Giant coercivity of dense nanostructured spark plasma sintered barium hexaferrite

Due to the limited rare-earth elements resources, ferrite magnets need to be improved drastically. Ideally, for a true hard magnet, the coercive field should be larger than the saturation magnetization, which is not yet realized for ferrites. Thus, an alternative can be found in making very fine grain ferrite magnets, but it is usually impossible to get small grains and dense material together. In this paper, it is shown that the spark plasma sintering method is able to produce approximately 80% of dense material with crystallites smaller than 100 nm. The as-prepared bulk sintered anisotropic magnets exhibits coercive field of 0.5 T which is approximately 60% of the theoretical limit and only a few percentage below that of loose nanopowders. As a result, the magnets behave nearly ideal (-1.18 slope in the BH plane second quadrant) and the energy product reaches 8.8 kJ m-3, the highest value achieved in the isotropic ferrite magnet to our knowledge

Uniaxial anisotropy and enhanced magnetostriction of CoFe2_2O4_4 induced by reaction under uniaxial pressure with SPS

In this study, we have compared magnetic and magnetostrictive properties of polycrystalline CoFe$_2$O$_4$ pellets, produced by three different methods, focusing on the use of Spark Plasma Sintering (SPS). This technique allows a very short heat treatment stage while a uniaxial pressure is applied. SPS was utilized to sinter cobalt ferrite but also to make the reaction and the sintering (reactive sintering) of the same ceramic composition. Magnetic and magnetostrictive measurements show that the reactive sintering with SPS induces a uniaxial anisotropy, while it is not the case with a simple sintering process. The induced anisotropy is then expected to be a consequence of the reaction under uniaxial pressure. This anisotropy enhanced the magnetostrictive properties of the sample, where a maximum longitudinal magnetostriction of $-229$~ppm is obtained. This process can be a promising alternative to the magnetic-annealing because of the short processing time required (22 minutes)

Analytical modeling of demagnetizing effect in magnetoelectric ferrite/PZT/ferrite trilayers taking into account a mechanical coupling

In this paper, we investigate the demagnetizing effect in ferrite/PZT/ferrite magnetoelectric (ME) trilayer composites consisting of commercial PZT discs bonded by epoxy layers to Ni-Co-Zn ferrite discs made by a reactive Spark Plasma Sintering (SPS) technique. ME voltage coefficients (transversal mode) were measured on ferrite/PZT/ferrite trilayer ME samples with different thicknesses or phase volume ratio in order to highlight the influence of the magnetic field penetration governed by these geometrical parameters. Experimental ME coefficients and voltages were compared to analytical calculations using a quasi-static model. Theoretical demagnetizing factors of two magnetic discs that interact together in parallel magnetic structures were derived from an analytical calculation based on a superposition method. These factors were introduced in ME voltage calculations which take account of the demagnetizing effect. To fit the experimental results, a mechanical coupling factor was also introduced in the theoretical formula. This reflects the differential strain that exists in the ferrite and PZT layers due to shear effects near the edge of the ME samples and within the bonding epoxy layers. From this study, an optimization in magnitude of the ME voltage is obtained. Lastly, an analytical calculation of demagnetizing effect was conducted for layered ME composites containing higher numbers of alternated layers (). The advantage of such a structure is then discussed

Temperature dependence of core loss in cobalt substituted Ni-Zn-Cu ferrites

The temperature dependence of core loss in cobalt substituted Ni-Zn-Cu ferrites was investigated. Co2+ ions are known to lead to a compensation of the magneto-crystalline anisotropy in Ni-Zn ferrites, at a temperature depending on the cobalt content and the Ni/Zn ratio. We observed similar behaviour in Ni-Zn-Cu and it was found that the core loss goes through a minimum around this magneto-crystalline anisotropy compensation. Moreover, the anisotropy induced by the cobalt allowed a strong decrease of core loss, a ferrite having a core loss of 350 mW/cm3 at 80 ^\circ C was then developed (measured at 1.5 MHz and 25 mT). This result represents an improvement of a factor 4 compared to the state of art Ni-Zn ferrites

Temperature dependence of spin resonance in cobalt substituted NiZnCu ferrites

Cobalt substitutions were investigated in Ni0.4Zn0.4Cu0.2Fe2O4 ferrites, initial complex permeability was then measured from 1 MHz to 1 GHz. It appears that cobalt substitution led to a decrease in the permeability and an increase in the \mus\timesfr factor. As well, it gave to the permeability spectrum a sharp resonance character. We also observed a spin reorientation occurring at a temperature depending on the cobalt content. Study of the complex permeability versus temperature highlighted that the most resonant character was obtained at this temperature. This shows that cobalt contribution to second order magnetocrystalline anisotropy plays a leading role at this temperature

