diffusive regime either neglect the dynamic characteristics of transport or do not provide a scalable and robust platform for full micromagnetic simulations and inclusion of other effects like spin Hall effect and spin-orbit torque. In this thesis, we propose an improved stochastic magnetization dynamics/time-dependent spin transport model based on a finite-difference scheme of both the temporal and spatial derivatives to capture the key features of ASL. The approach yields new finite-difference conductance matrices, which, in addition to recovering the steady-state results, captures the dynamic behavior. The new conductance matrices are general in that the discretization framework can be readily applied and extended to other spintronic devices. Also, we provide a stable algorithm that can be used to simulate a generic ASL switch using the developed model.

This thesis discusses spin-transfer torques in MgO-based magnetic tunnel junctions. The voltage-field switching phase diagrams have been experimentally determined for in-plane CoFeB/MgO/CoFeB magnetic tunnel junctions. In order to limit the effect of thermal activation, experiments have been carried out using nanosecond voltage pulses, as well as at low-temperature (4.2 K). The bias-dependence of the two spin-torque terms (Slonczewski-like and field-like) has been determined from thermally-excited ferromagnetic resonance measurements, yielding values which are in good agreement with previous reports. Additionally, material parameters such as the effective magnetisation and the damping factor have also been extracted. Using these values as input, the switching voltages as function of the applied magnetic field have been calculated numerically and analytically by solving the modified Landau-Lifshitz-Gilbert equation. Unlike previous studies, the field-like spin-torque has also been included. Moreover, different configurations have been considered for the magnetic anisotropy directions of the reference and free layer, respectively. / Diese Arbeit befasst sich mit Spin-Transfer-Torque-Effekten in MgO-basierten magnetischen Tunnelstrukturen. Die Phasendiagramme als Funktion von Spannung und Magnetfeld von CoFeB/MgO/CoFeB-Tunnelstrukturen mit Magnetisierung in der Ebene wurden experimentell bestimmt. Um thermische Anregungseffekte zu limitieren, wurden die Experimente einerseits mit nanosekundenlangen Spannungspulsen und andererseits bei niedrigen Temperaturen (4.2 K) durchgeführt. Die Spannungsabhängigkeit der beiden Spin-Torque-Parameter (in-plane und senkrechter Spin-Transfer-Torque) wurde aus Messungen der thermisch angeregten ferromagnetischen Resonanz bestimmt, wobei sich Werte ergaben, die gut mit vorangegangenen Untersuchungen übereinstimmen. Zusätzlich wurden Werte für Materialparameter wie die effektive Magnetisierung und den Dämpfungsparameter gewonnen. Unter Verwendung der erhaltenen Werte wurden die Schaltspannungen als Funktion des angelegten Magnetfeldes analytisch und numerisch berechnet, indem die erweiterte Landau-Lifshitz-Gilbert-Gleichung gelöst wurde. Im Gegensatz zu vorangegangenen Untersuchungen wurde der senkrechte Spin-Transfer-Torque dabei mit einbezogen. Darüber hinaus wurden verschiedene Konfigurationen für die Richtung der magnetischen Anisotropie der freien und fixierten Schicht berücksichtigt.

This thesis discusses spin-transfer torques in MgO-based magnetic tunnel junctions. The voltage-field switching phase diagrams have been experimentally determined for in-plane CoFeB/MgO/CoFeB magnetic tunnel junctions. In order to limit the effect of thermal activation, experiments have been carried out using nanosecond voltage pulses, as well as at low-temperature (4.2 K). The bias-dependence of the two spin-torque terms (Slonczewski-like and field-like) has been determined from thermally-excited ferromagnetic resonance measurements, yielding values which are in good agreement with previous reports. Additionally, material parameters such as the effective magnetisation and the damping factor have also been extracted. Using these values as input, the switching voltages as function of the applied magnetic field have been calculated numerically and analytically by solving the modified Landau-Lifshitz-Gilbert equation. Unlike previous studies, the field-like spin-torque has also been included. Moreover, different configurations have been considered for the magnetic anisotropy directions of the reference and free layer, respectively.:1 Introduction 2 Fundamentals 2.1 Magnetoresistance 2.1.1 Giant magnetoresistance 2.1.2 Tunnel magnetoresistance 2.2 Spin-transfer