Publications (58)71.96 Total impact
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Article: Magnetization study of Fe-doped ZnO co-doped with Cu: Synthesized by wet chemical method
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ABSTRACT: Fe- and Cu-doped ZnO of nominal compositions Zn0.95Fe0.05O and Zn0.94Fe0.05Cu0.01O were synthesized by a wet chemical route. X-ray diffraction analysis of the samples annealed at 575K showed that they are single phase without any secondary phases. DC magnetization measurements of Cu co-doped samples (Zn0.94Fe0.05Cu0.01O) as a function of field at room temperature showed ferromagnetic signature while the samples without Cu co-doping (Zn0.95Fe0.05O) are paramagnetic in nature. On increasing the temperature of annealing from 575K to 1,075K an impurity phase emerges in both the samples, which has been identified as a variant of ZnFe2O4. Both the samples heated at and above 1,075K are found to be paramagnetic at room temperature. These observations, the absence of room temperature ferromagnetism in Zn0.95Fe0.05O and the disappearance of ferromagnetism in Zn0.94Fe0.05Cu0.01O on raising the temperature of annealing clearly rules out the likelihood of room temperature ferromagnetism arising from the impurity phases like γ-Fe2O3 and/or ZnFe2O4 that might have been formed during the synthesis. Our results strongly suggest that room temperature ferromagnetism in Zn0.94Fe0.05Cu0.01O can be attributed to the formation of a secondary phase of Cu-doped ZnFe2O4.Journal of Materials Science 04/2012; 41(15):4706-4712. · 2.02 Impact Factor -
Article: Sphere-to-rod transition of triblock copolymer micelles at room temperature
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ABSTRACT: A room temperature sphere-to-rod transition of the polyethylene oxide-polypropylene oxide-polyethylene oxide-based triblock copolymer, (PEO)20(PPO)70 (PEO)20 micelles have been observed in aqueous medium under the influence of ethanol and sodium chloride. Addition of 5–10% ethanol induces a high temperature sphere-to-rod transition of the micelles, which is brought to room temperature upon addition of NaCl. The inference about the change in the shape of the micelles has been drawn from small-angle neutron scattering (SANS) and viscosity studies.Pramana 04/2012; 63(2):277-283. · 0.57 Impact Factor -
Chapter: Phase Stability, Structural and Magnetic Properties of Some CMR Manganites
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ABSTRACT: Discoveries of colossal magneto-resistance (CMR) in the perovskite manganites, Ln1−x AxMnO3 (Ln = La, rare earth; A = divalent ions), as well as in the layered manganites, (La,Sr)3Mn2O7, has created a renewed interest in them. Their physical characteristics point to the existence of a fine interplay between spin, charge and lattice interactions. Substitutional studies, particularly at the rare earth and Mn sites in these compounds, can throw light on important crystal chemical aspects. Through systematic site-selective substitutions we have tried to evaluate the phase stability of some of these layered and perovskite manganites. In particular, our study on the layered manganites, La1.2(Sr1−x Cax)1.8Mn2O7, and Ca3−x LaxMn2O7, establishes that the compositions Ca3–x LaxMn2O7 (1.2 ≤ x ≤ 2.3) do not form layered compounds with Sr3Ti2O7 - structure, in contrast to literature reports. Instead, they form multiphase mixtures with La1−x CaxMnO3 as the majority phases which, in fact, determine their magnetic and transport behavior. By careful structural and magnetic studies on La0.7Ce0.3MnO3 and La0.7MnO3 we have also proved that the compositions La1−x CexMnO3 do not form electron-doped manganites, but actually yield multiphase mixtures comprising La1−x MnO3 and CeO2. Lastly, we demonstrate that both Co and Cr as dopant ions destabilize the double-exchange mechanism driven ferromagnetism and metallic characters in La0.67Ca0.33Mn1−x CoxO3 and La0.67Ca0.33Mn1−y CryO3, and highlight the differences in the nature of the magnetic exchange interaction of Mn ions with Co, and with Cr ions in these hole-doped perovskite manganites.01/2008: pages 228-251; -
Article: Room temperature Ferromagnetism in Th1-xFexO2-d (x = 0.0, 0.05, 0.10, 0.15, 0.20 and 0.25) nanoparticles
