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Mon propos est centré sur la division du moi que produit un état modifié de conscience nommé « somnambulisme magnétique » découvert en 1784. Le sujet change alors de personnalité, parle et tient des discours qui, pour ceux qui l’écoutent, semblent venir d’un inconnu. J’étudie l’évolution de ce phénomène sous les trois formes qu’il prend : somnambulisme magnétique, médiumnité et hypnose jusqu’au début du XXe siècle. Selon le temps et les lieux, ces dires et leurs interprétations comme leurs formes se diversifient mais une constante apparaît, très vite remarquée et notée par ceux qui magnétisent : certaines, surtout de très jeunes femmes, acquièrent une liberté de parole impensable en état « normal ». Ces verbalisations prennent de l’ampleur à certains moments puis semblent s’effacer pour resurgir dans une discontinuité du temps. L’inscription de ces phénomènes dans l’évolution de l’histoire sociale, culturelle, médicale et politique du XIXe siècle et du début du XXe siècle, avec leurs soubassements factuels et idéels, ouvre des voies de compréhension que j’explore en tant qu’historienne. This article explores how one’s self gets divided by a modified state of consciousness called “magnetic somnambulism”, identified in 1784. Individuals experience a change in personality, talk and say things that, for the audience that knows them, seem to come from a stranger. In this article I study how this phenomenon has evolved in 3 stages: magnetic somnambulism, mediumism, and hypnosis up to the start of the 20th century. Despite a lot of differences in what is being said in these states and their interpretation, depending on the time and location, on constant emerges, noted by those using magnetism: some, especially very young women, exercise a freedom of speech that would be impossible in a “normal” state. These discourses expand at specific times, and then seem to disappear to surface again at different times. How these episodes interact with the social, cultural, medical and political history of the 19th and early 20th century, what their factual and idealized foundations are, bring a new level of understanding that I, as an historian, explore.

Cet article porte sur la question de l’attraction magnétique telle qu’elle est abordée dans le Commentaire de la Physique de Paul de Venise. Comme la plupart des commentateurs médiévaux, il est tributaire à la fois du Grand commentaire de la Physique d’Averroès et de l’Expositio sur la Physique de Gilles de Rome. Ces deux autorités occupent‑elles chez lui une place particulière compte tenu de sa carrière universitaire en Italie (notamment à Padoue) et de son appartenance à l’ordre des Ermites de saint Augustin ? Quoi qu’il en soit, son commentaire ne se contente pas de redites, il semble innover en introduisant l’expérience du fer rouillé qui n’est plus attiré par l’aimant. Il adopte aussi une position originale dans le débat qui avait opposé Walter Burley à Guillaume d’Ockham sur l’attraction magnétique. This paper addresses the argument concerning the magnetic attraction in Paul of Venice’s commentary on Physics. Like most of medieval commentators, he is indebted to Averroes’s Long Commentary on Physics and to Giles of Rome’s Expositio on Physics. Do both authorities probably play a more important part in Paul of Venice’s work, due to the fact that he spent his academic life in Italy (notably in Padova) and was a member of the order of hermits of S. Augustine? Anyway, his writing is not a mere repetition of previous commentaries, he seems to innovate when he introduces the experience of the rusted iron which is no longer attracted by the magnet. He also puts forward an original viewpoint in the debate between Walter Burley and William of Ockham on magnetic attraction.

A recent proof of concept showed that cavity photons can mediate superconducting (SC) signatures to a ferromagnetic insulator (FI) over a macroscopic distance [A. T. G. Janssønn et al., Phys. Rev. B 102, 180506(R) (2020)]. In contrast with conventional proximity systems, this facilitates long-distance FI–SC coupling, local subjection to different drives and temperatures, and studies of their mutual interactions without proximal disruption of their orders. Here we derive a microscopic theory for these interactions, with an emphasis on the leading effect on the FI, namely, an induced anisotropy field. In an arbitrary practical example, we find an anisotropy field of 14–16µT, which is expected to yield an experimentally appreciable tilt of the FI spins for low-coercivity FIs such as Bi-YIG. We discuss the implications and potential applications of such a system in the context of superconducting spintronics. Cavity-mediated superconductor–ferromagnetic-insulator coupling

Many-particle effects in driven systems far from equilibrium lead to a rich variety of emergent phenomena. Their classification and understanding often require suitable model systems. Here we show that microscopic magnetic particles driven along ordered and defective lattices by a traveling wave potential display a nonlinear current-density relationship, which arises from the interplay of two effects. The first one originates from particle sizes nearly commensurate with the substrate in combination with attractive pair interactions. It governs the colloidal current at small densities and leads to a superlinear increase. We explain such effect by an exactly solvable model of constrained cluster dynamics. The second effect is interpreted to result from a defect-induced breakup of coherent cluster motion, leading to jamming at higher densities. Finally, we demonstrate that a lattice gas model with parallel update is able to capture the experimental findings for this complex many-body system. Emergent phenomena in complex many-body systems driven far from equilibrium are currently a subject of intense study. Here, the authors report on a nonlinear current-density relationship in experiments of magnetic colloids driven above disordered energy landscapes, and explain the underlying mechanisms through analytical modeling.

This thesis work concerns the installation of an experimental setup to perform In-field Mössbauer spectrometry experiments, and the study of thermoelectric sulphide : chalcopyrite CuFeS2 and Co1−xFexS2compounds. The device that was installed consists of a cryostat equipped with a cold head and a 7 T superconducting magnet. The mounting of a Mössbauer spectrometer on the system enabled the acquisition of Fe standard spectra at 300 K. Structural and magnetic characterizations were performed on the antiferromagnetic semiconductor compound CuFeS2. Mössbauer spectrometry was used to study the iron valence state and to determine the Debye temperature (θD = 415 K). A weak ferromagnetic signal is present over the entire temperature range (5 K300 K), and could be related to the presence of point defects in the structure. The influence of iron doping on the magnetic and thermoelectric properties of pyrites Co1−xFexS2 with 0 ≤ x ≤ 0.5 was studied as a function of temperature. The introduction of iron into the pyrite CoS2 leads to an increase of the Curie temperature, as well as the Debye temperature. The transition from the paramagnetic to the ferromagnetic state is followed by an increase in the magnonic contribution of the Seebeck coefficient, showing a large peak at low temperature. The thermal conductivity can be reduced by substitution of Co by Fe, but the lattice contribution being almost constant, there is no significant improvement in the thermoelectric figure of merit for these compounds.; Ce travail de thèse porte d’une part sur l’installation d’un montage expérimental pour effectuer des expériences de spectrométrie Mössbauer sous champ magnétique, et d’autre part sur l’étude de sulfures thermoélectriques : la chalcopyrite CuFeS2 et les composés Co1−xFexS2. Le dispositif qui a été installé est composé d’un cryostat équipé d’une tête froide et d’un aimant supraconducteur de 7 T. Le montage d’un spectromètre Mössbauer sur le système a permis l’acquisition de spectres d’étalon fer à 300 K. Des caractérisations structurales et magnétiques ont été effectuées sur le composé semiconducteur antiferromagnétique CuFeS2. La spectrométrie Mössbauer a permis d’étudier la valence du fer et de déterminer la température de Debye (θD = 415 K). Un faible signal ferromagnétique est présent sur toute la gamme de température (5 K-300 K), etpourrait être lié à la présence des défauts ponctuels dans la structure. L’influence du dopage en fer sur les propriétés magnétiques et thermoélectriques de pyrites Co1−xFexS2 avec 0 ≤ x ≤ 0,5 a été étudié en fonction de la température. L’introduction de fer dans la pyrite CoS2 permet d’augmenter la température de Curie, ainsi que la température de Debye. La transition de l’état paramagnétique à ferromagnétique s’accompagne d’une augmentation de la contribution magnonique du coefficient Seebeck qui présente alors un pic assez large à basse température. La substitution du Co par le Fe permet de réduire la conductivité thermique, mais la contribution due au réseau étant peu modifiée, il n’y a pas d’amélioration significative du facteur de mérite thermoélectrique pour ces composés

As it becomes more and more difficult to miniaturize electronic circuits, the information industry is faced with an existential crisis: soon, it will no longer be possible to significantly expand the computational power of tried-and-trusted electronic technology. It should come as no surprise that both science and industry are frantically searching for a way to avert this impending catastrophe, and are even willing to entertain the notion of abandoning conventional electronics altogether if a more future-proof alternative can be found. One field of research that has this potential is spintronics: the use of intrinsic angular momentum---better known as spin---of electrons to store information. One of the key promises of spintronics is the ability to transport digital information without the need to shuttle around electrons, thereby avoiding the adverse phenomenon of Joule heating. To this end, one may simply perturb the magnetic order of a magnetic material. Doing so generates a spin wave or magnon, in which spin is passed between neighboring electrons while their position remains unchanged. In the subfield of magnonics---the study of magnons---the use of electrically insulating magnetic materials is currently being studied extensively by both experimentalists and theoreticians. In this thesis, I study the theoretical properties of magnons in three different systems involving a magnetic insulator and a heavy metal. In Chapter 4, I investigate whether ferromagnetic magnons can contribute to a phenomenon known as unidirectional spin-Hall magnetoresistance (USMR): a change in magnetoresistence of spintronic systems that occurs when the direction of an electric current is reversed. I predict that such an effect can indeed exist, but will most likely be very small. In Chapter 5, I focus on ballistic transport of magnons in one-dimensional ferromagnetic insulator (FI) chains exhibiting strong aniotropy. The anisotropy causes the magnons to become elliptically polarized, which breaks spin conservation and gives rise to characteristics not seen in systems with circular magnons, one example of which is squeezing: a fundamental asymmetry in quantum noise. The strong anisotropy required to produce significant magnon ellipticity is uncommon in real FIs. In Chapter 6, I therefore extend the work of Chapter 5 to antiferromagnetic spin chains, which bear mathematical semblance to anisotropic ferromagnets, but have ellipticity-producing terms that are intrinsically large. I show that the behavior of these systems depends strongly on the coupling to the antiferromagnet's different sublattices. Although fairly minimal representations of real systems are developed in this work, they nevertheless have large, mostly unexplored parameter spaces, providing ample opportunity for further research in the near future. In the case of magnonic USMR in particular, recent experimental work by Liu et al. [Phys. Rev. Lett., 127:207206, Nov 2021] provides observations that run counter to our model, suggesting an extension of our work is necessary to capture the full phenomenology. On longer terms, a thorough understanding of the behavior of magnons may lead to pure-spintronic devices featuring low dissipation and extremely high operating frequencies. This, in turn, may revitalize advancement of computer hardware after the expected breakdown of Moore's law.

