Morphology control of the magnetization reversal mechanism in Co80Ni20 nanomagnets

Nanowires with very different size, shape, morphology and crystal symmetry can give rise to a wide ensemble of magnetic behaviors whose optimization determines their applications in nanomagnets. We present here an experimental work on the shape and morphological dependence of the magnetization reversal mechanism in weakly interacting Co80Ni20 hexagonal-close-packed nanowires. Non-agglomerated nanowires (with length L and diameter d) with a controlled shape going from quasi perfect cylinders to diabolos, have been studied inside their polyol solution in order to avoid any oxidation process. The coercive field HC was found to follow a standard behavior and to be optimized for an aspect ratio L/d > 15. Interestingly, an unexpected behavior was observed as function of the head morphology leading to the strange situation where a diabolo shaped nanowire is a better nanomagnet than a cylinder. This paradoxical behavior can be ascribed to the growth-competition between the aspect ratio L/d and the head morphology ratio d/D (D being the head width). Our experimental results clearly show the importance of the independent parameter (t = head thickness) that needs to be considered in addition to the shape aspect ratio (L/d) in order to fully describe the nanomagnets magnetic behavior. Micromagnetic simulations well support the experimental results and bring important insights for future optimization of the nanomagnets morphologyComment: 7 pages, 5 figure

CoFe2O4 NANOSTRUCTURED MAGNETIC MATERIALS: INFLUENCE OF NOT-CONVENTIONAL METHODS OF COMPACTION (SPS, HIP) ON THE MICROSTRUCTURE AND PHYSICAL CHARACTERISTICS.

This work presents a Bottom-Up strategy implementing methods of soft chemistry followed by processes of not conventional compaction for making of CoFe2O4 spinel nanostructured materials. The optimization of the process routes to obtain bulk and dense materials will be described in details along with the material nanostructures and magnetic properties. Initially, the nanopowders (10 nm) are obtained in solution by hydrolysis forced in polyol medium. CoFe2O4 nanoparticles have been obtained starting from ionic salts (cobalt acetate and iron chlorate) dissolved in a polyol and heated at a boiling point. The chemical reactions are made possible by several properties of polyols, including high boiling point, dissolving, complexing, hydrolysing and protective properties. This route enables to synthesize particles of size and morphology controlled. These powders prove to have interesting magnetic properties in comparison with those worked out by other ways of soft chemistry [1]: high saturation magnetization near to the bulk materials and temperature of blocking higher than the ambient one

The effect of pH and the process of direct or inverse synthesis of silicon-Substituted hydroxyapatite prepared by hydrolysis in aqueous medium

Nanosized hydroxyapatite with silicon substitution Ca10(PO4)6−x(SiO4)x(OH)2−xâ–¡x (0 ≤ x ≤ 2)  of same silicon concentrations, variation of pH and the method of inverse and direct synthesis were successfully prepared first time by the theoretical maximum  of incorporation of Si into the hexagonal apatite structure   by   precipitation method aqueous. The effects        of the Si substitution on crystallite size, particle size and morphology of the powders were investigated. The crystalline phase, microstructure, morphology and particle size of hydroxyapatite and silicon substituted hydroxyapatites were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), EDX coupled with SEM and transmission electron microscopy (TEM).The samples were successfully synthesized as a single-phase apatite, and crystallization of apatite was enhanced during heating. The results obtained in this study show that the kinetics between different direct and inverse process showed different reactivities, in the presence of varying pH. Compared with the two methods, the inverse method have higher kinetic in the formation of hydroxyapatite silicate because of the difference in lattice parameters. The grain size of Si-HA samples is clearly finer than that of pure HA sample and this decreases with increasing Si content. The growth of HA nanorods with temperature can be described by “oriented attachmentâ€. According to this theory the adjacent HA crystallites would coalesce in one particular direction on the (1 1 0) high energy planes, creating templates                        to form elongated rod-like structure.  Fourier Transform Infrared Spectroscopy analysis reveals,  the silicon incorporation to hydroxyapatite lattice occurs via substitution of silicate groups for phosphate groups. Substitution of phosphate group    by silicate in the apatite structure results in a increase in the lattice parameters in both a-axis and c-axis of the unit cell

Lamellar nickel hydroxy-halides: anionic exchange synthesis, structural characterization and magnetic behavior:

