Department of Physics

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A series of amorphous iron-cobalt alloys with varying metalloid, boron and silicon contents were studied for their thermal stability and magnetic behaviour. The crystallization temperature and thermal stability increased with the silicon content Good soft magnetic properties were observed for the materials with nominal composition, (Fe0.79Co0.21) 77Si12.2B10.8. The magnetic properties were further improved by annealing. © Indian Academy of Sciences.

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Bulletin of Materials Science

Effect of metalloids on crystallization and magnetic behaviour of FeCoSiB based metallic glass

Meso-scale self-assembly of doped semiconductor nanocrystals leading to the formation of monocrystalline nanorods showing enhanced photo- and electro-luminescence properties are reported. Polycrystalline ZnS: Cu + -Al 3+ nanoparticles of zinc-blended (cubic) structure with an average size of ∼4 nm were aggregated in aqueous solution and grown into nanorods of length ∼400 nm and aspect ratio ∼12. Transmission electron microscope (TEM) images indicate crystal growth mechanisms involving particle-to-particle oriented-attachment assisted by sulphur-sulphur catenation leading to covalent-linkage. The nanorods exhibit self-assembly dependant luminescence properties such as quenching of the lattice defect-related emissions accompanied by enhancement of dopant-related emission, efficient low-voltage electroluminescence (EL) and super-linear voltage-brightness EL characteristics. This study demonstrates the technological importance of aggregation based self-assembly in doped semiconductor nanosystems. © 2005 Elsevier B.V. All rights reserved.

Applied Surface Science

Self-assembly of doped semiconductor nanocrystals leading to the formation of highly luminescent nanorods

ZnO plasma produced by third harmonic 355 nm of Nd:YAG laser at various ambient pressures of oxygen was used for depositing quality nanocrystalline ZnO thin films. Time and space resolved optical emission spectroscopy is used to correlate the plasma properties with that of deposited thin films. The deposited films showed particle size of 8 and 84 nm at ambient oxygen pressure of 100 and 900 mTorr, respectively. Third harmonic generation observed in ZnO thin films deposited under 100 mTorr of ambient oxygen is reported. © 2005 Elsevier B.V. All rights reserved.

Optics Communications

Harmonic generation in ZnO nanocrystalline laser deposited thin films

This is the report of flavor physics and model building working group at WHEPP-9. While activities in flavor physics have been mainly focused on B-physics, those in model building have been primarily devoted to neutrino physics. We present summary of working group discussions carried out during the workshop in the above fields, and also briefly review the progress made in some projects subsequently. © Indian Academy of Sciences.

Pramana - Journal of Physics

Working group report: Flavor physics and model building

It appears that there is a genuine shortage of radio pulsars with surface magnetic fields significantly smaller than ∼10 8 G. We propose that the pulsars with very low magnetic fields are actually strange stars locked in a state of minimum free energy and therefore at a limiting value of the magnetic field which cannot be lowered by the system spontaneously. © 2005 RAS.

Monthly Notices of the Royal Astronomical Society

Strange pulsar hypothesis

The structural and soft magnetic properties of Fe and FeCo-based nanocrystalline alloys have been investigated. These alloys were initially prepared in the form of amorphous ribbons with consistent properties by optimising different melt-spinning parameters. The structural behavior and soft magnetic properties depended on the alloy chemistry. The effect of metalloids in the Fe 73.5Nb 3Cu 1Si 22.5-XB X (X = 5, 9, 10, 11.25 and 19 at %) was studied. X-ray diffractograms showed that formation of a-Fe(Si) and /orFe 3Si nanoparticles were responsible for the superior soft magnetic properties of the alloy with 9 at% Boron. All other alloys (X = 5, 10, 11.25 and 19at%) exhibited early appearance of highly magnetocrystalline anisotropic boride phases leading to deterioration in soft magnetic properties. The role of extra alloying elements Al and Mn in the FeNbCuSiB system was also investigated. The alloy exhibited superior soft magnetic properties with a coercivity value of 0.32A/m (∼ 4mOe) when heat-treated at 790K for 15min. Transmission electron microscopy study showed that this was due to the formation of ∼ 6.0nm sized a-Fe(Si,Al) and /or Fe 3(Si,AI) nanoparticles. However, this alloy has a limitation on its use for high temperature soft magnetic application due to its low Curie temperature in nanocrystalline state. Hence, a new Fe 40Co 40Cu 0.5Al 2Zr 9Si 4B 4.5 alloy system was developed in which the Curie temperature of 736K in amorphous state increased above 1000K on annealing to nanocrystalline state. The saturation magnetization of the annealed alloy was also found to increase due to the formation of nanocrystalline. α-(Fe,Co)(Si,Al) phase with higher magnetization suggesting the suitability of the alloy for high temperature soft magnetic applications.