As it becomes more and more difficult to miniaturize electronic circuits, the information industry is faced with an existential crisis: soon, it will no longer be possible to significantly expand the computational power of tried-and-trusted electronic technology. It should come as no surprise that both science and industry are frantically searching for a way to avert this impending catastrophe, and are even willing to entertain the notion of abandoning conventional electronics altogether if a more future-proof alternative can be found. One field of research that has this potential is spintronics: the use of intrinsic angular momentum---better known as spin---of electrons to store information. One of the key promises of spintronics is the ability to transport digital information without the need to shuttle around electrons, thereby avoiding the adverse phenomenon of Joule heating. To this end, one may simply perturb the magnetic order of a magnetic material. Doing so generates a spin wave or magnon, in which spin is passed between neighboring electrons while their position remains unchanged. In the subfield of magnonics---the study of magnons---the use of electrically insulating magnetic materials is currently being studied extensively by both experimentalists and theoreticians. In this thesis, I study the theoretical properties of magnons in three different systems involving a magnetic insulator and a heavy metal. In Chapter 4, I investigate whether ferromagnetic magnons can contribute to a phenomenon known as unidirectional spin-Hall magnetoresistance (USMR): a change in magnetoresistence of spintronic systems that occurs when the direction of an electric current is reversed. I predict that such an effect can indeed exist, but will most likely be very small. In Chapter 5, I focus on ballistic transport of magnons in one-dimensional ferromagnetic insulator (FI) chains exhibiting strong aniotropy. The anisotropy causes the magnons to become elliptically polarized, which breaks spin conservation and gives rise to characteristics not seen in systems with circular magnons, one example of which is squeezing: a fundamental asymmetry in quantum noise. The strong anisotropy required to produce significant magnon ellipticity is uncommon in real FIs. In Chapter 6, I therefore extend the work of Chapter 5 to antiferromagnetic spin chains, which bear mathematical semblance to anisotropic ferromagnets, but have ellipticity-producing terms that are intrinsically large. I show that the behavior of these systems depends strongly on the coupling to the antiferromagnet's different sublattices. Although fairly minimal representations of real systems are developed in this work, they nevertheless have large, mostly unexplored parameter spaces, providing ample opportunity for further research in the near future. In the case of magnonic USMR in particular, recent experimental work by Liu et al. [Phys. Rev. Lett., 127:207206, Nov 2021] provides observations that run counter to our model, suggesting an extension of our work is necessary to capture the full phenomenology. On longer terms, a thorough understanding of the behavior of magnons may lead to pure-spintronic devices featuring low dissipation and extremely high operating frequencies. This, in turn, may revitalize advancement of computer hardware after the expected breakdown of Moore's law.

[eng] Purely organic radical-based materials constitute a promising approach for the miniaturization of devices due to their interesting optical, electronic and magnetic properties, and are good candidates to substitute scarce and/or environmentally harmful transition metal and lanthanide compounds. However, the inclusion of any type of paramagnetic molecular entity faces critical issues related to the stability of the materials and temperature range applicability. Nevertheless, advances in the last 30 years in producing stable persistent paramagnetic organic molecules provided stable enough organic radicals and polyradicals that can be used to produce molecular materials with a wide range of properties. The use of organic radicals in the development of organic (semi)conductors gives rise naturally to multifunctional materials because the spin moment associated with the unpaired electron of the radicals endows the (semi)conductor with magnetic properties. The multifunctional character of this type of material can become even more relevant when charge transport and magnetism are not considered separately. Indeed, the magnetoresistance featured by some organic conducting magnets holds great promise for the development of spintronic devices. In organic-radical based semiconductor materials, both charge and spin of the unpaired electron of the spin-carrying units play a key role. Indeed, the unpaired electrons of radicals are not only charge carriers but also the source of magnetic moments. The correct modelling of the electronic structure and the properties of these systems is thus a challenge due to the competition between charge localization or charge transport. Typically, organic molecular materials present low charge mobility, and hence, hopping model usually dominates the charge transport process. Computational studies based on hopping charge transfer models have been successfully applied in the analysis of closed-shell organic materials. However, in the literature, there are few studies that deal with the applicability of these hopping models to open-shell systems, and as far as we know, none of them tackles the calculation of electric conductivity. Bisdithiazolyl (bisDTA) radicals have furnished in recent years multiple examples of molecular materials with promising conductive and magnetic properties. This large and well-characterized family of compounds have been constructed in the quest to find a radical-based single component conductor, following different synthetic strategies that aim to enhance their electric properties whereas preventing dimerization. As a result, the bisDTA family of compounds display a wide range of conductive properties (going from insulator to metallic materials), as well as a wide range of magnetic properties (going from materials with no long-range magnetic order to materials that order antiferromagnetically or ferromagnetically). Our computational work focuses on the study of four isostructural pyridine- bridged bisDTA-multifunctional materials triggered by their magnetic and conducting properties being strongly dependent on the different S/Se ratio in the neutral radical skeleton. The electronic structure of the four bisDTA-derived materials has been characterized by means of periodic unrestricted hybrid DFT calculations. The analyses of their band structure and density of states have served as a crucial starting point for the rationalization of their electric properties and the relevant intermolecular contacts involved in the description of the charge transport process. Furthermore, the study of their open-shell ground state and the spin delocalization has proved that the molecular building blocks act as localized spin-carrying units, allowing the rationalisation of their magnetic interactions using a HDVV Hamiltonian. A systematic bottom-up strategy has been used in order to thoroughly compute all the relevant microscopic parameters that govern both: magnetism (magnetic exchange couplings) and charge transport (electronic coupling and reorganization energy). Microscopic interactions have been put to test by computing the macroscopic properties (Magnetic susceptibility, Critical Temperature and Electric Conductivity) and comparing them with the available experimental data. Furthermore, structural-property correlations analysis (ie. Magneto structural correlation maps and distance analysis) has proved that properties in these materials are sensitive to small geometry distortions., [cat] Els materials basats en radicals orgànics constitueixen una prometedora proposta per a la miniaturització de dispositius tecnològics gràcies a les seves propietats òptiques, elèctriques i magnètiques, i són bons candidats per a substituir els escassos i/o mediambientalment nocius metalls de transició i compostos derivats dels lantànids. L'ús de radicals orgànics en el desenvolupament de (semi)conductors dona lloc de forma natural a materials multifuncionals, degut a que el moment d'espín associat a l'electró desaparellat dota addicionalment al (semi)conductor amb propietats magnètiques. En aquesta tesi, ens centrarem en l'estudi de materials moleculars constituïts per radicals orgànics, en els quals, l'electró desaparellat del radical servirà a la vegada com a portador de càrrega i com a font de moment magnètic. La correcta modelització de l'estructura electrònica i les propietats en aquests sistemes es un repte pels mètodes actuals, degut a la competició entre localització de càrrega i el seu transport. Típicament, els estudis computacionals dedicats a la conductivitat elèctrica en materials moleculars orgànics fan servir el que s'anomena model de hopping, degut als baixos valors de conductivitat que presenten generalment aquests materials. Malgrat els avenços reportats amb aquests models en l'estudi de sistemes de capa tancada, hi ha pocs estudis dedicats a l'anàlisi de materials de capa oberta i cap en què es calculi la conductivitat elèctrica a partir de models de hopping. S'han seleccionat quatre materials isoestructurals d'una gran família de derivats del bisditiazolil, degut a l'ampli espectre de propietats magnètiques i elèctriques que presenten, per tal de testejar una estratègia bottom-up sistemàtica per a l'estudi dels paràmetres microscòpics rellevants en la descripció del magnetisme i la conductivitat elèctrica en materials moleculars de capa oberta. Els resultats obtinguts corroboren que l'anàlisi, mitjançant càlculs periòdics, de l'estructura electrònica, la densitat d'estats i l'estructura de bandes estableixen un punt de partida clau per a la descripció de les propietats en aquests sistemes. Mitjançant un estudi sistemàtic bottom-up s'han pogut caracteritzar tots els paràmetres microscòpics rellevants que governen tant el magnetisme com la conductivitat en aquests sistemes. Els resultats s'han pogut corroborar comparant-los amb les dades experimentals reportades. Finalment, mitjançant una anàlisi completa de les distàncies i mapes de correlació estructura-propietat s'ha evidenciat que les propietats en aquests sistemes són sensibles als subtils canvis que pot patir l'estructura cristal·lina.

In this work we establish reliable correlations between density and magnetic susceptibility in three paramagnetic granites from the Pyrenees. In total, 128 sites (310 density measurements and >2600 susceptibility ones) were studied in the Mont Louis-Andorra, Maladeta and Marimanha granitic plutons covering the main range of variability of magnetic susceptibility. Regressions were calculated for every granitic body and an integrated linear function was obtained for the entire dataset: ρ (kg/m3) = 2566 (kg/m3) + 0.541κ (10−6 S.I.) (R:0.97). This relationship is only valid in the paramagnetic domain, where iron is mostly fractioned in iron-bearing phyllosilicates and the occurrence of magnetite is negligible (or at least its contribution to the bulk susceptibility). This relationship, likely different in other bodies, allows for transforming magnetic susceptibility data into density data, helping to constrain gravity modelling when density data from rock samples are scarce. Given the large amount of AMS studies worldwide, together with the quickness and cost-effectiveness of susceptibility measurements with portable devices, this methodology allows for densifying and homogenizing the petrophysical data when modelling granite rock volumes based on both magnetic and gravimetric signals., This work was financed by the projects GeoPiri3D (CGL2017-84901-C2-2-P), UKRIA4D (PID2019-104693GB-I00/CTA) and IMAGYN (PID2020-114273GB-C22) from the Spanish Ministry of Science (funded by MCIN/AEI/10.13039/501100011033 and “ERDF A way of making Europe”). This work is methodologically related also with the 3DGeoEU project financed by the European Commission under the ERANET Cofound action GeoERA (Grant No.: 731166). The GeoAp Research group from the Aragonian Government is also acknowledged. We are also in debt to the staff of the Petrophysical Laboratory (IGME, Tres Cantos) and to the Geophysics technicians (José Mª Llorente and Agustín González). The help of the Rock Magnetism Laboratory of the Centre Européen de Recherche et d’Enseignement de Géosciences de l’Environnement (CEREGE) in Aix en ProvenceMarseille is also acknowledged. P.C. acknowledges funding from PTA2017-14779-I and FJC2019- 041058-I (AEI-Spain) contracts. E.B. thanks the Geomodels Research Institute of the University of Barcelona and GGAC-2017SGR596 (Generalitat de Catalunya).

