Dry High speed and wet milling strategies have both been used to machine hardened die and mold H13 tool steel (HRC 45-58). The TiAlCrSiYN-based family of PVD coatings prepared with various architectures (mono-, multi- and multilayer with an TiAlCrN interlayer) were studied to evaluate the coating micro-mechanical properties that affect tool life during dry high-speed milling of H13 tool steel. A systematic design of varying TiAlCrN interlayer thickness within a multilayer coating structure was developed and its influence on coating properties and cutting performance was investigated. A comprehensive characterization of the coatings was performed using a transmission electron microscope (TEM), focused ion beam (FIB), scanning electron microscope (SEM), X-ray powder diffraction (XRD), room-temperature nanoindentation, a nano-impact, ramped load scratch and a repetitive load wear test. The incorporation of an interlayer into the multilayer coating structure was found to increase the crack propagation resistance (CPRs) to 5.8 compared to 1.9 for the multilayer and 1.6 for the monolayer coatings, which resulted in a 60% tool life increase. The wear test at a load of 1.5 N showed that although the 500nm interlayer exhibited the best coating adhesion, a decline in the H3/E2 ratio was observed to worsen the machining performance. An approximate 40% increase in the tool life was achieved with the 300 nm interlayer by obtaining a balance between mechanical and adhesion properties. To investigate the tool performance during the wet milling of hardened tool steels, the (AlCrN-TiAlN) bi-layer PVD coating was post-treated by WPC (Wide Peening Cleaning) at various pressures and times. Fatigue resistance of the coating following the application of post treatment was observed to improve as the micro-mechanical characteristics (such as H3/E2 ratio, yield stress) were increased. A deterioration in the coating’s adhesion with increasing WPC pressure was also observed as measured by wear test applying a load of 1 N. Through experimentation a balance between fatigue resistance and adhesion was found with tool life being improved by 35% at a WPC applied pressure of 0.2 MPa. / Dissertation / Doctor of Philosophy (PhD) / Over the last 50 years, PVD (physical vapor deposition) coatings have played an increasingly important role in manufacturing where tool cost takes up 3% of the total expenses of the production process. Optimization of these coatings can expedite production wherever machining is conducted under extreme cutting conditions and consequent high material removal rates. These considerations assert significant importance on conducting research on PVD coating development specifically for milling of H13 tool steel, the material widely used in the mold and die industry. This research work seeks to enhance the micro-mechanical and adhesion properties of PVD coatings through architectural design and careful process development while relating desired properties to the high-performance milling of H13 tool steel.

Additive manufacturing (AM) is a rapidly growing and evolving form of product development that has the potential to revolutionize both the industrial and academic spheres. For example, AM offers much greater freedom of design while producing significantly less waste than most traditional manufacturing techniques such as injection and blow molding. Filament-based material extrusion AM, commonly referred to as fused filament fabrication (FFF), is one of the most well-known AM modalities using a polymeric feedstock; however, several obstacles currently prohibit widespread use of this manufacturing technique to produce end-use products, which will be discussed in this dissertation. Specifically, a severely limited material catalog restricts tailored product development and the variety of applications. Additionally, poor interlayer adhesion results in anisotropic mechanical properties which can lead to failure, an issue not often observed in traditional manufacturing techniques. A review of the current state of the art research in the field of FFF, focusing on the multiphysics-based modeling of the system and exploring some empirically determined relationships, is presented herein to provide a more thorough understanding of FFF and its complexities. This review further guides the work discussed in this dissertation. The primary focus of this dissertation is to expand the fundamental understanding of the FFF process, which has proven difficult to measure directly. On this size scale, introduction of measurement devices such as thermocouples and pressure transducers can significantly alter the behavior of the process or require major changes to the geometry of the system, leading to spurious measurements, incorrect outcomes, and/or conclusions. Therefore, the research presented in this dissertation focuses on the development and validation of predictive models based on first principles approaches that can provide information leading to the optimization of printing parameters and exploration of novel and/or modified materials without an exhaustive and inefficient trial-and-error process. The first potential issue a novel material may experience in FFF is an inability to extrude from the heated nozzle. Prior to this work, no efforts were focused on the molten material inside the liquefier and its propensity to flow in the reverse direction through the annular region between the filament and the nozzle wall, referred to as annular backflow. The study presented in this dissertation explores this phenomenon, determining its cause and sensitivity to processing parameters and material properties. A dimensionless number, named the "Flow Identification Number" or FIN, is defined that can predict the propensity to backflow based on the material's shear thinning behavior, the filament diameter, the nozzle diameter, and the filament feed rate and subsequent pressure inside the nozzle. An analysis of the FIN suggested that the backflow potential of a given material is most sensitive to the filament diameter and its shear thinning behavior (power law