Nickel-layered hydroxy-halides LHS-Ni-X (X = Cl, Br, and I) have been prepared by exchange reactions conducted in an aqueous medium under an inert atmosphere starting from the parent nickel-layered hydroxyacetate. The latter was prepared by a hydrolysis reaction conducted in a polyol medium. IR and X-ray diffraction (XRD) studies show total exchange. These compounds exhibit a brucite-like structure with a turbostratic nature. Their interlamellar distance varies linearly with the radius of the halide anion in the range 7.9-8.7 angstrom while the hydroxyacetate interlamellar distance is 10.53 angstrom. In comparison with the acetate ion which replaces hydroxyl groups in the brucite-like layer, EXAFS and XRD investigations show that halide ions are intercalated into the interlayer space along with water molecules without any covalent bonding to the nickel ion. All compounds have similar structural features and can be considered as alpha-type nickel hydroxides, alpha-Ni(OH)(2). These compounds exhibit a ferromagnetic character. The latter is discussed on the basis of the Drillon-Panissod model of ferromagnetic layers interacting via dipole interactions and taking into account the structural features established by XANES and XRD studies along with the intrinsic properties of the halide anions

High temperature structural and magnetic properties of cobalt nanowires

We present in this paper the structural and magnetic properties of high aspect ratio Co nanoparticles (~10) at high temperatures (up to 623 K) using in situ X ray diffraction (XRD) and SQUID characterizations. We show that the anisotropic shapes, the structural and texture properties are preserved up to 500 K. The coercivity can be modelled by u0Hc=2(Kmc+Kshape)/Ms with Kmc the magnetocrystalline anisotropy constant, Kshape the shape anisotropy constant and Ms the saturation magnetization. Hc decreases linearly when the temperature is increased due to the loss of the Co magnetocrystalline anisotropy contribution. At 500K, 50% of the room temperature coercivity is preserved corresponding to the shape anisotropy contribution only. We show that the coercivity drop is reversible in the range 300 - 500 K in good agreement with the absence of particle alteration. Above 525 K, the magnetic properties are irreversibly altered either by sintering or by oxidation.Comment: 8 pages, 7 figures, submitted to Journal of Solid State Chemistr

OXYDES ET HYDROXYACETATES LAMELLAIRES DE METAUX DE TRANSITION (ZINC, COBALT, NICKEL) (NOUVELLE VOIE DE SYNTHESE PAR HYDROLYSE EN MILIEU POLYOL, CARACTERISATION)

CETTE ETUDE PRESENTE LA SYNTHESE PAR HYDROLYSE EN MILIEU POLYOL D'OXYDES ET DES HYDROXYACETATES LAMELLAIRES DE ZINC DE COBALT ET DE NICKEL ET LEUR CARACTERISATION STRUCTURALE (DRX ET IR RESOLUS EN TEMPERATURE, XANES, EXAFS, UV-VISIBLE) ET MORPHOLOGIQUE (MEB, TEM). ON SAVAIT QUE LES POLYOLS SONT DES MILIEUX FAVORABLES A LA SYNTHESE DE METAUX PAR REDUCTION. ON MONTRE ICI QU'ILS PEUVENT AUSSI ETRE PROPICES A LA SYNTHESE D'AUTRES MATERIAUX INORGANIQUES (OXYDES, SELS D'HYDROXYDES) PAR HYDROLYSE. NOUS AVONS PU METTRE EN EVIDENCE LE ROLE DETERMINANT DE L'ANION ASSOCIE AU METAL DANS LE COMPOSE DE DEPART ET EN PARTICULIER CELUI DE L'ANION ACETATE (QUI DECOULE DE SES PROPRIETES ACIDO-BASIQUES ET A SON POUVOIR COMPLEXANT) DANS LES REACTIONS MISES EN JEU. DANS CES MILIEUX REDUCTEURS, C'EST LE TAUX D'HYDROLYSE QUI APPARAIT COMME LE FACTEUR DETERMINANT POUR ORIENTER LA REACTION VERS LA FORMATION D'OXYDE PLUTOT QUE VERS LA REDUCTION EN METAL. PAR AILLEURS, NOUS AVONS MONTRE QUE LE TAUX D'HYDROLYSE INFLUE AUSSI SUR LE MODE DE CROISSANCE DES PARTICULES D'OXYDE. SON AUGMENTATION EMPECHE EN EFFET LA CROISSANCE PAR AGGREGATION DES PARTICULES PRIMAIRES ET FAVORISE EN REVANCHE LEUR CROISSANCE PAR DIFFUSION. UN MODELE STRUCTURAL A ETE PROPOSE POUR CHAQUE HYDROXYACETATE. CEUX DES COMPOSES AU ZINC ET AU COBALT DERIVENT DU TYPE HYDROZINCITE, ALORS QUE CELUI AU NICKEL EST CONSTITUE D'EMPILEMENT DE FEUILLETS DE TYPE BRUCITE. L'ANION ACETATE Y EST COORDONNE AUX CATIONS METALLIQUES DANS LES PHASES AU COBALT ET AU NICKEL, ALORS QU'IL EST INSERE ENTRE LES FEUILLETS DANS CELLE DU ZINC. L'EAU, ELLE, EST INSEREE EN MONOCOUCHE ENTRE LES FEUILLETS DANS LE CAS DU COBALT ET DU NICKEL, ALORS QU'ELLE EST LIEE AU CATION DANS L'HYDROXYACETATE DE ZINC. ENFIN, L'ETUDE MAGNETIQUE DES HYDROXYACETATES DE NICKEL ET DE COBALT ET DES HYDROXYCARBONATES CORRESPONDANTS OBTENUS PAR ECHANGE, A MIS EN EVIDENCE UN COMPORTEMENT D'AIMANT A BASSE TEMPERATURE, CE QUELLES QUE SOIENT LA STRUCTURE DES FEUILLETS, LEUR ESPACEMENT ET LA NATURE DU CATION.PARIS-BIUSJ-Thèses (751052125) / SudocCentre Technique Livre Ens. Sup. (774682301) / SudocPARIS-BIUSJ-Physique recherche (751052113) / SudocSudocFranceF

