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Jitendra Kumar

Bio: Jitendra Kumar is an academic researcher from Indian Institutes of Technology. The author has contributed to research in topics: Thin film & Medicine. The author has an hindex of 37, co-authored 533 publications receiving 6363 citations. Previous affiliations of Jitendra Kumar include Indian Institute of Technology Dhanbad & Dongguk University.


Papers
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TL;DR: In this paper, a comparative study of the magnetic and electron paramagnetic resonance (EPR) parameters of bulk and Co3O4 nanoparticles (NP), synthesized by a sol-gel process, is presented.
Abstract: A comparative study of the magnetic and electron paramagnetic resonance (EPR) parameters of bulk and Co3O4 nanoparticles (NP), synthesized by a sol–gel process, is presented. Both samples possess the cubic phase with a slightly lower (by 0.34%) lattice parameter for the Co3O4 NP. The average crystallite size D = 17 nm determined by x-ray diffraction (XRD) for the Co3O4 NP is quite consistent with the electron microscopic observations. The bulk Co3O4 has particle size in the 1–2 µm range. A Neel temperature of TN = 30 K (lower than the 40 K usually quoted in the literature) is determined from the analysis of the magnetic susceptibility versus temperature data for bulk Co3O4. This TN = 30 K is in excellent agreement with the TN = 29.92 K reported from specific heat measurements. The Co3O4 NP powder exhibits a still lower TN = 26 K, possibly due to the associated finite size effects. The values of coercivity, Hc = 250 Oe, and exchange bias, He = −350 Oe, together with the training effect have been observed in the Co3O4 NP sample (cooled in 20 kOe). Both Hc and He approach zero as . For T>TN, the χ versus T data for both samples fit the modified Curie–Weiss law (χ = χ0+C/(T+θ)). The magnitudes of C, θ and TN are used to determine the following: exchange constants J1ex = 11.7 K, J2ex = 2.3 K, and magnetic moment per Co2+ ion μ = 4.27 μB for bulk Co3O4; and J1ex = 11.5 K, J2ex = 2.3 K and μ = 4.09 μB for Co3O4 NP. EPR yields a single Lorentzian line near g = 2.18 in both samples but with a linewidth ΔH that is larger for the Co3O4 NP. Details of the temperature dependence of ΔH, line intensity I0, and disappearance of the EPR on approach to TN are different for the two samples. These effects are discussed in terms of spin–phonon interaction and additional surface anisotropy present in Co3O4 NP.

204 citations

Journal ArticleDOI
TL;DR: In this paper, current-voltage characteristics of Pd2Si/p-Si(111) Schottky barrier diodes studied over a wide temperature range (60-201 K) are shown to follow a thermionic emission-diffusion mechanism under both the forward and reverse bias conditions.
Abstract: Current-voltage characteristics of Pd2Si/p-Si(111) Schottky barrier diodes studied over a wide temperature range (60-201 K) are shown to follow a thermionic emission-diffusion mechanism under both the forward and the reverse bias conditions. The barrier parameters as evaluated from the forward I-V data reveal a decrease of zero-bias barrier height ( phi b0) but an increase of ideality factor ( eta ) and series resistance (Rs) with decrease in temperature. Moreover, the changes in phi b0, eta and Rs become quite significant below ~100 K. An In(Is/T2) versus 1/T plot is found to fit well with two straight lines in different temperatures regimes giving an activation energy of 0.33 eV (201-107 K) and 0.24 eV (below 107 K) and an effective Richardson constant of 33 A cm-2 K-2. However, the activation energy of 0.33 eV corresponds to the zero-bias barrier height at absolute zero. An In(Isf/T2) versus 1/ eta T plot is suggested to obtain the flat-band barrier height and the effective Richardson constant; the corresponding values obtained are 0.401 eV and 32.2 A cm-2 K-2 respectively. It is shown that the `T0 effect` cannot account for the apparent increase in ideality factor and decrease of barrier height at low temperatures. Finally, the decrease of barrier height with voltage under the reverse bias condition is attributed mainly to interfacial layer effects with a small contribution due to image force lowering.

195 citations

Journal ArticleDOI
TL;DR: In this paper, the core-shell description for NiO nanoparticles was investigated and it was shown that the shell contains randomly oriented spins with low co-ordination and are possibly responsible for sharp increase in M ZFC below 30 K as a result of collective freezing effect.

