Showing papers by "Harish Verma published in 2015"

Magnetic and Dielectric Properties of Multiferroic BiFeO3 Nanoparticles Synthesized by a Novel Citrate Combustion Method

Abstract: Single phase BiFeO3 nanoparticles have been successfully synthesized for the first time by a novel citrate combustion method without using any solvent. Well mixed metal nitrates along with citric acid which is used as fuel combust to give BiFeO3 nanoparticles after annealing. These particles are single phase in nature and crystallize in the rhombohedral distorted perovskite structure (space group-R3c) which has been confirmed by the Rietveld refinement of the room temperature powder x-ray diffraction data. Nearly spherical particles of average particle size 47 nm have been seen from transmission electron micrograph. Room temperature magnetic hysteresis measurement shows weak ferromagnetism though the magnetization does not saturate upto 1.75 T applied field. The coercive field value is calculated to be 180 Oe which is 3 times higher than that prepared by solvent free combustion method using Glycine. 57Fe Mossbauer spectrum can be fitted with a sextet corresponding to single magnetic state of hyperfine field about 49.5 T corresponding to Fe3+ state of the iron atom. The dielectric relaxation and ac conductivity as a function of frequency have been discussed. High dielectric permittivity has not been found in these nanoparticles like other reported BiFeO3 ceramics.

Preparation, structural and magnetic studies on BiFe1-xCrxO3 (x=0.0, 0.05 and 0.1) multiferroic nanoparticles

Abstract: BiFe1-xCrxO3 (x=0.0, 0.05 and 0.1) nanoparticles are prepared by a combustion method without using any solvent. All the synthesized nanoparticles are single phase in nature, nearly spherical in shape and crystallize in distorted perovskite structure and space group R3c with an average crystallite size of the order of 40 nm. The room temperature magnetization observed in BiFeO3 nanoparticles is larger than that in the bulk. Increasing Cr doping leads to increase in the magnetization and coercivity. Strong superexchange interaction between Fe3+ and Cr3+ atoms is likely to give rise to such increase in magnetization with Cr-doping. M\"ossbauer data of these nanoparticles show ordered magnetic state in which Fe atoms are in 3+ oxidation states.

Ion-beam-assisted fabrication and manipulation of Metallic nanowires

Abstract: Metallic nanowires (NWs) are the key performers for future micro/nanodevices. The controlled manoeuvring and integration of such nanoscale entities are essential requirements. Presented is a discussion of a fabrication approach that combines chemical etching and ion beam milling to fabricate metallic NWs. The shape modification of the metallic NWs using ion beam irradiation (bending towards the ion beam side) is investigated. The bending effect of the NWs is observed to be instantaneous and permanent. The ion beam-assisted shape manoeuvre of the metallic structures is studied in the light of ion-induced vacancy formation and reconfiguration of the damaged layers. The manipulation method can be used for fabricating structures of desired shapes and aligning structures at a large scale. The controlled bending method of the metallic NWs also provides an understanding of the strain formation process in nanoscale metals.

Implication of Mossbauer Spectra on the Mixing Model of Eucrites and Diogenites (Resulting in Howardites)

Abstract: In the present communication, we show that Mossbauer spectra of cumulate eucrites are characteristically different from those of non-cumulate eucrites In cumulate eucrites, iron occupies only one site, ie the M2 site in pyroxene crystal lattice, while it is distributed in both M1 and M2 sites in non-cumulate eucrites We discuss the importance of asymmetric doublet observed in the Mossbauer spectrum of cumulate body, especially in Vissannapeta cumulate eucrite (fallen in Andhra Pradesh, India), where an appreciable asymmetry was observed The Mossbauer parameters of diogenite almost exactly replicate those of cumulate eucrites, suggesting that they originate from the same magma ocean Howardites which are mixed eucrites and diogenites, show iron mineralogy which is different from what one would expect from a physical mixture model The possible reasons for this difference are also discussed

novel interpenetrating polymer network mucoadhesive microspheres of locust bean gum and poly(vinyl alcohol) for the delivery of Famotidine

Abstract: Novel interpenetrating polymer network (IPN) of locust bean gum (LBG) and poly vinyl alcohol (PVA) were prepared and crosslinked with glutaraldehyde (GA) to form mucoadhesive microspheres by emulsion cross-linking method to deliver model anti-ulcer drug, famotidine. Various formulations were prepared by changing the ratio of LBG: PVA, extent of cross-linking in order to optimize the formulation variables on drug encapsulation efficiency and release rate. FTIR spectroscopy was done to confirm the formation of interpenetrating network and the chemical stability of famotidine after penetration of microspheres. Microspheres formed were spherical with smooth surfaces as revealed by SEM and mean particle size as measured by optical microscopy ranged between 10.83±0.75μm to 21.13±0.74μm. Drug entrapment efficiency was ranges between 65.44±2.57% to 84.67±2.58%. Percentage mucoadhesion of the microspheres was found to be in the range between 63.33±2.57% to 86.66±3.65%. Equilibrium and dynamic swelling studies were performed in 0.1N HCl buffer solution of pH 1.2 and diffusion coefficients were calculated by considering the spherical geometry of the matrices. In vitro release studies were performed in pH 1.2 media. Release data indicated that a drug release which depends on the extent of cross-linking and the ratio of LBG: PVA present in the microsphere. The release data were fitted to an empirical equation to estimate the transport parameters, which indicated that the release follows Super Case II transport mechanism. Based on the results of in-vitro studies it was concluded that these IPN mucoadhesive microspheres provided oral controlled release of famotidine.

M\"ossbauer and Magnetic Studies of Surfactant Mediated Ca-Mg Doped Ferrihydrite Nanoparticles

Abstract: Ultrafine (2-5 nm) particles of amorphous Ca-Mg co-doped ferrihydrite have been synthesized by surfactant mediated co-precipitation method. The evolution of the amorphous ferrihydrite by Ca-Mg co-doping is quite different from our earlier investigations on individual Ca and Mg doping studies. Amorphous phase of ferrihydrite for the present study has been confirmed by X-ray diffraction (XRD) and M\"ossbauer spectroscopy at room temperature and low temperatures (40 K and 20 K). Hematite nanoparticles with crystallite size about 8, 38 and 70 nm were obtained after annealing the as-prepared samples at 400, 600 and 800$^0$C respectively in air atmosphere. Superparamagnetism has been found in 8 nm sized hematite nanoparticles which has been confirmed from the magnetic hysteresis loop with zero remanent magnetization and coercive field and also from the superparamagnetic doublet of its room temperature M\"ossbauer spectrum. The magnetic properties of the 38 and 70 nm sized particles have been studied by room temperature magnetic hysteresis loop measurements and M\"ossbauer spectroscopy. The coercive field in these hematite nanoparticles increases with increasing particle size. Small amount of spinel MgFe$_{2}$O$_{4}$ phase has been detected in the 800$^0$C annealed sample.