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International audience; The actual mechanisms occurring at interfaces underlying the Dzyaloshinskii-Moriya interaction (DMI) remain a question in nanomagnetism. In this study, we investigate the origin of the interfacial DMI, aiming at estimating how independent the DMI contributions of the two interfaces of a FM layer are and what their relative weight in the effective DMI amplitude is. To this aim, we explore the correlation between the effective interfacial DMI and the metal properties, namely, atomic number, electronegativity, and the work function of the metal M. A clear linear relationship is found between the interfacial DMI and the work function difference at the Co/M interface. This result is strong evidence of the independent DMI contributions of the two interfaces for the chosen Co thickness(1 nm). It also suggests that the Co/Cu interface bears no interfacial DMI. These findings can guide the optimization of the magnetic properties of future devices.

International audience; We experimentally investigate the range of the Dzyaloshinskii-Moriya interaction (DMI) occurring at magnetic interfaces within metallic heterostructures. To this aim we perform Brillouin light scattering spectroscopy on a set of Co-based, asymmetric metallic heterostructures, incorporating atomically thin continuous films obtained by room-temperature sputtering, and of identical orientation and quality. We thus access to the intrinsic dependence of the interfacial DMI and other magnetic interactions on the thickness of the non-magnetic layer adjacent to Co, which is chosen among Pt, Ru and Au. Notably, we observe that a robust DMI is already generated by as few as two atomic planes of Pt, and that interfacial DMI can be efficiently suppressed by a dusting of Ru equivalent to a single atomic plane coverage. These results point directly towards a mechanism where DMI is generated within the two first atomic planes away from the interface, in agreement with first-principles calculations. This locally generated DMI is however likely to be modulated by more distant atoms in the case of strain effects. The short-range aspect of the interfacial DMI opens up the synthesis of dense magnetic multilayers, allowing for a strong interfacial DMI even with very thin layers, which can be further tuned by strain engineering.

Noncollinear chiral spin textures in ferromagnetic multilayers are at the forefront of recent research in nano-magnetism with the promise for fast and energy-efficient devices. The recently demonstrated possibilities to stabilize such chiral structures in synthetic antiferromagnets (SAF) has raised interests as they are immune to dipolar field, hence favoring the stabilization of ultra small textures, improve mobility and avoid the transverse deflections of moving skyrmions limiting the efficiency in some foreseen applications. However, such systems with zero net magnetization are hence difficult to characterize by most of the standard techniques. Here, we report that the relevant parameters of a magnetic SAF texture, those being its period, its type (N\'eel or Bloch) and its chirality (clockwise or counterclockwise), can be directly determined using the circular dichroism in x-ray resonant scattering (CD-XRMS) at half integer multilayer Bragg peaks in reciprocal space. The analysis of the dependence in temperature down to 40K allows us moreover to address the question of the temperature stability of a spin spiral in a SAF sample and of the temperature scaling of the symmetric and antisymmetric exchange interactions.

Antiferromagnetic materials are promising platforms for next-generation spintronics owing to their fast dynamics and high robustness against parasitic magnetic fields. However, nanoscale imaging of the magnetic order in such materials with zero net magnetization remains a major experimental challenge. Here we show that non-collinear antiferromagnetic spin textures can be imaged by probing the magnetic noise they locally produce via thermal populations of magnons. To this end, we perform nanoscale, all-optical relaxometry with a scanning quantum sensor based on a single nitrogen-vacancy (NV) defect in diamond. Magnetic noise is detected through an increase of the spin relaxation rate of the NV defect, which results in an overall reduction of its photoluminescence signal under continuous laser illumination. As a proof-of-concept, the efficiency of the method is demonstrated by imaging various spin textures in synthetic antiferromagnets, including domain walls, spin spirals and antiferromagnetic skyrmions. This imaging procedure could be extended to a large class of intrinsic antiferromagnets and opens up new opportunities for studying the physics of localized spin wave modes for magnonics., 7 pages, 5 figures

We experimentally study the thermoelectrical signature of individual skyrmions in chiral $\mathrm{Pt}/\mathrm{Co}/\mathrm{Ru}$ multilayers. Using a combination of controlled nucleation, single skyrmion annihilation, and magnetic field dependent measurements the thermoelectric signature of individual skyrmions is characterized. The observed signature is explained by the anomalous Nernst effect of the skyrmion's spin structure. Possible topological contributions to the observed thermoelectrical signature are discussed. Such thermoelectrical characterization allows for noninvasive detection and counting of skyrmions and enables fundamental studies of topological thermoelectric effects on the nanoscale.

