Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Neste trabalho abordamos algumas propriedades físicas associadas ao transporte spintrônico de nanoestruturas formadas por camadas de semicondutor diluído magnético (SDM) e semicondutor convencional submetidas a campos elétrico e magnético cruzados. O campo elétrico é aplicado na direção de crescimento da nanoestrutura e o campo magnético é aplicado perpendicularmente a essa direção. Estuda mos duas configurações de nanoestruturas onde o SDM localiza-se no poço quântico ou nas barreiras. Mostramos que é possível encontrar um potencial efetivo tipo poço de potencial duplo para um intervalo de intensidades de campos externos, altura da barreira de potencial e largura de poço quântico parabólico. Em tal condição esse sistema pode ser visto como um dispositivo spintrônico chamado filtro de spin, pois consegue selecionar polarizações de spin em diferentes regiões da nanoestrutura. / In the present work we studied properties of the spintronic transport of nanostructures formed by layers of diluted magnetic semiconductors (DMS) and conventional semiconductors with crossed fields applied. The electric field is in the growth direction and the magnetic field is perpendicular t o this one. We studied two configurations of nanostructures where the DMS is located in the barriers or in the well. We will show the possibility of the formation of a double quantum well like effective potential for different values of the applied fields intensities, barriers height and quantum well width. In this situation the system can be seen as a spintronic device called spin filter, since it can control the spin polarization in different regions of the nanostructure.

Neste trabalho, apresentamos estudos sobre o magnetotransporte em um sistema de bicamadas com uma rede de antipontos triangulares em campos magnéticos baixos sob a aplicação de campos elétricos externos, que são produzidos por voltagens de porta. A bicamada é feita em poços quânticos largos (wide quantum well) de alta densidade eletrônica, formado em heteroestruturas semicondutoras de AlxGa1xAs=GaAs. Oscila- ções magneto-inter-sub-banda (MIS) são observadas em poços quânticos largos de alta densidade eletrônica com duas sub-bandas ocupadas. Estas são originadas pelo espalhamento inter-sub-bandas e tem um máximo para campos magnéticos B que satisfazem a condição de alinhamento entre os leques dos níveis de Landau de cada sub-banda. Oscila- ções de comensurabilidade são observadas na magnetoresistência que é sensível ao arranjo do potencial dos antipontos. A aplicação de campos elétricos faz diminuir o número de oscilações na magnetoresistência para campos magnéticos compreendidos entre 0; 1T e 0; 4T, observando-se uma transição das oscilações MIS aos efeitos de comensurabilidade. Aplicando voltagens de porta podemos variar a amplitude do potencial dos antipontos. / In this work, we present studying about magnetotransport in a bilayer system with triangular antidot lattices in low magnetic elds under the application of external electric eld. The bilayer forms inside a wide quantum well of high electron density in semiconductor heterostructures formed by AlxGa1xAs=GaAs. Magneto-inter-subband (MIS) oscillations are observed in a wide quantum wells of high electron density with two subbands occupied, and they are caused by intersubband scattering and have a maximum for a magnetic eld B that satises the alignment condition between the staircase of Landau level. Commensurability oscillations are observed in magnetoresistance, which is sensitive to the potential of antidot arrangements. The application of electric elds decrease the number of oscillations in the magnetoresistance for magnetic elds between 0; 1T and 0:4T, showing a transition of MIS oscillations to commensurability oscillations. We varied the amplitude of the potential of the antidots applying dierent gate voltages.

