Department of Physics

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The investigation addresses the bilayer meltspun ribbons in which the positively magnetostrictive layer Fe 77.5Si 7.5B 15 is toward the free surface, while the negatively magnetostrictive layer of Co 72.5Si 12.5B 15 forms the one in contact with the quench wheel. Scanning electron microscopy (SEM) elemental scan showed drastic changes in concentration profiles of Co, Fe and Si across the bilayer, indicating the efficacy of rapid quenching by melt spinning. Crystallization onsets, saturation magnetization and dilatation studies of the single-layered alloys distinctly reflected the properties of the bilayered ribbons. The thermal variation of coercivity below crystallization onset in the case of a bilayer revealed a softening mechanism due to reduction of stresses. Ribbon deflection studies showed interesting results. © Springer Science+Business Media, LLC 2010.

World University root node

Journal of Superconductivity and Novel Magnetism

Development of FeSiB/CoSiB bilayered melt-spun ribbon melt-spinning technique

We have fabricated a unique memristive device by molecular engineering and demonstrated that the leakage current tuning in the device is 100 times more efficient than that in a standard device. Molecular analogs of the memristive matrices used here are an electrochemically active conjugated Co(III) polymer (CP) and a nonconjugated Co(III) polymer (NCP), which have been synthesized in good yield and characterized by 1H NMR spectroscopy. Redox switching of an organic-metallic hybrid polymer generates bistable states with a large ON/OFF ratio that supports random flip-flops for several hours. Thus, we provide a synthetic solution to leakage current restriction, one of the fundamental problems faced when fabricating state-of-the-art electronic devices. © 2011 American Chemical Society.

Journal of the American Chemical Society

Tuning of nonvolatile bipolar memristive switching in Co(III) polymer with an extended Azo aromatic ligand

We present a new form of a Parrondo game using discrete-time quantum walk on a line. The two players A and B with different quantum coins operators, individually losing the game can develop a strategy to emerge as joint winners by using their coins alternatively, or in combination for each step of the quantum walk evolution. We also present a strategy for a player A (B) to have a winning probability more than player B (A). Significance of the game strategy in information theory and physical applications are also discussed. © 2011 Elsevier B.V. All rights reserved.

Fulltext

Physics Letters, Section A: General, Atomic and Solid State Physics

Parrondos game using a discrete-time quantum walk

Noisy quantum walks are studied from the perspective of comparing their quantumness as defined by two popular measures, measurement-induced disturbance (MID) and quantum discord (QD). While the former has an operational definition, unlike the latter, it also tends to overestimate nonclassicality because of a lack of optimization over local measurements. Applied to quantum walks, we find that MID, while acting as a loose upper bound on QD, still tends to reflect correctly trends in the behavior of the latter. However, there are regimes where its behavior is not indicative of nonclassicality: in particular, we find an instance where MID increases with the application of noise, where we expect a reduction of quantumness. © 2011 American Physical Society.

Physical Review A - Atomic, Molecular, and Optical Physics

Quantumness of noisy quantum walks: A comparison between measurement-induced disturbance and quantum discord

We study the early stage kinetics of thermodynamically unstable systems with quenched disorder. We show analytically that the growth of initial fluctuations is amplified by the presence of disorder. This is confirmed by numerical simulations of morphological phase separation in thin liquid films and spinodal decomposition in binary mixtures. We also discuss the experimental implications of our results. © 2011 American Chemical Society.

Journal of Physical Chemistry B

Amplification of fluctuations in unstable systems with disorder

The investigation addresses low temperature magnetization behavior in Co36Fe36Si3Al1Nb4B 20 alloy ribbons in their as-spun as well as annealed state. Optimum heat treatment at 875 K led to nanocrystallization whereby bcc-(FeCo)SiAl nanoparticles were dispersed in an amorphous matrix as evidenced from transmission electron microscopy. Low temperature magnetization studies were carried out in the range 77300 K. Using the method of mathematical fittings, magnetization extrapolated to 0 K was obtained. The dependence of the magnetization with respect to temperature of BT3/2 was used to determine the Bloch coefficient "B" and spin wave stiffness constant "D". Magnetic softening revealed by lowering in the coercivity in the optimum nanostructured state was also the cause of a drop in the stiffness constant. The range of exchange interaction given by D/TC was higher in the nanostructured state compared to the as-spun amorphous state. The effect of nanocrystallization and the resulting ferromagnetic coupling was further evidenced by low temperature magnetization studies. © 2010 Elsevier B.V. © 2010 Elsevier B.V. All rights reserved.