index). The predictive model and FIN were explored using three materials with significantly different onsets of shear thinning. The experiments validated both the backflow model and a previously derived buckling model, leading to the development of a rapid screening technique to efficiently estimate the extrudability of a material in FFF. Following extrusion from the nozzle, the temperature profile of the deposited filament will determine nearly all of the mechanical properties of the printed part as well as the geometry of the individual roads and layers because of its temperature dependent viscoelastic behavior. Therefore, to better understand the influence of the temperature profile on the evolution of the road geometry and subsequent interlayer bonding, a three-dimensional finite element heat transfer analysis was developed. The focus of this study is the high use temperature engineering thermoplastic polymer polyetherimide, specifically Ultem™ 1010, which had not been studied in prior modeling analyses but presents significant challenges in terms of large thermal gradients and challenging AM machine requirements. Through this analysis, it was discovered that convective cooling dominated the heat transfer (on the desktop FFF scale) producing a significant cross-sectional temperature gradient, whereas the gradient along the axis was observed to be significantly smaller. However, these results highlighted a primary limitation in computer modeling based on computational time requirements. This study, utilizing a well-defined three-dimensional model based on a geometry measured empirically, produced results describing 0.5 s of printing time in the printing process and elucidated great details in the road shape and thermal profile, but required more than a week of computation time, suggesting a need for to modify the modeling approach while still accurately capturing the physics of the FFF layer deposition process. The determination of the extensive time required to converge the three-dimensional model, as well as the identification of a relative lack of axial thermal transfer, led to the development of a two-dimensional, cross-sectional heat transfer analysis based on a finite difference approach. This analysis was coupled with a diffusion model and a stress development model to estimate the recovery of the bulk strength and warping potential of a printed part, respectively. Through this analysis, it was determined that a deposited road may remain above Tg for 2-10 s, depending on the layer time, or time required for the nozzle to pass a specific point in the x-y plane between each layer. The predicted strength recovery was significantly overestimated, leading to the discovery of the extreme sensitivity of the predictive models to the relaxation time of a material, particularly at long layer times. When the deposited filament has enough time to attain an equilibrium temperature, small changes in the relaxation time of the material resulted in significant changes in the predicted healing results. These results highlight the need for exact estimations of the material parameters to accurately predict the properties of the final print. / Doctor of Philosophy / Additive manufacturing (AM), particularly filament-based material extrusion additive manufacturing, commonly known as fused filament fabrication (FFF), has recently become the subject of much study with the goal of utilizing it to produce parts tailored to specific purposes quickly and cheaply. AM is especially suited to this purpose due to its ability to produce highly complex parts with the ability to change design very easily. Furthermore, AM typically produces less waste than many traditional manufacturing techniques due to the process building a part layer by layer rather than removing unneeded material from a larger piece, resulting in a cheaper process. These freedoms make AM, and FFF in particular, highly prized among industrial producers. However, numerous challenges prevent the adoption of FFF by these companies. Particularly, a lack of available material options and anisotropic material properties lead to issues when attempting to produce a part targeted for use in a specific field. FFF is primarily commercially limited to two materials: polylactic acid (PLA) and acrylonitrile-butadiene-styrene (ABS) with a few other materials available in more specialized fields. However, essentially all these materials are limited to low use temperatures (less than 300 °C) and are primarily amorphous or with nearly negligible amounts of crystallinity. This severely limits the ability to tailor a printed part to a specific purpose and restricts the use of printed parts to applications requiring very low strengths. This is one reason why FFF, and most types of AM, is limited to the prototyping field rather than end-use applications. The other reason, anisotropic mechanical properties, is caused by the building methodology of AM. Creating a part layer by layer naturally introduces potential areas of weakness at the joining of the layers. If bulk properties are not recovered, the interlayer bond acts as a stress concentrator under load and will break before the bulk material. The work presented in this dissertation proposes methods to better understand the FFF system in order to address these two issues, leading to the optimization of the printing process and ability to expand the material catalog, particularly in the direction of high use temperature materials. The research discussed herein attempts to develop predictive models that may allow exploration into the FFF system which can be difficult to do experimentally, and by predicting the properties of a printed part, the models can guide future experimentation in FFF without the need for an extensive trial-and-error process. The work presented in this dissertation includes exploring the flow phenomena inside the FFF nozzle to determine extrudability as well as two-dimension and three-dimension heat transfer models with the goal of describing the viscoelastic, flow, diffusion, and stress development phenomena present in FFF.