L'EMCD, Energy Loss Magnetic Chiral Dichroism, est une technique récente, mise en œuvre dans le microscope électronique à transmission (TEM), qui utilise la spectroscopie de pertes d'énergie d'électrons (EELS). Elle a pour objectif la mesure du moment magnétique local d'un élément chimique donné. Son utilisation contribue à progresser dans la compréhension des phénomènes magnétiques à l'échelle nanométrique. Cette thèse propose d'élargir les domaines d'applications de l'EMCD. Nous avons exploité l'EMCD pour l'étude de films minces de MnAs épitaxiés sur un substrat de GaAs(001). Ce travail montre l'utilité de cette technique dans le cas de structures hexagonales présentant une anisotropie magnéto-cristalline élevée. Le rapport des moments orbital et de spin du Mn dans les films de MnAs ferromagnétique de structure hexagonale a été mesuré par EMCD et comparé à des calculs DFT, ceci le long des axes magnétiques facile, difficile et intermédiaire. Une rupture de l'ordre ferromagnétique a par ailleurs été observée et mesurée in situ dans le microscope grâce à un porte-objet chauffant, lors de la transition cristallographique de a-MnAs hexagonal à ß-MnAs quasi-hexagonal. La technique EMCD a également été mise en œuvre pour sonder le moment 4f de composés de terres rares à base de dysprosium. Il s'agissait d'étudier des super-réseaux DyFe2/YFe2. Les règles de somme ont été établies pour le seuil M4,5 du Dy. En outre, le couplage antiparallèle des moments Dy et Fe a été confirmé en comparant leurs signaux dichroïques et en prenant en compte la théorie dynamique de la diffraction. Ce travail de thèse illustre pour la première fois d'une part la faisabilité de la technique EMCD pour l'étude quantitative de l'anisotropie et des transitions magnétiques, et d'autre part son potentiel pour étudier les terres rares et leur moment 4f, ainsi que le couplage avec des éléments de transition. / EMCD (Energy-Loss Magnetic Chiral Dichoism) is an emerging technique based on energy-loss spectroscopy (EELS) in a transmission electron microscopy (TEM). It aims at measuring the element-specific local magnetic moment of solids at a nanometer scale, and hence improving our understanding of magnetic local magnetic phenomena. This thesis presents the exploring work on developing the EMCD technique and its applications. We have applied EMCD to epitaxial MnAs thin films grown on a GaAs(001) substrate, extending the application of this technique to hexagonal structure with high magnetocrystalline anisotropy. The 3d orbital-to-spin moment ratio of Mn in hexagonal ferromagnetic MnAs along easy, hard and intermediate magnetic axes has been respectively estimated and then compared to DFT calculations. Moreover, a breaking of the ferromagnetic order in MnAs thin film, together with the crystallographic transition from hexagonal a-MnAs to quasi-hexagonal ß-MnAs, has been locally studied in-situ by modifying the temperature of the crystal inside the electron microscope. EMCD has also been settled to probe 4f moment in rare earth compounds, by investigating Dy-M4,5 edges in DyFe2/YFe2 superlattices. We have derived sum rules which are specified for 4f moment and applied them to the obtained dichroic signal over Dy-M4,5 edges. In addition, antiparallel coupling of Dy and Fe moments has been confirmed by comparing their dichroic signals, taking into account the dynamic diffraction effect. The work in this thesis illustrates for the first time the feasibility of EMCD technique for quantitative study of magnetocrystalline anisotropy and magnetic transition, and also proves its potential as a tool to investigate 4f moment as well as moment coupling in magnetic materials.

