Department of Physics

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The frequency and the amplitude of the driving AC current dependence on the harmonic behavior of the giant magneto-impedance (GMI) voltage of Co-rich amorphous wire have been studied. Single-peak, two-peak and three-peak behavior in the GMI characteristics was studied with the change of amplitude and frequency of the AC current. GMI ratio was calculated from the first harmonic signals which were initially increased and then decreased monotonically with the increase of frequency (f) and the amplitude (IAC) of the driving current. The response of the GMI voltage was found non-linear with the generation of higher harmonics at higher amplitude of the driving current. The second and third harmonic signals were also evaluated and their dependence on the driving current amplitude and frequency were presented in the paper. The experimental results were analyzed using single domain rotational model. The voltage harmonics were calculated through Fourier transform of the time derivative of the estimated circular magnetization of the sample. © 2006 Elsevier B.V. All rights reserved.

World University root node

Journal of Magnetism and Magnetic Materials

Dependence of the driving current on the harmonic behavior of giant magneto-impedance voltage of Co-based amorphous wires

Thermal electrical resistivity, magnetic hysteresis and magneto-impedance behaviour of melt spun and annealed Co71-XFeXCr 7Si8B14 (X = 0, 2, 3.2, 4, 6, 8 and 12 at.%) were investigated. The addition of Fe in the system changed crystallization as well as the magnetic properties of the materials. The alloy containing 6 at.% Fe showed an increase in resistivity during the first crystallization process. A TEM micrograph indicated the formation of nanostructure during the crystallization process. The GMI properties of the alloys are evaluated at a driving current amplitude of 5 mA and a frequency of 4 MHz. The two-peak behaviour in the GMI profile was observed for all the samples. It is found that the alloy with 4 at.% Fe has the maximum GMI ratio because of the nearly zero magnetostriction value of the sample. About 62% change in the GMI ratio was observed in the alloy with 4 at.% Fe when annealed at 673 K. The anisotropy field was also minimum for the annealed alloy. The results were explained by the formation of directional ordering and the reduction of the magnetostriction constant of the alloy due to nanocrystallization during the annealing process. © 2006 IOP Publishing Ltd.

Journal of Physics D: Applied Physics

Effect of Fe addition on the magnetic and giant magneto-impedance behaviour of CoCrSiB rapidly solidified alloys

ZnS: Mn nanophosphor has been doped with quencher impurity Ni using the colloidal precipitation method with capping agent polyvinylpyrrolidone. The formation of ∼2.5 nm sized nanoparticles has been confirmed by x-ray diffraction and transmission electron microscope studies. Energy and time resolved photoluminescence spectra of the synthesized nanophosphors have been studied at room temperature. Photoluminescent spectra for ZnS: Mn, Ni show three peaks at 412 nm, 433 nm and 590 nm corresponding to Ni impurity, sulphide vacancies (Vs) and Mn impurity, respectively. The ZnS: Mn nanophosphor show typical nanosecond lifetimes for defect-related emission and millisecond lifetimes for Mn impurity-related emission. However, the ZnS: Mn, Ni samples showed lifetime shortening, with variation of dopant concentration for defect-related (420 nm) as well as impurity-related emission (590 nm), which is attributed to exchange interaction between Mn2+ and nearest neighbour Ni2+ impurities. © 2006 IOP Publishing Ltd.

Lifetime shortening in doped ZnS nanophosphors

In the present paper, we report electrical conductivity and dielectric studies on the composites of conducting polyanillne (PANI) with crystalline semiconducting ZnS powder, wherein PANI has been taken as inclusion and ZnS crystallites as the host matrix. From the studies, it has been observed that the value of room temperature d.c. conductivity of the composites with volume fraction of PANI > 0.65 shows an unusual behaviour wherein, conductivity values of the composites exceed that of PANI itself with maximum value as high as 6 times that of PANI at the volume fraction of 0.85. A similar trend has also been observed for the real and imaginary parts of complex dielectric constant values of the composites. This unusual behaviour in the d.c. conductivity and dielectric properties has been attributed to the enhancement in the degree of crystalllnlty of PANI as a consequence of its interfacial interaction with ZnS matrix. The results of optical microscopy show coating of PANI all around the ZnS particles. The temperature dependent conductivity studies suggest the quasi one-dimensional VRH conduction in PANI as well as its composites with ZnS. FTIR and XRD studies have also been reported. © Indian Academy of Sciences.

Fulltext

Bulletin of Materials Science

Studies on conductivity and dielectric properties of polyaniline-zinc sulphide composites

The frequency and the amplitude of the driving ac current dependence of the Giant Magneto-Impedance (GMI) behaviour in (Fe6 Co94)72.5Si12.5B15 amorphous wire have been studied. The single and two-peak behaviour in the GMI characteristics are observed which depends on the amplitude and frequency of the ac driving current flowing through the sample. The GMI ratio initially increased and then decreased monotonically with the increase of frequency, f, and the amplitude of the ac current, Iac. With the increase of amplitude of ac current, the response of the GMI voltage is found non-linear with the generation of higher harmonics. With the increase of higher harmonics, the first harmonic component of the GMI voltage started decreasing. With the increase of the ac current, the field sensitivity of the first harmonic components of the GMI voltage decreases and in higher harmonics it shows an increasing trend. The maximum field sensitivity was observed 7.5% per A/m for Iac = 2 mA and at frequency 100 kHz. The paper investigates the response of the second and third harmonics with the frequencies and amplitude of the driving current. A voltage equation derived from the rotational model to study the response of the GMI voltage. © 2005 Elsevier B.V. All rights reserved.