The present work deals with the behavior of ancient railway sub-structure in France. A statistical study was firstly undertaken on problems occurred in the whole ancient French railway network. The analysis evidenced the particular importance of sub-grade quality for the performance of the sub-structure and the track geometry. Afterwards, an ancient railway line in the West of France was investigated. The analysis showed that the degradation speed of this line was correlated with different parameters such as the nature of sub-grades and the thickness of different layers. An increase trend of degradation speed with the increase in interlayer thickness was identified. The interlayer has a positive impact since it reduces the train-induced stress applied to the sub-grade. The hydro-mechanical behavior of interlayer soil under different conditions (water content, fines content, stress, number of cycles) was investigated. A set of triaxial tests and infiltration tests were performed for this purpose. By analyzing the shear strength properties, the permanent axial strain and the resilient modulus of interlayer soil, we found that the water content and the fines content must be considered together. Adding more fines into the interlayer presents a positive impact under unsaturated conditions thanks to the suction effect, but a negative impact under saturated conditions. The infiltration column tests with drying/wetting cycles showed that the hydraulic conductivity of interlayer soil is governed by fines fraction but did not change significantly with fines content. In order to study the mechanism of interlayer creation and mud pumping, a physical model of 550 mm inner diameter was developed. Soil samples representing the ancient French railway substructure with a ballast layer overlying an artificial silt layer (mixture of crushed sand and kaolin were tested. The effects of monotonic and cyclic loadings, water content and dry unit mass of sub-soil were investigated. It was found that the pore water pressure developed in the sub-soil and the sub-soil stiffness are the key factors for the migration of fine particles or the creation of interlayer/mud pumping. Water is the necessary condition, but it is the soil compressibility that governs the phenomenon to occur

<p>Magnetic properties of selected compounds and superlattices have been experimentally studied using SQUID (superconducting quantum interference device) and VSM (vibrating sample magnetometer) magnetometry, neutron diffraction and Mössbauer spectroscopy measurements combined with theoretical <i>ab initio</i> calculations. </p><p>The magnetic compounds (Fe_1-xM_x)₃P, M=Co or Mn have been studied extensively. It was found that Co can substitute Fe up to <i>x</i>=0.37. Increasing the Co content leads to a reduction of the Curie temperature and the magnetic moment per metal atom. Mn can substitute Fe up to<i> x</i>=0.25 while Fe can be substituted into Mn₃P to 1-<i>x</i>=0.33. On the iron rich side, the drop in Curie temperature and magnetic moment when increasing the Mn content is more rapid than for Co substitution. On the manganese rich side an antiferromagnetic arrangement with small magnetic moments was found. </p><p>The interlayer exchange coupling and the magnetocrystalline anisotropy energy of Fe/V superlattices were studied. The coupling strength was found to vary with the thickness of the iron layers. To describe the in-plane four-fold anisotropy, the inclusion of surface terms proved necessary. </p><p>The in-plane four fold anisotropy was also studied in a series of Fe/Co superlattices, where the thickness of the Co layers was kept thin so that the bcc structure could be stabilized. Only for samples with a large amount of iron, the easy axis was found to be [100]. The easy axis of bulk bcc Co was therefor suggested to be [111]. </p>

Magnetic properties of selected compounds and superlattices have been experimentally studied using SQUID (superconducting quantum interference device) and VSM (vibrating sample magnetometer) magnetometry, neutron diffraction and Mössbauer spectroscopy measurements combined with theoretical ab initio calculations. The magnetic compounds (Fe1-xMx)3P, M=Co or Mn have been studied extensively. It was found that Co can substitute Fe up to x=0.37. Increasing the Co content leads to a reduction of the Curie temperature and the magnetic moment per metal atom. Mn can substitute Fe up to x=0.25 while Fe can be substituted into Mn3P to 1-x=0.33. On the iron rich side, the drop in Curie temperature and magnetic moment when increasing the Mn content is more rapid than for Co substitution. On the manganese rich side an antiferromagnetic arrangement with small magnetic moments was found. The interlayer exchange coupling and the magnetocrystalline anisotropy energy of Fe/V superlattices were studied. The coupling strength was found to vary with the thickness of the iron layers. To describe the in-plane four-fold anisotropy, the inclusion of surface terms proved necessary. The in-plane four fold anisotropy was also studied in a series of Fe/Co superlattices, where the thickness of the Co layers was kept thin so that the bcc structure could be stabilized. Only for samples with a large amount of iron, the easy axis was found to be [100]. The easy axis of bulk bcc Co was therefor suggested to be [111].