<div> <div> <div> <p>Process variations and increasing leakage current are major challenges toward memory realization in deeply-scaled CMOS devices. Spintronic devices recently emerged as one of the leading candidates for future information storage due to its potential for non-volatility, high speed, low power and good endurance. In this thesis, we start with the basic concepts and applications of three spintronic devices, namely spin or- bit torque (SOT) based spin-valves, SOT-based magnetic tunnel junctions and the magnetic skyrmion (MS) for both logic and machine learning hardware. </p> <p>We propose a new Spin-Orbit Torque based Domino-style Spin Logic (SOT-DSL) that operates in a sequence of Preset and Evaluation modes of operations. During the preset mode, the output magnet is clocked to its hard-axis using spin Hall effect. In the evaluation mode, the clocked output magnet is switched by a spin current from the preceding stage. The nano-magnets in SOT-DSL are always driven by orthogonal spins rather than collinear spins, which in turn eliminates the incubation delay and allows fast magnetization switching. Based on our simulation results, SOT-DSL shows up to 50% improvement in energy consumption compared to All-Spin Logic. Moreover, SOT-DSL relaxes the requirement for buffer insertion between long spin channels, and significantly lowers the design complexity. This dissertation also covers two applications using MS as information carriers. MS has been shown to possess several advantages in terms of unprecedented stability, ultra-low depinning current density, and compact size. </p><p><br></p><p>We propose a multi-bit MS cell with appropriate peripheral circuits. A systematic device-circuit-architecture co-design is performed to evaluate the feasibility of using MS-based memory as last-level caches for general purpose processors. To further establish the viability of skyrmions for other applications, a deep spiking neural network (SNN) architecture where computation units are realized by MS-based devices is also proposed. We develop device architectures and models suitable for neurons and synapses, provide device-to-system level analysis for the design of an All-Spin Spiking Neural Network based on skyrmionic devices, and demonstrate its efficiency over a corresponding CMOS implementation.</p> <div> <div> <div> <p><br></p><p>Apart from the aforementioned applications such as memory storage elements or logic operation, this research also focuses on the implementation of spin-based device to solve combinatorial optimization problems. Finding an efficient computing method to solve these problems has been researched extensively. The computational cost for such optimization problems exponentially increases with the number of variables using traditional von-Neumann architecture. Ising model, on the other hand, has been proposed as a more suitable computation paradigm for its simple architecture and inherent ability to efficiently solve combinatorial optimization problems. In this work, SHE-MTJs are used as a stochastic switching bit to solve these problems based on the Ising model. We also design an unique approach to map bi-prime factorization problem to our proposed device-circuit configuration. By solving coupled Landau- Lifshitz-Gilbert equations, we demonstrate that our coupling network can factorize up to 16-bit binary numbers. </p> </div> </div> </div> </div> </div> </div>

L'utilisation de matériaux organiques pour l'électronique de spin suscite actuellement un fort intérêt. En effet, le long temps de diffusion de spin, la possibilité de manipuler l'état de spin d'une molécule ainsi que son interaction avec une surface magnétique offrent a priori de nouvelles possibilités pour la réalisation de nouveaux dispositifs d'électronique de spin. L'incorporation dans des dispositifs de molécules possédant deux états de spin nécessite la compréhension du phénomène de transition de spin une fois que les molécules sont en contact direct avec des surfaces métalliques.L'objectif de ce travail de thèse est l'étude des interfaces molécule-métal. Dans une première partie, nous avons étudié le magnétisme d'interfaces ferromagnétique-organique en utilisant différentes molécules et différents métaux ferromagnétiques. Nous nous sommes particulièrement intéresses a l'anisotropie magnétique dans ces systèmes. Dans une deuxième partie, nous avons étudié le phénomène de transition de spin moléculaire en contact avec une surface métallique. La spectroscopie d'absorption et le dichroïsme magnétique des rayons x ont d'abord permis de mettre en évidence cette transition à l'échelle globale ensuite, nous avons utilise la microscopie a effet tunnel pour étudier ce phénomène à l'échelle moléculaire dans un cristal 2d de molécule. Nous avons notamment observe la dynamique de la transition sous irradiation laser pour la première fois à l'échelle moléculaire. / The use of organic materials in spintronic devices has recently raised a lot of interest. Large spin diffusion time in organic materials along with the flexibility of manipulating the spin state of the molecule and their interaction with the ferromagnetic metal electrode offers new functionalities in molecular spintronics. Understanding the spin crossover (sco) phenomenon for spin active molecules attached to metallic substrate is also necessary for a primary step towards device application.The main goal of the thesis work was to study these molecule—metal interfaces. In one part, we have studied the magnetism of the organic—ferromagnetic interface with different molecules and different ferromagnetic metals. The study was mainly focused on the magnetic anisotropy at the molecule-metal interfaces. In other part, we focused on the spin crossover phenomena of sco molecules attached to metallic substrates. X—ray absorption spectroscopy and magnetic circular dichroism techniques enabled us to study globally the spin crossover phenomenon. Using scanning tunneling microscopy we were able to study the sco phenomena at the single molecular level in a 2d crystal of molecules on a metal substrate. We have then studied locally the dynamics of the spin transition phenomenon upon laser exposure on a single 2d layer molecular crystal.

