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Your search keyword '"Garg, V. K."' showing total 27 results
Start Over Author "Garg, V. K." Publication Type Books
27 results on '"Garg, V. K."'

26. Size dependence of the magnetic and hyperfine properties of nanostructured hematite (α-Fe2O3) powders prepared by the ball milling technique.

Author

André-Filho, J., León-Félix, L., Coaquira, J. A. H., Garg, V. K., and Oliveira, A. C.

Abstract

In this work we present the study of hematite (α-Fe2O3) nanostructures synthesized by the ball milling technique. The structural characterization and the crystallite size estimation have been carried out using the X-ray diffraction (XRD) technique. Data analyses indicate that the hematite phase (space group, R-3C) is preserved after the milling process. As the milling time is increased, a second phase (α-Fe) appears. The mean crystallite size shows a decreasing tendency as the milling time is increased. High-resolution transmission electron microscopy (HRTEM) images show the formation of grains composed of crystallites with irregular shapes. Mössbauer spectra of milled powders carried out at 297 and 77 K are well modeled with a histogram distribution of hyperfine fields. The presence of one additional sextet which corresponds to the ℝ-Fe phase is also determined in agreement with XRD data analysis. Magnetic measurements suggest the suppression of the Morin transition in the milled samples and the absence of thermal relaxation effects in agreement with the Mössbauer spectroscopy results. [ABSTRACT FROM AUTHOR]

Published
2014
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27. Synthesis and characterization of uncoated and gold-coated magnetite nanoparticles.

Author

León-Félix, L., Chaker, J., Parise, M., Coaquira, J. A. H., De Los Santos Valladares, L., Bustamante, A., Garg, V. K., Oliveira, A. C., and Morais, P. C.

Abstract

We report on the synthesis and characterization of uncoated and gold coated magnetite nanoparticles. Structural characterizations, carried out using X-ray diffraction, confirm the formation of magnetite phase with a mean size of ~7 and ~8 nm for the uncoated and gold covered magnetite nanoparticles, respectively. The value of the gold coated Fe3O4 nanoparticles is consistent with the mean physical size determined from transmission electron microscopy images. Mössbauer spectra at room temperature are consistent with the thermal relaxation of magnetic moments mediated by particle-particle interactions. The 77 K Mössbauer spectra are modeled with four sextets. Those sextets are assigned to the signal of iron ions occupying the tetrahedral and octahedral sites in the core and shell parts of the particle. The room-temperature saturation magnetization value determined for the uncoated Fe3O4 nanoparticles is roughly ~60 emu/g and suggests the occurrence of surface effects such as magnetic disorder or the partial surface oxidation. These surface effects are reduced in the gold-coated Fe3O4 nanoparticles. Zero-field–cooled and field-cooled curves of both samples show irreversibilities which are consistent with a superparamagnetic behavior of interacting nanoparticles. [ABSTRACT FROM AUTHOR]

Published
2014
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