abstract: Material extrusion based rapid prototyping systems have been used to produceprototypes for several years. They have been quite important in the additive manufacturing field, and have gained popularity in research, development and manufacturing in a wide field of applications. There has been a lot of interest in using these technologies to produce end use parts, and Fused Deposition Modeling (FDM) has gained traction in leading the transition of rapid prototyping technologies to rapid manufacturing. But parts built with the FDM process exhibit property anisotropy. Many studies have been conducted into process optimization, material properties and even post processing of parts, but were unable to solve the strength anisotropy issue. To address this, an optical heating system has been proposed to achieve localized heating of the pre- deposition surface prior to material deposition over the heated region. This occurs in situ within the build process, and aims to increase the interface temperature to above glass transition (Tg), to trigger an increase in polymer chain diffusion, and in extension, increase the strength of the part. An increase in flexural strength by 95% at the layer interface has been observed when the optical heating method was implemented, thereby improving property isotropy of the FDM part. This approach can be designed to perform real time control of inter-filament and interlayer temperatures across the build volume of a part, and can be tuned to achieve required mechanical properties. / Dissertation/Thesis / Masters Thesis Mechanical Engineering 2016

When joining steel to aluminium there is a reaction between iron and aluminium which results in the formation of brittle intermetallic compounds (IMC). These compounds are usually the reason for the poor mechanical strength of the dissimilar metallic joints. The research on dissimilar metal joining is vast but is mainly focused on the automotive industry and therefore, the material in use is very thin, usually less than 1 mm. For materials with thicker sections the present solution is a transition joint made by explosion welding which permits joining of steel to aluminium and avoids the formation of IMCs. However, this solution brings additional costs and extra processing time to join the materials. The main goals of this project are to understand the mechanism of formation of the IMCs, control the formation of the IMCs, and understand their effects on the mechanical properties of the dissimilar Fe-Al joints during laser welding. Laser welding permits accurate and precise control of the welding thermal cycle and thereby the underpinning mechanism of IMC formation can be easily understood along with the factors which control the strength of the joints. The further goal of this project is to find an appropriate interlayer to restrict the Fe-Al reaction. The first stage of the work was focused on the formation and growth of the Fe-Al IMCs during laser welding. The understanding of how the processing conditions affect the IMC growth provides an opportunity to act and avoid its formation and thereby, to optimize the strength of the dissimilar metal joints. The results showed that even with a negligible amount of energy it was not possible to prevent the IMC formation which was composed of both Fe2Al5 and FeAl3 phases. The IMC growth increases exponentially with the applied specific point energy. However, for higher power densities the growth is more accentuated. The strength of the Fe-Al lap-joints was found to be not only dependent on the IMC layer thickness but also on the bonding area. In order to obtain sound joints it is necessary to achieve a balance between these two factors. The thermal model developed for the laser welding process in this joint configuration showed that for the same level of energy it is more efficient to use higher power densities than longer interaction iv times. Even though a thicker IMC layer is formed under this condition due to higher temperature there is also more melting of aluminium which creates a larger bonding area between the steel and the aluminium. The joint strength is thus improved ... [cont.].

