Department of Physics

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IIT Jodhpur

We have studied the precessional dynamics of Co/Cu/Py (where Py Ni 81Fe19) trilayers by time-resolved x-ray resonant magnetic scattering at the synchrotron radiation facility BESSY II. We have found that the magnetic precessional decay time of Fe magnetic moments in Py layers decreases when changing the mutual orientation of the magnetization direction of Py and Co layers from parallel to antiparallel. The observed changes of the decay time can be associated with the spin pumping induced damping effect. © 2011 American Institute of Physics.

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Applied Physics Letters

Precessional dynamics and damping in Co/Cu/Py spin valves

In this paper, the crystallization behaviour of amorphous Cu56Zr7Ti37alloy using thermal electrical resistivity (TER) and differential scanning calorimetry (DSC) studies has been described. Isochronal TER and DSC measurements indicate that crystallization occurs in two stages. Isothermal crystallization studies of the alloy by TER show that the kinetics conforms to Johnson-Mehl-Avrami model. Avrami exponents derived from kinetics, between 1.1 and 1.2, imply that the crystallization processes are diffusion controlled with near zero nucleation. Activation energy has been found to increase with the transformed volume fraction. A plausible explanation has been presented by separating the contributions due to nucleation and crystal growth towards total activation energy. © 2011 The Chinese Society for Metals.

Journal of Materials Science and Technology

Crystallization Study of Cu56Zr7Ti37 Metallic Glass by Electrical Resistivity Measurement

Optics Communications

Erratum: Localization of light in evanescently coupled disordered waveguide lattices: Dependence on the input beam profile (Optics Communications (2010) 284 (201-206) (DOI: 10.1016/j.optcom.2010.09.032)

In this paper a Xenon filled coaxial dielectric barrier discharge (DBD) has been studied to understand the high pressure, non-equilibrium, nonthermal plasma discharge. A quartz coaxial DBD tube (ID: 6mm, OD: 12 mm) at 400 mbar Xenon filled pressure has been used in the experiment. Different applied voltage waveforms at 30 kHz using RF generator as well as pulse power source have been applied to the discharge electrodes for the generation of microdischarges. Visual images of discharge and electrical waveform confirm the diffused type discharges. The knowledge obtained by dynamic processes of DBDs in the discharge gap explains quantitatively the mechanism that is obtained in ignition, development and extinction of DBDs. The behaviour of different discharge parameters has also been analyzed. From the experimental results and equivalent electrical circuit, the dynamic nature of equivalent capacitance has been reported. The relative intensity analysis of the second continuum of the Xe discharge (172 nm) has been carried out for different applied voltages and it is found that the radiation power has increased with voltage. © 2011 IEEE.

2011 IEEE International Vacuum Electronics Conference, IVEC-2011

Investigation of discharge parameters in Xenon filled coaxial DBD tube

In this paper, a xenon-filled coaxial dielectric barrier discharge (DBD) has been studied to understand the high-pressure nonequilibrium nonthermal plasma discharge. A quartz coaxial DBD tube (ID: 6 mm, OD: 12 mm) at 400-mbar xenon-filled pressure has been used in the experiment. A unipolar pulselike voltage up to a -6-kV peak working at 30 kHz has been applied to the discharge electrodes for the generation of microdischarges. A single discharge is observed per applied voltage pulse. Visual images of the discharge and electrical waveform confirm the diffused-type discharges. The knowledge obtained by dynamic processes of DBDs in the discharge gap explains quantitatively the mechanism that is obtained in the ignition, development, and extinction of DBDs. The behavior of different discharge parameters has also been analyzed. From the experimental results and equivalent electrical circuit, the dynamic nature of equivalent capacitance has been reported. The relative intensity analysis of the Xe peak in the optical emission spectra (172 nm) has also been carried out for different supplied powers, and it is found that the radiation power has increased with supplied power. © 2011 IEEE.

IEEE Transactions on Plasma Science

Analysis of discharge parameters in xenon-filled coaxial DBD tube

We report about a combined structural and magnetometric characterization of self-assembled magnetic nanoparticle arrays. Monodisperse iron oxide nanoparticles with a diameter of 20nm were synthesized by thermal decomposition. The nanoparticle suspension was spin-coated on Si substrates to achieve self-organized arrays of particles and subsequently annealed at various conditions. The samples were characterized by x-ray diffraction, and bright and dark field high resolution transmission electron microscopy. The structural analysis is compared to magnetization measurements obtained by superconducting quantum interference device magnetometry. We can identify either multi-phase FexO/γ-Fe2O3 or multi-phase Fe xO/Fe3O4 nanoparticles. The Fe xO/γ-Fe2O3 system shows a pronounced exchange bias effect which explains the peculiar magnetization data found for this system. © 2011 IOP Publishing Ltd.

Journal of Physics Condensed Matter

Structural and magnetic characterization of self-assembled iron oxide nanoparticle arrays

The nonlinear optical (NLO) and optical limiting (OL) properties of covalently linked graphene-porphyrin composite materials were investigated using Z-scan technique in nanosecond regime. We observed enhanced NLO and OL properties of graphene-porphyrin composites in comparison to the individual graphene and porphyrins. The improved OL property of composites is attributed to energy transfer between porphyrin and graphene, which improved excited state absorption and nonlinear scattering. Nonlinear optical susceptibilities X(3) of graphene and graphene-porphyrin composites were, in the order of 10 -12 esu, measured using degenerate four wave mixing technique in nanosecond regime. High values of excited state absorption and two-photon absorption were observed for the composites. © 2011 American Institute of Physics.

Nonlinear optical properties of covalently linked graphene-metal porphyrin composite materials

An all-solid LMA Bragg fibre (mode area exceeding 1100μm2) is presented for midinfrared applications, based on a new design strategy that induces large differential loss between fundamental and higher order modes for effective single-mode operation. © OSA/OFC/NFOEC 2011.

Optics InfoBase Conference Papers

Soft glass based large mode area photonic bandgap fibre for mid-infrared applications

We investigate how the transverse localization of light in evanescently coupled, disordered, lossless waveguide lattices depends on the shape and size of an input beam. Our detailed numerical study not only reveals waveguide-like propagation of the localized state inside such a disordered discrete medium but also shows that a specific localized state is independent of the spatial profile of the input beam. Dependence of the localized state on input beam parameters and lattice parameters is also reported. Our results should be of interest for engineering light propagation with discrete diffractive optics in practical optical geometries (e.g., microstructured arrays of optical waveguides, fiber arrays, etc.) and for realizing waveguide-like (without any diffractive spread) propagation even in the presence of structural disorders and refractive index perturbations. © 2010 Elsevier B.V. All rights reserved.

Localization of light in evanescently coupled disordered waveguide lattices: Dependence on the input beam profile

We report direct observation of the signature of transverse localization of light in laser-inscripted disordered array of evanescently coupled one-dimensional optical waveguides in an Er-doped Bismuthate glass. © 2011 Optical Society of America.