torque effect 2.2.1 Physical picture of the STT 2.2.2 In-plane and perpendicular STT 2.3 Equation of motion for the magnetisation 2.3.1 The Landau-Lifshitz-Gilbert equation 2.3.2 Extension including spin-transfer-torque (LLGS) 2.4 Applications of MR and spin-transfer torque 2.4.1 Read heads in hard disk drives 2.4.2 Spin-transfer torque magnetic random access memory 2.5 STT effects in magnetic tunnel junctions 2.5.1 Current-induced switching 2.5.2 Magnetisation precession 2.5.3 Bias-dependence of STT 2.5.4 Back-hopping 3 Experimental 3.1 Samples 3.1.1 Stack composition 3.1.2 Properties of samples used in this work 3.2 Experimental setup 3.2.1 Overview of equipment for the different measurement techniques 3.2.2 Electromagnet and Kepco power supply 3.2.3 Contacting of the sample 3.2.4 Principle specifications of equipment 3.3 Experimental techniques 3.3.1 Measurement of DC R-H and R-I loops 3.3.2 Measurement of phase diagrams: off and on-pulse 3.3.3 Thermally-excited ferromagnetic resonance 4 Results and discussion 4.1 Switching phase diagrams of MTJs 4.1.1 Theory: Calculating the phase diagram 4.1.2 Experimental phase diagrams 4.2 Thermally excited ferromagnetic resonance 4.2.1 Smoothing and fitting of raw data 4.2.2 Determination of Ms 4.2.3 Signal evolution with bias voltage 4.2.4 Analysis of peak position: perpendicular STT 4.2.5 Analysis of peak linewidth 5 Summary and outlook A Appendix List of figures List of tables Bibliography / Diese Arbeit befasst sich mit Spin-Transfer-Torque-Effekten in MgO-basierten magnetischen Tunnelstrukturen. Die Phasendiagramme als Funktion von Spannung und Magnetfeld von CoFeB/MgO/CoFeB-Tunnelstrukturen mit Magnetisierung in der Ebene wurden experimentell bestimmt. Um thermische Anregungseffekte zu limitieren, wurden die Experimente einerseits mit nanosekundenlangen Spannungspulsen und andererseits bei niedrigen Temperaturen (4.2 K) durchgeführt. Die Spannungsabhängigkeit der beiden Spin-Torque-Parameter (in-plane und senkrechter Spin-Transfer-Torque) wurde aus Messungen der thermisch angeregten ferromagnetischen Resonanz bestimmt, wobei sich Werte ergaben, die gut mit vorangegangenen Untersuchungen übereinstimmen. Zusätzlich wurden Werte für Materialparameter wie die effektive Magnetisierung und den Dämpfungsparameter gewonnen. Unter Verwendung der erhaltenen Werte wurden die Schaltspannungen als Funktion des angelegten Magnetfeldes analytisch und numerisch berechnet, indem die erweiterte Landau-Lifshitz-Gilbert-Gleichung gelöst wurde. Im Gegensatz zu vorangegangenen Untersuchungen wurde der senkrechte Spin-Transfer-Torque dabei mit einbezogen. Darüber hinaus wurden verschiedene Konfigurationen für die Richtung der magnetischen Anisotropie der freien und fixierten Schicht berücksichtigt.:1 Introduction 2 Fundamentals 2.1 Magnetoresistance 2.1.1 Giant magnetoresistance 2.1.2 Tunnel magnetoresistance 2.2 Spin-transfer torque effect 2.2.1 Physical picture of the STT 2.2.2 In-plane and perpendicular STT 2.3 Equation of motion for the magnetisation 2.3.1 The Landau-Lifshitz-Gilbert equation 2.3.2 Extension including spin-transfer-torque (LLGS) 2.4 Applications of MR and spin-transfer torque 2.4.1 Read heads in hard disk drives 2.4.2 Spin-transfer torque magnetic random access memory 2.5 STT effects in magnetic tunnel junctions 2.5.1 Current-induced switching 2.5.2 Magnetisation precession 2.5.3 Bias-dependence of STT 2.5.4 Back-hopping 3 Experimental 3.1 Samples 3.1.1 Stack composition 3.1.2 Properties of samples used in this work 3.2 Experimental setup 3.2.1 Overview of equipment for the different measurement techniques 3.2.2 Electromagnet and Kepco power supply 3.2.3 Contacting of the sample 3.2.4 Principle specifications of equipment 3.3 Experimental techniques 3.3.1 Measurement of DC R-H and R-I loops 3.3.2 Measurement of phase diagrams: off and on-pulse 3.3.3 Thermally-excited ferromagnetic resonance 4 Results and discussion 4.1 Switching phase diagrams of MTJs 4.1.1 Theory: Calculating the phase diagram 4.1.2 Experimental phase diagrams 4.2 Thermally excited ferromagnetic resonance 4.2.1 Smoothing and fitting of raw data 4.2.2 Determination of Ms 4.2.3 Signal evolution with bias voltage 4.2.4 Analysis of peak position: perpendicular STT 4.2.5 Analysis of peak linewidth 5 Summary and outlook A Appendix List of figures List of tables Bibliography

<p>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.</p><p>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.</p><p>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.</p>

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.

