Department of Physics

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A precursor based method has been developed for the synthesis of nanostructured, single phase Ni-Zn ferrite powders (Ni1-xZn xFe2O4 with x50.20, 0.35, 0.50 and 0.60). Precursor powders were synthesised by reacting aqueous solutions of metal nitrates and ethylene diamine tetraacetic acid and then evaporating them to dryness. The precursors were calcined in air for 2.30 h at different temperatures ranging from 250 to 450°C. The powders synthesised in this manner were characterised by using X-ray diffraction, thermogravimetric differential scanning calorimetric analysis, Brunauer-Emmett-Teller surface area measurement and SEM. Magnetic characterisation was performed by using a vibrating sample magnetometer. The method provides a simple and cost effective route to produce single phase, Ni-Zn ferrite nanopowders, with average crystallite size of ∼25 nm, at comparatively low temperature. © 2009 W. S. Maney &amp; Son Ltd.

World University root node

Materials Technology

Development of simple chemical method for synthesis of single phase Ni-Zn ferrite nanopowders

The significance of beam's phase front in light localization in a disordered medium from application point of view is studied. The results show the advantage of plane phase front irrespective of the input beam profile. © 2009 IEEE.

2009 14th OptoElectronics and Communications Conference, OECC 2009

Effect of phase front curvature on transverse localization of a light beam

We estimate the CP asymmetry ACP(q2) in the decays B→Xsμ+μ- and B→Xdμ+μ- in the standard model (SM) with an additional fourth generation. We use a parametrization that allows us to explore the complete parameter space of the 4×4 quark mixing matrix, and constrain these parameters from the current data on B decays. We find that the enhancement in ACP(q2) depends strongly on the mass of the t′, the up-type quark in the fourth generation. For mt′ around 400 GeV, the CP asymmetry in the high-q2 region (q2>14.4GeV2) can be enhanced by more than an order of magnitude for B→Xsμ+μ- and up to a factor of 6 for B→Xdμ+μ-. There is no enhancement in the low-q2 region (1<q2<6GeV2). With increasing mt′, ACP(q2) in the high-q2 (low-q2) region first decreases (increases) and then saturates at a value a few times the SM prediction. In the high-q2 region of B→Xsμ+μ-, this saturation value may be up to 25 times the SM expectation. © 2009 The American Physical Society.

Fulltext

Physical Review D - Particles, Fields, Gravitation and Cosmology

CP asymmetry in the decays B→(Xs,Xd)μ+μ- with four generations

We study the bulk viscosity of neutron star matter including Λ hyperons in the presence of quantizing magnetic fields. Relaxation time and bulk viscosity due to both the nonleptonic weak process involving Λ hyperons and direct Urca processes are calculated here. In the presence of a strong magnetic field of 1017G, the hyperon bulk viscosity coefficient is reduced, whereas bulk viscosity coefficients due to direct Urca processes are enhanced compared with their field free cases when many Landau levels are populated by protons, electrons, and muons. © 2009 The American Physical Society.

Hyperon bulk viscosity in strong magnetic fields

We have investigated the effects of UV irradiation on the electrical and optical properties of polycrystalline In2 O3 films. We found that UV illumination at a peak wavelength of 365 nm leads to a sharp drop in resistance and increase in carrier concentration. This highly conductive state persists for a timescale of hours in air at room temperature after illumination. We observe distinct changes in the optical absorption spectra and the associated change in carrier concentration, which is consistent with a Burstein-Moss shift of ∼0.1 eV. The relaxation rate of this persistent conducting state depends strongly on temperature. We find that the conductance relaxation in an oxygen-free environment can be described by a stretched exponential while the behavior of the samples in air is better described by a logarithmic relaxation, both of which may be associated with glassy behavior. © 2009 American Institute of Physics.

Applied Physics Letters

Robust room temperature persistent photoconductivity in polycrystalline indium oxide films

We have fabricated InN thin films using rf magnetron sputtering from an indium (In) metal target. Optical and electrical measurements show that these as-grown films are n -type with carrier concentrations ranging from 10 20 to 1021 cm-3. This variation in carrier density is produced by controlling the conditions during the deposition. We used Rutherford backscattering spectrometry to identify possible sources for n -type carriers. We found that in addition to strong direct bandgap optical absorption ranging from 1.4 to 2.0 eV, a large plasmon absorption peak in the infrared region (0.45-0.8 eV) is also observed. This tunable IR absorption suggests that these highly degenerate InN films could be used for a number of applications, including optical filters and infrared devices. © 2009 American Institute of Physics.