Journal of Magnetism and Magnetic Materials

Low temperature magnetization behavior in Co36Fe 36Si3Al1Nb4B20 (at%) nanostructured alloy

Series of single-phase Ni1-xZnxFe2O4 (x=0.20, 0.35, 0.50 and 0.60) nanopowders with average particle size of ∼35nm have been synthesized by using oxalate based precursor method. Precursor powders were synthesized by reacting aqueous solutions of metal nitrates and oxalic acid by using different total metal ions: oxalic acid molar ratios and then evaporating them to dryness. Pure, single-phase Ni-Zn ferrite nanopowder was formed by calcining the precursor with total metal ion: oxalic acid ratio of 1:0.125 at a temperature of 850°C. The synthesized nanopowders were characterized by using X-ray diffraction, Thermo-gravimetric and Differential Scanning Calorimetric analysis, Transmission Electron Microscope and Scanning Electron Microscope. Room temperature DC resistivity of the nanopowders was measured with respect to temperature by the two-probe method and was of the order of ∼107Ωcm. Room temperature saturation magnetization was measured by using Vibrating Sample Magnetometer and it varied between 34-49emu/g depending on the composition. This aqueous solution based method provides a simple and cost-effective route to synthesize single phase, Ni-Zn ferrite nanopowders. © 2010 Elsevier B.V.

Powder Technology

Synthesis and characterization of pure single phase Ni-Zn ferrite nanopowders by oxalate based precursor method

Pure and (0.5-3 at%) vanadium doped TiO2 nanoparticles have been synthesized by wet chemical method. The as synthesized materials have been characterized by using XRD, atomic force microscope (AFM), Raman, EPR and UV-vis spectroscopy techniques. From XRD studies, both pure as well as vanadium doped TiO2 have been found to show pure anatase phase. The value of lattice constant c is smaller in doped TiO2 as compared to undoped and has been found to decrease with increase in vanadium concentration. AFM studies show formation of spherical particles with particle size ∼23 nm in all the samples. Photochromic behavior of these materials has been studied by making their films in alkyd resin. Vanadium doped TiO2 films show reversible change in color from beige-yellow to brownish violet on exposure to UV light. The mechanism of coloration and bleaching process has been discussed. © 2009 Elsevier B.V. All rights reserved.

Journal of Photochemistry and Photobiology A: Chemistry

Synthesis and studies on photochromic properties of vanadium doped TiO2 nanoparticles

Water-quenched modified 9Cr-1Mo steel was creep tested in the laboratory at a temperature of 600 °C and 125 MPa stress. Magnetic Barkhausen emissions (MBE) measurements were carried out by interrupting the test at different lengths of time. Creep damage in such steel was observed by an increase in root mean square (RMS) voltage of the MBE. The magnetic softening was corroborated with the decrease in pinning density in the material for the coarsening of carbides (M23C6) and formation of massive phases (Fe 2Mo), which comes at the expense of a large number of finer carbides. Before failure, the rate of increase in RMS voltage of the MBE decreased due to the demagnetizing field offered by the massive phases. The microstructural analysis was carried out using scanning electron microscopy (SEM) and transmission electron microscopy (TEM) study. © 2010 The Minerals, Metals &amp; Materials Society and ASM International.

Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science

Magnetic nondestructive evaluation of creep behavior in water-quenched modified 9Cr-1Mo steel

A texture analysis is performed by means of the electron-backscatter diffraction technique (EBSD) on melt-spun ribbon-like samples of the composition Ni52.5Mn24.5Ga23 (at.-%) were prepared. A dedicated surface treatment is required in order to achieve high quality Kikuchi patterns. For this purpose, mechanical polishing plus ion polishing was employed. EBSD analysis and transmission electron microscopy revealed that the samples have a polycrystalline, granular morphology, with grain sizes around 1 - 2 μm. Several larger grains being present in the region selected for EBSD analysis, and many small grains are found, even embedded in the larger ones. The larger grains exhibit a common direction of elongation, yielding to a specific texture. © 2010 IOP Publishing Ltd.