Effect of Si/Ge ratio on resistivity and thermopower in Gd5SixGe4−x magnetocaloric compounds

The effect of Si/Ge ratio on resistivity and thermopower behavior has been investigated in the magnetocaloric ferromagnetic Gd₅Si_xGe_4−x compounds with x=1.7-2.3. Microstructural studies reveal the presence of Gd₅(Si,Ge)₄-matrix phase (5:4-type) along with traces of secondary phases (5:5 or 5:3-type). The x=1.7 and 2.0 samples display the presence of a first order structural transition from orthorhombic to monoclinic phase followed by a magnetic transition of the monoclinic phase. The alloys with x=2.2 and 2.3 display only magnetic transitions of the orthorhombic phase. A low temperature feature apparent in the AC susceptibility and resistivity data below 100 K reflects an antiferromagnetic transition of secondary phase(s) present in these compounds. The resistivity behavior study correlates with microstructural studies. A large change in thermopower of −8 μV/K was obtained at the magneto-structural transition for the x=2 compound.     

Investigations of magnetic and dielectric properties of cupric oxide nanoparticles

Cupric oxide nanoparticles of ∼8-10 nm width and 40-45 nm length self assembled as large particles ∼1-1.5 μm have been investigated, in the 10-325 K temperature range, using magnetic and dielectric measurements. In magnetic measurements a single broad peak at ∼230 K in a zero field cooled sample has been observed. Coercivity, in magnetization measurements at 10 K, suggests that the nanoparticles are core-shell type particles with an antiferromagnetic core and a ferromagnetic shell. Dielectric measurements, at various frequencies from 3.7 Hz to 949 kHz, exhibit a sharp peak at 284 K followed by weak anomalies around 213 and 230 K.     

Generation of femtosecond pulses at 1350 nm by Cerenkov radiation in higher-order-mode fiber

We demonstrate a method of generating short pulses at 1350 nm by exciting Cerenkov radiation in a higher-order-mode fiber with a 1064 nm femtosecond fiber laser. We measure a 106 fs, 0.66 nJ output pulse. Cerenkov radiation in fibers allows for energy transfer between a soliton and a dispersive wave, providing an effective and engineerable platform to shift the wavelength of a femtosecond source. With appropriate design of the higher-order-mode fiber, this method of generating short pulses at 1350 nm can be extended to other wavelengths and to higher pulse energies.     

Thermal properties of 15-mol% gadolinia doped ceria thin films prepared by pulsed laser ablation

Thermal properties of 15-mol% gadolinia doped ceria thin films (Ce_0.85Gd_0.15 O_1.925) prepared by pulsed laser ablation on silicon substrates in the temperature range 473–973 K are presented. Thermal diffusivities and thermal conductivities were evaluated using photoacoustic spectroscopy. The influence of grain size on thermal properties of the films as a function of deposition temperature is studied. It is observed that the thermal diffusivity and the conductivity of these films decreases up to 873 K and then increases with substrate temperatures. The thermal properties obtained in these films are discussed on the basis of influence of grain size on phonon scattering.     

Angular momentum and cross sections for fusion with weakly bound nuclei: breakup,a coherent effect

Results for the cross section and average angular momentum for complete fusion at energies around the Coulomb barrier are presented for 7Li with 165Ho. Comparison of the cross sections with a one-dimensional barrier penetration model, using a potential consistent with the measured elastic scattering, showed a reduction above the barrier and an enhancement below it. An increase in the measured average angular momentum, , above the barrier and its consistency with that obtained from the fusion excitation function for weakly bound nuclei, is reported. These results together with a reanalysis of existing data conclusively demonstrate that the effect of breakup on fusion is coherent, like coupling to any nonelastic channel.     