International audience; Au début des années 1880, la nécessité de disposer d'une carte de l'ensemble du territoire national à échelle moyenne devient de plus en plus pressante. Pour sa part, le ministère de l'Intérieur s'est engagé en 1879 dans la préparation d'une carte de France à l'échelle 1:100 000. C'est dans ce contexte que le Dépôt de la guerre décide de publier une nouvelle carte, en couleurs et en courbes de niveau, à l'échelle 1:200 000. Il s’agit alors de produire un document à une échelle intermédiaire entre la carte au 1:320 000 qui couvre la métropole en une trentaine de feuilles et la carte d’état-major au 1:80 000 qui n'en compte pas moins de 270. Cette série constitue un tournant important dans la production cartographique militaire dans la mesure où elle constitue un laboratoire quant à la mise au point de la production cartographique en couleurs

[eng] The aim of this Ph.D. thesis is the synthesis and characterization of nanoparticles to understand and optimize their macroscopic properties. The manuscript is divided into seven chapters. Chapter 1 is a general introduction to nanoscience and nanotechnology and the synthesis of nanoparticles. Also, it includes a brief introduction to the properties of the magnetic, semiconductor, and plasmonic nanoparticles and their potential applications in the nanoscale. At the end of this chapter, the objectives of this work are presented. Chapter 2 is devoted to briefly introducing the characterization techniques used in this thesis such as transmission electron microscopy, X-ray powder diffraction, X-ray photoelectron spectroscopy, inductively coupled plasma optical emission spectroscopy, Fourier transform infrared spectroscopy, SQUID magnetometry, and ultraviolet-visible spectroscopy. In addition, experimental details for each technique are included. Chapter 3 is dedicated to the optimization of the synthesis of iron oxide nanoparticles through the thermal decomposition method. In particular, it is focused on the monitoring of the effects on the structural and magnetic properties induced by the changes on the amount of 1,2-hexadecanediol and 1-octadecene, which were used as stabilizing agent and solvent, respectively. Chapter 4 is focused on a thorough structural characterization of multi-core iron oxide nanoparticles to understand their outstanding magnetic properties. In Chapter 5, the optimization of the synthesis by hot injection of Bi2S3 nanoparticles is presented. In this section, the effect of the reaction temperature and time on the morphology and crystallinity of the samples was studied. In addition, their effect on the optoelectronic properties was analyzed using ultraviolet-visible spectroscopy. Chapter 6 is devoted to the combination of semiconductor Bi2S3 nanoparticles with plasmonic Au nanoparticles in order to achieve multifunctional hybrid nanostructures. In this chapter, a similar synthesis procedure to the one used in Chapter 5 with an additional step to include the Au precursor, was used. Also, the effect of the morphology of the semiconductor Bi2S3 scaffold was studied. Finally, the last chapter Chapter 7 is the collection of the major remarks of the previous chapters to conclude all the work performed in this thesis., [cat] mEn els últims vint anys, l’interès pels nanomaterials ha anat augmentant gràcies a les seves aplicacions potencials en camps com la biomedicina, l’emmagatzematge d’energia, el tractament d’aigües residuals, entre d’altres. La seva característica principal és l’aparició d’una nova fenomenologia a causa de la seva mida nanomètrica. Un dels reptes pendents, és la comprensió dels mecanismes de reacció que permeten l’optimització de la síntesi de nanopartícules per mitjà de mètodes químics. Així doncs, aquesta tesi està centrada en la síntesi i caracterització de nanopartícules magnètiques d’òxid de ferro i semiconductores de Bi2S3, i la preparació de nanoestructures híbrides de Bi2S3-Au per a aconseguir materials multifuncionals. Pel que fa a les nanopartícules d’òxid de ferro s’ha estudiat l’efecte que tenen l’1,2-hexadecandiol i 1-octadecè emprats com a agent estabilitzant i solvent, en la síntesi per descomposició tèrmica. Mitjançant caracterització estructural s’ha pogut determinar que condicionen la mida, la cristal·linitat i els estats d’oxidació de l’òxid de ferro, i això conseqüentment afecta les propietats magnètiques. També s’ha estudiat les nanopartícules multinuclears (multi-core) de maghemita, que consisteixen en grans agregats amb forma de nanoflor formats per “nuclis” (cores) d’uns 5 nm. S’ha observat que existeix una textura cristal·lina en aquests agregats que permet un comportament magnètic col·lectiu. En el cas de la síntesi de nanopartícules de Bi2S3 mitjançant el mètode d’injecció en calent, s’ha estudiat l’efecte de la temperatura d’injecció i el temps de reacció en la morfologia, cristal·linitat i resposta òptica de les nanopartícules de Bi2S3. A més, utilitzant aquestes nanopartícules de bastida s’ha afegit Au per a formar nanoestructures híbrides de Bi2S3-Au. En global, aquesta tesi demostra que un estudi dels paràmetres de síntesis permeten l’optimització de les propietats magnètiques o optoelectròniques de les nanopartícules, i apropar-nos una mica més al seu ús en aplicacions.

This doctoral thesis studies the Kondo effect of rare earth compounds measured by X-ray absorption spectroscopy (XAS). Two diluted intermetallic systems: A non-Kondo system Er0.025Pd0.975 and a Kondo system Yb0.005Au0.995 have been measured by XAS with circular polarized X-ray under strong magnetic field and weak magnetic field for temperatures from 0.2 K to 300 K. X-ray Magnetic Circular Dichroism (XMCD) spectra and X-ray Magnetic Linear Dichroism (XMLD) spectra have been extracted. The magnetic moment of the spin and of the orbit of the diluted impurity atom are obtained by applying the magneto-optical sum rules. Calculations by Ligand Field Multiplet (LFM) theory are performed to simulate the magnetic properties. The comparison between the Kondo system and the non-Kondo system, as well as the experimental measurements and the simulations allows the discovery of the local Kondo signature around the critical Kondo temperature TK for the Kondo system Yb0.005Au0.995. To achieve the experimental objective, part of this thesis has been devoted to instrumental developments. Hence a new 3He-4He dilution insert, named DICHRO50 which is able to cool the sample down to 180 mK, has been installed in the cryomagnet of DEIMOS beamline at Synchrotron SOLEIL; it is aimed to soft X-ray XAS-XMCD measurements. Moreover, a former dilution insert hosted in so-called TBT-mK cryomagnet has been upgraded to be installed on ID12 beamline at ESRF; it is aimed for hard X-ray XAS-XMCD measurements., Cette thèse doctorale étudie l’effet Kondo des composés de terre rare par spectroscopie d’absorption des rayons X (XAS). Deux systèmes intermétalliques dilués : un système non-Kondo d’Er0.025Pd0.975 et un système Kondo d’Yb0.005Au0.995 ont été mesurés par XAS avec des rayons X polarisés circulairement sous champ magnétique fort et aussi en champ magnétique faible pour une température variant de 0.2 K à 300 K. Les signaux de dichroïsme circulaire magnétique de rayons X (XMCD) et les spectres de dichroïsme linéaire magnétique de rayons X (XMLD) ont été extraits. Les moments magnétiques de spin et d'orbite ont été obtenus par application des règles de somme magnéto-optiques. Des calculs dans le cadre de la théorie des multiplets en champ de ligands (LFM) ont été faits pour simuler les signaux expérimentaux et ainsi remonter aux propriétés magnétiques. Dans le système Kondo, celui de l’ytterbium dans l’or, on observe pour des champs magnétiques ≤ 0.5 T et des températures inférieures à 1 K une différence prononcée entre l’aimantation attendue pour un atome isolé et celle observée expérimentalement : c’est le signe de l’effet Kondo. Pour arriver aux objectifs expérimentaux, une partie de travail de cette thèse a été consacrée à des développements instrumentaux. Un nouvel insert DICHRO50 qui fonctionne avec la dilution d’3He-4He a été installé dans le cryo-aimant de la ligne DEIMOS du Synchrotron SOLEIL. Cet instrument est développé pour des mesures de XAS, de XMCD ou des XMLD dans le domaine des rayons X mous. Il permet de refroidir un échantillon jusqu’à 180 mK. Un autre cryo-aimant, le TBT-mK, a été installé sur la ligne ID12 à l'ESRF où j’ai participé à des mesures de XMCD dans le domaine des rayons X durs.

A new series of mononuclear Ho3+ complexes derived from the β-diketonate anions: 4,4,4-trifluoro-1-phenyl-1,3-butanedioneate (btfa−) and 4,4,4-trifuoro-1-(naphthalen-2-yl)-1,3-butanedionate (ntfa−) have been synthesized, [Ho(btfa)3(H2O)2] (1a), [Ho(ntfa)3(MeOH)2] (1b), (1), [Ho(btfa)3(phen)] (2), [Ho(btfa)3(bipy)] (3), [Ho(btfa)3(di-tbubipy)] (4), [Ho(ntfa)3(Me2bipy)] (5), and [Ho(ntfa)3(bipy)] (6), where phen is 1,10-phenantroline, bipy is 2,2′-bipyridyl, di-tbubipy is 4,4′-di-tert-butyl-2,2′-bipyridyl, and Me2bipy is 4,4′-dimethyl-2,2′-bipyridyl. These compounds have been characterized by elemental microanalysis and infrared spectroscopy as well as single-crystal X-ray difraction for 2–6. The central Ho3+ ions in these compounds display coordination number 8. The luminescence-emission properties of the pyridyl adducts 2–6 display a strong characteristic band in the visible region at 661 nm and a series of bands in the NIR region (excitation wavelengths (λex) of 367 nm for 2–4 and 380 nm for 5 and 6). The magnetic properties of the complexes revealed magnetically uncoupled Ho3+ compounds with no field-induced, single-molecule magnet (SMMs).

The object of this thesis is to study plasticity of chromium, considered as a coating layer of zirconium fuel claddings, and in these conditions needs to be able to accommodate the deformation which is imposed to it without cracking. Chromium is one of the seven pure body-centered cubic transition metals, however the only one with a magnetic structure close to antiferromagnetism at temperatures below ambient. At the atomic scale, plastic deformation of these metals at low temperature is mainly governed by the motion of screw dislocations with a ½ Burgers vector, which experience a strong friction with the crystal lattice. However, plasticity of chromium still raises numerous questions (types of dislocations, influence of magnetism), and has been the focus of a few studies aiming at characterizing its mechanical behavior. Comparing chromium to the other body-centered cubic metals, this work helped conclude on the similarities and differences it presents.Using ab initio calculations, properties of ½ screw dislocations were studied in the two non-magnetic and antiferromagnetic phases of chromium, in order to qualify the impact of magnetism on its plasticity at low temperature. This study revealed the only consequence of magnetism is the generation of magnetic faults when these dislocations shear the crystal, since their Burgers vector disrupts the magnetic order of chromium at low temperature. Thus, ½ dislocations are constrained to move while dragging a magnetic fault behind them. This fault was then studied at finite temperature using Monte Carlo simulations coupled with a Heisenberg model developed for this work, evidencing their disappearance at a temperature below the transition to magnetic disorder, close to ambient, letting dislocations free to move without dragging magnetic faults. Magnetism therefore has an impact on the plasticity of chromium at very low temperature only, where these faults exist.Accounting for the atomic properties of dislocations, as well as their thermally activated glide through nucleation of kink pairs using a line tension model, we then developed a plastic flow law predicting the yield stress as a function of the mechanical loading and the temperature, until the athermal temperature. Through a systematic study across all body-centered cubic metals, for which numerous experimental data are available, predictions of the model were both compared to experiments and between metals, in order to confirm the plastic behavior of chromium is comparable to the other metals. This systematic approach allowing at the same time for a better understanding of the plasticity of chromium and the other body-centered cubic metals was then extended to the study of a new mechanism explaining anomalous slip at low temperature observed experimentally, operating through a cooperative motion of multiple dislocations leading to their fast motion, reproduced by our atomistic simulations. We then looked at the properties of dislocations having a Burgers vector, with close energy compared to ½ and observed in all these metals, to explain under which conditions they can participate to the plastic deformation, our atomistic simulations showing a locking of the multiplication mechanisms of these dislocations., L'objet de cette thèse est d'étudier la plasticité du chrome, envisagé comme revêtement des gaines combustibles en zirconium, et qui dans ces conditions doit être capable de supporter la déformation qui lui est imposée sans se fracturer. Le chrome est l'un des sept métaux de transition purs à structure cubique centrée, étant cependant l'unique d'entre eux ayant une structure magnétique proche de l'antiferromagnétisme à température inférieure à l'ambiante. A l'échelle atomique, la déformation plastique de ces métaux à basse température s'opère principalement par le mouvement des dislocations vis de vecteur de Burgers ½, subissant une friction importante avec le réseau cristallin. Or, la plasticité du chrome soulève encore de nombreuses questions (types de dislocations, effet du magnétisme), et a été l'objet de peu d'étude visant à caractériser son comportement mécanique. En comparant le chrome aux autres métaux cubiques centrés, cette étude a permis de conclure sur les similitudes et différences que celui-ci présente.A l'aide de calculs ab initio, les propriétés des dislocations vis ½ ont été étudiées dans les deux phases non-magnétique et antiferromagnétique du chrome, de manière à caractériser l'influence du magnétisme sur sa plasticité à basse température. Cette étude a révélé que la seule conséquence du magnétisme est la génération de fautes magnétiques lorsque les dislocations cisaillent le cristal, puisque leur vecteur de Burgers ne respecte pas l'ordre magnétique du chrome à basse température. Ainsi, les dislocations ½ sont contraintes à se déplacer en traînant derrière elles une faute. Celle-ci a ensuite été étudiée à température finie par simulations Monte Carlo couplées à un modèle de Heisenberg développé pour cette étude, mettant en évidence leur disparition à une température inférieure à la transition vers le désordre magnétique, proche de l'ambiante, laissant les dislocations libres de se déplacer sans traîner de faute. Le magnétisme n'a donc un impact sur la plasticité du chrome qu'à très basse température, où ces fautes existent.Tenant compte des propriétés atomiques des dislocations, ainsi que de leur mouvement thermiquement activé par germination de doubles décrochements à l'aide d'un modèle de tension de ligne, nous avons ensuite développé une loi d'écoulement plastique donnant la limite d'élasticité en fonction du chargement mécanique et de la température, jusqu'à la température athermale. Par le biais d'une étude systématique sur l'ensemble des métaux cubiques centrés, pour lesquels une grande variété de données expérimentales est disponible, les prédictions du modèle ont pu à la fois être comparées à l'expérience ainsi qu'entre métaux, de manière à confirmer que le comportement plastique du chrome est semblable à l'ensemble de ces métaux. Cette approche systématique permettant à la fois de mieux comprendre la plasticité du chrome et des autres métaux cubiques centrés s'est ensuite étendue à l'étude d'un nouveau mécanisme expliquant le glissement anomal à basse température observé expérimentalement, s'opérant par un mouvement coopératif de plusieurs dislocations entraînant leur déplacement rapide, reproduit par nos simulations atomiques. Nous nous sommes enfin intéressés aux propriétés de dislocations ayant un vecteur de Burgers , d'énergie proche des dislocations ½ et observées dans l'ensemble de ces métaux, afin d'expliquer dans quelles conditions celles-ci pourraient participer à la déformation plastique, nos simulations montrant un blocage des mécanismes de multiplication de ces dislocations.