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ABSTRACT: Nanocrystalline (Th1-xFex)O2-d particles with different Fe concentrations (x = 0.0, 0.05, 0.10, 0.15, 0.20 and 0.25) have been prepared by a gel combustion method. Rietveld refinement analyses of X-ray diffraction data revealed the formation of an impurity free cubic type Th1-xFexO2-d structure up to x = 0.20. This observation is further confirmed from the detailed studies conducted on 10 at. percent Fe doped ThO2 using high-resolution transmission electron microscopy (HRTEM) imaging and indexing of the selected-area electron diffraction (SAED) patterns. DC Magnetization studies as a function field indicate that they are ferromagnetic with Curie temperature (Tc) well above room temperature.08/2007; -
Article: Structural and magnetic properties of (In1-xFex)2O3 (0.0 <x< 0.25) system: Prepared by gel combustion method
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ABSTRACT: �In1−xFex�2O3 polycrystalline samples with x=�0.0, 0.05, 0.10, 0.15, 0.20, and 0.25� have been synthesized by a gel combustion method. Reitveld refinement analysis of x-ray diffraction data indicated the formation of single phase cubic bixbyite structure without any parasitic phases. This observation is further confirmed by high resolution transmission electron microscopy imaging, indexing of the selected-area electron diffraction patterns, x-ray absorption spectroscopy, and Raman Spectroscopy. dc magnetization studies as a function of temperature and field indicate that they are ferromagnetic with Curie temperature �TC� well above room temperature.Applied Physics Letters 07/2007; 91:052504. · 3.84 Impact Factor -
Article: The structural and magnetic properties of (In1-xFex)2O3 (0.0 <= x <= 0.25) system : prepared by gel combustion method
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ABSTRACT: (In1-xFex)2O3 polycrystalline samples with x = (0.0, 0.05, 0.10, 0.15, 0.20 and 0.25) have been synthesized by a gel combustion method. Reitveld refinement analysis of X raydiffraction data indicated the formation of single phase cubic bixbyite structure without any parasitic phases. This observation is further confirmed by high resolution transmission electron microscopy (HRTEM) imaging, and indexing of the selected-area electron diffraction (SAED) patterns, X-ray Absorption Spectroscopy (XAS) and Raman Spectroscopy. DC Magnetization studies as a function of temperature and field indicatethat they are ferromagnetic with Curie temperature (TC) well above room temperature.07/2007; -
Article: Structural and magnetic properties of (In1−xFex)2O3 (0.0<x<0.25) system: Prepared by gel combustion method
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ABSTRACT: (In1−xFex)2O3 polycrystalline samples with x=(0.0, 0.05, 0.10, 0.15, 0.20, and 0.25) have been synthesized by a gel combustion method. Reitveld refinement analysis of x-ray diffraction data indicated the formation of single phase cubic bixbyite structure without any parasitic phases. This observation is further confirmed by high resolution transmission electron microscopy imaging, indexing of the selected-area electron diffraction patterns, x-ray absorption spectroscopy, and Raman Spectroscopy. dc magnetization studies as a function of temperature and field indicate that they are ferromagnetic with Curie temperature (TC) well above room temperature.Applied Physics Letters 07/2007; 91:052504. · 3.84 Impact Factor -
Article: Magnetic behavior of manganese-doped ZnSe quantum dots
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ABSTRACT: Magnetic properties of manganese-doped ZnSe quantum dots with the size of approximately 3.6 nm are investigated. The amount of Mn in the ZnSe quantum dots has been varied from 0.10% to 1.33%. The doping level in the quantum dots is much less than that used in the precursor. The co-ordination of Mn in the ZnSe lattice has been determined by electron paramagnetic resonance (EPR). Two different hyperfine couplings 67.3×10−4 and 60.9×10−4 cm−1 observed in the EPR spectrum imply that Mn atoms occupy two distinct sites; one uncoordinated (near the surface) and other having a cubic symmetric environment (nanocrystal core), respectively. Photoluminescence measurements also confirm the incorporation of Mn in ZnSe quantum dots. From the Curie-Weiss behavior of the susceptibility, the effective Mn-Mn antiferromagnetic exchange constant (J1) has been evaluated. The spin-glass behavior is observed in 1.33% Mn-doped ZnSe quantum dots, at low temperature. Magnetic behavior at a low temperature is discussed.Journal of Applied Physics 05/2007; 101(10):103906-103906-5. · 2.17 Impact Factor -