No description available.

Ce mémoire présente les travaux réalisés durant ces trois années de thèse. Ils se sont orientés autour de l'étude des propriétés électroniques et magnétiques des matériaux pour la spintronique. Ce domaine d'avenir doit encore trouver les matériaux adaptés qui permettraient de réaliser les concepts liés à la spintronique. Nos résultats sont les suivants. Nous avons proposé un nouveau modèle qui décrit l'arrangement magnétique dans les couches minces ferromagnétiques possédant une anisotropie uniaxiale. Le modèle apporte une meilleure description des largeurs de domaine en fonction de l'épaisseur ainsi qu'une bonne estimation de l'épaisseur critique à partir de laquelle les domaines de Weiss ne sont plus stables. L'ensemble d'équations en unité réduite découlant du modèle apporte quant à lui un outil supplémentaire aux expérimentateurs. L'étude ab-Initio fait sur les semi-Conducteurs magnétiques dilués à mis en évidence l'importance de la corrélation forte et de l'effet Jahn-Teller dans les matériaux tel que le (Ga,Mn)N et le (Zn,Cr)S. Ces calculs confirment l'ensemble des données expérimentales existantes sur le (Ga,Mn)N. La modélisation analytique apporte un complément aux calculs ab-Initio en faisant le lien entre les paramètres expérimentaux et la théorie de Vallin, très largement utilisée pour interpréter les mesures optiques du (Zn,Cr)S. Nos calculs ab-Initio ont montré que le métacinabre est un isolant topologique robuste, qui se distingue par la présence d'un cône de Dirac extrêmement anisotrope. Les effets de passivation à l'hydrogène influencent les états de surface des isolants topologiques de la série HgX (X : S, Se, Te). / This thesis contains the scientific work of three years. The main topic can be defined as follows : study of electronic and magnetic properties of materials for spintronics. That technology of the future has still to find the necessary materials to realize new concepts. Our results are the following : We propose a new model to describe the magnetic configuration in thin ferromagnetic film with uniaxial anisotropy. It gives a better description of domain widths in function of film thickness and permits to obtain a good evaluation of the critical thickness where domains of Weiss type are no longer stable. The set of equations in reduced units is a useful tool to analyze experimental data. The ab-Initio study of diluted magnetic semiconductors has demonstrated the combined effect of strong correlations and Jahn-Teller distortion in (Ga,Mn)N and (Zn,Cr)S. The calculations confirm the experimental results of (Ga,Mn)N. We develop an analytical model that is complementary to the ab-Initio calculations and permits to create a link between several experimental parameters, the ab-Initio calculations and the former theory of Vallin. It has been used to interpret the optical measurements of (Zn,Cr)S. Our ab-Initio studies show that metacinnabar is a strong topological insulator with one peculiarity, it has a highly anisotropic Dirac cone. The passivation with hydrogen atoms influences the surface states of the topological insulator in the series HgX (X : S, Se, Te). When the dangling bonds are saturated by hydrogen, the trivial surface states disappear.

