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

Spectroscopic Ellipsometry Study of Spark Plasma Sintered Nano Silver

International audienceSpark Plasma Sintered (SPS) silver layers were studied by Spectroscopic Ellipsometry (SE) using an M-2000V spectroscopic ellipsometer from J. A. Woollam Co., Inc. which operate in rotating compensator mod

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

From Ni–P Metastable Alloy Nanoparticles to Bulk Submicrometer Grain-Sized MMCs with Tunable Mechanical and Magnetic Properties

In this study, submicrometer grain-sized metal matrix composites (MMCs) based on nickel were elaborated via a bottom-up strategy combining the polyol process and a non-conventional heat treatment route. First, four sets of nano-sized NiP metastable alloy nanopowders with an average particle size centered at 50, 100, 130, and 220 nm were prepared by the polyol process modified by the addition of hypophosphite (strong reducing agent) and heterogeneous nucleation using silver nitrate and platinum salt (nucleating agents). The heat treatment step was realized by reactive spark plasma sintering (R-SPS) at identical heat treatment conditions (600 • C, 53 MPa, and 10 min as holding time). R-SPS transformed the NiP metastable alloys into bulk submicrometer grain-sized MMCs with Ni as the matrix and Ni 3 P as the reinforcement. Mechanical and magnetic properties of the four MMC samples were found to be closely related to the grain size of the Ni matrix, which varied from 247 to 638 nm. Yield stress, maximum stress, and coercive field increased when the grain size decreased, while plastic strain and magnetization saturation decreased. The reinforcement Ni 3 P phase enhanced the mechanical characteristics of the composite. Crossover behavior was observed at around 350 nm Ni grain size, where a ductile and soft magnetic composite was tuned into a hard mechanical and semi-hard magnetic one

Microstructure and optical properties of alumina sintered from various phases

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Substitution effect of Me = Al, Bi, Cr and Mn to the microwave properties of polyaniline/BaMeFe 11 O 19 for absorbing electromagnetic waves

International audiencePolyaniline/substituted barium hexaferrites (abbreviated Pani/BaMeFe11O19, where Me = Al, Bi, Cr and Mn) composites are investigated to be potential electromagnetic wave absorber from 1 to 18 GHz frequency range. Solid-Based Polymerization method is used to prepare the samples with 10% volume fraction of hexaferrite. The effects of iron substitution in hexaferrite composites by trivalent ions Al3+, Bi3+, Cr3+ and Mn3+ on permittivity, permeability and microwave absorption properties are studied. Structural and morphological investigations confirm the presence of Polyaniline and barium hexaferrite phases, which are in interaction in the composites regardless the substitution. Thermogravimetric analysis exhibits an improved thermostability when small ions (Al3+ and Cr3+) are used to substitute Fe3+ in hexaferrite compared to the large cations substitution (Bi3+ and Mn3+), since these latter interfere between the ferrite and intermolecular interaction between Pani macromolecules. Magnetic studies show a ferromagnetic behaviour for all the composites. Saturation magnetization is mainly related to the substituting cations nature in hexaferrite which is determined using measured magnetic data. Coercivity values increase slightly due to the Pani matrix that precludes the movement of the domain wall. The EM parameters ε׳, ε׳׳, μ׳and μ׳׳ are measured using a Vector Network Analyzer. It is found that the dielectric constant increases with the addition of hexaferrite. The maximum of the magnetic losses diminishes and shifts to higher frequencies with Fe3+ doping. These measured EM parameters are used to determine the reflexion loss for different composites. Pani/BaFe12O19 composite shows two minimum reflection losses (RL) in Ku-band. The properties of these ferrites arise from exchange interactions between the oxygen and metallic ions occupying particular positions in its crystalline structure. For the substituted ferrite composites, the minimum RL shifts from in Ku-band to X-band when substituting Fe3+ in hexaferrites by means of the variation of ferromagnetic resonance frequency which influences the microwave absorption propertie

The effect of Ti substitution by Zr on the microstructure and mechanical properties of the cermet Ti1-xZrxC sintered by SPS

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Effect of spark plasma sintering process on the microstructure and mechanical properties of Nano crystalline hydroxyapatite ceramics prepared by hydrolysis in polyol medium

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Microstructure and mechanical properties of bulk highly faulted fcc/hcp nanostructured cobalt microstructures

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Physico-chemical and mechanical properties of Ti3SiC2-based materials elaborated from SiC/Ti by reactive spark plasma sintering

Abstract In this paper, the synthesis of Ti3SiC2 from SiC/Ti powder using reactive spark plasma sintering (R-SPS) in the temperature range of 1300–1400 °C is reported. The results show that the purity of Ti3SiC2 is improved up to 75 wt% when the holding time is increased from 10 to 20 min at 1400 °C. The thermodynamic and experimental results indicate that Ti3SiC2 formation takes place via the reaction of a pre-formed TiC phase with the silicides, formed from the eutectic compositions. Detailed analysis of mechanical behaviour indicates that samples with higher percentage of secondary phases exhibit higher microhardness and better resistance compared to the near single phase Ti3SiC2