[eng] The urgent need to reduce our footprint on the earth environment is leading to ever more stringent commitments to decrease greenhouse gases emissions, which entails one of the greatest challenges that mankind has to tackle. As a direct consequence, it is of utmost importance to develop novel, energy-efficient and environmentally-friendly refrigeration technologies that do not require the use of climate-damaging substances. In this regard, solid-state refrigerants based on the large thermal response exhibited by a variety of materials when field-inducing a ferroic phase transition are among the best alternatives. Specifically, materials undergoing a first-order phase transition are of particular interest as the latent heat associated with the phase transition contributes on enhancing the magnitude of the thermal response. Depending on the nature of the external field that drives the phase transition one distinguishes between magnetocaloric, electrocaloric, elastocaloric or barocaloric effects. In spite of all the intensive research devoted to the study of the diverse caloric effects, there are still a series of bottlenecks to overcome. Firstly, they require the application of strong external fields in order to induce a large thermal response. Secondly, the hysteresis associated with the phase transition can drastically reduce the efficiency and compromises its reversibility. A way out of such issues can be provided by materials exhibiting a strong coupling between the structural, magnetic or electronic degrees of freedom, denoted as multicaloric materials, which allow to drive their phase transition by the combination of diverse external fields, giving rise to multicaloric effects. Despite the high potential they exhibit, the research on multicaloric materials is germinal as it requires the use of non-commercial experimental systems. In this dissertation, we have focused on the study of materials displaying a magnetostructural first- order phase transition with a strong coupling between the structural and magnetic degrees of freedom. For such purpose, we have used distinct purpose-built calorimetric and adiabatic thermometry systems to investigate their caloric and multicaloric effects by direct methods. We have concentrated on two distinct families of multicaloric materials: Fe-Rh and Ni-Mn-based Heusler alloys. Our research is aimed at thoroughly characterizing the diverse advantages of multicaloric effects: showing that lower driving fields are required, that the operating temperature windows of the materials can be enlarged and discussing how their inherent hysteresis can be mastered or even exploited., [cat] La necessitat urgent de reduir la nostra empremta en el clima s’està materialitzant en compromisos globals per disminuir l’emissió de gasos d’efecte hivernacle que cada cop son més estrictes, representat avui en dia un dels majors reptes que la humanitat ha d’afrontar. Com a conseqüència directa, és de la màxima importància desenvolupar noves tecnologies de refrigeració que siguin eficients i respectuoses amb el medi ambient. En aquest sentit, entre les millors alternatives es troben els refrigerants en estat sòlid basats en materials que presenten una resposta tèrmica gran quan s’indueix una transició de fase ferroica mitjançant un camp extern. En concret, són d’especial interès els materials que presenten una transició de fase de primer ordre, ja que la calor latent associada a la transició de fase incrementa la magnitud de la resposta tèrmica. Depenent de la naturalesa del camp extern que s’utilitza per induir la transició de fase, es distingeix entre els efectes magnetocalòric, electrocalòric, elastocalòric o barocalòric. Malgrat els grans esforços dedicats en l’estudi dels diversos efectes calòrics, hi ha una sèrie d’obstacles que cal superar. En primer lloc, es necessiten camps intensos per induir una resposta tèrmica gran. En segon lloc, la histèresi associada a la transició de fase pot reduir dràsticament la seva eficiència i comprometre la reversibilitat de l’efecte calòric. Una possible sortida a aquests problemes pot venir donada pels materials que presenten un fort acoblament entre els graus de llibertat estructural, magnètic o electrònic, anomenats materials multicalòrics, ja que permeten que la seva transició de fase s’indueixi mitjançant la combinació de diversos camps externs, donant lloc als anomenats efectes multicalòrics. Malgrat l’alt potencial que presenten a l’hora d’abordar algunes de les mancances que s’han posat de manifest ens els diversos efectes calòrics, l’interès en la seva recerca és molt recent ja que requereix l’ús de sistemes experimentals no comercials. En aquesta tesi, ens hem centrat en l’estudi de materials que presenten transicions magnetoestructurals de primer ordre amb un fort acoblament entre els graus de llibertat magnètic i estructural. Amb aquest propòsit, hem utilitzat diversos dispositius experimentals dissenyats ad hoc que permeten realitzar mesures calorimètriques o termomètriques sota la influència de camp magnètic i esforç uniaxial per tal de caracteritzar-ne els efecte calòrics i multicalòrics mitjançant mètodes directes. Ens hem centrat en dues famílies de materials multicalòrics: Fe-Rh i aliatges tipus Heusler de base Ni-Mn. La recerca duta a terme s’ha centrat en caracteritzar a fons els diversos avantatges que presenten els efectes multicalòrics: demostrant que requereixen camps de menor intensitat per induir una resposta tèrmica gran, que permeten ampliar el rang de temperatura de treball dels materials o que proporcionen estratègies per controlar o fins i tot aprofitar la histèresi associada a la transició de fase.

Aquesta Tesi doctoral comprèn el disseny, la fabricació i la caracterització magnetoelèctrica d'heteroestructures ferromagnètiques/ferroelèctriques artificials; en particular, de titanat de ferro-alumini/plom-magnesi-niobat-plom (FeAl/PMN-PT). Aquests sistemes híbrids estan destinats a reduir la dissipació de calor i el consum d'energia quan s'accionen magnetoelèctricament. Una de les principals estratègies per a controlar el magnetisme amb voltatge és l'ús de materials híbrids magnetostrictius/piezoelèctrics, com les heteroestructures ferromagnètiques/ferroelèctriques. No obstant, quan aquestes heteroestructures s'exposen a un camp elèctric es poden produir simultàniament diferents processos, com efectes de piezodeformació, acumulació de càrrega electrònica i la migració d'oxigen induïda per voltatge (magnetoiònica). Això fa que la interpretació dels efectes magnetoelèctrics no sigui senzilla i que sovint es produeixin errors d'interpretació. Atès que la deformació induïda (i les variacions en la magnetització) són proporcionals al quadrat de la polarització ferroelèctrica, la resposta magnetoelèctrica deguda a la deformació sol ser simètrica respecte al signe de la tensió aplicada. Per contra, es poden obtenir respostes asimètriques pel que fa a l'acumulació de càrrega electrònica i la migració d'oxigen induïda per voltatge. En aquest cas, les heteroestructures ferromagnètiques/ferroelèctriques basades en FeAl i PMN-PT orientat segons [011] han estat dissenyades en relació al gruix de la capa, composició i microestructura per a mostrar una resposta magnetoelèctrica altament asimètrica i poder desentrellaçar els efectes magnetoelèctrics esmentats. En concret, el % atòmic de Fe al voltant del 75 i els grans gruixos de la capa de FeAl (> 20 nm) permeten descartar qualsevol possible efecte d'acumulació de càrrega, mentre que no s'observa experimentalment cap evidència de magnetoiònica, com calia esperar per l'alta resistència a l'oxidació de l'aliatge Fe75Al25, cosa que deixa la deformació com a únic mecanisme per a modular la resposta magnetoelèctrica asimètrica. Paral·lelament, aquesta estratègia també s'ha miniaturitzat fent discos de FeAl a la microescala sobre substrats de PMN-32PT orientats segons [011], utilitzant litografia UV. Cal destacat que el comportament magnetoelèctric dels discos de 50 nm de gruix de Fe75Al25 (at. %) crescuts sobre PMN-32PT orientat segons [011], prèviament cobert amb 10 nm de Cu, mostren una àmplia gamma de propietats magnètiques, que van des del comportament multidomini fins al de tipus vòrtex, com a conseqüència de la interacció entre les propietats magnètiques al pla i l'actuació de la tensió. La presente Tesis doctoral abarca el diseño, la fabricación y la caracterización magnetoeléctrica de heteroestructuras ferromagnéticas/ferroeléctricas artificiales; en particular, de hierro-aluminio/ niobato de plomo y magnesio - titanato de plomo (FeAl/PMN-PT). Estos sistemas híbridos están destinados a reducir la disipación de calor y el consumo de energía cuando se accionan magnetoeléctricamente. Una de las principales estrategias para controlar el magnetismo con voltaje es el uso de materiales híbridos magnetostrictivos/ferroeléctricos. Sin embargo, cuando estas heteroestructuras se exponen a un campo eléctrico pueden producirse simultáneamente diferentes procesos, como los efectos mediados por la piezodeformación, la carga electrónica y la migración de oxígeno inducida por voltaje (magnetoiónica). Esto hace que la interpretación de los efectos magnetoeléctricos no sea sencilla y que, a menudo, se produzcan errores de interpretación. Dado que la deformación inducida (y las variaciones en la magnetización) son proporcionales al cuadrado de la polarización ferroeléctrica, la respuesta magnetoeléctrica mediada por la deformación suele ser simétrica respecto al signo de la tensión aplicada. Por el contrario, se pueden obtener respuestas asimétricas a partir de la carga electrónica y la migración de oxígeno inducida por voltaje. En esto caso, las heteroestructuras ferromagnéticas/ferroeléctricas basadas en FeAl y PMN-PT orientado según [011] han sido diseñadas en términos de espesor de capa, composición y microestructura para mostrar una respuesta magnetoeléctrica altamente asimétrica y poder desentrelazarlos efectos magnetoeléctricos mencionados. En concreto, el % atómico de Fe en torno al 75 y los grandes espesores (> 20 nm) permiten descartar cualquier posible efecto de acumulación de carga, mientras que no se observa experimentalmente ninguna evidencia de magnetoiónica, como era de esperar por la alta resistencia a la oxidación de la aleación Fe75Al25, lo que deja a la deformación como único mecanismo para modular la respuesta magnetoeléctrica asimétrica. Paralelamente, este enfoque se ha miniaturizado a discos de FeAl en la microescala sobre sustratos de PMN-32PT orientados según [011], utilizando litografía UV. Curiosamente, el comportamiento magnetoeléctrico de los discos de 50 nm de espesor de Fe75Al25 (at. %) crecidos sobre PMN-32PT orientado según [011], previamente cubierto con 10 nm de Cu, muestran una gama de propiedades magnéticas, que van desde el comportamiento multidominio hasta el de tipo vórtice, como consecuencia de la interacción entre las propiedades magnéticas en el plano y la actuación mediante voltaje aplicado. This Thesis dissertation tackles the design, fabrication and magnetoelectric characterization of artificial multiferroic ferromagnetic/ferroelectric heterostructures; in particular, iron-aluminum/lead-magnesium-niobate-lead titanate (FeAl/PMN-PT). These hybrid systems are intended to reduce heat dissipation and power consumption when magnetoelectrically actuated. One of the main strategies to control magnetism with voltage is the use of magnetostrictive/ferroelectric hybrid materials. However, different processes can occur simultaneously when these heterostructures are exposed to an electric field such as piezostrain-mediated effects, electronic charging, or voltage-driven oxygen migration (magnetoionics). This makes the interpretation of magnetoelectric effects not straightforward and, often, it leads to misconceptions. Because the induced strain (and variations in the magnetization) is proportional to the square of the ferroelectric polarization, the strain-mediated magnetoelectric response is usually symmetric with the sign of the applied voltage. Conversely, asymmetric responses can be obtained from electronic charging and voltage-driven oxygen migration. Here, ferromagnetic/ferroelectric heterostructures based on FeAl/[011]-oriented PMN-PT have been engineered in terms of layer thickness, composition, and microstructure to exhibit a highly asymmetric magnetoelectric response to be able to disentangle the aforementioned magnetoelectric effects. Specifically, Fe atomic % around 75 and large thicknesses (> 20 nm) allow dismissing any possible charge accumulation effect, whereas no evidence of magnetoionics is observed experimentally, as expected from the high resistance to oxidation of Fe75Al25, leaving strain as the only mechanism to modulate the asymmetric magnetoelectric response. In parallel, this approach has been scaled down to microscale patterned FeAl dots on [011]-oriented PMN-32PT substrates, using UV-lithography. Interestingly, 50 nm thick Fe75Al25 (at. %) disks grown onto 10 nm Cu/[011]-oriented PMN-32PT show a range of magnetic properties, ranging from multidomain to vortex-like behavior, as a consequence of the interplay between in-plane magnetic properties and voltage actuation.