Ce travail porte sur l'étude des propriétés opto- et magnéto-électroniques des oxydes et fluorures de zinc. Dans une première partie, nous avons étudié les propriétés d'absorption/réflexion dans le proche-IR de poudres d'oxyde de zinc dopées de manière aliovalente par l'aluminium ou le gallium. Une grande partie du travail a consisté en la détermination précise du taux de dopant introduit pour les différentes conditions expérimentale utilisées. Les taux de dopant déterminés ont ensuite été corrélés aux propriétés optiques mesurées par spectrométrie de réflexion diffuse. Nous avons voulu réaliser le même travail sur le fluorure de zinc mais nous avons été confrontés à la difficulté de doper ce composé par l'aluminium à cause de la grande stabilité chimique du fluorure AlF3. En revance, une étude structurale approfondie a été réalisée sur un hydroxyfluorure de zinc ZnOHF, précurseur pouvant être dopé de manières aliovalente. Dans la dernière du manuscrit, nous avons utilisé nos compétences relatives au suivi du dopage pour étudier l'effet des porteurs libres sur les propriétés magnétiques des oxydes de zinc dopés au cobalt. D'un point de vue expérimental, aucun effet des porteurs n'a été recensé, seul un comportement paramagnétique ayant été observé. / This work deals with the opto-electronic and magnetic properties of zinc oxides and fluorides. In a first part, NIR absorption / reflection properties of aluminium and gallium doped zinc oxides powders have been studied. Dopant rates have been accurately determined for different experimental conditions and correlated with optical properties which were measured by diffuse reflection spectrometry. The same investigation has been performed on zinc fluoride but this compound could not have been doped by aluminium because of high chemical stability of aluminium fluoride. However, a structural study has been carried out on zinc hydroxyfluoride, which can be doped by aluminium. The last part of this dissertation deals with the investigation of carriers effect, which can be followed by diffuse reflection, on magnetic properties of cobalt doped zinc oxide. Free carriers have beeb no effect, only a paramagnetic behaviour has been observed.

With CMOS technology scaling reaching its limitations rigorous research of alternate and competent technologies is paramount to push the boundaries of computing. Spintronic and resistive memories have proven to be effective alternatives in terms of area, power and performance to CMOS because of their non-volatility, ability for logic computing and easy integration with CMOS. However, deeper investigations to understand their physical phenomenon and improve their properties such as writability, stability, reliability, endurance, uniformity with minimal device-device variations is necessary for deployment as memories in commercial applications. Application of these technologies beyond memory and logic are investigated in this thesis i.e. for security of integrated circuits and systems and special purpose memories. We proposed a spintonic based special purpose memory for search applications, present design analysis and techniques to improve the performance for larger word lengths upto 256 bits. Salient characteristics of RRAM is studied and exploited in the design of widely accepted hardware security primitives such as Physically Unclonable Function (PUF) and True Random Number Generators (TRNG). Vulnerability of these circuits to adversary attacks and countermeasures are proposed. Proposed PUF can be implemented within 1T-1R conventional memory architecture which offers area advantages compared to RRAM memory and cross bar array PUFs with huge number of challenge response pairs. Potential application of proposed strong arbiter PUF in the Internet of things is proposed and performance is evaluated theoretically with valid assumptions on the maturity of RRAM technology. Proposed TRNG effectively utilizes the random telegraph noise in RRAM current to generate random bit stream. TRNG is evaluated for sufficient randomness in the random bit stream generated. Vulnerability and countermeasures to adversary attacks are also studied. Finally, in thesis we investigated and extended the application of emerging non-volatile memory technologies for search and security in integrated circuits and systems.