Transactions of the Indian Institute of Metals

Development of nanocrystalline materials for soft-magnetic applications

Canonical transformations are defined and discussed along with the coherent and the ultracoherent vectors. It is shown that the single-mode and the n-mode squeezing operators are elements of the group of canonical transformations. An application of canonical transformations is made, in the context of open quantum systems, by studying the effect of squeezing of the bath on the decoherence properties of the system. Two cases are analysed. In the first case, the bath consists of a massless bosonic field with the bath reference states being the squeezed vacuum states and squeezed thermal states while in the second case a system consisting of a harmonic oscillator interacting with a bath of harmonic oscillators is analysed with the bath being initially in a squeezed thermal state. © 2005 IOP Publishing Ltd.

Journal of Physics A: Mathematical and General

Applications of canonical transformations

We report investigations of ZnO plasma at various ambient pressures of oxygen produced by third harmonic 355 nm of neodymium: yttrium aluminum garnet laser for depositing quality nanocrystalline ZnO thin films. Time- and space-resolved optical emission spectroscopy is used to correlate the plasma properties with that of the deposited thin films. The temporally resolved images of the plumes are correlated with the time-resolved emission spectrum of plasma species in the plume. The deposited films of ZnO at 100 mTorr of ambient oxygen exhibited third-harmonic generation. Mgx Zn(1-x) O alloy thin films of different molar percentage of MgO were deposited on glass substrates with the aim of achieving variable band gap using pulsed laser deposition in 100-mTorr oxygen ambient at substrate temperatures ranging from 200 to 500 °C. The films with x=0.1 and 0.3 exhibit single hexagonal phase with (002) as the preferred orientation, however, with x=0.5, a transition to mixed phase with hexagonal phase of (100) and cubic phase of (200) orientation is observed. The absorption edge is blueshifted with and increase of x and deposition temperature. The band gap of the deposited films increases with molar percentage and deposition temperature. The deposited films exhibited high degree of transparency (>85%) over visible range. © 2005 American Institute of Physics.

Journal of Applied Physics

Laser-ablated ZnO for thin films of ZnO and Mg xZn (1-x)O

A natural self-assembly process of semiconductor nanoparticles leading to the formation of doped, monocrystalline nanorods with highly enhanced dopant-related luminescence properties is reported. ∼4 nm sized, polycrystalline ZnS nanoparticles of zinc-blende (cubic) structure, doped with Cu+-Al3+ or Mn2+ have been aggregated in the aqueous solution and grown into nanorods of length ∼400 nm and aspect ratio ∼12. Transmission electron microscopic (TEM) images indicate crystal growth mechanisms involving both Ostwald-ripening and particle-to-particle oriented-attachment. Sulphur-sulphur catenation is proposed for the covalent-linkage between the attached particles. The nanorods exhibit self-assembly mediated quenching of the lattice defect-related emission accompanied by multifold enhancement in the dopant-related emission. This study demonstrates that the collective behavior of an ensemble of bare nanoparticles, under natural conditions, can lead to the formation of functionalized (doped) nanorods with enhanced luminescence properties. © 2005 Elsevier Ltd. All rights reserved.

Journal of Physics and Chemistry of Solids

Spontaneous organisation of ZnS nanoparticles into monocrystalline nanorods with highly enhanced dopant-related emission

Aggregation based meso-scale self-assembly of doped semiconductor nanocrystals leading to the formation of monocrystalline nanorods showing enhanced photo- and electro-luminescence properties is reported. ∼4 nm sized, polycrystalline ZnS nanoparticles of zinc-blende (cubic) structure, doped with Cu+-Al3+ have been aggregated in the aqueous solution and grown into nanorods of length ∼400 nm and aspect ratio ∼12. Transmission electron microscopic (TEM) images indicate crystal growth mechanisms involving particle-to-particle oriented-attachment assisted by sulphur-sulphur catenation leading to covalent-linkage. The nanorods exhibit self-assembly dependant luminescence properties such as quenching of the lattice defect-related emissions accompanied by the enhancement in the dopant-related emission, efficient low-voltage electroluminescence (EL) and super-linear voltage-brightness EL characteristics. This study demonstrates the technological importance of aggregation based self-assembly in doped semiconductor nanosystems. © 2005 Elsevier Ltd. All rights reserved.