Aquesta tesi està dedicada a la modelització teòrica d'estructures esquirmiòniques i la seva interacció amb altres agents. En primer lloc, considerem com els defectes del material poden afectar les trajectòries dels esquirmions. A partir d'un defecte atòmic, proposem un model de partícules per tenir en compte els defectes extensos (a l'espai), com ara les dislocacions de gra. Aquest model ens permet obtenir expressions analítiques dels punts crítics de les trajectòries dels esquirmions i de la velocitat de corrent llindar per sobre de la qual aquests punts crítics deixen d'existir. Hem trobat que un defecte de línia (per exemple, la dislocació del gra) pot guiar els esquirmions al llarg del defecte i accelerar-los. També es troba que una disposició periòdica d'aquests defectes crea una matriu de fixació periòdica per als esquirmions. D'aquesta manera obtenim un escenari en el qual apareixen aquest tipus de potencials, donant una certa base física a potencials ad hoc utilitzats anteriorment. Aleshores, considerem la interacció d'un disc ferromagnètic amb un disc superconductor coaxial. La interacció està mediada pels camps creats per les estructures de magnetització i els corrents, mitjançant un acoblament bidireccional. Per al ferromagnètic, utilitzem el model micromagnètic i per al superconductor, utilitzem el model de London. Això ens permet obtenir la magnetització i les distribucions de corrent simultàniament. Per caracteritzar el sistema en funció del camp aplicat, primer considerem un bucle d'histèresi del camp aplicat. Hem caracteritzat les transicions entre diferents estats magnètics. En particular, trobem una transició addicional de esquirmió a 2pi causada per la presència d'un superconductor. Els resultats es complementen amb càlculs del mètode de bandes elàstiques geodèsiques, que ens permeten estudiar l'estabilitat dels estats magnètics. També estudiem el comportament del sistema en funció de la distància de separació entre plaques trobant les seves forces d'interacció. En resum, en aquesta tesi proposem diferents models que podrien permetre desenvolupar nous dispositius esquirmiònics. Discutim algunes possibles aplicacions, com ara racetracks esquirmiònics, trampes magnètiques atòmiques basades en esquirmions, lògica ternària i metamaterials esquirmiònics. Esta tesis está dedicada a la modelización teórica de las estructuras de esquirmión y su interacción con otros agentes. En primer lugar, consideramos cómo los defectos del material pueden afectar a las trayectorias del esquirmión. A partir de un defecto atómico, proponemos un modelo de partículas para tener en cuenta los defectos extendidos (en el espacio), como las dislocaciones de grano. Este modelo nos permite obtener expresiones analíticas para los puntos críticos de las trayectorias del esquirmión y para la velocidad de corriente umbral por encima de la cual estos puntos críticos dejan de existir. Encontramos que un defecto de línea (por ejemplo, una dislocación de grano) puede guiar los esquirmiones a lo largo del defecto y acelerarlos. También se encuentra que una disposición periódica de dichos defectos crea un conjunto de pinning periódico para los esquirmiones. De este modo, derivamos un escenario en el que aparecen estos tipos de potenciales, dando alguna base física a los potenciales ad hoc utilizados anteriormente. A continuación, consideramos la interacción de un disco ferromagnético con un disco superconductor coaxial. La interacción está mediada por los campos creados por las estructuras de magnetización y las corrientes, a través de un acoplamiento bidireccional. Para el ferromagnético, utilizamos el modelo micromagnético y para el superconductor, el modelo de London. Esto nos permite obtener las distribuciones de magnetización y de corriente simultáneamente. Para caracterizar el sistema en función del campo aplicado, consideramos primero un bucle de histéresis de campo aplicado. Hemos caracterizado las transiciones entre diferentes estados magnéticos. En particular, encontramos una transición adicional de esquirmión a 2pi causada por la presencia de un superconductor. Los resultados se complementan con cálculos por el método de bandas elásticas geodésicas, que nos permiten estudiar la estabilidad de los estados magnéticos. También se estudia el comportamiento del sistema en función de la distancia de separación entre placas encontrando sus fuerzas de interacción. En resumen, en esta tesis proponemos diferentes modelos que podrían permitir el desarrollo de nuevos dispositivos de esquirmión. Discutimos algunas posibles aplicaciones como los racetracks esquirmiónicos, las trampas magnéticas atómicas basadas en esquirmiones, la lógica ternaria y los metamateriales esquirmiónicos. This thesis is devoted to the theoretical modeling of skyrmionic structures and their interaction with other agents. First, we consider how defects in the material can affect the skyrmion trajectories. From an atomic defect, we propose a particle model to take into account extended (in space) defects, such as grain dislocations. This model allows us to obtain analytical expressions for the critical points of the skyrmion trajectories and for the threshold current velocity above which these critical points cease to exist. We found that a line defect (e.g. grain dislocation) can guide the skyrmions along the defect and speed them up. It is also found that a periodic arrangement of such defects creates a periodic pinning array for skyrmions. In this way we derive a scenario in which these types of potentials appear, giving some physical basis to previously used ad hoc potentials. Then, we consider the interaction of a ferromagnetic disk with a coaxial superconducting disk. The interaction is mediated via the stray fields created by the magnetization structures and the currents, through a two-way coupling. For the ferromagnetic, we use the micromagnetic model and for the superconductor, we use the London model. This allows us to obtain the magnetization and current distributions simultaneously. To characterize the system as a function of the applied field, we first consider a hysteresis loop of applied field. We have characterized the transitions between different magnetic states. In particular, we find an additional skyrmion-to-2pi transition caused by the presence of a superconductor. The results are complemented with geodesic nudged elastic band method calculations, which allow us to study the magnetic states' stability. We also study the system's behavior as a function of the separation distance between plates finding their interaction forces. To sum up, in this thesis we propose different models that could enable novel skyrmionic devices to be developed. We discuss some possible applications such as skyrmionic racetracks, skyrmion-based atomic magnetic traps, ternary logic, and skyrmionic metamaterials.

