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[en] Electron paramagnetic resonance (EPR) spectra of VO2+, Mn2+, Cu2+ and Gd3+ ions in lithium fluoroborate glasses have been studied at room temperature. Spectral studies reveal that VO2+ ions occupy tetragonally compressed octahedral sites while Cu2+ ions occupy tetragonally elongated octahedral sites. The site symmetry around the Mn2+ ions is predominantly octahedral. The Gd3+ ions dictate their own environment in these glasses and occupy sites surrounded by polyhedra of more or less irregularly distributed ligands with high coordination number ≥ 6. (author). 16 refs., 4 figs
[en] The kinetics of the long-range spherical model evolving from various initial states is studied. In particular, the large-time auto-correlation and auto-response functions are obtained, for classes of long-range-correlated initial states, and for magnetized initial states. The ageing exponents can depend on certain qualitative features of initial states. We explicitly find the conditions for the system to cross over from ageing classes that depend on the initial conditions to those that do not
[en] We bosonize (2+1)-dimensional fermionic theory using coherent states. The gauge-invariant subspace of boson-Chern-Simons Hilbert space is mapped to fermionic Hilbert space. This subspace is then equipped with a coherent state basis. These coherent states are labelled by a dynamic spinor field. The label manifold could be assigned a physical meaning in terms of density and spin density. A path-integral representation of the evolution operator in terms of these physical variables is given. The corresponding classical theory when restricted to LLL is described by spin fluctuations alone and is found to be the NLSM with Hopf term. The formalism developed here is suitable to study quantum Hall skyrmions semiclassically and/or beyond the hydrodynamic limit. The effects of Landau level mixing or the presence of slowly varying external fields can also be easily incorporated
[en] In this study, we investigated the microstructure, phase evolution and magnetic properties of nanogranular films of Sm–Co compounds processed by the sol-gel method. By controlling the compositional ratio of Sm:Co precursor concentration, nanogranular films consisting of three distinct hard magnetic phases namely, Sm2Co7, SmCo5 and Sm2Co17 with coercivity values of 1.78, 2.94 and 2.12 kOe, respectively, were obtained through this technique. - Highlights: ► Sol-gel method is exploited for the processing of Sm–Co nanogranular films. ► Role of Sm:Co precursor ratio on the film characteristics is investigated. ► SmCo5, Sm2Co7 and Sm2Co17-phases crystallized for molar ratios of 1:5, 1:7 and 1:9. ► Hc values of 1.78, 2.94 and 2.12 kOe resulted for the three distinct magnetic phases.
[en] Annealed AuGe/Ni/Au film structures on GaAs/AlGaAs multilayers have been examined for contact resistance, roughness, magnetization and melting as functions of anneal temperature, Ni-layer thickness and three AuGe compositions. Magnetization data indicate that a solid state, solubility-limited dissolution of Ni into AuGe takes place even for low-temperature anneals and that this dissolution is complete when alloying occurs at ∼400 °C. An apparent melting temperature, detected in differential scanning calorimetry, increases with increasing Ni-layer thickness and decreasing Ge content in the AuGe alloy. Electrical contact formation and roughening of the surface occur in the range of melting temperatures of the structure. The eutectic alloy with a Ni-layer thickness of ∼25–30 nm gives the optimum contact resistance. The contact resistance can be traded off for the reduction in roughness by either increasing the Ni-layer thickness or reducing the Ge content, with the latter being the better choice of the two. The temperature dependence (4–300 K) of the contact resistance shows indications of both thermionic and tunneling behaviors. The barrier height for the current conduction increases with the increase of the Ni-layer thickness and a decrease of the Ge content in the AuGe layer, relative to that of the structure with optimum contact resistance
[en] Highlights: • The porosity was increased with increasing dopant concentration of Zr and Cu from the 10.57% to 20.11%. • The force constant and wave numbers in octahedral and tetrahedral site is increased with increasing the dopant concentration of Zr and Cu. • The compositional dielectric constant at 100 kHz is increased from the 9.85 to 86.53, with increasing dopant concentration of Zr and Cu. - Abstract: Zr and Cu Ni0.5Zn0.5Fe2O4 ferrites have been prepared by the sol-gel auto combustion method using the nitrates. The ethylene glycol and citric acid were mixed as the combustion agents. The synthesized powders were calcinate at 800 °C for 3 h and they are pressed in desired shaped and sintered at 1200 °C for 2 h in air atmosphere. The X-ray diffraction analysis confirms the single phase cubic spinel structure. The SEM pictures revels that the substitution of higher valence ions results fine grained intragranular pore free microstructure. The dielectric properties of substituted ferrites exhibits decreasing trend at lower frequencies up to 1000 Hz beyond which it should in stable response. All the results are explained in terms of compositional and frequency variation.
[en] CuIn1-xAlxSe2 thin films (x = 0-1.0) were prepared by the four-source co-evaporation technique onto soda lime glass substrates held at 673 K. The films are found to be nearly stoichiometric as determined from Rutherford back scattering (RBS) analysis. Surface analysis of the films was carried out by x-ray photoelectron spectroscopy. X-ray diffraction and scanning electron microscopy are used to examine the structure of the films. The films are found to be single phase and chalcopyrite in structure. The lattice parameters are found to vary nonlinearly with x. Optical absorption studies reveal a three-fold optical band structure and the band gaps are found to increase nonlinearly with the increase in Al content. Crystal field and spin-orbit parameters are determined from the band gaps using a quasi-cubic model. The deformation potential and the percentage of d-orbital contribution to p-d hybridization are determined using the deduced crystal field and spin-orbit parameters. All the films are p-type conducting and the resistivity is found to increase with the increase in Al content. Room temperature Hall mobility and the carrier concentration of the films are determined
[en] Zn1-xFexS (x=0.0, 0.1, 0.2, 0.4 and 0.6) nanocrystals have been obtained by chemical co-precipitation from homogeneous solutions of zinc and iron salt compounds, with S2- as precipitating anion formed by decomposition of thiophenol. The TEM micrographs show a spherical shape for ZnS nanocrystals and their average size is around 7 nm. The optical absorption spectra indicate a blue shift of the absorption edge with increasing Fe-content. The luminescence of nanoparticles excite at about 370 nm with an emission peak at around 490 nm. At room temperature, ESR signal characteristic of Fe3+ was observed in samples of all concentrations.