This work presents a detailed investigation of magnetization dynamics in synthetic antiferromagnets (SAFs), which has been studied both experimentally, using electrically-detected ferromagnetic resonance (ED-FMR) and vector-network analyzer-based ferromagnetic resonance (VNA-FMR), and theoretically. Two modes, one with in-phase and one with 180° out-of-phase precessing magnetizations of the layers, are identified in all applied field regimes, namely, a low-field antiferromagnetically coupled regime (when magnetizations of the layers have opposite directions), a spin-flop regime at intermediate field values (when magnetizations are non-collinear) and a high-field saturation regime (when both magnetazations are collinear to each other and the external magnetic field direction). The qualitative theoretical description, found to be in good agreement with the experimental data, is given using a system of coupled Landau-Lifshitz equations. In this work, for the first time to our knowledge, it is shown that for SAFs with different magnetic moments of the individual layers, dynamic, and not static, Zeeman and interlayer exchange coupling energies are solely resposible for the frequency-field dependence in the antiferromagnetically coupled regime. The changes in the dynamical energy terms lead to the changes in the dynamical components of the precessing magnetizations. As the external magnetic field is varied, the amplitude of the components vary continiously in different ways for different modes, dropping to zero in the spin-flop regime, which is reflected in the amplitudes of ED-FMR and VNA-FMR. This effect appears only in SAFs with different magnetic moments of the layers and is related to the different increase in the Zeeman energy of the layers as the externally applied field increases. The variation of the dynamical components leads to the modulation of an exchange of spin-angular momentum between the layers (so called spin-pumping effect).This is directly reflected in the measured linewidths for the modes in both ED-FMR and VNA-FMR. As was shown before in the literature and is also confirmed here, spin-pumping leads to a constant difference in linewidths between two modes for SAFs in the saturated case. Here, we extend the previous findings to non-saturated regimes. We show that in non-saturated states, the linewidth difference does not remain constant and varries with the external magnetic field. This linewidth difference changes can be qualitatively explained using the modulation of the dynamical magnetization components. In order to directly model the spin-pumping effects, additional terms are introduced in the coupled Landau-Lifshitz equations, related to the intrinsic damping in the magnetic layers and spin-pumping induced effects. The calculations of linewidth dependences using the extended model are not in full agreement with the experiments, suggesting that additional effects must be added to the model (for example, potential domain formations). Additionly, due to the dependence of the effect on the Zeeman energy asymmetry between the layers of the SAF, SAFs with different ratio of thicknesses are studied. Although the trends described above are common to all the samples, no significant enhancement of spin-pumping effects are observed. Modeling shows that, although the evolution of the dynamical magnetization components does depend on the magnetic moment ratio between the layers, the difference between maximum and minimum values remains almost constant and does not alter the observed linewidth-field dependence.:1 Fundamentals 1 1.1 Magnetic moment 1 1.2 Magnetic energy contributions 6 1.2.1 Zeeman energy 6 1.2.2 Demagnetization energy 7 1.2.3 Magnetic anisotropy 9 1.2.4 Direct Exchange Energy 13 1.2.5 Indirect Exchange. Interlayer Exchange Coupling Energy 15 1.3 Magnetoresistance 17 1.3.1 Ordinary Magnetoresistance 17 1.3.2 Anisotropic Magnetoresistance 20 1.3.3 Giant Magnetoresistance 22 1.4 Magnetization dynamics 25 1.4.1 Classical motivation 25 1.4.2 Quantum mechanical justification 27 1.5 Spin-currents and Spin-pumping 29 2 Experimental methods 33 2.1 Vibrating Sample Magnetometry 33 2.2 Ferromagnetic resonance 34 2.2.1 Cavity-FMR 35 2.2.2 VNA-FMR 36 2.3 Electrically detected ferromagnetic resonance 39 3 Synthetic antiferromagnets. Theoretical model 47 3.1 Static model 47 3.2 Dynamical model 54 4 Sample fabrication and characterization 58 4.1 Fabrication 58 4.2 Static