[eng] Spin crossover (SCO) complexes and single-molecule magnets (SMMs) are promising prototypes that can reach magnetic bistability within the molecular scale required for data storage. Despite the extensive library of versatile compounds exhibiting SCO and SMM behaviour, continuous growth in the knowledge of such molecular magnetic complexes is pursued to understand its fundamental insights. Here, we contribute on unveiling crucial aspects on their magnetic foundations. Starting from the synthesis of 3-bpp (bpp: 2-(pyrazol-1-yl)-6-(1H-pyrazol-3- yl)pyridine) derivatives, diverse mononuclear compounds of Fe(II) were accessed. The magnetic study of these compounds offered fruitful opportunities to unveil specific insights related to the SCO (Chapters 2 to 4). In chapter 2, we can drastically modulate the SCO temperature for a series of three Fe(II) derivatives of 1,3-bpp: [Fe(1,3-bpp)2](ClO4)2 (1), [Fe(met1,3-bpp)2](ClO4)2 (2), [Fe(dimet1,3-bpp)2] (ClO4)2 (3). The direct influence of the methyl substituents on the SCO temperature (with TSCO (3) > TSCO (1) > TSCO (2)), was observed through by magnetic studies in sold-state. In solution, the crystal packing is excluded as a contributor to their overall macroscopic properties, being the T1/2 tuned through ligand design. In Chapter 3, we studied the metal composition effects on the SCO thermal transition of compound [Fe(met1,3-bpp)2](ClO4)2 (2). For such purpose, the isostructural [Zn(met1,3-bpp)2](ClO4)2 (4) complex and the series [Fe1-xZnx(Me-1,3bpp)2](ClO4)2 (5x; 0.1, 0.153, 0.219, 0.333, 0.412, 0.476, 0.559 and 0.636) were synthesized. The structural study unveils the gradual evolution of the crystallographic parameters with the metal composition at three levels: at the local, at the level of intermolecular interactions and in terms of the crystal lattice parameters. We observed a decrease on the SCO temperature and an increase of the residual HS Fe (II) ascribed to the negative chemical pressure induced by the Zn(II). We quenched the samples at 2K, observing that the relaxation temperature of the metastable state, T(TIESST), is unaffected by the composition. In Chapter 4, an unprecedented heteroleptic compound, [FeL(bpp)](ClO4)2 (6), showing four markedly different magnetic responses at the same temperature range (300-340K) near room temperature is presented. The system undergoes a succession of irreversible phase transitions 6·ac → 6α → 6β → 6γ in the solid-state upon several thermal cycles. An intimate connection between the SCO and structural phase transitions (SPTs) through single-crystal X-ray diffraction (SCXRD) is described. Compound (7·ac) is presented as good candidate for similar study. We tried to elucidate some insights on the importance of the N-H interactions within complex 6 by using its methylated derivative. Nevertheless, it was not possible since homoleptic [FeL2](ClO4)2·2H2O (8), [Fe(Me2bbp)2](ClO4)2 (9) complexes and the [FeL(H2O)2(C3H6O)](ClO4)2 ·2C3H6O (10) were obtained. The design of polytopic ligands containing pyrazolyl-pyridine moieties is discussed in chapter 5. Five new organic ligands (H2L3 to H2L7) were synthesized and fully characterized. A new promising synthetic route to access multitopic ligands, which allows to obtain satisfactorily ligand H2L8, is also proposed. A triple-stranded helicate [Co2(H2L)3]4+ (11) containing Co(II), which often behaves as SMM, was synthesized (Chapter 6). The metal displays an adequate geometry between the trigonal prismatic (TP) and the trigonal antiprismatic (TAP) to study its small axial anisotropy through solution paramagnetic 1H NMR and solid-state magnetometry. The study of the [CoZn(H2L)3]4+ (13) helicate allows to discard the intramolecular magnetic interactions as a source of the low magnetic anisotropy. Two new [Fe9] grid-like clusters composed of an unprecedented flat nanosheet with the formula [Fe9O4(OH)8] as an inorganic core are described in Chapter 7. Both polynuclear coordination complexes with the proposed molecular formula Fe9O4(OH)10(H2L2)6(H2O)4](BF4)5 (17) and [Fe9O4Cl6(OH)8(H2L2)6]4(Cl) (18) display an interesting magnetic behaviour. Considering its first formation together with triple-stranded helicates with the general formula Fe(C2O4)3@[Fe2(H2L2)3] (14, 15 and 16), their obtaining and isolation is discussed. In chapter 8, we describe the first attempt on identifying the dynamics of a broken symmetry states, [HS-LS] and [LS-HS], of a binuclear X@[Fe2(H2L)3]3+ (19 and 20) helicates on the millisecond timescale by using paramagnetic NMR spectroscopy. New synthetically addressed jellyfish-like compounds, ([X@Fe(H2L5)3]2)3+ (24 to 27) were obtained by using the appropriate ligand H2L5 with additional aromatic groups concerning the original ditopic H2L ligand. Such compounds are attractive for studying in solution., [spa] Los complejos de transición de espín (SCO) y los imanes moleculares (SMM) son prototipos prometedores que pueden alcanzar la biestabilidad magnética dentro de la escala molecular requerida para el almacenamiento de datos. A pesar de la extensa biblioteca de compuestos versátiles que exhiben estos comportamientos, actualmente, se siguen estudiando para comprender sus propiedades fundamentales. En esta tesis contribuimos en desvelar aspectos cruciales relacionadas con su fundamento magnético. A partir de la síntesis de derivados de 3-(bpp: 2-(pyrazol-1-yl)-6-(1H-pyrazol-3- yl)pyridine), se accedió a diversos compuestos mononucleares de Fe(II). El estudio magnético de estos compuestos ofrece una valiosa oportunidad para el análisis y comprensión de efectos específicos relacionados con el comportamiento de SCO en términos de: • Ajuste de la transición de SCO por diseño de ligando (capítulo 2) para la serie de complejos: [Fe(1,3-bpp)2](ClO4)2 (1), [Fe(met-1,3-bpp)2](ClO4)2 (2) y [Fe(dimet1,3-bpp)2] (ClO4)2 (3). • Estudio de los efectos cooperativos (capítulo 3) del complejo [Fe(met- 1,3bpp)2](ClO4)2 (2) usando los complejos isoestructurales [Zn(met1,3- bpp)2](ClO4)2 (4) y la serie de complejos [Fe1-xZnx(Me-1,3bpp)2](ClO4)2 (5x; 0.1, 0.153, 0.219, 0.333, 0.412, 0.476, 0.559 and 0.636). • Polimorfismo y estudio de la íntima relación entre los datos cristalográficos y magnéticos sobre una sucesión de transformaciones en estado sólido (Capítulo 4) del complejo [FeL(bpp)](ClO4)2 (6). El diseño de ligandos politópicos que contienen unidades pirazolil-piridina se analiza en el capítulo 5. Se sintetizaron y caracterizaron cinco nuevos ligandos orgánicos (H2L3-H2L7). También se propone una nueva ruta sintética prometedora para acceder a ligandos multitópicos, que permite obtener satisfactoriamente el ligando H2L8. A partir de estos ligandos se han sintetizado diversos tipos de compuestos supramoleculares con interesantes propiedades magnéticas: • [Co2(H2L)3]4+ (11) y [CoZn(H2L)3]4+ (13) para el estudio del comportamiento de SMM mediante 1H NMR paramagnético en solución (Capítulo 6). • Fe9O4(OH)10(H2L2)6(H2O)4](BF4)5 (17) y [Fe9O4Cl6(OH)8(H2L2)6]4(Cl) (18) con una estructura cuadriculada sin precedentes formada por el núcleo inorgánico, [Fe9O4(OH)8], sustentado por seis H2L2 ligandos (Capítulo 7). • Complejos binucleares de Fe(II), X@[Fe2(H2L)3]3+ (19-20) estudiados mediante el uso de espectroscopía de RMN paramagnética. Se presenta el primer intento en identificar la dinámica de sus estados de simetría-rota, [HS-LS] y [LS-HS]. Se obtuvieron nuevos compuestos dimerizados ([X@Fe(H2L5)3]2)3+ (24-27) atractivos para el estudió magnético en solución (Capítulo 8).

Oxides, materials composed of oxygen atoms, have several remarkable functional properties : ferroelectricity, piezoelectricity, magnetism, superconductivity ... and a large number of technological advantages : stability, integrability on silicon and flexibility of their properties according to the desired functionality. These materials have numerous applications in spintronics, in quantum information technologies or in energy production and harvesting.Among this family of materials, I have studied the properties and excitations of several compounds : SrTiO3 and the multiferroics BiFeO3, TbMnO3 and CuO by implementing Raman spectroscopy, synchrotron Thz measurements and time-resolved acoustic measurements.On the perovskite SrTiO3, I have carried out Raman studies on the calcium and carrier doping. This study highlights the appearance of ferroelectricity in the 2D gas at the interface of SrTiO3by calcium doping. Under electric field, I participated to show the creation of a polarization at the interface of the material induced by a migration of charges.Multiferroics are materials in which at least two ferroic orders coexist in the same phase.By combining picosecond acoustic experiments with numerical simulations, the elastic constants of BiFeO3 and TbMnO3 have been determined. The knowledge of the elastic properties of BiFeO3 allows to consider its use in piezotransducers for example. On this same compound, measurements under uniaxial tension in Raman spectroscopy show the enhancement of its polarization and the tuning of the magnetic state and in particular the spin waves.Finally in the compound CuO, multiferroic between 208 and 230 K, we have high-lighted by Thz spectroscopy an additional electromagnon (polar spin wave) at high energy. Under hydrostatic pressure, the multiferroic phase expands in temperature towards room temperature and the low energy electromagnon sees its polar activity strongly enhanced., Les oxydes, matériaux composés d’atomes d’oxygène, présentent plusieurs propriétés fonctionnelles remarquables : ferroélectricité, piézoélectricité, magnétisme, supraconductivité. . . et un grand nombre d’avantages technologiques : stabilité, intégrabilité sur silicium et flexibilité de leurs propriétés selon la fonctionnalité désirée. Les perspectives d’applications de ces matériaux sont nombreuses en spintronique, dans les technologiques quantiques de l’information ou encore dans la production et la préservation d’énergie.Parmi cette famille de matériaux, j’ai étudié les propriétés et les excitations de plusieurs composés : SrTiO3 et les multiferroïques BiFeO3, TbMnO3 et CuO en mettant en œuvre la spectroscopie Raman, des mesures Thz en synchrotron et des mesures acoustiques résolues en temps.Sur la perovskite SrTiO3, j’ai mené des études Raman sur le dopage en calcium et en porteurs. Cette étude met en évidence l’apparition de la ferroélectricité dans le gaz 2D à l’interface de SrTiO3 par dopage en calcium. Sous l’effet d’un champ électrique, j’ai participé à montrer la création d’une polarisation à l’interface du matériau induite par une migration des charges.Les multiferroïques sont des matériaux dans lesquels au moins deux ordres ferroïques coexistent dans une même phase.En combinant des expériences d’acoustique picoseconde à des simulations numériques, les constantes élastiques de BiFeO3 et TbMnO3 ont été déterminées. La connaissance des propriétés élastiques de BiFeO3 permet d’envisager par exemple son utilisation dans des piézotransducteurs. Sur ce même composé, des mesures en tension uniaxiale en spectroscopie Raman ont permis d’exalter sa polarisation et de modifier l’état magnétique et en particulier les ondes de spins.Enfin pour le composé CuO, multiferroïque entre 208 et 230 K, nous avons mis en évidence par spectroscopie Thz un potentiel électromagnon (onde de spin polaire) additionnel à haute énergie. Sous pression hydrostatique, la phase multiferroïque s’élargie en température en direction de la température ambiante et l’électromagnon de basse énergie voit son activité polaire décuplée.

