Rohit Medwal

Enhanced phase stabilization of CoPt in the presence of Ag

We report the synthesis of CoPt and CoPt–Ag nanoparticles by the simultaneous reduction of platinum(II) acetylacetonate (Pt(acac)2), cobalt(II)acetylacetonate (Co(acac)2), and silver nitrate (AgNO3) (for CoPt–Ag) in the presence of poly(N-vinyl-2-pyrrolidone) (PVP). Here the changes in the structural and magnetic properties of these nanoparticles subjected to heat treatment and the effect of adding silver to CoPt in comparison to pure CoPt have been investigated. TEM observations reveal a narrow size distribution with particle diameter of about 2–3 nm. The XRD studies reveal a disordered fcc phase for the as synthesized nanoparticles which after annealing at higher temperatures show peaks corresponding to an ordered L10 phase. The structural phase transition is also followed by enhanced magnetic properties. The magnetic measurements show the transition of a magnetically soft alloy to a magnetically hard material with a maximum coercivity of ∼1 T after annealing at 700 °C. The addition of silver (Ag) to Co...

Processing temperature driven morphological evolution of ZnO nanostructures prepared by electro- exploding wire technique

This article presents an effective approach for the synthesis of ZnO nanoparticles with desired morphology via an environmentally benevolent electro-exploding wire (EEW) technique. In this process, ZnO nanoparticles evolve through the plasma generated from the parent Zn metal. Compared to other typical chemical methods, electro-exploding wire technique is a simple and economical technique that normally operates in water or organic liquids under ambient conditions. The effect of different processing temperatures in the range (5–80 °C), on the morphology of ZnO nanoparticles is clearly demonstrated. At 5 °C, nanoparticles with spherical morphology are observed. However, elliptical morphology is observed at room temperature and multipod nanorods at 50 °C and 80 °C. The evolution of ZnO phase is investigated with the help of time dependent UV-vis absorption and photoluminescence (PL) studies. The mechanism of formation and different morphologies of ZnO nanoparticles formed are also proposed.

Room temperature coercivity and interaction effects in L10 FePt nanoparticles

FePt alloy systems in the L10 phase are characterized by high anisotropy values that lead to exceptionally high coercive fields, making them a primary candidate for high density data storage. In this paper, we report the synthesis of L10 FePt nanoparticles by thermal annealing of chemically disordered FePt nanoparticles. The high degree of ordering and high coercivity achieved in these systems is further studied using Monte Carlo simulations by incorporating the effects of anisotropy, interactions, and disorder, with a view to understand the role of these interactions. A comparison of the simulation results with the experiment results also helps us to estimate an anisotropy value of ?2.25?2.5?MJ?m?3.

Structural and magnetic transformation in electrochemically synthesized FePt thin films on Si/Pt electrodes

FePt films were prepared by electrochemical deposition on to the platinum coated Si substrate. The appropriate composition of alloy was achieved by carrying out the potentiostatic deposition at −800 mV. After deposition, films were subjected to different annealing temperatures for 1h. Structural and magnetic studies were performed to investigate the phase transformation. At low annealing temperatures, presence of FePt3 was observed along with FePt phase. An increase in coercivity and squareness was observed with annealing temperature. A highest coercivity of 7.8 kOe was obtained after annealing at 700°C for 1h indicating the L10 phase formation.