characterization 62 5 Magnetization dynamics in asymmetric SAFs 68 5.1 Dynamical measurements on Py(3nm)/ Ru(0.85 nm)/Py(9 nm) 68 5.2 Theoretical explanation 71 5.3 Dynamics in SAFs with varying asymmetry of the layers 80 6 High-frequency spin-pumping in SAFs 86 6.1 Spin-pumping in magnetic trilayers 86 6.2 Spin-pumping in SAFs 88 6.3 Dependence on the asymmetry between the layers 94 7 Conclusions and outlook 99 A General description of the trilayer system without damping and spin-pumping contributions 102 A.1 Effective fields 103 A.2 Final equations 107 B Mathematica program used for the theoretical modeling 108 B.1 Matrix Elements 108 B.2 Frequency-Modes 109 B.3 Dynamical components and corresponding dynamical energies 112 B.4 Equilibrium condition 114 B.5 Dynamical Energies 118 B.6 Dynamical Trajectories 121 Bibliography 125

Unique layered structure with excellent electrical, mechanical, thermal, and optical properties gives graphene widespread application. Graphene based materials are extensively studied in the field of energy storage such as batteries, hydrogen storage and supercapacitors (SC’s). High surface area, electrical conductivity and mechanical flexibility are notable properties for the materials used in energy conversion systems. Porous spaced graphene oxide (PGO) structures were synthesized by hydrothermal and solvothermal reaction between GO and various pillaring molecules include Tetrakis (4-aminophenyl) methane (TKAm), Ethylenediamine (EDA), 2-Amino-5-diethylaminopentane (ADAP) and 2-Aminoethyl trimethylammonium chloride hydrochloride (ATA). Pristine GO shows interlayer distance of 7.2 Å. Characterisation techniques such as XRD, SEM, FTIR, BET and TGA were used understand the properties of these PGO. In contrast, these pillared structures show interlayer distance greater than of the pristine GO. Notably, GO/TKAm show interlayer distance of 14.30 Å. These pillared structures are considered to solve the restacking and aggregation issues found in 2D porous structures. Since these pillaring molecules help to achieve 3D porous network. Pristine GO shows only surface area of 14 m2/g whereas these materials also show excellent surface area as well. GO/TKAm shows high surface area of 450 m2/g. Followed it GO/ATA shows surface area of 106 m2/g. GO/pillared structures show low sheet resistance which means good electrical conductivity. Ultimately, these pillared structures not only solve the issues in 2D porous systems but also improve the surface area, mechanical stability, and electrical conductivity of those systems by means of 3D porous interconnected structures. All these excellent properties make them a great candidate for the energy conversion systems. / Unik skiktad struktur med utmärkta elektriska, mekaniska, termiska och optiska egenskaper ger grafen en utbredd tillämpning. Grafenbaserade material studeras omfattande inom området energilagring såsom batterier, vätelagring och superkondensatorer (SC). Hög yta, elektrisk ledningsförmåga och mekanisk flexibilitet är anmärkningsvärda egenskaper för de material som används i energiomvandlingssystem. Porösa grafenoxidstrukturer (PGO) syntetiserades genom hydrotermisk och solvotermisk reaktion mellan GO och olika pelarmolekyler inkluderar tetrakis (4-aminofenyl) metan (TKAm), etylendiamin (EDA), 2-amino-5-dietylaminopentan (ADAP) och 2 Aminoetyltrimetylammoniumkloridhydroklorid (ATA). Pristine GO visar mellanskiktsavstånd på 7,2 Å. Karakteriseringstekniker som XRD, SEM, FTIR, BET och TGA användes för att förstå egenskaperna hos dessa PGO. Däremot visar dessa pelarstrukturer mellanskiktsavståndet större än det för den orörda GO. Noterbart visar GO / TKAm mellanskiktsavstånd på 14.30 Å. Dessa pelarstrukturer anses lösa omstaplings- och aggregeringsproblemen som finns i 2D-porösa strukturer. Eftersom dessa pelarmolekyler hjälper till att uppnå 3Dporöst nätverk. Pristine GO visar endast en yta på 14 m2 / g medan dessa material också visar utmärkt yta också. GO / TKAm visar hög yta på 450 m2 / g. Följde den visar GO/ATA en yta på 106 m2/g. GO / pelarstrukturer visar lågt plåtmotstånd vilket innebär god elektrisk ledningsförmåga. I slutändan löser dessa pelarstrukturer inte bara problemen i 2D-porösa system utan förbättrar också ytarean, den mekaniska stabiliteten och den elektriska ledningsförmågan hos dessa system med hjälp av 3D-porösa sammankopplade strukturer. Alla dessa utmärkta egenskaper gör energiomvandlingssystem.