The main part of this work completes and clarifies previous studies on the YbMn6Ge6-xSnx compounds and their Fe derivatives. A second exploratory part focuses on potentially promising new compounds in which an anomalous rare earth is associated with a magnetic 3d sublattice.The YbMn6Ge6-xSnx series shows signatures of quantum criticality at the Yb magnetic instability near x ~ 5.23. The first specific heat measurements performed in this work show the heavy fermion character of the alloys (γ > 100 mJ.K-2.mol-1). These measurements also corroborate the existence of a quantum critical point around x ~ 5.23, given the increase in the Sommerfeld coefficient γ (thus the effective mass) in the corresponding alloys, in agreement with theoretical predictions. In addition, XANES and XMCD measurements under pressure, using a low-gradient transmitter medium (He), show the beginning of a peak in the pressure dependence of the signals, similarly to what is observed in the composition dependence. A thermoelectric study has confirmed the importance of this technique for the study of heavy fermion systems, with thermoelectric response strongly dependent on the state of Yb. The Fe for Mn substitution in YbMn6-yFeyGe0.85Sn5.15 alloys (0.00 ≤ y ≤ 1.00) enhances 3d antiferromagnetism. This yields the reduction of the exchange field generated at the Yb site and induces the collapse of the magnetic character of Yb. This kind of substitution constitutes a new way to cross the Yb magnetic instability.In the last part, we have investigated new compounds involving an anomalous rare earth associated with a magnetic 3d sublattice. The numerous synthesis of YbMn6-yCoyGe6-xSnx and CeMnGe1-xSix compounds allow to specify the stability domains and the structural transitions in these series. However, the quality of the samples needs to be improved. The YbMn6-yCoyGe6-xSnx series might be very promising since it could associate two critical points within the same systems., Ce travail de thèse vient essentiellement compléter et préciser les études menées sur les composés YbMn6Ge6-xSnx et leurs dérivés au fer. Une seconde partie, plus exploratoire, porte sur l'identification de nouveaux composés associant une terre rare anormale et un sous-réseau 3d magnétique. La série YbMn6Ge6-xSnx présente des signatures de criticité quantique associé à l'instabilité magnétique de l'ytterbium vers x ~ 5 ,23. Les premières mesures de chaleur spécifiques réalisées dans le cadre de ce travail ont permis d'évaluer le caractère « fermions lourds » de ses alliages (γ > 100 mJ.K-2.mol-1). Elles corroborent en outre l'existence du point critique quantique vers x ~ 5 ,23, étant donné l'augmentation du coefficient de Sommerfeld γ (donc de la masse effective) dans les alliages correspondants, en accord avec les prédictions théoriques. Par ailleurs, des mesures XANES et XMCD sous pression, utilisant un milieu transmetteur à bas gradient (He), ont permis de déceler les prémices d'un pic dans la dépendance en pression des signaux, de façon analogue à ce qui est observé dans la dépendance en composition. Une étude thermoélectrique a confirmé l'intérêt de cette technique pour l'étude des systèmes à fermions lourds, avec une réponse thermoélectrique fortement dépendante de l'état de l'ytterbium. Les essais de substitution partielle du fer au manganèse dans les alliages YbMn6-yFeyGe0,85Sn5,15 (0,00 ≤ y ≤ 1,00) ont montré, grâce, entre autres, à la diffraction des neutrons, un renforcement de l'antiferromagnétisme 3d. Cela entraine la réduction du champ d'échange généré au site de l'ytterbium et conduit à la disparition de son magnétisme. Cela constitue donc un autre moyen de traverser l'instabilité magnétique de l'ytterbium. La dernière partie de ce mémoire ouvre la voie sur l'étude de nouveaux composés mettant en jeu une terre rare anormale associée à un sous réseau magnétique 3d. Les nombreux essais de synthèse sur les familles YbMn6-yCoyGe6-xSnx et CeMnGe1-xSix, ont permis de préciser les domaines de stabilité ainsi que les évolutions structurales, malgré la qualité moyenne des échantillons. La série YbMn6-yCoyGe6-xSnx pourrait être particulièrement prometteuse puisque susceptible d'associer deux points critiques au sein d'un même système.

This thesis is a theoretical study on the temperature-dependent thermodynamic, point-defect formation and diffusion properties in fcc Fe-Ni alloys over the whole range of composition, with a focus on the magnetochemical effects. The results are derived from density functional theory (DFT) calculations and Monte Carlo simulations using a DFT-parametrized effective interaction model (EIM) with explicit atomic and spin variables. The first part of this work is focused on thermodynamics. We compute via DFT energetic, magnetic and vibrational properties and the bcc-fcc phase diagram below the Curie points, revealing the relative importance between magnetic and vibrational entropies. Combining Monte Carlo simulations with the EIM, we obtain an fcc phase diagram across the Curie points and demonstrate a close interplay between magnetic and chemical orders. Finally, we also discuss the effects of Mn and Cr additions on phase stability. The second part of the work is dedicated to point-defect properties. We develop Monte Carlo schemes to compute vacancy formation free energy in alloys. We show that vacancy formation in fcc Fe and Ni exhibits features that are well distinct from those in bcc Fe, pointing out the relevance of longitudinal spin fluctuations. The results in fcc Fe-Ni alloys reveal that magnetic disorder tends to increase vacancy formation free energy, while chemical disorder shows an opposite effect. Finally, we study via DFT the magnetic effects on the properties of self-interstitial atoms in fcc Fe and Ni. The final part of the work is devoted to vacancy-mediated diffusion. We perform kinetic Monte Carlo simulations to obtain temperature-dependent diffusion properties over the whole concentration range. The results allow to probe into the effects of magnetic and chemical transitions on diffusion properties and provide details inaccessible from experiments. This work fully takes into account the impacts of transversal and longitudinal spin fluctuations and the interplay between magnetism and chemical order. It provides an accurate and consistent prediction of thermodynamic, defect formation and diffusion properties in the Fe-Ni system, and contributes to a better understanding of effects of magnetism in austenitic steels. The applied approach is also transferable to the investigation of other magnetic alloys., Cette thèse porte sur les propriétés thermodynamiques, de formation des défauts ponctuels et de diffusion dans les alliages Fe-Ni cfc sur toute la gamme de composition et en fonction de la température, avec un intérêt particulier pour les effets magnétochimique. Les résultats sont obtenus à partir de calculs de la théorie fonctionnelle de la densité (DFT) et de simulations de Monte Carlo atomique incluant un modèle d'interaction effective (EIM) ajusté sur les calculs DFT. Ce modèle traite de façon explicite les interactions chimiques et magnétiques, et leur couplage. La première partie de ce travail est centrée sur la thermodynamique. Nous calculons via la méthode DFT, les propriétés énergétiques, magnétiques et vibrationnelles, ainsi que le diagramme de phase cc-cfc en-dessous de la température de Curie. Nous mettons en évidence les contributions relatives des effets magnétiques et vibrationnels. A l'aide des simulations Monte Carlo, nous obtenons le diagramme de phase cfc en-dessous et au-dessus des températures de Curie. Nous mettons en évidence un fort couplage entre les ordres magnétiques et chimiques. Enfin, nous étudions les effets d'un ajout de Mn ou de Cr sur le magnétisme et la stabilité des phases de l'alliage Fe-Ni. La deuxième partie du travail est consacrée à l'étude des propriétés des défauts ponctuels. Nous développons des algorithmes Monte Carlo pour calculer l'énergie libre de formation de la lacune dans les alliages. Nous montrons que la formation de lacune dans Fe et Ni cfc, présente des caractéristiques bien distinctes de celles dans Fe cc, soulignant ainsi l'importance des fluctuations de spin longitudinales. Nous montrons que dans les alliages, le désordre magnétique a tendance à augmenter l'énergie libre de formation de lacunes, tandis que le désordre chimique a un effet opposé. Enfin, nous étudions par la méthode DFT, les effets magnétiques sur les propriétés des atomes auto-interstitiels dans Fe et Ni cfc. La dernière partie du travail est consacrée à la diffusion atomique. Nous calculons les propriétés de diffusion de traceur et des défauts ponctuels en fonction de la température, sur la totalité de l'intervalle en composition de la phase austénitique. Nous mettons en évidence les effets des transitions magnétiques et chimiques sur les propriétés de diffusion et nous fournissons des données inaccessibles aux expériences. Ce travail prend pleinement en compte l'impact des fluctuations de spin transversales et longitudinales, ainsi que le couplage entre le magnétisme et l'ordre chimique. Il fournit une modélisation précise et cohérente des propriétés thermodynamiques, de formation des défauts et de diffusion du système Fe-Ni. Il contribue ainsi à une meilleure compréhension des effets du magnétisme dans les aciers austénitiques.

Sweat, tears, saliva: the connection that one usually makes between fluid(s) and theater is that of the tangible bodily substances the actor’s body produces. However, during a long cultural sequence lasting from the end of the 18th century to the first decades of the 20th century, French theater takes an avid interest in another kind of fluid: one which, invisible and intangible, circulates within human bodies and in-between. Interweaving the scientific with the spectacular and the spiritual with the erotic are indeed three significant models in 19th century French society, that put this motif at the heart of their manifestation: the theory of Animal Magnetism – which presents the fluid as an universal cure-all –, electricity – still apprehended as a « mysterious fluid » (Beltran and Carré), and the practice of Spiritualism – with its emanations of spectral fluids and other ectoplasms. Magnetism, electricity and Spiritualism thus elaborate the model of a permeable body; one which is both penetrated with a mysterious current and able to transmit it to other bodies. Theater appears as the most fitting medium for this model to develop itself, insofar as it can not only allude to the disturbing powers of the fluid via dramatic repertoire, but also testify, in critical discourses commenting on shows, to an actual transmission of current between stage and audience, the perception of which constitutes a paroxysm in the experience of theater. As far as repertoire is concerned, the nebula of new images conveyed by Magnetism, electricity and Spiritualism allows some 19th century playwrights to question the phenomenon of touching from a distance; of a remote influence both exerting itself in therapeutic and erotic relationships. As far as the theatrical event is concerned, the semantic field of the fluid provides the spectator with the means to formulate the captivating sensation of being a part of the crowd’s hic et nunc, but mostly to express their fascination towards the actor – who is being described, for the first time, as a « magnetic » being, capable of « electrifying » the audience. Firmly rooted in the 19th century, this PhD dissertation aims to uncover the origins of some fundamental categories in the contemporary theatrical lexicon (such as energy or presence), thus anchoring notions that are commonly thought as modern in their original cultural sequence. This work intends to demonstrate how Magnetism, electricity and Spiritualism – three distinct models sharing the same motif of the fluid – provide unprecedented tools for theater to examine the phenomenon of fascination, but also to question the fascination exerted by theater itself.; Sueur, larmes, salive : le lien que l’on fait ordinairement entre fluide(s) et théâtre est celui des substances corporelles tangibles que produit l’organisme de l’acteur. Or durant une longue séquence culturelle qui se déploie en France de la fin du XVIIIe siècle aux premières décennies du XXe siècle, le théâtre se passionne pour un autre fluide : celui qui, invisible et impalpable, circule dans et entre les corps. Entrelaçant le scientifique au spectaculaire et le spirituel à l’érotique, trois modèles prégnants dans la société française du XIXe siècle placent en effet ce motif au cœur de leurs manifestations : la théorie du magnétisme animal – et son fluide universel garant de bonne santé –, l’électricité – encore appréhendée comme un « fluide mystérieux » (Beltran et Carré), et la pratique du spiritisme – avec ses émanations de fluides fantomatiques et autres ectoplasmes. Ce faisant, magnétisme, électricité et spiritisme fabriquent le modèle d’un corps perméable, traversé par un courant mystérieux et lui-même capable de transmettre ce courant à d’autres corps en présence. Or le théâtre est l’endroit privilégié pour le déploiement de cette représentation : il peut non seulement évoquer les prodiges inquiétants du fluide via le répertoire dramatique, mais également convoquer, dans le discours critique qui commente la représentation, le passage d’un courant entre scène et salle dont la perception constituerait le paroxysme de la séance théâtrale. Sur le plan thématique, le réseau d’images inédites offert par le magnétisme, l’électricité et le spiritisme permet à certains auteurs dramatiques du XIXe siècle de questionner le phénomène d’un rapport sans toucher ; d’une influence à distance qui s’exerce à la fois dans les champs thérapeutique et érotique. Sur le plan de la représentation, l’imaginaire du fluide fournit au spectateur de quoi formuler la sensation de subjugation éprouvée à se tenir en foule dans l’hic et nunc de la séance théâtrale, mais lui donne surtout le moyen d’exprimer sa fascination pour l’acteur qu’il décrit, pour la première fois, comme un être magnétique capable d’électriser son public. Ce faisant, cette thèse résolument ancrée dans le XIXe siècle se propose de faire l’archéologie de catégories fondamentales du lexique théâtral contemporain (l’énergie, la présence), rattachant ainsi des notions que l’on pense très actuelles à une séquence culturelle plus ancienne. Ce travail entend donc démontrer que magnétisme, électricité et spiritisme – trois modèles distincts traversés par le motif commun du fluide – fournissent de nouveaux outils pour penser la fascination au théâtre, mais également la fascination du théâtre.