Ambiguïtés sémantiques et lexicographie bilingue

Communication affichée Colloque des doctorants et des jeunes chercheurs - Coldoc09 UMR 7114 MODYCO – Université Paris Ouest Nanterre la Défense L'ambiguïté dans les sciences du langageNotre communication porte sur la place accordée à l'ambiguïté sémantique en lexicographie bilingue. Nous nous intéresserons plus particulièrement aux articles associées aux entrées adjectivales polysémiques dans les dictionnaires français-anglais et anglais-français. Nous montrerons que l'éventail des traductions proposées pour ce type d'items peut souffrir de la non prise en compte des régularités intervenant au cours de la construction de la signification des expressions composées d'un nom et d'un adjectif polysémique. Nous verrons notamment que ne pas en faire état peut s'avérer problématique pour le traducteur et même l'induire en erreur. De telles régularités jouent en effet un rôle fondamental : elles orientent la construction du sens et permettent d'éviter l'apparition potentielle d'ambiguïtés liées aux sens multiples de l'adjectif polysémique en combinaison. Elles sont parfois prises en considération (par exemple pour les entrées pauvre, cher, etc.) mais pas de façon systématique

Construction of meaning in context. Polysems and multi-facets items within noun phrases.

The purpose of our communication concerns the French substantive livre (book) when it is combined with an adjective within a nominal phrase. Our goal is firstly to propose a conceptual modelling representing the semantic content of the item livre, and secondly to examine the way sense can be constructed in expressions composed of an adjective and that substantive, taking into account both semantic and syntactic structures

à propos d'un curieux adjectif : approche sémantico-cognitive de l'adjectif curieux

National audienceLe présent article se propose d'apporter une dimension cognitive à l'étude linguistique de l'adjectif curieux afin d'expliquer différents phénomènes, notamment les différences de sens observées. L'item polysémique curieux présente un sens actif 'qui éprouve de l'intérêt' et un sens passif 'qui suscite de l'intérêt'. Il est associé, au sein du lexique mental, à une structure conceptuelle véhiculant de nombreuses informations sémantiques, organisée en deux sous-structures conceptuelles. L'une contient [INTÉRESSÉ] pour principale information et renvoie au sens actif, l'autre contient [INTÉRESSANT] et renvoie au sens passif. Elles sont reliées par le concept [INTÉRÊT] qui constitue le cœur du sens schématique de curieux, à partir duquel sont élaborés les dits sens. Lors de sa combinatoire avec un nom, le lexème curieux peut montrer des variations sémantiques et être source d'ambiguïté du fait de son caractère polysémique. Dans la construction de la signification des expressions complexes nom-curieux et curieux-nom, il existe pourtant des régularités liées à la place de l'adjectif au sein du syntagme nominal ainsi qu'à la classe du nom en combinaison. Toutefois, pour certaines configurations, seul le recours à un contexte plus large permet de lever l'ambiguïté

Conceptual modelling of multi-facets items: Between polysemy and vagueness

This communication is dedicated to multi-facets items (Cruse). "A facet is a word sense that is due to the part-whole structure of an entity and selected by a specific utterance context" (Evans). Firstly, we analyze the semantic pole of multi-facets items so as to elaborate a conceptual modelling within the framework of Langacker's Cognitive Grammar. Secondly, we suggest that the representation of multi-facets items can be integrated within the ambiguity-vagueness continuum proposed by D. Tuggy. By hypothesis, linguistic items are associated with an organized conceptual structure composed of numerous semantic pieces of information. More specifically, the structure of a multi-facets item (mother, book, bank, CD, chicken, etc.) can be organized into different informational sets, representing not only its facets but also the global sense resulting from the unification of the facets. Thus, multi-facets words differ from polysems whose senses cannot be unified. The activation of a facet, as well as the activation of the global sense, is context-dependent. Let us consider the noun mother (Croft & Cruse). When *CARE-GIVER* is activated (a good mother), it makes reference to a woman who treats somebody (the child) with protection and care. When the facet *BIRTH-GIVER* is selected, mother designates the female person who engendered a child (a surrogate mother). In Let me introduce you John's mother, the global sense is activated (if John has not been adopted). To elaborate the semantic representation of a multi-facets item in a conceptual perspective, we consider that its global sense is part of its schematic value and that the facets correspond to elaborations of that schematic value. They are all entrenched and salient, directly accessible from the phonological pole and can be activated in context. Consequently, we suggest that multi-faciality can be integrated within Tuggy's continuum, between polysemy (whose schematic meaning is not salient nor directly accessible) and vagueness