Showing papers by "Ashok Kumar published in 2010"

Low-temperature synthesis and Raman scattering of Mn-doped ZnO nanopowders

Abstract: Nanocrystalline Mn-doped zinc oxides Zn1−xMnxO (x = 0–0.10) were synthesized by the sol–gel technique at low temperature. The calcination temperature of the as-prepared powder was found at 350 °C using differential thermal analysis. A thermogravimetric analysis showed that there is a mass loss in the as-prepared powder till 350 °C and an almost constant mass till 800 °C. The X-ray diffraction patterns of investigated nanopowders calcined at 350 °C correspond to the hexagonal ZnO structure without any foreign impurities. The average grain size of the nanocrystal that was observed around ∼25–40 nm from transmission electron microscopy matched well with the crystallite size calculated from the line shape of X-ray diffraction. The chemical bonding structure in Zn1−xMnxO nanopowders was examined using X-ray photoelectron spectroscopy techniques, which indicate substitution of Mn2+ ions into Zn2+ sites in ZnO lattice. Micro Raman spectroscopy confirmed the insertion of Mn ions in the ZnO host matrix, and similar wurtzite structure of Zn1−xMnxO (x < 10%) nanocrystals. Temperature-dependent Raman spectra of the nanocrystals displayed suppression of luminescence and enhancement in full width at half maximum in pure ZnO nanocrystals with increase in temperature, which suggests an enhancement in particle size at elevated temperature. Copyright © 2009 John Wiley & Sons, Ltd.

Novel room temperature multiferroics for random access memory elements

Abstract: We have fabricated a variety of PZT-PFW (PbZr0.52Ti0.48O3)1_x(PbFe2/3W1/3O3)x [PZTFWx; 0.2 <; × <; 0.4] single-phase tetragonal ferroelectrics via chemical solution deposition [polycrystalline] and pulsed laser deposition [epitaxial] onto Pt/Ti/SiO2/Si(100) and SrTiO3/Si substrates. These exhibit ferroelectricity and (weak) ferromagnetism above room temperature with strain coupling via electrostriction and magnetostriction. Application of modest magnetic field strength (μoH <; 1.0 T) destabilizes the long-range ferroelectric ordering and switches the polarization from approximately 22 μC/cm2 (0.22 C/m2) to zero (relaxor state). This offers the possibility of three-state logic (+P, 0, -P) and magnetically switched polarizations. Because the switching is of large magnitude (unlike the very small nanocoulomb per centimeter squared values in terbium manganites) and at room-temperature, commercial devices should be possible.

Novel room temperature Multiferroics for Random Access Memory Elements

Abstract: We have fabricated a variety of "PZT-PFW" (PbZr0.52Ti0.48O3)1-x(PbFe2/3W1/3O3)x [PZTFWx; 0.2 < x < 0.4] single-phase tetragonal ferroelectrics via chemical solution deposition (CSD) [polycrystalline] and pulsed laser deposition (PLD) [epitaxial] onto Pt/Ti/SiO2/Si(100) and SrTiO3/Si substrates. These exhibit ferroelectricity and (weak) ferromagnetism above room temperature with strain coupling via electrostriction and magnetostriction. Application of modest magnetic field strength ((mu)0H < 1.0 Tesla) destabilizes the long-range ferroelectric ordering and switches the polarization from ca. 22 (mu)C/cm2 (0.22 C/m2) to zero (relaxor state). This offers the possibility of three-state logic (+P, 0, -P) and magnetically switched polarizations. Because the switching is of large magnitude (unlike the very small nC/cm2 values in terbium manganites) and at room-temperature, commercial devices should be possible.

Investigation on (Sr,Co)Bi2Nb2O9 thin films: A lead‐free room temperature multiferroics

Abstract: Novel room temperature single phase multiferroic 10% Co doped SrBi2Nb2O9 (SCBN) thin films were fabricated on Pt/Ti/SiO2/Si(100) substrate by pulse laser deposition. The surface morphology indicates homogeneous grains with average grain size and surface roughness of ∼40–130 nm and 6 nm, respectively. High dielectric constant, low dielectric loss <2–5%, negligible frequency independent conductivity, moderate polarization, frequency dependent coercive field, and weak saturation magnetization were observed. The change in the shape of magnetic hysteresis and values of coercive field along in-plane and out-of-plane M–H hysteresis indicates a magnetic anisotropy. The presence of magnetic moments and electric dipole in the same plane suggest mutual cooperation between electric and magnetic ordering on the mesoscopic and microscopic scale. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Improved Properties of Li-Mn-Ti Ferrites by Microwave Sintering

Abstract: Substituted Li-ferrites are attractive materials for research due to their important properties like high Curie temperature leading to high thermal stability, high and wide range of saturation magn...