X-ray attenuation around <Emphasis Type="Italic">K</Emphasis>-edge of Zr,Nb, Mo and Pd: A comparative study using proton-induced X-ray emission and <Superscript>241</Superscript>Am gamma rays

Mass attenuation coefficients (μ/ρ) for Zr, Nb, Mo and Pd elements around their K-edges are measured at 14 energies in the range 15.744–28.564 keV using secondary excitation from thin Zr, Nb, Mo, Rh, Pd, Cd and Sn foils. The measurements were carried out at the K _α and K _β energy values of the target elements by two techniques: (1) Proton-induced X-ray emission (PIXE) and (2) ²⁴¹Am (300 mCi) source. In PIXE, 2 MeV proton-excited X-rays were detected by a Si(Li) detector. In the second case, X-rays excited by 59.54 keV photons from the targets were counted by an HPGe detector under a narrow beam good geometry set-up with sufficient shielding. The results are consistent with theoretical values derived from the XCOM package and indicate that the PIXE data have better statistical accuracy.     

Structural and magnetic studies on spark plasma sintered SmCo5/Fe bulk nanocomposite magnets

SmCo₅+x wt% Fe (x=0$x=0$, 5 and 10) nanocomposite powders were synthesized by mechanical milling and were consolidated into bulk shape by spark plasma sintering (SPS) technique. The evolution of structure and magnetic properties were systematically investigated in milled powders as well as in SPS samples. A maximum coercivity of 8.9 kOe was achieved in spark plasma sintered SmCo₅+5 wt% Fe sample. The exchange spring interaction between the hard and soft magnetic phases was evaluated using δM–H measurements and the analysis revealed that the SPS sample containing 5 wt% Fe had a stronger exchange coupling between the magnetic phases than that of the sample with10 wt% Fe.     

Spin state selective coherence transfer: a method for discrimination and complete analyses of the overlapped and unresolved 1H NMR spectra of enantiomers

In general, the proton NMR spectra of chiral molecules aligned in the chiral liquid crystalline media are broad and featureless. The analyses of such intricate NMR spectra and their routine use for spectral discrimination of R and S optical enantiomers are hindered. A method is developed in the present study which involves spin state selective two dimensional correlation of higher quantum coherence to its single quantum coherence of a chemically isolated group of coupled protons. This enables the spin state selective detection of proton single quantum transitions based on the spin states of the passive nuclei. The technique provides the relative signs and magnitudes of the couplings by overcoming the problems of enantiomer discrimination, spectral complexity and poor resolution, permitting the complete analyses of the otherwise broad and featureless spectra. A non-selective 180 degrees pulse in the middle of MQ dimension retains all the remote passive couplings. This accompanied by spin selective MQ-SQ conversion leads to spin state selective coherence transfer. The removal of field inhomogeneity contributes to dramatically enhanced resolution. The difference in the cumulative additive values of chemical shift anisotropies and the passive couplings, between the enantiomers, achieved by detecting Nth quantum coherence of N magnetically equivalent spins provides enhanced separation of enantiomer peaks. The developed methodology has been demonstrated on four different chiral molecules with varied number of interacting spins, each having a chiral centre.     

A theoretical investigation of soliton induced supercontinuum generation in liquid core photonic crystal fiber and dual core optical fiber

The supercontinuum generation (SCG) in liquid core photonic crystal fiber (LCPCF) with versatile nonlinear response and the spectral broadening in dual core optical fiber is presented. The analysis is presented in two phase, phase I deals with the SCG in LCPCF with the effect of saturable nonlinearity and re-orientational nonlinearity. We identify and discuss the generic nature of the saturable nonlinearity and reorientational nonlinearity in the SCG, using suitable model. For the physical explanation, modulational instability and soliton fission techniques is implemented to investigate the impact of saturable nonlinear response and slow nonlinear response, respectively. It is observed that the saturable nonlinearity inevitably suppresses the MI and the subsequent SCG. On the other hand, the re-orientational nonlinearity contributes to the slow nonlinear response in addition to the conventional fast response due to the electronic contribution. The phase II features the exclusive investigation of the spectral broadening in the dual core optical fiber.