Materials Science and Engineering A

Dependence of frequency and amplitude of the ac current on the GMI properties of Co based amorphous wires

The crystallization behaviour, electrical resistivity, magnetic and mechanical properties of as-quenched bulk amorphous Fe72Si 4B20Nb4 alloy was investigated. The alloy, prepared in the form of rods by a copper mould casting technique, revealed an amorphous structure as observed from x-ray diffractometry. Differential scanning calorimetry and thermal variation of electrical resistivity measurements showed distinct glass transition temperature, Tg occurring 50-60 K below the crystallization onset (TX). Such a wide supercooled range was also attributed to the highly reduced glass transition temperature, T rg which was in the range of 0.56-0.58 found to be prevalent in good glass forming alloys. The alloy also showed a non-linear decrease in stability time at different temperatures between Tg and TX. The bulk amorphous alloy exhibited a drastic decrease in electrical resistivity around the glass transition temperature which was attributed to high electron propagation due to enhanced stress relaxation as result of a decrease in viscosity. The material exhibited superior soft magnetic properties with a coercivity value of 212 mOe, which is fairly low with respect to reported bulk amorphous alloys. The amorphous alloy also showed saturation induction of 12 kG and a moderate Curie temperature of 595 K. The as-quenched bulk amorphous alloy exhibited a high mechanical hardness of 1250 HV (Vickers). The superior soft magnetic properties coupled with high mechanical hardness opens up the scope for bulk amorphous Fe-Si-B systems with Nb incorporation. © 2006 IOP Publishing Ltd.

Electron transport behaviour and soft magnetic properties of bulk amorphous Fe72Si4B20Nb4 alloy

The energetics, structural, electronic and optical absorption properties of the bismuth nanowires Bin with n ≤ 1, 6 have been investigated using density functional theory (DFT) in the local density approximation (LDA) including the spin-orbit coupling (SOI). The inclusion of the SOI appreciably affects all the physical properties of the wires. The stable structures form four groups: the planar structures, the caged configurations, the pyramidal structures and the helical configurations. This finding may be a guide for the construction of atomic configurations of the nanowires possessing a larger number of atoms per unit cell. The most stable wire configurations are the 5-Bi pentagonal, and the 6-Bi hexagonal and 6-Bi triple zigzag wires, which should be seen in the experiments. All the wires are metallic. The behaviour of the electron states of the second category structures is quite near to that of a linear chain where the parabolic bands cross the EF, and the number of the channels available for the electric conduction is large. Thus, one should grow the wire structures falling into the second category for achieving high conduction. For the 5-Bi pentagonal and 6-Bi hexagonal cross-sectional wires, the number of channels available for the electric conduction are ten and twelve, respectively. The SOI drastically affects the calculated optical absorption, especially in the low energy region. The absorption peaks are different in terms of the number and the energy locations for the different wires, and may be used for the characterization of the structure of a wire. Our analysis of the calculated electronic structure and the optical data of all the studied structures supports the occurrence of the 4-Bi double and/or 6-Bi triple zigzag chains in the samples of Romanov. © 2006 IOP Publishing Ltd.

Nanotechnology

Ab initio study of the structural, electronic and optical properties of ultrathin bismuth nanowires

The (in)finite dimensional symplectic group of homogeneous canonical transformations is represented on the bosonic Fock space by the action of the group on the ultracoherent vectors, which are generalizations of the coherent states. © World Scientific Publishing Company.

Infinite Dimensional Analysis, Quantum Probability and Related Topics

Ultracoherence and canonical transformations

INTERMAG 2006 - IEEE International Magnetics Conference

Evaluation of deformation behaviours of HSLA-100 steel using magnetic measurement techniques

The giant magnetoimpedance is the sensitive change in ac impedance value with the application of dc magnetic field when ac current passes through the sample. In the present work GMI properties of positive (Fe77.5Si 7.5B15), negative (Co72.5Si 12.5B15) and nearly zero ((Co94Fe 6)72.5Si12.5B15) magnetostrictive amorphous wires have been studied. The result indicates that the magnetostriction constant plays an important role in GMI property. The maximum GMI ratio (330%) and maximum field sensitivity (7% per A/m) are observed in (Co94Fe6)72.5Si12.5B15 amorphous wire. The frequency response of the GMI characteristics of the above alloys has been measured and zero magnetostrictive (Co94Fe 6)72.5Si12.5B15 material showed better frequency response. © 2005 Elsevier B.V. All rights reserved.