Daisuke Kodama

Synthesis of submicron sized Fe20Ni80 particles and their magnetic properties

Fe–Ni alloy nanoparticles were synthesized by polyol process using hydrazine as a reduction assist reagent. Particle size, crystallite size, and crystal phases varied with the type of polyol. The saturation magnetizations of the as-synthesized Fe–Ni particles synthesized in ethylene glycol (EG) and 1-heptanol were similar to the bulk and were 73 emu/g and 83 emu/g, respectively. On the other hand, the coercivities of the same were 41 and 123 Oe. The coercivity of the Fe–Ni particles synthesized in EG decreased to 27 Oe after heat treatment. Though the magnetic properties were very similar irrespective of the polyol used in this study, the Mossbauer spectroscopic measurements revealed that Fe–Ni particles with single permalloy phase was synthesized only when EG was used.

Synthesis of Fe-Co Alloy Particles by Modified Polyol Process

The successful synthesis of Fe-Co nanoparticles by using a modified polyol process is reported. The formation of the alloy nanoparticles was confirmed by X-ray diffraction and X-ray extended absorption fine structure analyses. The concentration of iron in these particles could be varied between 40% and 90% by controlling the reaction conditions such as initial Fe/Co ratio, reaction temperature and hydroxyl ion concentration. The shape of the particles changed from spherical to cubic when the concentration of Fe was increased from 40 to above 60 at. %. The highest magnetization of 225 emu/g was recorded for Fe70Co30 nanoparticles. The magnetization of these particles decreased by about 20% when exposed to severe oxidizing atmosphere for seven days

Synthesis and magnetic properties of platelet Fe–Co particles

The synthesis scheme for hexagonal shaped Fe–Co platelets with magnetic properties comparable to the bulk is reported for the first time. The hexagonal Fe–Co platelets with the size of about 8 μm and an aspect ratio of about 5.4 were prepared by reducing the platelet shaped intermediate obtained in ethylene glycol-metal salts-sodium hydroxide system. The saturation magnetization and coercivity of the Fe–Co hexagonal platelets obtained by reducing the solid intermediate at 673 K in hydrogen atmosphere were above 220 emu/g and 25 Oe, respectively. Since the use of such particles in high frequency applications demand further reduction in size and increment in aspect ratio, a synthesis scheme for particle morphology control was devised. The proposed synthesis scheme using nucleating agents clearly demonstrated that the shape, size, and aspect ratio of the platelets can be controlled freely. Consequently, platelets with elongated shape and thickness of about few hundred nanometers were produced. Though further...

Potential of sub-micron-sized Fe-Co particles for antenna applications

High frequency properties of (a) as-synthesized and (b) flattened by ball milling Fe-based alloys particles and their potential as antenna materials is reported. The high frequency properties of Fe-Co nanoparticles exhibited a resonance peak in the range of a few gigahertz (GHz), and the resonance peak shifted to a higher region for decreasing particle size. However, magnetic permeability was not high enough to be used as high performing electromagnetic wave absorbers. On the other hand, the permeability of Fe-Ni particles at 1 GHz was 2.5 and the magnetic loss was 0.36. However, permeability was enhanced to a value of more than 3 and the magnetic loss decreased by more than half, when the dispersibility and planular aggregates were realized through ball milling. Additional experiments suggested that the particle aggregation had greater influence in the high frequency properties than the composition and magnetic properties. Similarly, when Fe50Co50 particles were also subjected to ball milling, their magn...

Morphology Control of FeCo Alloy Particles Synthesized by Polyol Process

FeCo alloy is a soft magnetic material that possesses the highest saturation magnetization of 2.4 T and crystallizes in bcc structure as in the case of α‐Fe. However, the particles synthesized were highly agglomerated. Thus, in this paper, an attempt was made to control the morphology of the particles using different types and concentrations of surfactants such as oleic acid, oleyl amine, polyvinylpyrrolidone (PVP), etc., during the synthesis of the particles. Though all the surfactant experimented partially prevented the agglomeration, products had larger size distribution except for PVP, which provided nearly monodispersed particles. Furthermore, the FeCo particles synthesized in the presence of PVP were either cubic or nearly spherical depending on the concentration of Fe.

Synthesis of FeCo Alloy Particles by Modified Polyol Process and their Structural and Magnetic Properties

In this report, we present the synthesis of FeCo alloy particles with varying composition by using modified polyol process and their magnetic and structural properties are also reported. The morphology, composition, crystal phase and local atomic structures of the magnetic powders were analyzed using XRD, XAFS spectra and SEM. The saturation magnetisation was recorded for FeCo measured under applied field of 15 kOe.

Design of monoalcohol – Copolymer system for high quality silver nanowires

Research to improve the dimensional properties of silver nanowires (Ag NWs) for transparent conductive film (TCF) applications are being carried out intensively. However, the protocol for the designed synthesis of high-quality Ag NWs is yet to be developed due to the inadequacy of knowledge on the role of parameters. Here, we attempt to elucidate the role played by the parameters and propose a monoalcohol-copolymer based system for the designed synthesis of Ag NWs superior in quality to the one synthesized using conventional ethylene glycol (EG)-polyvinylpyrrolidone (PVP) system. The key findings of the study are as follows: (1) the solubility of Ag source and the partially formed AgCl particles in monoalcohols was found to play an important role not only in the reduction to metallic Ag but also on the uniaxial growth, (2) the adsorption of capping agents on Ag NWs was carried through O and N atoms in the base molecule and their binding energies indicated that the strength is the key parameter to obtain Ag NWs with high aspect ratio, (3) the properties of nanowire could be enhanced through copolymerization of VP and base molecules that have O- and N-based ligands, and (4) the influence of copolymerization on the physical and chemical properties of the surface active agent has been theoretically and experimentally verified. Consequently, we succeeded in the development of a new technique to synthesize high yield of Ag NWs with improved aspect ratio than EG-PVP system by using benzyl alcohol as reducing solvent and N-vinylpyrrolidone/N,N-diethylaminoethyl metacrylate copolymer as a capping agent. The optical transmittance and electrical resistivity of TCFs prepared using the Ag NWs with an average diameter of 43 nm, and an average length of 13 μm were 98.6% and R: 49.1 Ω/□, respectively.

Alloy Compositional Gradation in Surface Layer and Oxidation Resistance on Chemical Synthesized FeCo Nanoparticles

X-ray photoelectron spectroscopy (XPS) has been used for analyzing the surface composition of polyol process-derived Fe30Co70, Fe50Co50, and Fe70Co30 alloy nanoparticles with diameters 50, 100 and 150 nm, respectively. These Fe-Co alloy particles have high oxidation resistance in the atmospheric environment even though their particle size is so small. The XPS results revealed that the concentration of iron at the surface of the as-synthesized Fe-Co alloy nanoparticles was lower than that in bulk and increased with increasing bulk cobalt composition, although the surface of nanoparticles was covered with native oxide layer formed during their exposure to atmosphere. This low concentration of iron and very thin oxide layer at the surface are considered to protect the particle from oxidation. The concentration of iron at the surface of Fe70Co30 nanoparticles increased when they were annealed at 573 K in N2 and H2 atmosphere. The results indicate that nonuniformity of the chemical composition between particle surface and core occurs during the formation of the same in polyol, and atomic diffusion at the surface of particle can occur even at relatively low temperature. The above is considered to arise from the difference in the chemical characteristics of iron and cobalt during co-precipitation in the polyol.