In this chapter, we review the electrical nucleation and detection of magnetic skyrmion. Particular emphasis is on the reading and writing of skyrmions by longitudinal and perpendicular currents. We explain in detail the effects of spin-orbit torque and spin-transfer torque switching, anomalous Hall effect, and topological Hall effect. The chapter is completed by references to the large variety of other electrical reading and writing schemes such as gating, Seebeck effects, noncollinear magnetoresistance, among others.

Per the renewed interest in the magnetic properties of ultrathin multilayers for spintronics, the authors show how electrical-transport characterization can provide crucial information about reversal mechanisms between different magnetic configurations in synthetic antiferromagnetic (SAF) multilayers, with or without perpendicular anisotropy. Here competition between different magnetoresistive effects provides information about the system's magnetic properties and the proportions of all magnetization components in the stabilized magnetic textures. This work extends previous possibilities toward the detection of isolated magnetic domains, spin spirals, or even skyrmions in SAF systems.

Chiral magnetic textures in ultrathin perpendicularly magnetised multilayer film stacks with an interfacial Dzyaloshinskii-Moriya interaction have been the focus of much research recently. The chirality associated with the broken inversion symmetry at the interface between an ultrathin ferromagnetic layer and a heavy metal with large spin-orbit coupling supports homochiral N\'eel domain walls and hedgehog (N\'eel) skyrmions. Under spin-orbit torques these N\'eel type magnetic structures are predicted, and have been measured, to move at high velocities. However recent studies have indicated that some multilayered systems may possess a more complex hybrid domain wall configuration, due to the competition between interfacial DMI and interlayer dipolar fields. These twisted textures are expected to have thickness dependent N\'eel and Bloch contributions to the domain or skyrmion walls. In this work, we use the methods of Lorentz microscopy to measure quantitatively for the first time experimentally both; i) the contributions of the N\'eel and Bloch contributions and ii) their spatial spin variation at high resolution. These are compared with modelled and simulated structures which are in excellent agreement with our experimental results. Our quantitative analysis provides powerful direct evidence of the Bloch wall component which exists in these hybrid walls and will be significant when exploiting such phenomena in spintronic applications., Comment: 12 pages

Magnetic skyrmions are nanoscale windings of the spin configuration that hold great promise for technology due to their topology-related properties and extremely reduced sizes. After the recent observation at room temperature of sub-100 nm skyrmions stabilized by interfacial chiral interaction in magnetic multilayers, several pending questions remain to be solved, notably about the means to nucleate individual compact skyrmions or the exact nature of their motion. In this study, a method leading to the formation of magnetic skyrmions in a micrometer-sized nanotrack using homogeneous current injection is evidenced. Spin-transfer-induced motion of these small electricalcurrent-generated skyrmions is then demonstrated and the role of the out-of-plane magnetic field in the stabilization of the moving skyrmions is also analysed. The results of these experimental observations of spin torque induced motion are compared to micromagnetic simulations reproducing a granular type, non-uniform magnetic multilayer, in order to address the particularly important role of the magnetic inhomogeneities on the current-induced motion of sub-100 nm skyrmions, for which the material grains size is comparable to the skyrmion diameter., 11 pages, 5 figures