Article: Structural and magnetic properties of (In1−xFex)2O3 (0.0<x<0.25) system: Prepared by gel combustion method
Appl. Phys. Lett. 01/2007; 91:052504. -
Article: Significant enhancement of room temperature ferromagnetism in surfactant coated polycrystalline Mn doped ZnO particles
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ABSTRACT: We report a surfactant assisted synthesis of Mn doped ZnO polycrystalline samples showing robust room temperature ferromagnetism as characterized by X-ray diffraction analysis, Transmission Electron Microscopy, Electron Paramagnetic Resonance and DC magnetization mearurements. This surfactant assisted synthesis method, developed by us, is found to be highly reproducible. Further, it can also be extended to the synthesis of other transition metal doped ZnO.10/2006; -
Article: Magnetic properties of Hydrogenated Li and Co doped ZnO nanoparticles
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ABSTRACT: The effect of hydrogenation on magnetic properties of Zn0.85Co0.05Li0.10O nanoparticles is presented. It was found that the sample hydrided at room temperature (RT) showed weak ferromagnetism (FM) while that hydrided at 400oC showed robust ferromagnetism at room temperature. In both cases reheating the sample at 400oC in air converts it back into paramagnetic state (P) completely. The characterization of samples by X-ray and electron diffraction (ED) showed that room temperature ferromagnetism observed in the samples hydrogenated at RT is intrinsic in nature whereas that observed in the samples hydrogenated at 400oC is partly due to the cobalt metal clusters. Comment: 10 pages, 3 figures10/2006; -
Article: Surfactant‐Assisted Synthesis of Co‐ and Li‐Doped ZnO Nanocrystalline Samples Showing Room‐Temperature Ferromagnetism
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ABSTRACT: We have developed a simple, surfactant assisted synthesis route for the preparation, in gram quantities, of Co and Li doped ZnO nanocrystalline samples showing robust room temperature ferromagnetism. Our studies show that RTF is intrinsic to Zn0.85Co0.05Li0.10O and not due to any segregated secondary phases. In addition, it has been shown that the defects play an important role in activating RTF in these oxide systems. This also provide an explanation for the widely varying results observed in the literature. The method can also be extended for the synthesis of other transition metal doped ZnO.Advanced Materials 06/2006; 18(14):1857 - 1860. · 13.88 Impact Factor -
Article: Effect of SDS on the self-assembly behavior of the PEO-PPO-PEO triblock copolymer (EO)20(PO)70(EO)20.
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ABSTRACT: The mixed micellar system comprising the poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide)-based triblock copolymer (EO)(20)(PO)(70)(EO)(20) (P123) and the anionic surfactant sodium dodecyl sulfate (SDS) has been investigated in aqueous media by small-angle neutron scattering (SANS) and viscosity measurements. The aggregation number of the copolymer in the micelles decreases upon addition of SDS, but a simultaneous enhancement in the degree of micellar hydration leads to a significant increase in the micellar volume fraction at a fixed copolymer concentration. This enhancement in the micellar hydration leads to a marked increase in the stability of the micellar gel phase until it is destroyed at very high SDS concentration. Mixed micellar systems with low and intermediate SDS concentrations form the micellar gel phase in much wider temperature and copolymer concentration ranges than the pure copolymer micellar solution. A comparison of the observed results with those for the copolymers (EO)(26)(PO)(40)(EO)(26) (P85) and (EO)(99)(PO)(70)(EO)(99) (F127) suggests that the composition of the copolymers plays a significant role in determining the influence of SDS on the gelation characteristics of the aqueous copolymer solutions. Copolymers with high PO/EO ratios show an enhancement in the stability of the gel phase, whereas copolymers with low PO/EO ratios show a deterioration of the same in the presence of SDS.The Journal of Physical Chemistry B 06/2006; 110(20):9843-9. · 3.70 Impact Factor -
Article: Synthesis of manganese doped ZnO single crystals and their magnetization studies
Journal of Crystal Growth 01/2006; 294(2):432-436. · 1.73 Impact Factor -
Article: Sodium chloride and ethanol induced sphere to rod transition of triblock copolymer micelles.