162 citations

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TL;DR: Magnesium oxide (MgO) nano-size powder is synthesized using magnesium nitrate hexahydrate and oxalic acid as precursors with ethanol as a solvent as mentioned in this paper.

161 citations

Journal ArticleDOI
TL;DR: In this paper, the influence of incorporation of microfilament type polypropylene fibres into low strength recycled aggregate concrete on the basis of number of parameters such as compressive strength, split tensile strength, flexural strength, modulus of elasticity and non-destructive parameters was examined.

140 citations


Cited by
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Journal Article
TL;DR: This book by a teacher of statistics (as well as a consultant for "experimenters") is a comprehensive study of the philosophical background for the statistical design of experiment.
Abstract: THE DESIGN AND ANALYSIS OF EXPERIMENTS. By Oscar Kempthorne. New York, John Wiley and Sons, Inc., 1952. 631 pp. $8.50. This book by a teacher of statistics (as well as a consultant for \"experimenters\") is a comprehensive study of the philosophical background for the statistical design of experiment. It is necessary to have some facility with algebraic notation and manipulation to be able to use the volume intelligently. The problems are presented from the theoretical point of view, without such practical examples as would be helpful for those not acquainted with mathematics. The mathematical justification for the techniques is given. As a somewhat advanced treatment of the design and analysis of experiments, this volume will be interesting and helpful for many who approach statistics theoretically as well as practically. With emphasis on the \"why,\" and with description given broadly, the author relates the subject matter to the general theory of statistics and to the general problem of experimental inference. MARGARET J. ROBERTSON

13,333 citations

Journal ArticleDOI
Imran Ali1

1,531 citations

Journal ArticleDOI
05 Apr 2013-Science
TL;DR: It is demonstrated that a low-temperature process, photochemical metal-organic deposition, can produce amorphous (mixed) metal oxide films for OER catalysis, which contain a homogeneous distribution of metals with compositions that can be accurately controlled.
Abstract: Large-scale electrolysis of water for hydrogen generation requires better catalysts to lower the kinetic barriers associated with the oxygen evolution reaction (OER). Although most OER catalysts are based on crystalline mixed-metal oxides, high activities can also be achieved with amorphous phases. Methods for producing amorphous materials, however, are not typically amenable to mixed-metal compositions. We demonstrate that a low-temperature process, photochemical metal-organic deposition, can produce amorphous (mixed) metal oxide films for OER catalysis. The films contain a homogeneous distribution of metals with compositions that can be accurately controlled. The catalytic properties of amorphous iron oxide prepared with this technique are superior to those of hematite, whereas the catalytic properties of a-Fe100-y-zCoyNizOx are comparable to those of noble metal oxide catalysts currently used in commercial electrolyzers.

1,258 citations

Journal Article
TL;DR: This work shows that the spectral distribution and time-dependent decay of light emitted from excitons confined in the quantum dots are controlled by the host photonic crystal, providing a basis for all-solid-state dynamic control of optical quantum systems.
Abstract: Control of spontaneously emitted light lies at the heart of quantum optics. It is essential for diverse applications ranging from miniature lasers and light-emitting diodes, to single-photon sources for quantum information, and to solar energy harvesting. To explore such new quantum optics applications, a suitably tailored dielectric environment is required in which the vacuum fluctuations that control spontaneous emission can be manipulated. Photonic crystals provide such an environment: they strongly modify the vacuum fluctuations, causing the decay of emitted light to be accelerated or slowed down, to reveal unusual statistics, or to be completely inhibited in the ideal case of a photonic bandgap. Here we study spontaneous emission from semiconductor quantum dots embedded in inverse opal photonic crystals. We show that the spectral distribution and time-dependent decay of light emitted from excitons confined in the quantum dots are controlled by the host photonic crystal. Modified emission is observed over large frequency bandwidths of 10%, orders of magnitude larger than reported for resonant optical microcavities. Both inhibited and enhanced decay rates are observed depending on the optical emission frequency, and they are controlled by the crystals’ lattice parameter. Our experimental results provide a basis for all-solid-state dynamic control of optical quantum systems.

1,019 citations