International audience; Room-temperature skyrmions in ferromagnetic films and multilayers show promise for encoding information bits in new computing technologies. Despite recent progress, ferromagnetic order generates dipolar fields that prevent ultrasmall skyrmion sizes, and allows a transverse deflection of moving skyrmions that hinders their efficient manipulation. Antiferromagnetic skyrmions could lift these limitations. Here we demonstrate that room-temperature antiferromagnetic skyrmions can be stabilized in synthetic antiferro-magnets (SAFs), in which perpendicular magnetic anisotropy (PMA), antiferromagnetic coupling and chiral order can be adjusted concurrently. Utilizing interlayer electronic coupling to an adjacent bias layer (BL), we demonstrate that spin-spiral states obtained in a SAF with vanishing PMA can be turned into isolated antiferromagnetic skyrmions. We also provide model-based estimates of skyrmion size and stability, showing that room-temperature antiferromagnetic skyrmions below 10 nm in radius can be anticipated in further optimized SAFs. Antiferromagnetic skyrmions in SAFs may thus solve major issues associated with ferromagnetic skyrmions for low-power spintronic devices.

We present a comprehensive micromagnetic model of isolated axisymmetric skyrmions in magnetic multilayers with perpendicular anisotropy. Most notably, the essential role of the internal dipolar field is extensively considered with a minimum amount of assumptions on the magnetization profiles. The tri-dimensional structure of the multilayered skyrmions is modeled by their radial profiles in each layer. We first compare the results of the model against a full micromagnetic description in Cartesian coordinates. Our model combines information on both layer-dependent size and chirality of the skyrmions. We also provide a convenient criterion in order to characterize the stability of skyrmions against anisotropic elongations that would break their cylindrical symmetry, which allows to confirm the stability of the determined solutions. Because this model is able to treat magnetization configurations twisted through the thickness of multilayered skyrmions, it can provide predictions on any potential hybrid chirality in skyrmions due to the interplay of Dzyaloshinskii-Moriya and dipolar interactions in multilayers. We finally apply the results of our model to the description of the current-driven dynamics of hybrid chiral skyrmions. Using the Thiele formalism, we show that we can predict the forces exerted on the multilayered skyrmions by vertical spin-polarized currents, which provides a method to conform hybrid skyrmion chiralities and spin-current injection geometries in order to optimize skyrmion motion in multilayers, to the aim of maximizing the current-induced velocity, or canceling the skyrmion Hall angle., 19 pages, 9 figures

The Dzyaloshinskii-Moriya interaction (DMI), which is essential for the stabilization of topologically non-trivial chiral magnetic textures such as skyrmions, is particularly strong in heterostructures of ultra-thin magnetic materials and heavy elements. We explore by density-functional theory calculations the possibility to modify the magnetic properties at Co/Pt interfaces with chemical disorder. In these systems, we find a particular robustness of the DMI against intermixing. Upon dusting the interface with a third element (all $4d$ transition metals and B, Cu, Au and Bi), a strong reduction of the DMI is predicted. This opens up possibilities to tune the DMI through the degrees of intermixing and dusting.

Chirality in condensed matter is now a topic of the utmost importance because of its significant role in the understanding and mastering of a large variety of new fundamental physicals mechanisms. Versatile experimental approaches, capable to reveal easily the exact winding of order parameters are therefore essential. Here we report X-ray resonant magnetic scattering (XRMS) as a straightforward tool to identify directly the properties of chiral magnetic systems. We show that it can straight-forwardly and unambiguously determine the main characteristics of chiral magnetic distributions: i.e. its chiral nature, the quantitative winding sense (clockwise or counter-clockwise) and its type (N\'eel/cycloidal or Bloch/helical). This method is model-independent, does not require a-priori knowledge of magnetic parameters and can be applied to any system with magnetic domains ranging from few nanometers (wavelength limited) to several microns. By using prototypical multilayers with tailored magnetic chiralities based on the Co|Pt interface we illustrate the strength of this method., Comment: 8 pages, 3 figures

International audience; Sub-100-nm skyrmions are stabilized in magnetic metallic multilayers and observed using transmission electron microscopy, magnetic force microscopy, scanning transmission X-ray microscopy and X-ray resonant magnetic scattering. All these advanced imaging techniques demonstrate the presence of "pure" Néel skyrmion textures with a determined chirality. Combining these observations with electrical measurements allows us to demonstrate reproducible skyrmion nucleation using current pulses, and measure their contribution to the transverse resistivity to detect them electrically. Once nucleated, skyrmions can be moved using charge currents. We find predominantly a creep-like regime, characterized by disordered skyrmion motion, as observed by atomic force microscopy and scanning transmission X-ray microscopy. These observations are explained qualitatively and to some extent quantitatively by the presence of crystalline grains of about 20 nm lateral size with a distribution of magnetic properties.

