Shalendra Kumar

Structural, electronic, and magnetic properties of Co doped SnO2 nanoparticles

We present a detailed study on the structural, electronic, and magnetic properties of chemically synthesized Sn1−xCoxO2 (x=0.00 to 0.05) nanoparticles. X-ray diffraction and transmission electron microscope measurements were performed to analyze the crystal structure and morphology of Sn1−xCoxO2 nanoparticles. The energy dispersive x-ray analysis measurements were performed to check the possible presence of any impurity elements in the nanocrystals. The near edge x-ray absorption fine structure (NEXAFS) experiments at Snu2009M5,4-edge and Cou2009L3,2-edge were performed to probe the local environment of Sn and Co ions in the SnO2 matrix. The NEXAFS at Cou2009L3,2-edge, along with multiplet calculations, indicate that the Co is substituted at the Sn site in SnO2 matrix with +2 charge state and do not form metallic clusters and other oxide phases. The ferromagnetic nature of these materials was confirmed by x-ray magnetic circular dichroism and room temperature magnetization hysteresis loop measurements.

Structural and magnetic properties of Fe doped CeO2 thin films

Pure and Ce0.95Fe0.05O2 thin films have been fabricated on LaAlO3 (100) substrate using pulsed laser deposition techniques at 200mTorr oxygen partial pressure and then characterized by various techniques viz. X-ray diffraction, atomic force microscopy, NEXAFS, and dc- magnetization measurements to explore the structural and magnetic properties of pure and Fe doped CeO2 thin films. The XRD patterns indicate that pure and Ce0.95Fe0.05O2 films have single phase polycrystalline behavior. The surface roughness measured using AFM microscopy found to decrease with Fe doping and revealed that both the films are nanocrystalline. The electronic structure measured at Fe L3,2 edge infer that Fe-ions in mixed valence states (Fe3+ and Fe2+) in Fe doped CeO2film. DC-magnetization measurements showed that pure and Fe doped CeO2 films have ferromagnetic ordering at room temperature.Pure and Ce0.95Fe0.05O2 thin films have been fabricated on LaAlO3 (100) substrate using pulsed laser deposition techniques at 200mTorr oxygen partial pressure and then characterized by various techniques viz. X-ray diffraction, atomic force microscopy, NEXAFS, and dc- magnetization measurements to explore the structural and magnetic properties of pure and Fe doped CeO2 thin films. The XRD patterns indicate that pure and Ce0.95Fe0.05O2 films have single phase polycrystalline behavior. The surface roughness measured using AFM microscopy found to decrease with Fe doping and revealed that both the films are nanocrystalline. The electronic structure measured at Fe L3,2 edge infer that Fe-ions in mixed valence states (Fe3+ and Fe2+) in Fe doped CeO2film. DC-magnetization measurements showed that pure and Fe doped CeO2 films have ferromagnetic ordering at room temperature.

Structural and Mössbauer analysis of pure and Ce-Dy doped cobalt ferrite nanoparticles

Ce and Dy doped Cobalt ferrites with the chemical composition CoCexDyxFe2-2xO4 (x = 0.00 and 0.04) werexa0synthesized via the chemical route using citrate-gel auto-combustion method. The structural analysis has been carried out with the help of x-ray diffraction (XRD). Formation of spinel cubic structure of the ferrites was confirmed by XRD analysis. Mossbauer spectra were recorded for both samples at room temperature. Presence of the well resolved sextet spectra corresponding to A and B sub-lattice clearly shows that both the samples have ferrimagnetic ordering at room temperature. Isomer shift observed from fitting of the Mossbauer spectra infers that Fe3+ ions are in high valence state. The decrease in the hyperfine field due to the doping of Ce and Dy clearly showed that magnetic interactions diluted due to the doping of Ce and Dy ions.Ce and Dy doped Cobalt ferrites with the chemical composition CoCexDyxFe2-2xO4 (x = 0.00 and 0.04) werexa0synthesized via the chemical route using citrate-gel auto-combustion method. The structural analysis has been carried out with the help of x-ray diffraction (XRD). Formation of spinel cubic structure of the ferrites was confirmed by XRD analysis. Mossbauer spectra were recorded for both samples at room temperature. Presence of the well resolved sextet spectra corresponding to A and B sub-lattice clearly shows that both the samples have ferrimagnetic ordering at room temperature. Isomer shift observed from fitting of the Mossbauer spectra infers that Fe3+ ions are in high valence state. The decrease in the hyperfine field due to the doping of Ce and Dy clearly showed that magnetic interactions diluted due to the doping of Ce and Dy ions.

Effect of Co2+ substitution in Mg0.5Zn0.5−xCoxFe2O4 ferrite nanoparticles: Study of structural, dielectric and magnetic properties

Polycrystalline samples of Mg0.5Zn0.5−xCoxFe2O4 (0 ≤ x ≤ 0.5) with x varying from 0.0-0.5 synthesized by sol-gel auto ignition method. The X-ray diffraction analysis with Retvield refinement reveals the formation of single phase cubic spinel structure. The frequency dependent of real part of dielectric constant has been measured at room temperature and at 100 °C by using an ac impedance analyzer. Except x = 0.5, an increase in the dielectric constant is observed with increase in Co2+ substitution. Magnetic response has been seen by vibrating sample magnetometer (VSM) at room temperature. The saturation magnetization (MS) and coercivity (HC) increase with increasing the Co2+ substitution. The cation distribution estimated by Mossbauer spectroscopy shows that Co2+ and Mg2+ ions have their preference towards octahedral B site, on the other hand Zn2+ ions preferentially occupy tetrahedral A site, whereas Fe3+ ions are randomly distributed over A- and B-site. The as obtained results indicated that the substitu...

175 MeV Au{sup +13} ion irradiation induced structural and morphological modifications in zinc oxide thin films

Thin films of ZnO were deposited, on Si substrates, using the RF-sputtering technique and irradiated by the 175 MeV Au+13 beams. The structural changes were investigated by x-ray diffraction (XRD) measurements. The particle size found to increase with the increasing ion fluence up to 1×1012 ion/cm2. At highest irradiation fluence of 5×1012 ion/cm2 the average particle size decreases. The Raman spectroscopy measurements were performed to understand the local phonon mode of the samples. The surface morphology of the as-deposited and irradiated thin films is measured by the Atomic Force Microscopy (AFM).

Thermoluminescence Characteristics of Nanocrystalline LiF Phosphors Synthesized at Different pH Values

Nanocrystalline lithium fluoride (LiF) phosphors have been prepared by the chemical co-precipitation method at different pH values (7.0, 8.0, 9.0). The formation of nanocrystalline structure has been confirmed by X-ray diffraction and transmission electron microscope. The thermolumniscence (TL) properties of LiF phosphors irradiated with gamma rays at different doses have been studied. The analysis of TL glow curve has revealed the existence of two well resolved glow peaks, one low temperature peak at around 145 deg. C and other one at higher temperature around 375 deg. C. The LiF nano-crystallites synthesized at 8.00 pH have been found to show maximum TL intensity at studied gamma doses (0.1 Gy-15 Gy).