Le but de cette thèse est l'étude des propriétés de jonctions tunnel magnétiques à aimantation perpendiculaire, en utilisant l'anisotropie perpendiculaire présente à l'interface entre un métal magnétique et un oxyde. En théorie, dans le cas des applications mémoires, les jonctions tunnel perpendiculaires devraient nécessiter moins d'énergie (courant) pour l'écriture par courant polarisé en spin. Mais la fabrication de telles structures représente un défi et une tâche difficile puisque les propriétés de transport (TMR) et d'anisotropie imposent des contraintes sur les matériaux utilisées en limitant la fenêtre de travail, notamment en ce qui concerne l'épaisseur des couches magnétiques. Pour atteindre cet objectif nous avons tout d'abord étudié les propriétés de ces structures comme l'anisotropie de l'interface métal magnétique-oxyde, le transport tunnel et le couplage entre les couches magnétiques à travers la barrière isolante. L'amplitude de l'anisotropie d'interface entre un métal magnétique et un oxyde dépend de l'épaisseur des couches magnétiques, de la température de recuit et la concentration de l'oxygène à l'interface. Différentes structures ont été réalisées afin de choisir la structure la mieux adaptée pour les applications mémoires MRAM. Une corrélation entre la TMR et l'anisotropie a été observée permettant de valider l'origine de l'anisotropie perpendiculaire : la formation de liaisons métal magnétique-oxygène. Un couplage antiferromagnétique à été aussi observé entre les couches magnétiques à anisotropie perpendiculaire à travers l'oxyde. Une étude détaillée sur le couplage a été faite en fonction de la température de recuit et de l'épaisseur des couches magnétiques pour mieux comprendre l'origine du couplage et une possible relation avec l'amplitude de l'anisotropie perpendiculaire. Finalement des jonctions perpendiculaires ont été nano-lithographiées et des mesures de commutation d'aimantation par transfert de spin sur des piliers nanométriques ont été réalisées avec de faibles courants critiques. / The aim of this thesis is the study of magnetic tunnel junctions with perpendicularly magnetized electrodes (pMTJ), using perpendicular magnetic anisotropy (PMA) arising from the magnetic metal/oxide interfaces. For magnetic memories applications, it was predicted in theory that perpendicular junctions should need less energy (current) for spin transfer torque (STT) writing applications. However, the engineering of such structures is a real challenge and a difficult task since simultaneous transport (TMR) and PMA properties impose constraints on materials being used and also limit the working window of the device, especially in terms of magnetic layer thickness. In order to reach our goal we first studied different properties of these structures, such as the origin of PMA from the metal/oxide interface, tunnel transport and interlayer exchange coupling phenomena. The PMA at magnetic metal/oxide interface was showed to strongly depend on different parameters like annealing temperature, oxygen concentration, layer thickness etc. Several pMTJ structures were tested in order to choose the best one for MRAM memories applications. A correlation between TMR and PMA was observed and confirms the PMA origin from the magnetic metal-oxygen bond formation at the interface. Furthermore, antiferromagnetic interlayer exchange coupling was observed in our structures in the presence of out of plane anisotropy. A detailed study was made as a function of annealing temperature and layers thickness, in order to understand the origin of this coupling and its possible relationship to the anisotropy strength. Finally the STT-pMTJ concept was validated and low critical currents were observed on submicronic dots prepared by electron beam lithography.