Magnetization dynamics in nano-contact spin torque oscillators (STOs) is investigated from an experimental and theoretical point of view. The fundamentals of magnetization dynamics due to spin transfer torque are given. A custom-made high frequency (up to 46 GHz) in large magnetic fields (up to 2.2 T) microwave characterization setup has been built for the purpose and described in this thesis. A unique feature of this setup is the capability of applying magnetic fields at any direction θe out of the sample plane, and with high precision. This is particularly important, because the (average) out-of-plane angle of the STO free magnetic layer has fundamental impact on spin wave generation and STO operation. By observing the spin wave spectral emission as a function of θe, we find that at angles θe below a certain critical angle θcr, two distinct spin wave modes can be excited: a propagating mode, and a localized mode of solitonic character (so called spin wave bullet). The experimental frequency, current threshold and frequency tuneability with current of the two modes can be described qualitatively by analytical models and quantitatively by numerical simulations. We are also able to understand the importance, so far underestimated, of the Oersted field in the dynamics of nano-contact STOs. In particular, we show that the Oersted field strongly affects the current tuneability of the propagating mode at subcritical angles, and it is also the fundamental cause of the mode hopping observed in the time-domain. This mode hopping has been observed both experimentally using a state-of-the-art real-time oscilloscope and corroborated by micromagnetic simulations. Micromagnetic simulations also reveal details of the spatial distribution of the spin wave excitations. By investigating the emitted power as a function of θe, we observed two characteristic behaviors for the two spin wave modes: a monotonic increase of the power for increasing out-of-plane angles in the case of the propagating mode; an increase towards a maximum power followed by a drop of it at the critical angle for the localized mode. Both behaviors are reproduced by micromagnetic simulations. The agreement with the simulations offers also a way to better understand the precession dynamics, since the emitted power is strongly connected to the angular variation of the giant magnetoresistance signal. We also find that the injection locking of spin wave modes with a microwave source has a strong dependence on θe, and reaches a maximum locking strength at perpendicular angles. We are able to describe these results in the theoretical framework of non-linear spin wave dynamics. / QC 20101130

Depuis 2004, les composants radiofréquence (RF) suscitent un intérêt croissant au sein de la communauté spintronique, tant du point de vue de la physique fondamentale que des applications potentielles. Ces composants ont émergé suite à la découverte du couple de transfert de spin (STT) qui permet d'exciter l'aimantation grâce à un courant électrique. Dans ce contexte, j'ai étudié des oscillateurs à vortex basés sur des jonctions tunnel magnétiques à très faible résistance dans lesquelles un vortex magnétique suit un mouvement périodique dû au STT.On observe des oscillations de ce vortex lorsque la jonction est polarisée par un large courant dc sous un faible champ planaire. En effet, le courant produit à la fois un fort champ d'Ampère, qui contribue à la nucléation du vortex, et génère le STT qui met le vortex en mouvement. Grâce à l'oscillation du vortex, ces composants émettent un signal RF d'une forte puissance (jusqu'à 20nW) avec une fréquence naturelle d'environ 450MHz.J'ai étudié la synchronisation de ces oscillateurs en injectant, en plus courant continu, une excitation RF. Lorsque ce signal d'excitation est suffisamment puissant, l'oscillateur se verrouille sur la source externe. On observe une diminution du bruit autour du pic fondamental et une augmentation de l'amplitude de celui-ci. J'explique ces observations en modélisant le système en tant qu'oscillateur paramétrique. Cette modélisation permet de décrire certains phénomènes observés expérimentalement, comme le fait qu'il est plus facile d'atteindre le régime d'instabilité dynamique quand la fréquence de l'excitation est égale à deux fois la fréquence naturelle de l'oscillateur.Ensuite, j'ai réalisé une expérience de modulation de fréquence (FM), en excitant l'échantillon avec une onde RF à basse fréquence. L'expérience consiste à mesurer la densité spectral de puissance du signal tout en balayant la fréquence de l'onde de modulation et ceci à différente puissance. Il apparait alors que la description usuelle de la FM ne puisse plus être utilisée dans notre cas, car la fréquence de modulation est trop grande par rapport à la fréquence naturelle. Cela est dû au fait que le vortex met un certain temps à répondre à une excitation. Pour expliquer mes mesures, j'ai donc dû introduire le concept de sensibilité à la déviation, qui correspond à la dépendance de la fréquence de l'oscillateur avec le courant quand celui-ci varie périodiquement. / Since 2004, research on radiofrequency (RF) spintronic devices has been very active, both from a fundamental point of view as well as for their potential applications as RF oscillators or spin-diodes. These devices are based on spin transfer torque (STT). In this context, I studied vortex oscillators based on ultra-low resistance magnetic tunnel junctions in which vortex dynamics is driven into a periodic motion by STT. The vortex oscillations are observed when the junction is subjected to a large dc bias current and a low in-plane field. The dc current