Five new mononuclear lanthanide complexes are synthesized by adding the several lanthanide nitrate hexahydrate salts, which for lanthanide (Ln) are Eu, Tb, Dy, Er, and Yb, with 9-anthracenecarboxylic acid (9-Hanthc) and 2,2′:6,2″-terpyridine (TPY) in mixed solution of methanol and dimethylformamide (DMF). The general formula is [Eu(9-anthc)3(TPY)(DMF)]·H2O (1Eu) where Eu(III) is ennea-coordinated or [Ln(9-anthc)3(TPY)(H2O)]·H2O·DMF (Ln = Tb (2Tb), Dy (3Dy), Er (4Er), and Yb (5Yb)) where Ln(III) is octa-coordinated. For compounds 3Dy, 4Er, and 5Yb, the dynamic ac magnetic study indicated field-induced single molecule magnet (SMM) behavior. The photoluminescence studies in the solid state of these complexes show the sensitization of 4f-4f transitions for 4Er and 5Yb in the NIR region.

Molecule-based magnetism is a solid-state property that results from the microscopic interaction between magnetic centres or radicals. The observed magnetic response is due to unpaired electrons whose coupling leads to a particular magnetic topology. Therefore, to understand the magnetic response of a given molecule-based magnet and reproduce the available experimental magnetic properties by means of statistical mechanics, one has to be able to determine the value of the J(AB) magnetic exchange coupling between radicals. The calculation of J(AB) is thus a key point for modelling molecule-based magnetism. In this Perspectives article, we will build upon our experience in modelling molecular magnetism to point out some pitfalls on evaluating J(AB) couplings. Special attention must be paid to the cluster models used to evaluate J(AB), which should account for cooperative effects among J(AB) interactions and also consider the environment (counterions, hydrogen bonding) of the two radicals whose interaction has to be evaluated. It will be also necessary to assess whether a DFT-based or a wavefunction-based method is best to study a given radical. Finally, in addition to model and method, the J(AB) couplings have to be able to adapt to changes in the magnetic topology due to thermal fluctuations. Therefore, it is most important to appraise in which systems molecular dynamics simulations would be required. Given the large number of issues one must tackle when choosing the correct model and method to evaluate J(AB) interactions for modelling magnetic properties in molecule-based materials, the "human factor" is a must to cross-examine and challenge computations before trusting any result. MD, JRA, and JJN acknowledge financial support from MINECO (CTQ2017-87773-P/AEI/FEDER, UE), Spanish Structures Excellence Maria de Maeztu program (MDM-2017-0767), and Catalan DURSI (2017SGR348).

This theoretical work presents the electronic and magnetic properties of Cr doped SrFe12O19 using first-principles calculations based on density functional theory. An improvement in the magnetic properties of SrFe12O19 is predicted when doped with the Cr3+ ion. It was found that the magnetic Cr3+ ion preferentially replaces Fe3+ ion at 2a, 4f1, and 12k sites. The calculation demonstrates that if Cr ion occupies the 4f1 site, a total magnetization of 52.920 emu/g is obtained. On the other hand, SrFe11.5Cr0.5O19 behaves as a semiconductor when Cr occupies the 2a and 12k sites while behaves like half-metal when Cr occupies the 4f1 site. The higher magnetization, identified for the SrFe11.5Cr0.5O19 compound, provides unique qualities in the applications of permanent magnets and/or related devices like spintronics and magnetic semiconductors.

Six homodinuclear lanthanide complexes with formula [Ln2(μ2-9-AC)4(9-AC)2(phen)2] (Ln(III) = Nd (1), Eu (2), Gd (3), Tb (4), Er (5) and Yb (6) are reported and complexes 1–3 and 6 are structurally characterized. 9-HAC = 9-anthracenecarboxylic acid, phen = 1,10-phenanthroline. The luminescence properties of compounds 1–6 have been studied at different temperatures in the solid state and show the sensitization of the 4f–4f emission bands in the NIR range for compounds 1, 5 and 6. The molar magnetic susceptibility measurements of 1–6 in the 2–300 K temperature range indicate weak antiferromagnetic exchange for the isotropic Gd(III) compound 3. Furthermore, slow relaxation of the magnetization is found in complexes 5 and 6 with effective energy barriers of 9.5 cm−1 (0.1 T) and 22.7 cm−1 (0.15 T), respectively.

Organic radicals have been consistently regarded as promising building blocks for the next generation of applied materials. Multiple radical families have been developed and characterized in the last decades, fostered by the ever-growing capabilities of organic synthesis. Thiazyl-, spiro-biphenalenyl-, 1,2,4-benzotriazinyl-, and nitroxide-based radicals have furnished striking examples of metal-free switchable materials, whose phase transitions are accompanied by changes in the magnetic, optical and/or electrical response. While similar in origin, their actual mechanism, driving force(s), and spin state stabilities often depict a different landscape. Fundamental knowledge on such aspects, as well as on the underlying network of spin exchange couplings and non-covalent interactions (including pancake bonding), are key to understand their spin transition, and the tailored modification of their properties. These complex features cannot be extracted based solely on experimental input, but rely on a computational interpretation. In this Perspective article, we discuss the insight gained from computational modelling into the magnetism and phase transitions of organic radical-based materials. We focus on the key importance of dynamic effects due to the labile nature of π-stack interactions assembling those materials, the structural distortions driven by spin changes, the coupling between electronic structure and order-disorder transitions, and the dependence of spin correlation upon temperature. All these phenomena uncovered by simulations should assist in the rational design of new dynamic organic crystals.

The need in permanent magnets is increasing steadily because they are used in many electronic devices in our daily life. However, they are composed of materials that are either toxic (like cobalt) or extremely polluting to extract (like neodymium or samarium) and rare in Europe. To reduce our dependence on rare earths and have more environment friendly and sustainable materials at our disposal, the study of new magnetic phases is essential. Among the suitable materials, iron nitrides are very promising and especially the alpha"-Fe_16N_2 phase. This semi-hard material has a saturation magnetization greater than bulk iron, a magnetic anisotropy close to that of rare earths-based magnetic materials, and it is constituted by inexpensive and non-toxic elements. All the above make this phase ideal for the development of new permanent magnets. Thus the subject of this thesis is the study of the nitriding process of iron (0) nanoparticles in order to obtain the alpha"-Fe_16N_2 phase. Producing this material at the nanometric scale has several advantages: 1) a higher surface/volume ratio which increases reactivity and should facilitate the incorporation of nitrogen, which allows to use milder treatment conditions (

La tècnica de reconstrucció de Grad-Shafranov (GSRT) és una metodologia ben establerta basada en una equació fonamental de la magnetohidrodinàmica (MHD). Aquest mètode ha estat àmpliament aplicat en l’anàlisi de cordes de flux magnètic a partir de mesures in-situ de missions espacials. Aquestes estructures magnètiques han sigut tradicionalment reconstruïdes utilitzant models analítics. Un d’ells, el circular-cilíndric (CC) de 2016 i la seva extensió a geometries més complexes, l’el·líptic-cilíndric (EC) de 2018 han demostrat ser capaços de descriure, amb alt nivell de precisió, les cordes de flux magnètic. L’objectiu d’aquesta investigació és determinar les connexions entre els mètodes descrits anteriorment. Una versió actualitzada i fàcil d’usar de la GSRT ha estat desenvolupada amb Python. Aquesta eina ha estat utilitzada per a reconstruir esdeveniments amb mesures in-situ simulades creades amb els models CC i EC. Finalment, la GSRT ha estat aplicat a la reconstrucció d’un esdeveniment real observat per STEREO A, i usada per inferir les propietats dels camps magnètics, densitats de corrent, distorsió i altres paràmetres geomètrics. La técnica de reconstrucción de Grad-Shafranov (GSRT) es una metodología bien establecida basada en una ecuación fundamental de la magnetohidrodinámica (MHD). Este método ha sido ampliamente aplicado en el análisis de cuerdas de flujo magnético a partir de medidas in-situ de misiones espaciales. Estas estructuras magnéticas han sido tradicionalmente reconstruidas usando modelos analíticos. Uno de ellos, el circular-cilíndrico (CC) de 2016 y su extensión a geometrías más complejas, el elíptico-cilíndrico (EC) de 2018 han demostrado ser capaces de describir, con alto nivel de precisión, las cuerdas de flujo magnético. El objetico de esta investigación es determinar las conexiones entre los métodos descritos anteriormente. Una versión actualizada y fácil de usar de la GSRT ha sido desarrollada en Python. Esta herramienta ha sido utilizada para reconstruir eventos con medidas in-situ simuladas creadas con los modelos CC y EC. Finalmente, la GSRT ha sido aplicada a la reconstrucción de un evento real observado por STEREO A, y usada para inferir las propiedades de campos magnéticos, densidades de corriente, distorsión y otros parámetros geométricos. The Grad-Shafranov reconstruction technique (GSRT) is a well-established methodology based on a fundamental magnetohydrodynamics (MHD) equation that has been widely applied to analyse magnetic flux ropes from in-situ measurements of spacecrafts. These structures are also traditionally reconstructed based on analytical models. One of them, the 2016 Circular-Cylindrical (CC) model and its extension to complex geometries, 2018 Elliptical-Cylindrical (EC) model have also been proven to describe, with high level of accuracy, the magnetic flux ropes. The goal of this research is to determine what are the connections between the above mentioned methods. An updated and easy-to-use version of the GSRT has been developed using Python. This tool has been used to reconstruct synthetic events using simulated in-situ measurements created with the CC and EC models. Finally, the GSRT has been applied to reconstruct a real event observed by STEREO A, and used to infer the properties of the magnetic fields, current densities, distortion and other geometrical parameters. Outgoing

Slow magnetic relaxation in dinuclear dysprosium and holmium phenoxo bridged complexes: a Dy2 single molecule magnet with a high energy barrier Matilde Fondo,a,* Julio Corredoira-Vázquez,a Ana M. García-Deibe,a Jesús Sanmartín-Matalobos,a Silvia Gómez-Coca,b Eliseo Ruizb and Enrique Colacioc Dinuclear [M(H3L1,2,4)]2 (M = Dy, Dy2; M = Ho, Ho2) complexes were isolated and recrystallised in pyridine. The crystal structures of Dy2·2THF and the pyridine adducts Dy2·2Py and Ho2·2Py show that the complexes are dinuclear, with unsupported double phenoxo bridges, and that the N4O4 environment of the LnIII centres is distorted triangular dodecahedral. The magnetic analysis of Dy2 and Ho2 shows that Dy2 is a single molecular magnet (SMM), with a thermal-activated zero-field effective energy barrier (Ueff) of 367.7 K, the largest barrier shown by double unsupported phenoxo-bridged dinuclear dysprosium complexes. Ho2 is one of the scarce dinuclear complexes showing slow relaxation of the magnetisation, although it does not even show field-induced SMM behaviour. Ab initio calculations were done in order to shed light on the magnetic anisotropy of the complexes and the magnetic relaxation pathways, which support the experimental magnetic results.