The magnitude of spin-orbit torque (SOT), exerted to a ferromagnet (FM) from an adjacent heavy metal (HM), strongly depends on the amount of spin currents absorbed in the FM. We exploit the large spin absorption at the Ru interface to manipulate the SOTs in HM/FM/Ru multilayers. While the FM thickness is smaller than its spin dephasing length of 1.2 nm, the top Ru layer largely boosts the absorption of spin currents into the FM layer and substantially enhances the strength of SOT acting on the FM. Spin-pumping experiments induced by ferromagnetic resonance support our conclusions that the observed increase in the SOT efficiency can be attributed to an enhancement of the spin-current absorption. A theoretical model that considers both reflected and transmitted mixing conductances at the two interfaces of FM is developed to explain the results., Comment: Accepted for publication in Physical Review Letters

Spin transfer torque-MRAM is a viable non-volatile memory solution for replacing conventional memories and can cover a broad range of embedded memory applications. Recently discovered spin orbit torque combined with spin transfer torque could be engineered for efficient switching. We present the challenges and the recent developments in spin-transfer and spin-orbit torque MRAM.

Summary Introduction Jaw osteonecrosis is, in most cases, caused by external irradiation. It is otherwise a rare occurrence. Observation A 52-year-old patient was referred to this hospital for several tooth extractions. In the procedure follow-up, the external aspect of the mandible was more and more exposed. This led to the spontaneous loss of a voluminous bone fragment. The patient had never undergone radiotherapy or a course of bisphosphonates but had a long-term cardio-vascular history. He had undergone endarterectomy of both carotids, an ilio-femoral by-pass, and a coronary dilatation. The diagnosis of bone infarction on a chronic osteomyelitis was made. Discussion Blood coagulation disorders are responsible for most cases of bone infarction. Other risk factors include local trauma, chemotherapy, corticoids, and bisphosphonates. Necrosis of the jawbones is rare even though these are prone to trauma and infections. Symptoms are not specific and imaging is contributive late in the evolution. The results of medical treatment (antibiotherapy, vasodilators, and hyperbaric oxygenotherapy) and surgical debridement are very inconsistent.

The recently discovered spin-orbit torque could be used to flip bits in spintronic devices. The authors investigate its less-studied component, the fieldlike torque, and find that with the help of this piece, there is no need for an external magnetic field to achieve the deterministic reversal of magnetization. In principle this solves one of the critical issues in spintronics, and is promising for applications in terms of speed and energy efficiency.

Current-induced spin-orbit torque (SOT) is a very recently discovered phenomenon which provides efficient ways to control and manipulate the magnetization. It allows to use the spin-orbit interaction in the bulk or at the interface of a heavy metal (HM) to inject angular momentum in an adjacent ferromagnet (FM) [1-3]. Even though its origin either from Rashba or spin Hall effects is still under debate, switching the magnetization of nanostructures by spin-orbit torques is very promising for applications both in terms of speed and energetic efficiency. In this work, we study the influence of one of the components of the torques, the field-like torque, for example in Ta/CoFeB/MgO trilayers [4]. This study focuses on the macrospin-based magnetization switching of small devices with a uniform magnetization (50×50 nm2) which are of significant interest for applications.