Nanohybrides inorganique-organiques à base de ZnO, Zn0,95Ni0,05O,coeur-coquille ZnO@g-Fe2O3 et de polymères bioactifs ( Elaboration,propriétés optiques et magnétiques, cytotoxicité.)

Des nanoparticules des oxydes : ZnO, Zn0,95Ni0,05O et coeur-coquille ZnO@g-Fe2O3 ont été synthétisées par hydrolyse forcée en milieu polyol. Les particules sont quasi-sphériques de diamètre moyen 20-30 nm. Les trois classes présentent des propriétés de photoluminescence alors que les nanoparticules de l oxyde de zinc dopé au nickel et les nanoparticules ZnO@g-Fe2O3 sont superparamagnétiques. Grâce à la polymérisation radicalaire contrôlée, deux polymères bioactifs (le poly(sodium-4-styrenesulfonate) et le poly(sodium-4-styrenesulfonate co sodium methacrylate)) ont été greffés à la surface de ces nanoparticules. Les nanocomposites ainsi obtenus conservent leurs performances magnétiques et voient leurs caractéristiques optiques s améliorer. L enrobage des nanoparticules d oxyde par les polymères bioactifs réduit la cytotoxicité de ces nanoparticules. Mots-Clés : nanoparticules, propriétés magnétiques et optiques, polymère bioactif,nanohybrides, cytotoxicité.ZnO, Zn0.95Ni0.05O and core@shell ZnO@g-Fe2O3 nanoparticles have been prepared using forced hydrolysis of acetate metallic salts in a polyol medium and coated with poly(sodium-4- styrenesulfonate) and poly(sodium-4-styrenesulfonate co sodium methacrylate) via surfaceinitiated atom transfer radical polymerization. The bare nanoparticles display sphericalmorphology with a diameter size laying in the range 20 - 30 nm. The polymer chains weregrown from the surface to yield hybrid nanoparticles with an organic shell of 1 to 3 nm width. The surface modification with polymer did not alter the magnetic and optical properties of bare particles allowing their potential use for biomedical applications. The viability of human endothelial cells was not affected by coated nanoparticles after 48 h of exposition and normal proliferation occurred up to 8 days without alteration of the cell structure. Keywords: nanoparticles, magnetic and optical properties, bioactive Polymer, nonohybrids,cytotoxicity.PARIS13-BU Sciences (930792102) / SudocSudocFranceF

Nouvelles phases hybrides dans les systèmes (M (élément de transition 3d, lanthanide ou cadium) - Carboxylate (succinate, malonate ou pyridine-2,5-dicarboxylate - Eau)