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ABSTRACT: Dynamic light scattering (DLS), small-angle neutron scattering (SANS), and viscosity studies have been carried out to examine the influence of NaCl and ethanol on the structure of triblock copolymer [(EO)20(PO)70(EO)20] (EO = ethylene oxide; PO = propylene oxide) micelles in aqueous medium. The studies show that while the pure triblock copolymer solutions do not show any significant growth of the micelles on approaching the cloud point, the presence of a small amount of ethanol (5-10%) induces a sphere to rod shape transition of micelles at high temperatures. Interestingly, this ethanol induced sphere to rod transition of micelles can be brought down to room temperature (25 degrees C) with the addition of NaCl. It is also found that NaCl alone cannot induce such sphere to rod transitions and excess ethanol suppresses them by increasing their transition temperature.The Journal of Physical Chemistry B 04/2005; 109(12):5653-8. · 3.70 Impact Factor -
Article: On the Presence of Cu1+ in the Superconducting (Hg,M)Sr2CuO4+δ; M = Cr, Mo, or Re
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ABSTRACT: The Cu K-edge measurements on the optimum T c 1201 compounds (Hg1–x M x )Sr2CuO4+ (M = Cr, Mo, or Re; 0.10 x 0.30) show besides Cu2+ (predominant) a very weak but distinct signature of Cu1+, only in the superconducting (SC) samples. The Cu1+ feature is conspicuously absent when these compositions are non-superconducting because of different processing conditions. Our finding of monovalent Cu in SC (Hg,M)/Sr-1201 favors the presence of Cu at the Hg-site and this seems to facilitate superconductivity in these cuprates.Journal of Superconductivity 01/2003; 16(3):581-584. -
Article: Magnetization Study of (Hg,Cr)Sr2CuO4 + δ Superconductor
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ABSTRACT: (Hg,Cr)-Sr-1201 type superconductor of nominal composition Hg0.7Cr0.3Sr2CuO4 + was synthesized by the sealed quartz-tube method. X-ray diffraction analysis of the sample showed it has tetragonal symmetry with lattice parameters a = 3.841(1) , and c = 8.664(3) . The as-prepared sample is superconducting at 60 K as shown by dc-magnetization and dc-resistivity measurements. The irreversibility line (IL) obtained from the merging point of the zero-field-cooled and the field-cooled magnetization measurements at several applied fields was found to obey the equation H = A(1 – T/T c) n and gave a value of 2.55 for the exponent n. Using magnetic hysteresis loops the critical current density of superconducting (Hg,Cr)-Sr-1201 was estimated. The irreversibility line and magnetic hysteresis showed reduced pinning properties of (Hg,Cr)-Sr-1201 as compared to HgBa2CuO4 + .Journal of Superconductivity 07/2001; 14(4):519-523. -
Article: Annealing Effects in (Hg,Cr)Sr2CuO4+δ: Transport and X-Ray Absorption Studies
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ABSTRACT: Superconducting (Hg1–x Cr x )Sr2CuO4+, x 0.36, samples of 1201-type, synthesized in partial vacuum, show T c onset of 58 K, T c (R = 0) 52 K. It is found that T c is not affected by the subsequent Ar or O2 annealing treatment. Remarkably, the annealed samples show significant improvement in the diamagnetic signal. Hg L3-edge measurements on 1201 samples show divalent state of mercury. The Cu K-edge spectra for the samples, after taking due account of the impurity phases, show noticeable modifications in the split main peak features on Ar or O2 annealing, suggesting changes in the crystal field asymmetry. In the superconducting (SC) samples, a weak but distinct signature of Cu1+ is seen. The Cu1+ feature is absent in all the non-SC 1201 samples as well as in the impurity phase SrCuO2 and Sr2CuO3 samples. An attempt is made to explain the observed Cu1+ feature in SC (Hg,Cr)-1201 in the light of the available reports.Journal of Superconductivity 05/2001; 14(3):429-435. -
Article: Comment on `The metal-insulator transition and ferromagnetism in the electron-doped layered manganates La2.3-xYxCa0.7Mn2O7 (x = 0.0,0.3,0.5)'
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ABSTRACT: We show that the report of Raychaudhuri et al (1998 J. Phys.: Condens. Matter 10 L191), that the samples of nominal compositions La2.3-xYxCa0.7Mn2O7 (x = 0.0,0.3,0.5) are electron doped layered manganates, is incorrect. Rietveld profile refinement of the x-ray diffraction data of the sample La2.3Ca0.7Mn2O7 (x = 0.0) synthesized by us following the same synthesis process as reported by Raychaudhuri et al clearly shows that it forms a multiphase mixture comprising hole doped perovskite manganates and lanthanum oxide.Journal of Physics Condensed Matter 04/2001; 13(16):3805. · 2.55 Impact Factor -
Article: Electrical resistivity and the magnetic phase transitions of CrMn alloys
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ABSTRACT: Electrical resistivity data, as a function of temperature, are presented for dilute CrMn alloys containing 0.1, 0.2, 0.3 and 0.8 at.% Mn. The results are discussed in terms of the magnetic transitions occurring at the different phase boundaries of the magnetic phase diagram of the Cr-Mn system. It is argued that the triple point should occur at a Mn concentration a little above 0.30 at.% with a positive slope for the paramagnetic-incommensurate antiferromagnetic phase boundary.Journal of Physics F Metal Physics 11/2000; 14(4):923.
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Institutions
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1987–2012
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Bhabha Atomic Research Centre
- • Chemistry Division
- • Solid State Physics Division
Mumbai, State of Maharashtra, India
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