Introduction Les osteonecroses maxillo-mandibulaires sont exceptionnelles en dehors du contexte d’une radiotherapie cervico-faciale. Les bisphosphonates sont des analogues non metabolises de pyrophosphates. Ils menent a l’inhibition de l’activite osteoclastique et sont prescrits dans le traitement de l’hypercalcemie associee aux processus tumoraux, dans le traitement des metastases osteolytiques, dans la maladie de Paget et dans l’osteoporose. L’incidence des osteonecroses maxillo-mandibulaires sur prise de bisphosphonates est de 1/10 000 patients, mais elle est probablement sous-estimee par manque d’examens bucco-dentaires chez les patients traites. Materiel et methodes Nous decrivons six cas de necrose mandibulaire associee a la prise de bisphosphonates, cinq dans un contexte de tumeurs malignes, un cas dans le cadre du traitement de l’osteoporose. Resultats L’apparition de l’osteonecrose a ete spontanee chez deux patients ; elle faisait suite a une extraction dentaire chez deux autres. Il preexistait, chez les deux derniers, un foyer infectieux dentaire. Le delai d’apparition de l’osteonecrose a varie de 1 a 6 ans. Toutes les biopsies etaient colonisees par de l’actinomycose. Discussion La predisposition a la necrose maxillo-mandibulaire semble s’expliquer par l’exposition de l’os dans la cavite buccale. La symptomatologie va de la gene localisee au sequestre osseux avec fracture. Le traitement est essentiellement conservateur. Une mise en etat bucco-dentaire avant tout traitement par bisphosphonates est recommandee.

The spin orbit torques (SOTs) in perpendicularly magnetized Co-Ni multilayers sandwiched between two heavy metals (HM) have been studied. By exploring various HM materials, we show an efficient enhancement or cancellation of the total SOT, depending on the combination of the two HM materials. The maximum SOT effective field is obtained in Pt/Co-Ni/W heterostructures. We also model our double HM system and show that the effective spin Hall angle has a peak value at certain HM thicknesses. Measuring the SOT in Pt/Co-Ni/W for various W thicknesses confirms an effective spin Hall angle up to 0.45 in our double HM system.

