Department of Physics

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IIT Jodhpur

A simple aqueous solution-based chemical methodology has been developed for the preparation of single-phase Ni1-xZnxFe 2O4 nanopowder, where x= 0.2, 0.35.0.5 and 0.6. The average particle size of the synthesized powders was in the range of 30-50 nm. Precursor powders were synthesized by reacting aqueous solutions of metal nitrates with polyvinyl alcohol and sucrose and then evaporating the resulting solution to dryness. The precursors were calcined in air for 2.30 h at different temperatures ranging from 650 to 950°C. The synthesized powders were characterized by using thermogravimetric analysis-differential scanning calorimetric analysis, X-ray diffraction, transmission electron microscopy, scanning electron microscopy. Change of DC electrical resistivity with change in sintering temperature and microstructure was measured by using the two-probe method. The as synthesized nanopowders possess a high room temperature resistivity of ∼106-107 cm. They exhibit a good amount of magnetization in the range of 49-61 emu/g and a wide range of coercivity of 20-73 Oe. The novelty of this method lies in its simplicity and cost effectiveness. This method has the capability of being an alternative route to the other reported synthetic methods. Copyright © Taylor &amp; Francis Group, LLC.

World University root node

Integrated Ferroelectrics

Development of a novel aqueous solution based chemical methodology for synthesis of Ni(1-x)ZnxFe2O4 nanopowders and their electrical and magnetic property

Quantum walk models have been used as an algorithmic tool for quantum computation and to describe various physical processes. This article revisits the relationship between relativistic quantum mechanics and the quantum walks. We show the similarities of the mathematical structure of the decoupled and coupled forms of the discrete-time quantum walk to that of the Klein-Gordon and Dirac equations, respectively. In the latter case, the coin emerges as an analog of the spinor degree of freedom. Discrete-time quantum walk as a coupled form of the continuous-time quantum walk is also shown by transforming the decoupled form of the discrete-time quantum walk to the Schrödinger form. By showing the coin to be a means to make the walk reversible and that the Dirac-like structure is a consequence of the coin use, our work suggests that the relativistic causal structure is a consequence of conservation of information. However, decoherence (modeled by projective measurements on position space) generates entropy that increases with time, making the walk irreversible and thereby producing an arrow of time. The Lieb-Robinson bound is used to highlight the causal structure of the quantum walk to put in perspective the relativistic structure of the quantum walk, the maximum speed of walk propagation, and earlier findings related to the finite spread of the walk probability distribution. We also present a two-dimensional quantum walk model on a two-state system to which the study can be extended. © 2010 The American Physical Society.

Fulltext

Physical Review A - Atomic, Molecular, and Optical Physics

Relationship between quantum walks and relativistic quantum mechanics

The superconducting properties of magnesium diboride (MgB2) films prepared by electroless deposition on various substrates including silver, gold and silicon are reported. In this study, MgB2 films were fabricated on silver, gold, and silicon using an electroless plating technique, while controlling the redox potential to improve the deposition quality. The structure, morphology, and superconducting properties of the samples were investigated using X-ray diffraction, magnetometry, scanning electron microscopy, and Raman spectroscopy. X-ray diffraction and Raman spectroscopy confirmed that the films are polycrystalline MgB2 but also contain some impurity phases. All the MgB2 films show superconducting transitions near 39 K, the value for bulk MgB2, with the superconducting volume fraction ranging from approximately 1 to 2%. We find a strong dependence of film quality with the oxidation potential of the bath. © 2010 Elsevier B.V. All rights reserved.

Thin Solid Films

Electroless deposition of superconducting MgB2 films on various substrates

We study Bs→μ+μ- in the context of the R-parity violating minimal supergravity in the high-tan β regime. We find that the lowest value of the branching ratio can go well below the present LHCb sensitivity and hence Bs→μ+μ- can even be invisible to the LHC. We also find that the present upper bound on Br (Bs→μ+μ-) puts strong constraint on the minimal supergravity parameter space. The constraints become more severe if the upper bound is close to its standard model prediction. © Springer-Verlag / Società Italiana di Fisica 2009.

