Neeru Sehdev

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...

Magnetic memory effects in nickel ferrite/polymer nanocomposites

Memory effects are reported in the field cooled (FC) magnetization of pure nickel ferrite powders and nickel ferrite nanocomposites prepared by the solution casting method. Studies carried out at different concentrations of the nanocomposite indicate that memory effects are suppressed with increasing concentration of the magnetic component in the nanocomposite. This is linked to the increase in the dipolar interaction strength in the nanocomposites, which increase with increasing concentration, as confirmed by the Henkel plots. Model simulations of the FC magnetization carried out on an interacting array of monodispersed magnetic nanoparticles indicate that growing cluster sizes inhibit memory effects.

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.

Engineering strain, densification, order parameter and magnetic properties of FePt thin films by dense electronic excitations

FePt films prepared by DC sputtering on Si ⟨100⟩ substrates when annealed at 600 °C for 1 h exhibited a structurally ordered and magnetically hard L10 phase. These FePt films were exposed to dense electronic excitations by using 100 MeV oxygen ions as a function of increasing fluences. Such excitations induce pressure and result in the enhancement of order parameter by increasing strain on the FePt films. Apart from this, the surface morphological images from field emission scanning electron microscopy reveal a densification of the films consequent to irradiation and are correlated with the details obtained from Rutherford back scattering analysis. The variation in the values of coercivity correlates well with the change in volume percentage of face centered tetragonal and face centered cubic phase. A coercivity of 14.7 kOe with order parameter 0.92 is achieved at a fluence of 5 × 1012 ions/cm2. The theoretical simulation of the demagnetization curve shows a strong correlation of coercivity and order para...

Dense-plasma-driven ultrafast formation of FePt organization on silicon substrate

AbstractThis article demonstrates the removal of organic capping and promotion of long-range 2D organization of chemically synthesized FePt nanoparticles dispersed on Si 〈100 〉 substrate by means of pulsed H+ energetic ion irradiation using a dense plasma focus (DPF) device. The irradiation of energetic H+ ions on FePt nanoparticles clearly resulted in enhanced structural and magnetic behaviour of the FePt nanoparticles as a function of plasma focused irradiation shots. Transmission electron microscopy (TEM)/scanning electron microscopy (SEM) images of the FePt nanoparticles clearly show a marked enhancement in average particle size from 2.5 nm for non-irradiated sample to about 28 nm for four plasma focus shots irradiation. The gradual removal of organic capping over chemically synthesized FePt nanoparticles with increasing plasma focus shots exposure is confirmed using Raman spectroscopy. A uniform 2D organization of bimetallic FePt nanoparticles over 1 cm × 1 cm silicon substrate is obtained with three plasma focus shots with better magnetic properties as compared with plasma-untreated FePt nanoparticles. Graphical AbstractPlasma focused irradiation shots