Magneto-Impedance behavior of Co-Fe-Nb-Si-B-based ribbons

The giant magneto-impedance of melt spun Co_xFe_72−xNb₄Si₄B₂₀(x=10, 20, 36, 50) amorphous and nanostructured ribbons have been investigated. Alloys have been optimized at the driving current amplitude, frequency and found that amorphous ribbon of nominal composition of Co₃₆Fe₃₆Nb₄Si₄B₂₀ shown maximum GMI ratio of 13%. The behaviour of the driving current amplitude on the GMI behaviour was studied and the sample was optimized for driving current amplitude, I_ac=10 mA. The frequency dependence of the GMI behaviour was studied for the ribbon sample Co₃₆Fe₃₆Nb₄Si₄B₂₀ at frequency in the range of 100 kHz-1.2 MHz of the optimized driving current amplitude and it was found that the sample showed the maximum GMI behaviour at f=700 kHz. The optimized samples were Joule heated at the current density J=0-35 A/m² for a period of 1 min. The GMI ratio initially increased then progressively deteriorated with J, but after a certain range it shows up to 16% of improvement in the magneto-impedance value due the increase of nanocrystalline volume fraction. The asymmetry in the GMI profile was observed for the sample Joule heated at J=1-5 A/m² for 1 min.     

Electrical and thermal properties of bulk superconductors Eu0.95Pr0.05Ba2(Cu1−xMx)3O7−δ (M = Fe,Ni, Zn and Mn)

Measurements of transition temperature, magneto-resistance, thermal conductivity, thermo-electric power and specific heat have been carried out on co-doped samples of Eu_0.95Pr_0.05Ba₂(Cu_1?xM_x)₃O_7?δ (M = Fe, Ni, Zn and Mn) compounds. It is found that all samples exhibit metallic behavior, except the co-doped sample of Fe that shows semiconducting behavior. It is seen that the upper-critical field H_c2 decreases with Pr-doping. However, an increase in H_c2 for dopants like Fe and Mn is observed. Thermal conductivity for the pristine sample of EuBa₂Cu₃O_7?δ (Eu-123) exhibits a pronounced hump below the superconducting transition temperature T_C. However, the peak height of the hump decreases with Pr-doping and such a feature is further suppressed in the co-doped samples. The negative sign of the measured thermo-electric power of Eu-123 indicates that the dominant carrier in this sample is electron-like, whereas it turns to hole-like for all of the doped samples. A jump in specific heat C_P is detected in the pure sample of Eu-123 at T_C, while only a change in slope in C_P is seen around the transition temperature in the Pr-doped sample.     

Quantum phase diagram of a spin-1/2 antiferromagnetic chain with magnetic impurity

We present the renormalization group (RG) flow diagram of a spin-half antiferromagnetic chain with magnetic impurity and one altered link. In this two parameters (competing interactions) model, one can find the complex phase diagram with many interesting fixed points. There is no evidence of intermediate stable fixed point in weak coupling phase. It may arise at the strong coupling phase. Depending on the strength of couplings the phases correspond either to a decoupled spin with Curie law behavior or a logarithmically diverging impurity susceptibility as in the two channel Kondo problem.     

Dynamically generated resonances from the vector octet-baryon decuplet interaction and their radiative decays into γ-baryon decuplet

The dynamically generated resonances from vector meson-baryon decuplet are studied using La-grangians of the hidden gauge theory for vector interactions. One shows that some of the generated states can be associated with some known baryon resonances in the PDG data, while others are predictions for new states. Furthermore, we calculate the radiative decay widths of these resonances into a photon and a baryon decuplet.     

Disorder driven optical processes in nanocrystalline ZnO

A systematic study on the modification of optical properties in mechanically milled ZnO powder has been reported here. The average grain size of the powder becomes ～20 nm within 4 h of milling. Fluctuations of average grain size have been noticed at the initial stage of milling (within 15 min). Changes in grain morphology with milling have also been noticed in scanning electron micrographs of the samples. Room temperature optical absorption data shows a systematic red shift of absorption band edge (～3.25 eV). The band tail parameter (extracted from the optical absorption just below the band edge) follows a simple exponential relation with the inverse of the average grain size. Significant increase of the band tail parameter has been noticed at low grain size regime. It has been analyzed that high values of band tail parameter is a representative of V_Zn–V_O type divacancy clusters. Room temperature photoluminescence spectra show decrease (except for 120 min milling) of band edge emission intensity with increase of milling time. Subsequent decrease of sub-band edge emission is, however, less prominent. The variation of PL intensity ratio (intensity at band edge peak with that at 2.3 eV) follows simple exponential decrease with the increase of band tail parameter. This indeed shows that band edge emission in ZnO is related with the overall disorder in the system, not grain size induced only.     

Connecting dark energy to neutrinos with an observable Higgs triplet

To connect the scalar field (acceleron) responsible for dark energy to neutrinos, the usual strategy is to add unnaturally light neutral singlet fermions (right-handed neutrinos) to the Standard Model. A better choice is actually a Higgs triplet, through the coupling of the acceleron to the trilinear Higgs triplet–double–doublet interaction. This hypothesis predicts an easily observable doubly-charged Higgs boson at the forthcoming Large Hadron Collider (LHC).     

Magnetism and superconductivity in Eu0.2Sr0.8(Fe0.86Co0.14)2As2 probed by 75As NMR

We report bulk superconductivity (SC) in Eu(0.2)Sr(0.8)(Fe(0.86)Co(0.14))(2)As(2) single crystals by means of electrical resistivity, magnetic susceptibility and specific heat measurements with T(c) is approximately equal to 20 K and an antiferromagnetic (AFM) ordering of Eu(2+) moments at T(N) is approximately equal to 2.0 K in zero field. (75)As NMR experiments have been performed in the two external field directions (H is parallel to ab) and (H is parallel to c). (75)As-NMR spectra are analysed in terms of first-order quadrupolar interaction. Spin-lattice relaxation rates (1/T(1)) follow a T(3) law in the temperature range 4.2-15 K. There is no signature of a Hebel-Slichter coherence peak just below the SC transition, indicating a non-s-wave or s(±) type of superconductivity. In the temperature range 160-18 K 1/T(1)T follows the C/(T+θ) law reflecting 2D AFM spin fluctuations.     

On localized tachyon condensation in and

We study some aspects of localized tachyon condensation on non-supersymmetric orbifolds of the form C²/Z_n and C³/Z_n. We discuss the gauged linear sigma models for these orbifolds. We show how several features of the decay of orbifolds of C³ can be realised in terms of orbifolds of C².     

Vibrational Spectroscopy of CH/CD Stretches in Propadiene: An Algebraic Approach

Using Hamiltonian based on Lie algebraic method, the stretching vibrational modes of C3H4 and C3D4 molecules are calculated up to higher overtones. The model appears to describe C-H and C-D stretching modes with less number of parameters. The locality parameter ξ confirms the highly local behaviour of the stretching modes of these molecules.     

Microstructural characterization of ultrafine-grain interstitial-free steel by X-ray diffraction line profile analysis

This paper highlights the microstructural features of commercially available interstitial free (IF) steel specimens deformed by equal channel angular pressing (ECAP) up to four passes following the route A. The microstructure of the samples was studied by different techniques of X-ray diffraction peak profile analysis as a function of strain (ε). It was found that the crystallite size is reduced substantially already at ε=2.3 and it does not change significantly during further deformation. At the same time, the dislocation density increases gradually up to ε=4.6. The dislocation densities estimated from X-ray diffraction study are found to correlate very well with the experimentally obtained yield strength of the samples.