produces both a large Oersted field which contributes to the vortex nucleation and a STT that starts the vortex oscillation. This oscillation leads to a large output power up to 20nW with a fundamental frequency around 450MHz and many harmonics.Synchronization with an external signal was then tested by adding a RF current to the dc bias current. With a large enough input power, the oscillator locks on the external source: the noise is then drastically reduced and the spectral purity of the signal significantly increases. These observations are explained by describing the system as a parametric oscillator. This model predicts, as experimentally observed, that, for a small amplitude of the RF excitation, a dynamical instability can be more easily reached when its frequency is twice the natural frequency of the oscillator than for any other frequencies.Then, I performed frequency modulation measurements by exciting the dc-biased sample with a low frequency ac-current. The power spectral density was measured as I swept the modulation frequency for various modulation powers. It appears that the description previously used to describe modulation experiments does not apply when the modulation frequency is a significant fraction of the natural frequency. The vortex response time appears to play a significant role, so that the concept of deviation sensitivity has to be introduced to explain the observations: it corresponds to the dynamical dependence of the oscillator frequency with an applied current that varies with time.

Dans le contexte actuel des technologies de l’information, le traitement séquentiel effectué par les ordinateurs d’architecture classique bute sur des problématiques de consommation d’énergie. En s’inspirant de la nature, et tout particulièrement du cerveau, une solution alternative apparaît à travers les réseaux de neurones artificiels. Dans ce cadre, la réalisation de nano-composants, appelés memristors, qui miment la plasticité synaptique, permet grâce à leur taille nanométrique d’envisager la réalisation de réseaux neuronaux densément interconnectés. Dans ce travail de thèse, notre intérêt est porté sur la réalisation d’un tel composant, défini comme une nano-résistance variable et non-volatile, et dont le fonctionnement repose sur le principe de la spintronique (ou l’utilisation du spin des électrons comme vecteur d’information), qui présente les avantages de compatibilité avec les technologies actuelles (CMOS, MRAM, …etc). En utilisant une jonction tunnel magnétique, le concept de memristor spintronique repose sur le déplacement d’une paroi de domaine magnétique par transfert de spin, où chaque position de paroi défini un état de résistance intermédiaire. Afin de maitriser les variations de résistance du dispositif memristif spintronique, l’étude des propriétés statiques et dynamiques de la paroi de domaine sous l’influence d’un courant polarisé en spin est requise. Grâce à l’étude du déplacement et de la résonance de la paroi dans des systèmes à aimantations planaires, comprenant un nombre limité de 3 états intermédiaires de résistance, nous avons pu établir un premier bilan (temps de commutation du dispositif inférieur à la nanoseconde et mis en avant d’un phénomène de ‘sur-amortissement’). En s’appuyant sur ces travaux préliminaires, nous avons par la suite optimisé des jonctions tunnel magnétiques à aimantations perpendiculaires, pour lesquels d’une part le nombre d’états intermédiaires de résistance se voit fortement augmenter (entre 15 et 20 états), autorisant l’utilisation de ce dispositif memristif spintronique pour la réalisation de tâches neuromorphiques. D’autre part, ce dispositif est optimisé pour exploiter le couple de transfert de spin le plus efficace afin de déplacer la paroi de domaine. / In the current context of information technology, the sequential processing carried out by classical computer architectures stumbles on problems of energy consumption. Inspired by nature, especially the brain, an alternative solution appears through artificial neural networks. In this background, the realization of nano-components, called memristors, which mimic synaptic plasticity, enables to consider achieving densely interconnected neural networks due to their small size. In this work, our focus is on the realization of such a component, defined as a tunable and non-volatile nano-resistor, and which operation is based on the principle of spintronics (use of the spin of electrons as information vector), which has the advantages of compatibility with current technologies (CMOS, MRAM …etc). By using a magnetic tunnel junction, the concept of the spintronic memristor is based on the motion of a magnetic domain wall by spin transfer effect, where each wall position defines an intermediate resistance state. In order to control the resistance of this spintronic memristive device, the study of static and dynamic properties of the domain wall under the influence of a spin polarized current is required. By the study of the displacement and resonance of the wall whithin an in-plane magnetized device, we established a first assessment (commutation time of the device below one nanosecond and observation of an over-damping). Based on these preliminary studies, we then optimized magnetic tunnel junctions with out-of-plane magnetizations. On one hand, we show that the number of intermediate resistance states is strongly increased (between 15 and 20 states), allowing this spintronic memristive device to be used to perform neuromorphic tasks. Furthermore, we show that the device is optimized to use the most efficient spin transfer torque to displace the magnetic domain wall.