La spintronique propose de nouvelles solutions en microélectronique en termes d’architecture, pour résoudre les problèmes de miniaturisation et de consommation. Son produit phare, les mémoires magnétiques à accès aléatoire (MRAM), est composé de jonctions tunnel magnétiques (JTM). Une alternative intéressante d’architecture MRAM, développée par Crocus Technology propose d’assister thermiquement le retournement du moment magnétique stockant l’information. L’aimantation de la couche de stockage est couplée à une couche antiferromagnétique afin de la stabiliser (couche piégée). Un chauffage par effet Joule à l’aide d’un courant traversant la barrière tunnel permet de libérer la couche de stockage pour écrire l’information à l’aide d’un champ magnétique. Générer un champ magnétique est encore coûteux en puissance. Pour résoudre ce problème, l’idée explorée dans cette thèse est d’exploiter avantageusement le couple de transfert de spin généré par le courant de chauffage pour réduire le champ d’écriture en changeant la polarité du courant de chauffage suivant l’état que l’on cherche à écrire. Pour ce faire, des dispositifs 1 kbit ont été testés, dans lesquels on montre que l’influence du couple de transfert permet de réduire le champ d’écriture. Une nouvelle structure à couche de stockage synthétique ferrimagnétique (SyF) piégée a été développée pour tirer parti du couple de transfert de spin au mieux sans dégrader relations d’épitaxie garantes des propriétés de stabilité et de signal. Pour étudier l’influence du couple de transfert de spin en détail, des diagrammes de phases en champ et tension ont été réalisés sur divers structures, en séparant les différentes composantes de l’empilement complet. En plus du couple de transfert de spin attendu, un effet pair du courant a été observé, favorisant toujours l’état antiparallèle quel que soit la polarité du courant. Cet effet se retrouve tant sur les couches piégées que les couches libres, et peut s’expliquer par un couple de transfert de spin perpendiculaire comme suggéré par la forme des diagrammes obtenus avec des couches libres. Par ailleurs, les diagrammes d’écriture de couche de stockage SyF révèlent une forme complexe qui serait liée à l’excitation d’une seule des deux couches du SyF par le couple de transfert de spin. En variant le produit résistance-surface (RA) de la JTM, on a montré que le couple de transfert de spin semble bien conserver sa proportionnalité avec la densité de courant sur des structures à couche de stockage piégée. Un autre pan du travail concerne la phase de refroidissement à la fin de l’écriture assistée thermiquement. L’influence de la vitesse de refroidissement sur l’efficacité du couple de transfert de spin a été mise en évidence, et il est montré qu’une diminution progressive de la tension permet d’atteindre un régime de refroidissement quasi-statique dans lequel le taux d’erreur est réduit d’un ordre de grandeur sur certaines structures. Les différents résultats sont mis en lien avec la dépendance en température du couplage RKKY au sein du SyF. Celui-ci permet de d’estimer l’évolution de la température en tension et en temps réel. Enfin, l’existence d’un effet thermoélectrique dû à l’asymétrie de chauffage est étudiée. / Spintronics offers new solutions in microelectronics regarding architecture, to solve scaling and consumption issues. Its main product, magnetic random access memories (MRAM), is composed of magnetic tunnel junctions (MTJ). Switching of the magnetic moment storing the data is facilitated by a thermally assisted writing method developed by Crocus Technology. The storage layer’s magnetization is coupled to an antiferromagnetic layer to stabilize it (pinned layer). Joule heating thanks to a tunneling current allows freeing the storage layer to write information thanks to a magnetic field. Generating a magnetic field still consumes power. To solve this issue, the idea explored in the thesis is to harness advantageously the spin transfer torque arising from the heating current in order to lower the writing field by changing the heating current polarity depending on the state to write. To do this, 1 kbit test vehicles have been tested, for which it is shown that spin transfer torque influence allows reducing the writing field. A new structure has been developed, consisting of a pinned synthetic ferrimagnetic (SyF) storage layer, to get benefits from the spin transfer torque without degrading epitaxial relations necessary to have a good stability and a good signal. To study the influence of spin transfer torque in details, field-voltage phase diagrams have been measured for various structures, by separating the elementary parts of the full structure. Apart from the expected spin transfer torque, an even effect of the current has been observed, favoring the antiparallel state whatever the current polarity. This effect can be found both in pinned layers and free layers, and can be explained thanks to perpendicular spin transfer torque as suggested by the shape of the diagrams obtained on free layers. Besides, writing diagrams of SyF storage layer have a complexe shape that may be related to the excitation of one only layer of the two of the SyF by spin transfer torque. By varying the resistance-area product (RA) of the MTJ, we showed that spin transfer torque seems to keep its proportionality to current density for structures with pinned storage layer. Another side of the work is related to the cooling phase at the end of the thermally assisted writing. Influence of the cooling rate on the efficiency of spin transfer torque was evidenced, and it is showed that a gradual decrease of the voltage let reach a quasistatic cooling regime in which the writing error rate is reduced by one order of magnitude on some structures. The different results are linked to the temperature dependence of RKKY coupling inside the SyF. This allows estimating real time change of temperature. Finally, thermoelectric effect due to heating asymmetry is studied.