Jeyadevan Balachandran

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 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...

Towards a designed synthesis of metallic nanoparticles in polyols – elucidation of the redox scheme in a cobalt–ethylene glycol system

The polyol process has been used to synthesize metal and alloy nanoparticles over a couple of decades. Its potential has been demonstrated through the synthesis of metallic nanoparticles with various sizes and shapes. However, although one of the roles of polyol is to act as a reducing agent, research studies related to the investigation of the redox reaction mechanism have been scarce. In this study, we report the results of a detailed study undertaken to investigate the polyol oxidation and metal reduction for the cobalt(II)–ethylene glycol system with the possible addition of a base (Na) to the system using several physico-chemical techniques such as NMR, FT-IR, ESI-TOFMS and XRD. The results suggested that in the reduction reaction, ethylene glycol first reacts with the base to produce the ethylene glycol monoanion, hereinafter denoted as EG−. This reaction not only occurs between ethylene glycol and the base, but also occurs with Co2+ species. In such a case, the formation of Co alkoxide and the subsequent reduction could progress even in the presence of a weak base such as acetate ion or any other solvent that has a lone pair of electrons such as oxygen in ether. On the other hand, in the case of oxidation of ethylene glycol, first the base attacks one of the two α-protons in Co alkoxide and along with the electron transfer to Co2+, ethylene glycol gets oxidized to aldehyde. Then, the aldehyde thus formed undergoes bond exchange with the neighboring coordinated ethylene glycol and an ester is formed. The above steps are repeated and the hydrogen atoms coordinated with Co get detached with the evolution of hydrogen gas, while ethylene glycol is oxidized to polyglycolic acid. The analytical techniques and the results obtained in this study could be used to enhance the properties of metals and alloy nanoparticles synthesized using the polyol process.

Local Structure of Directly Synthesized L1

The FePt particles synthesized by polyol process using tetraethylene glycol (TEG) as reducing agent at reaction temperatures 200degC and 300degC are superparamagnetic and ferromagnetic, respectively. The crystal structure of these particles is analyzed using XRD, XAS, and ASAXS to understand the formation of these particles at different heating temperatures. The results suggest that at 200degC particles with Pt rich FePt core and amorphous shell rich in Fe are formed. However, when the reaction solution is annealed at 300degC, sintering of several small particles occur. On the other hand, when hexachloroplatinum as nucleation control agent and a carboxylic acid as complex agent was added into the reaction solution, homogeneous alloy FePt particles with relatively large grain size of about 8 nm were obtained. In the process of forming the alloy nanoparticles, precipitated small particles were sintered at the amorphous interface and crystallization progresses along with ordering resulting in the formation of partially ordered ferromagnetic FePt

_0

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.

FePt Nanoparticles

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.