International audience; S o far, the electrical detection of skyrmions in the lattice phase has been achieved only at low temperatures, mainly in magnetic materials with B20 crystal structures 1-7. In this family of materials, contributions to the electrical transport properties are directly linked to the topological nature of skyrmions. Recently, a change in the differential tunnel conductance due to the non-collinearity of single magnetic skyrmions was reported for a PdFe atomic bilayer on Ir(111) 8,9. However, low temperatures preclude the use of magnetic skyrmions in common devices 10-12. The solution can be delivered by engineering magnetic multilayers in the form of stacks composed of ultrathin magnetic layers in contact with heavy-material thin films. Although significant advances have been achieved in the stabilization and current-induced motion of skyrmions at room temperature (RT) 13-17 , until now only imaging techniques have been used to show this 13,18-21. Importantly, no evidence of their detection through purely electrical means has been reported, but this is a crucial prerequisite for any of the potential applications. Here we focus on the transverse Hall resistivity as a sensitive probe for the electrical characterization of magnetic sky-rmions in patterned magnetic multilayer systems. The transverse resistivity ρ xy = V y t/I x (Fig. 1a) is associated with the voltage V y measured across an electrical conductor of thickness t, orthogonal to an applied current I x. In magnetic materials with non-trivial magnetic textures, this transverse resistivity is usually decomposed into three components 22 , = + + xy xy xy xy OHE A HE THE , contributions that arise from the ordinary, the anomalous and the topological Hall effects, respectively. The ordinary Hall effect (OHE) is described by = R H xy OHE 0 , where R 0 is the ordinary Hall coefficient and H ⊥ is the out-of-plane magnetic field component. The anomalous Hall effect (AHE), which contains intrinsic and extrinsic contributions that arise from spin-orbit interactions, can be observed only in materials with broken time-reversal symmetry 22 , as is the case for ferromagnets. The AHE resistivity xy AHE is generally considered as being proportional to the average out-of-plane magnetization, m z , in the sample. The third term is the topological Hall effect (THE) that results from the Berry phase acquired by spin-polarized carriers as they cross a topologically non-trivial magnetic texture, such as skyrmions. In the adiabatic approximation, that is, assuming a strong coupling of the charge with the local spin (which provides an upper-bound estimate), the topological contribution is generally expressed by = PR B xy THE 0 eff , where B eff is the emergent fictitious field in the rest frame of the electrons and P is the magnitude of the spin polarization of the electrons 23. As we recently demonstrated 15 , chiral magnetic skyrmions can be stabilized in multilayers at RT by a large Dzyaloshinskii-Moriya interaction (DMI) that arises at the interfaces of a thin Co layer inserted between two non-magnetic materials. For our study, we selected a similar magnetic multilayered system based on the asym-metric trilayer Pt|Co|Ir with large values of DMI, ranging from 1 to 2 mJ m −2 (refs 24-26). This allows sub-100 nm skyrmions to be stabilized 15,27 as a result of the balance between DMI, magnetic anisot-ropy and exchange coupling 12,28 , as well as the dipolar energy. In the present work, we combined RT electrical-transport measurements with local probe magnetic force microscopy (MFM) imaging, realized concomitantly, on patterned samples with the composition Ta(5)|Pt(10)|[Co(0.8)|Ir(1)|Pt(1)] 20 |Pt(3) (Supplementary Information). A first objective was to control, using large current-density pulses, the generation of small magnetic skyrmions in electron beam (e-beam) lithographed structures (Methods gives the details). Magnetic skyrmions can be generated by the injection of spin-polarized currents through a scanning transmission microscope (STM) tip 29. Another approach is to use inhomogeneous in-plane electrical currents, created by geometrical constrictions, to form bubble skyrmions due to the divergence of the spin torque acting on the magnetic domains walls, as shown by RT magneto-optical Kerr microscopy 13,30. Recently, we reported the thermally assisted nucleation of isolated skyrmions from non-uniform RT magnetiza-tion states in micrometre-sized tracks 21. Here we show how the latter mechanism allows the generation of a finite number of randomly distributed magnetic skyrmions starting from the magnetically saturated state. Fig. 1a shows a schematic view of the experimental setup that allows us to relate the Hall resistivity response directly with the local magnetic configuration in the sample track. The magnetization state Magnetic skyrmions are topologically protected whirling spin textures that can be stabilized in magnetic materials by an asym-metric exchange interaction between neighbouring spins that imposes a fixed chirality. Their small size, together with the robustness against external perturbations, make magnetic skyrmions potential storage bits in a novel generation of memory and logic devices. To this aim, their contribution to the electrical transport properties of a device must be characterized-however, the existing demonstrations are limited to low temperatures and mainly in magnetic materials with a B20 crystal structure. Here we combine concomitant magnetic force microscopy and Hall resistivity measurements to demonstrate the electrical detection of sub-100 nm skyrmions in a multilayered thin film at room temperature. Furthermore, we detect and analyse the Hall signal of a single skyrmion, which indicates that it arises from the anomalous Hall effect with a negligible contribution from the topological Hall effect.