European Physical Journal C

Bs→μ+μ- decay in the R-parity violating minimal supergravity

New physics in the form of scalar/pseudoscalar operators cannot lower the semileptonic branching ratio Br(B → K μ+μ-) below its standard model value. In addition, we show that the upper bound on the leptonic branching ratio Br(Bs → μ+μ -) sets a strong constraint on the maximum value of Br(B → K μ+μ-) in models with multiple Higgs doublets: with the current bound, Br(B → K μ+μ-) cannot exceed the standard model prediction by more than 2.5%. The conclusions hold true even if the new physics couplings are complex. However, these constraints can be used to restrict new physics couplings only if the theoretical and experimental errors in Br(B → K μ+μ-) are reduced to a few per cent. The constraints become relaxed in a general class of models with scalar/pesudoscalar operators. © 2010 World Scientific Publishing Company.

Modern Physics Letters A

Tension between scalar/pseudoscalar new physics contribution to B s → μ+μ- and B → K μ+μ-

We report on the defect structure and composition of vacuum-annealed In2O3 (VA-In2O3) ferromagnetic thin films. VA-In2O3 is highly (∼7 at.%) oxygen deficient. High-resolution microscopy reveals disordered glassy surface layers and crystalline defect states, O and In vacancies, and In-In clustering, predominantly in the vicinity of the surface. These defects are not observed in as-deposited In2O3 films. These structural defects are important for understanding many of the novel properties found in non-stoichiometric In2O3, including high conductivity and room-temperature ferromagnetism. © 2009 Acta Materialia Inc.

Scripta Materialia

Coexistence of anion and cation vacancy defects in vacuum-annealed In2O3 thin films

We use molecular dynamics to study the kinetics of surface enrichment (SE) in a stable homogeneous mixture (AB), placed in contact with a surface which preferentially attracts A. The SE profiles show a characteristic double-exponential behavior with two length scales: -, which rapidly saturates to its equilibrium value, and +, which diverges as a power-law with time (+ ∼ tθ). We find that hydrodynamic effects result in a crossover of the growth exponent from θ≃0.5 to θ≃1.0. There is also a corresponding crossover in the growth dynamics of the SE layer thickness. © 2010 American Institute of Physics.

Journal of Chemical Physics

Kinetics of surface enrichment: A molecular dynamics study

We have assembled molecular multi-level switches (0, 1, 2, 3) on an atomically flat metallic substrate (Figure 1 a). The molecules self-assemble in the form of an organic bi-layer. Each molecule functions as a cellular automata (CA) cell when assembled in an ordered pattern, otherwise they are conductance switch. The molecular bi-layer satisfies three fundamental criteria of cellular automaton circuitry. First, the single molecule cell, or a small area of molecules "updates" itself independently of the distant neighborhood (parallelism). Secondly, the new CA state depends on the distribution of states of its immediate surroundings (locality). Third, the laws that govern the state of a molecule do not change over the entire surface (homogeneity). In spite of following the fundamental properties of CA, there are crucial issues need to be addressed before we use the CA template for a real-time computation. In this letter, several such issues have been addressed leading to the conclusion that a simple realization of CA template can lead to the realization of remarkable computing power that was otherwise impossible to realize using existing hardware. ©2009 IEEE.

ISPACS 2009 - 2009 International Symposium on Intelligent Signal Processing and Communication Systems, Proceedings

Remarkable potential of pattern based computing on an organic molecular layer using the concept of cellular automata

The 25 mm wide ribbons of Fe-6.5 wt% Si alloy have been developed by melt spinning technique, showing sufficient ductility and white silver appearance. Two magnetic transitions take place at 676 and 760 °C due to the formation of B2 ordered phase and A2 disordered paramagnetic phase, respectively. The saturation magnetization of the ribbon is 17.5 kG under the applied field of 12 kG. The as-cast ribbons consist of disordered A2 structure with a low volume of B2 phases while the annealed microstructure comprises a dispersion of B2 domains in the disordered A2 matrix. The alloy shows the enhancement of the soft magnetic properties with a reduction in coercivity from 150 A/m in the as-cast state to 45 A/m in the annealed condition at 850 °C. © 2009 Elsevier B.V. All rights reserved.

Journal of Magnetism and Magnetic Materials

Effect of annealing treatment on soft magnetic properties of Fe-6.5 wt% Si wide ribbons

The general trend of magnetic behaviour of materials is that the mechanically hard materials are also magnetically hard. However for the high strength low alloy (HSLA) steel tempered at various aging temperatures, the correlation was reported as negative. The anomaly could not be explained by the magnetic parameters like RMS voltage calculated from the Barkhausen emission signal and the coercivity from the magnetic hysteresis loop. This paper reports another magnetic parameter known as power-law decay exponent which shows excellent correlation with the mechanical properties and thus explains the progressive evolution of the microstructural constituents in HSLA steel. © 2008 Elsevier B.V. All rights reserved.