Plusieurs nouvelles phases ont été isolées et caractérisées dans les systèmes ternaires : M (Métal de transition 3d, lanthanide ou cadmium) Anion carboxylate (succinate, malonate, pyridine-2,5-dicarboxylate) - Eau. La plupart de ces composés ont fait l objet de déterminations structurales sur monocristal. Parmi les trois anions, seul l anion succinate favorise l obtention de composés hybrides ionrganique-organiques de structures plus compactes et donc des interactions Métal-Métal plus fortes : Trois nouveaux types structuraux ont été mis en évidence : Cu[O2C(CH2)CO2H]2.2H2O, [Cd][(O2C(CH2)2CO2)] [Cd(OH)]2[O2C(CH2)2CO2]. Les composés des éléments de transition 3d manifestent des comportements magnétiques diverses : ferromagnétisme, ferrimagnétisme ou anti-ferromagnétisme avec des températures d ordre faibles. Les mesures de la fluorescence dans le cas des composés aux terres rares mettent en évidence plusieurs résultats intéressants: (i) le temps de demi-vie est plus élevé pour les composés de symétrie triclinique en comparaison avec ceux de structure monoclinique, (ii) le dopage au samarium améliore nettement le temps de demi-vie, (iii) le transfert d énergie est très important dans le cas de Ce3+ Sm3+. Enfin l étude RMN a permis de mettre en évidence une corrélation entre déplacement chimique du 113Cd et le nombre de groupements hydroxyles premiers proches engagés dans le polyèdre de coordinance autour de ce cation.Several new phases were isolated and characterized in the ternary systems: M (3d transition metal, lanthanide or cadmium) - Anion carboxylate (succinate, malonate, pyridine-2,5-dicarboxylate) - Water. Most of these compounds were the object of structural determinations on single crystal. Among the three anions, only succinate facilitates the obtaining of hybrid inorganic-organic compounds with more compact structures and thus stronger Metal-Metal interactions. Three new structural types were put in evidence: Cu[O2C(CH2)CO2H]2.2H2O, [Cd][(O2C(CH2)2CO2)], [Cd(OH)]2[O2C(CH2)2CO2 ]. 3d transition elements led to compounds with various magnetic behaviours: ferromagnetism, ferrimagnetism or antiferromagnetism with weak magnetic interactions. The measures of the fluorescence in the case of rare earth compounds bring to light several interesting results: i) the half-life time is longer for the compounds of a triclinic symmetry in comparison with those of monoclinic structure, (ii) doping with the samarium improves significantly the half-life time, iii) the transfer of energy is very important in the case of Ce3+ Sm3+. Finally the study RMN allowed bringing to light a correlation between the 113Cd chemical shift and the number of hydroxyl groups engaged in the coordination polyhedron around this cation.PARIS13-BU Sciences (930792102) / SudocSudocFranceF

New acetate-intercalated CoNiFe, ZnNiFe and CoZnFe layered double hydroxides: Synthesis by hydrolysis in polyol medium and characterization

New layered double hydroxides (LDHs) CoNiFe, ZnNiFe and CoZnFe with MII/MIII molar ratio of 3, with acetate ions in the interlayer region have been prepared by forced  hydrolysis in polyol medium.The physico-chemical properties of all products were characterized by the methods of powder X-ray Diffraction, Infrared Spectroscopy, UV-Spectroscopy, Elemental analysis, Thermal analysis, Transmission Electron Microscopy and Scanning Electron Microscopy.It was found that all compounds present the typical features of hydrotalcite-like structure and exhibit a turbostratic character.The insertion of acetate anions into LDHs was confirmed and the interlayer spacing values were respectively 12.47, 13.64 and 14.69 Å for CoNiFe, ZnNiFe and CoZnFe.We notice that there is a difference between the interlayer spacing for all synthesized phases with and without zinc. This can be explained by a structural modification on the level of the layers and/ or different arrangement from the inserted species (anions + water) in the interlayer space for zinc materials.57Fe Mössbauer spectrometry allows concluding the presence of Fe3+ cations which occupy octahedral sites and confirming the absence of Fe2+ in the as-prepared compounds

Nanocrystalline Hydroxyapatite Ceramics Prepared by Hydrolysis in Polyol Medium, Microstructure and Mechanical Properties after Spark Plasma Sintering

This Letter describes a new approach for the synthesis of hydroxyapatite (HA) nanoparticles by polyol process has been successfully conducted by spark plasma sintering process, resulting in a dense hydroxyapatite compacts. Besides, the sintering behaviour of hydroxyapatite powders at different temperatures ranging from 800°C to 950°C at 50 MPa was studied. The microstructure, Vickers microhardness, fracture toughness and density are described. The suitable sintering condition under the pressure of 50 MPa is 900°C for 5 min. A maximum value of the density was reached at around 900°C, and then decreased with further increase in the temperature due to the decomposition of hydroxyapatite into β-tricalcium phosphates