Magnetic skyrmions are nanoscale two-dimensional windings in the spin configuration of some magnetic materials subject to the Dzyaloshinskii-Moriya antisymmetric exchange interaction. They feature a non-trivial topology and show promise to be the smallest achievable magnetic textures. Very recently, magnetic skyrmions have been successfully stabilised up to room temperature by leveraging on the design of magnetic multilayer systems breaking the vertical inversion symmetry. Following up on this achievement, the main objective of this thesis is the understanding and the control of the various physical properties of skyrmions hosted by such multilayer systems. As a first approach to this objective, an original model allowing to predict the profiles adopted by multilayer skyrmions is described and then employed. This numerical model is very generic, as it exploits only the cylindrical symmetry of multilayer skyrmions, in order to determine the magnetostatic interactions with less effort. This model is further extended in order to approximate the thermal stability of multilayer skyrmions, which is key to their experimental realisation. The next aspect of this thesis consists in the experimental study of the electrical manipulation of multilayer skyrmions, demonstrating three main functionalities that are nucleation by local currents, displacement under spin currents and individual detection by transverse voltage. The third aspect of my thesis is the study of the physical properties influencing the current-induced motion of skyrmions in magnetic multilayers. A pinning behaviour is evidenced experimentally and analysed relying on micromagnetic modelling. One of the important results of this work is also the prediction of hybrid chirality for some multilayer magnetic configurations, which is then demonstrated experimentally using a synchrotron technique. The impact of hybrid chirality on current-induced skyrmion motion is discussed and leads to the optimisation of the multilayer design, resulting in the experimental observation of motion for skyrmions below 50 nm in radius at velocities reaching around 40 m/s. The last part of this thesis aims at leveraging on these theoretical and experimental advances in order to reduce the size of skyrmions at room temperature. After the analysis of the impact of dipolar interactions on skyrmion stability, the engineering of the materials and of the layers periodicity is attempted. I also investigate experimentally the conception of magnetic textures with compensated magnetization in multilayer structures known as synthetic antiferromagnets, and show that they can host antiferromagnetic skyrmions at room temperature. This last result opens up new prospects for achieving room-temperature skyrmions combining size in the single-digit nm range and high mobility, potentially allowing applications towards energy-efficient computation and storage devices with a very dense integration.; Les skyrmions magnétiques sont des enroulements bidimensionnels et nanométriques de la configuration de spin, pouvant être stabilisés dans certains matériaux magnétiques soumis à l’interaction d’échange antisymétrique Dzyaloshinskii-Moriya. Ils présentent une topologie non-triviale et s’annoncent peut-être comme étant les plus petites configurations magnétiques pouvant être réalisées. Très récemment, des skyrmions magnétiques ont pu être stabilisés à température ambiante grâce à la conception de multicouches magnétiques brisant la symétrie d’inversion selon la direction verticale. Suite à cette avancée, l’objectif central de cette thèse est la compréhension et la maîtrise des multiples propriétés physiques des skyrmions hébergés dans ces systèmes multicouches. Pour aborder cet objectif, un modèle original est décrit puis employé, permettant la prédiction des profils adoptés par les skyrmions multicouches. Ce modèle numérique est très générique, n’utilisant que la symétrie cylindrique des skyrmions afin de simplifier la détermination des interactions magnétostatiques. Ce modèle est ensuite étendu afin de pouvoir approximer la stabilité thermique des skyrmions, ce qui constitue un élément clé dans leur obtention expérimentale. Une seconde dimension de ce travail consiste en l’étude expérimentale de la manipulation électrique des skyrmions multicouches, démontrant la possibilité de trois fonctionnalités centrales que sont leur nucléation par courants locaux, leur déplacement sous courant de spin et leur détection électrique individuelle par tension transverse. Le troisième aspect de ma thèse est l’étude des propriétés physiques influençant le déplacement des skyrmions dans les multicouches magnétiques. Un comportement d’ancrage sur des défauts est mis en évidence expérimentalement et est analysé à l’aide d’une modélisation micromagnétique. Un des résultats importants de ce travail est aussi la prédiction d’une chiralité hybride dans les configurations magnétiques de certaines multicouches, qui est ensuite démontrée expérimentalement par des mesures au synchrotron. Les conséquences attendues de cette chiralité hybride sur le déplacement des skyrmions sont étudiées pour permettre l’optimisation des multicouches, aboutissant à l’observation expérimentale de la propagation de skyrmions de 50 nm de rayon à des vitesses atteignant environ 40 m/s. La dernière partie de cette thèse vise à mettre à profit ces avancées théoriques et expérimentales afin de parvenir à réduire la taille des skyrmions à température ambiante. Après avoir analysé l’impact des interactions dipolaires sur la stabilité des skyrmions, il est entrepris d’optimiser les matériaux et la périodicité des couches. Je m’intéresse aussi à la conception expérimentale de textures magnétiques dont l’aimantation est compensée au sein de structures multicouches appelées antiferromagnétiques synthétiques, dont je montre qu’elles peuvent héberger des skyrmions antiferromagnétiques à température ambiante. Ce résultat final ouvre de nouvelles perspectives vers l’obtention de skyrmions à la fois mesurant moins de 10 nm et très mobiles, qui pourraient être utilisés dans la conception de composants de calcul et de stockage d’information plus compacts et plus efficaces.