Journal of Applied Physics

Strong plasmon absorption in InN thin films

This investigation addresses the effect of nanocrystallization on ferromagnetic ordering in a series of (Fe72-XCox)Si 4B20Nb4, (X = 10, 20, 36, 50 at%) alloy ribbons prepared by the melt-spinning technique. Partial substitution of Fe by Co throughout this series affected the primary and secondary crystallization onsets observed from differential scanning calorimetry and the consequent generation of bcc-FeCo and (CoFe)3B, respectively, as observed from x-ray diffractometry. The reduction in the size of nanoparticles with increasing cobalt content was observed from transmission electron microscopy. At an elevated temperature, the alloy with X = 36 at% was found to reveal superior soft magnetic properties compared with other alloys. In the nanostructured state, this alloy also showed enhanced ferromagnetic ordering and low power losses exhibited its scope as a material for high temperature soft magnetic application. © 2009 IOP Publishing Ltd.

Journal of Physics D: Applied Physics

Enhanced ferromagnetic ordering through nanocrystallization in cobalt incorporated FeSiBNb alloys

The investigation addresses the effect of magnetizing field on the magnetic properties of melt spun Ni52.84Mn19.6Ga27.56 (at%) alloy ribbons. Magnetization behaviour at different fields was observed using a superconducting quantum interference device magnetometer for heating and cooling cycles. The plots showed distinct changes in magnetization around the characteristic temperatures at austenitic start and finish (AS, AF), martensitic start and finish (MS, MF). With increasing field AS, MF were unaffected. In the range of martensitic start and its finish temperature, the zero field cooled and field cooled measurements indicated magnetization drops indicating antiferromagnetic interactions, which is characteristic of the martensitic phase formation. It was shown from x-ray diffraction analysis that the low martensitic fraction in the majority austenite phase induced the splitting in the L21 austenitic ordering. This was further corroborated by the evidence of a few martensitic plates around grain boundaries at room temperature which is close to martensitic start temperature. © 2009 IOP Publishing Ltd.

Effect of magnetizing field on the martensitic transformations in a melt spun NiMnGa alloy

When pulled along the axis, double-strand DNA undergoes a large conformational change and elongates by roughly twice its initial contour length at a pulling force of about 70pN. The transition to this highly overstretched form of DNA is very cooperative. Applying a force perpendicular to the DNA axis (unzipping), double-strand DNA can also be separated into two single-stranded DNA, this being a fundamental process in DNA replication. We study the DNA overstretching and unzipping transition using fully atomistic molecular dynamics (MD) simulations and argue that the conformational changes of double-strand DNA associated with either of the above mentioned processes can be viewed as force induced DNA melting. As the force at one end of the DNA is increased the DNA starts melting abruptly/smoothly above a critical force depending on the pulling direction. The critical force fm, at which DNA melts completely decreases as the temperature of the system is increased. The melting force in the case of unzipping is smaller compared to the melting force when the DNA is pulled along the helical axis. In the case of melting through unzipping, the double-strand separation has jumps which correspond to the different energy minima arising due to sequence of different base pairs. The fraction of Watson-Crick base pair hydrogen bond breaking as a function of force does not show smooth and continuous behavior and consists of plateaus followed by sharp jumps. © 2009 IOP Publishing Ltd.

Journal of Physics Condensed Matter

Force induced DNA melting

A single step method was developed for the preparation of graphene oxide/Fe2O3 composites by exfoliation of graphite oxide with an oxygen-rich ferric acetyl acetonate complex. The synthesized materials were characterized by Fourier transform infrared spectroscopy, X-ray diffraction, vibrating sample magnetometry, atomic force microscopy, and low temperature dc conductivity measurements. After exfoliation, the Fourier transform infrared studies reveal the decomposition of epoxy groups and the simultaneous formation of composites of iron oxide particles within the graphene oxide. Atomic force microscopy reveals the formation of an ~5nm thick graphene oxide stack with layered morphology. The layered morphology of graphene oxide degrades at higher concentrations of iron oxide. The vibrating sample magnetometer studies show ferromagnetic behavior of all composites in the range of 0.13-5.5emu/g at room temperature. The conductivity of these composites is found to be governed by a quasi 1D hopping mechanism.