Le sujet de cette thèse concerne la dynamique auto-entretenue excitée par transfert de spin de vortex couplés, dans des structures de type nano-piliers vannes de spin (Py/Cu/Py). Un premier objectif a été de comprendre les processus de transport polarisé en spin et de transfert de spin associés à des configurations d’aimantation fortement non-homogènes. Cette étude a permis d‘identifier et ainsi de précisément contrôler les configurations magnétiques à base de vortex, et en particulier d’observer l’influence du transfert de spin sur les mécanismes de renversement du cœur de vortex. En combinant des calculs analytiques et des simulations micro-magnétiques, nous avons également pu déterminer les conditions sur les paramètres relatifs des deux vortex (chiralités et polarités) pour obtenir des oscillations gyrotropiques couplées auto-entretenues de deux vortex dans un pilier unique. Un cas très intéressant est prévu pour les piliers de plus grands diamètres (typiquement supérieurs à 200nm) pour lesquels le courant critique est réduit potentiellement à zéro. Les résultats expérimentaux confirment les prédictions sur l’existence d’une dynamique couplée de vortex, avec des largeurs de raies atteignant 200kHz, un record à champ nul (soit un facteur de qualité Q ≈ 5000, un ordre de grandeur plus grand que pour les auto-oscillations de vortex unique) et diminuant même jusqu’à 50kHz sous champ extérieur. Un second objectif de ce travail a été l’étude de la synchronisation de deux auto-oscillateurs à transfert de spin à base de vortex. Nous avons démontré que le verrouillage des phases par couplage dipolaire de deux oscillateurs identiques peut être théoriquement obtenu indépendamment des paramètres des deux vortex. Toutefois un couplage trois fois plus important est prévu dans le cas de vortex de polarités opposées. Du point de vue expérimental, des premiers résultats ont permis de démontrer une faculté de synchronisation de deux oscillateurs présentant un écart en fréquence atteignant jusqu'à 10% de leurs fréquences d'auto-oscillation. Ce travail de thèse, qui s’inscrit dans l’effort de recherche mené pour améliorer les performances rf des nano-oscillateurs à transfert de spin, a permis d’illustrer que l’excitation de modes d’aimantations couplées est une voie à poursuivre dans le but d’aboutir à des largeurs de raies de plus en plus faibles. / My PhD work is dedicated to the spin transfer induced self-sustained dynamics of two coupled vortices, in nano-pillars spin-valves structures (Py/Cu/Py). A first objective was to understand the spin-polarized transport processes as well as spin transfer mechanisms associated to highly non-homogeneous magnetic configurations. This study allows me to identify and then precisely tune the vortex based magnetic configurations, and notably to observe the influence of spin transfer on reversal mechanisms of the vortex core. Combining analytical calculations and micro-magnetic simulations, we determine the conditions on relative parameters for the two vortices (chiralities and polarities) necessary to obtain self-sustained gyrotropic oscillations of the coupled vortices in a single pillar. A very interesting case is predicted for the pillars with larger diameters (typically over 200nm) for which the critical current is reduced to zero. The experimental results confirm the predictions that a coupled dynamics exists with linewidths as narrow as 200kHz, that is a record at zero field (corresponding to a quality factor Q ≈ 5000, an order of magnitude over the self-sustained oscillations of a single vortex), and even down to 50kHz under external field.A second objective was to investigate the synchronization of two vortex based spin transfer oscillators. We demonstrate theoretically that the phase locking through dipolar coupling of two identical oscillators can be achieved for any parameters of the two vortex. However, the coupling is three times stronger when vortices have opposite core polarities. From an experimental point of view, the synchronization capability for two oscillators having a frequency mismatch reaching up to 10 % of the auto-oscillation frequency has been demonstrated. This work, being part of the research effort made to improve the rf properties of spin transfer nano-oscillators emphasizes how the excitation of coupled magnetizations modes is important to reach lower and lower linewidths.