Browsing by Author "A. Barman"

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Effect of Sr-doping on multiferroic properties of Bi 0.8La 0.2Fe 0.9Mn 0.1O 3
(2012) Anup K. Ghosh; H. Kevin; B. Chatterjee; G.D. Dwivedi; A. Barman; H.D. Yang; S. Chatterjee
The effect of Sr-doping on ferroelectricity and ferromagnetism at room temperature has been studied for Bi 0.8La 0.2Fe 0.9Mn 0.1O 3 ceramic system. X-ray diffraction shows that a structural phase transition occurs from rhombohedral structure of BiFeO 3 (space group R3c) to orthorhombic structure of Bi 0.8La 0.2FeO 3 (space group C222). Substitutions of Sr-ions in Bi-site and Mn-ions in Fe-site do not induce any further structural change. Moreover, doping of Sr-ions plays a crucial role to obtain single phased samples. DTA and TGA studies show that both the magnetic transition temperature ( TM) and the ferroelectric transition temperature ( TC) decrease for Bi 0.7Sr 0.1La 0.2Fe 0.9Mn 0.1O 3. Sr-doping enhances the ferroelectric property by increasing the electric polarization. MH measurement shows that Sr-ions partially destroy the spin cycloidal structure in it giving rise to weak ferromagnetism (nonlinearity) at room temperature. © 2011 Elsevier Ltd. All rights reserved.
Role of codoping on multiferroic properties at room temperature in BiFeO3 ceramic
(Elsevier Ltd, 2013) Anup K. Ghosh; G.D. Dwivedi; B. Chatterjee; B. Rana; A. Barman; S. Chatterjee; H.D. Yang
Role of codoping (20% La in Bi-site and 10% Mn in Fe-site) on mutiferroic properties in insulating BiFeO3 ceramic have been investigated. The X-ray diffraction (XRD) with Rietveld refinement shows that the structure of Bi0.8La0.2FeO3 is orthorhombic (Pnma). Furthermore, it shows that on substitution of 10% Mnions in Fe-site, no structural change occurs which has been supported by micro-Raman study. DTA study shows that ferroelectric transition temperature (TC) decreases very fast due with La-doping and slowly with the Mn-doping. Measurement on magnetization vs. applied magnetic field (M-H) shows increase of magnetization due to codoping of La and Mn in BiFeO 3. This may be due to partly destruction or suppression of the spin cycloid structure in it and/or the introduction of the mixed valance state. P-E measurement shows high leakage in Bi0.8La0.2Fe0.9Mn0.1O3. © 2013 Elsevier Ltd. All rights reserved.
Structural, optical and magnetic properties of sol-gel derived ZnO:Co diluted magnetic semiconductor nanocrystals: An EXAFS study
(2014) Shiv Kumar; S. Basu; B. Rana; A. Barman; S. Chatterjee; S.N. Jha; D. Bhattacharyya; N.K. Sahoo; Anup K. Ghosh
Structural, local structural, optical and magnetic properties of sol-gel derived Zn1-xCoxO (0 ≤ x ≤ 0.04) nanoparticles have been studied. The crystallite structure, size, and lattice strain have been estimated by X-ray diffraction (XRD) with Rietveld refinement and high-resolution transmission electron microscopy (HRTEM). The small linear increase in lattice parameter 'a' and decrease in lattice parameter 'c' have been observed which can be attributed to the small distortion of Zn tetrahedron. Extended X-ray Absorption Fine Structure (EXAFS) measurements show that Co-doping creates oxygen vacancies without causing any significant change in the host lattice structure. X-ray Absorption Near Edge Structure (XANES) measurements rule out the presence of metallic Co clusters in the samples. Raman spectroscopy has been employed to study the crystalline quality, structural disorder, and defects in the host lattice. The tetrahedral coordination of the oxygen ions surrounding the zinc ions and wurtzite structure has been studied by FTIR analysis. UV-Vis measurements have been used to study the effect of Co-doping on absorption spectra and hence on the band gap. The band gap initially decreases for low Co-concentration and increases with higher Co-concentration. The PL spectra show six peaks out of which the peak in the ultraviolet (UV) region has been assigned to the near band edge excitonic emission (NBE) and other peaks are related to different defect states. Room temperature ferromagnetism (weak) is observed and magnetization increases with increasing Co-concentration. The grain boundaries, oxygen vacancy and bound magnetic polarons (BMPs) jointly may be responsible for this room temperature ferromagnetism. Variation of resistivity with temperature shows that a thermally activated conduction (Arrhenius) mechanism is valid in the high temperature region whereas Mott's variable-range hopping (VRH) mechanism is valid in the low temperature region. © 2014 The Royal Society of Chemistry.