JOURNAL OF RESEARCH ON MANY BODY SYSTEMS
Year:2012 | Volume:2 | Issue:3|Papers Count:6

In this paper, by considering Lenard-Jones potential between disc-shape molecules, the radial distribution function, the direct correlation function and the structure factor are calculated by using compressibility and Ornstein-Zernike equations. In addition, the pressure and compressibility equations for this potential are calculated. Results show that for the L. J. potential, the radial distribution function does not approach zero in molecule's diameter range.

The most fundamental characteristic of liquid crystals, at least from a microscopic point of view, is the presence of long-range orientational order while the positional order is limited or absent. We introduce distribution functions which can help us in calculating order parameters and other relevant averages. The singlet and pair distributions are discussed. Equations for the relevant thermodynamic observables in terms of these distributions are given. Also, we introduce order parameters by expanding the singlet distribution in a complete basis set. The effect of molecular symmetry on the orientational order parameters is examined. Using the known order parameters, the orientation distribution function of hard ellipsoid and the Gay- Berne liquid crystals are calculated. The sixth rank order parameters of these liquid crystals are compared.

The structural, electronic and magnetic properties of Zn1-xMnxO dilute magnetic semiconductor (DMS) were studied by the full potential-linear augmented plane wave (FP-LAPW), and for the exchange correlation potential, Generalized Gradient approximation (GGA) was used. The study was done in the framework of the density functional theory (DFT) by implementing the Wien2k code. The density of states showed spin polarization in Fermi level by substitution of Mn atom in the ZnO compound. The values of spin polarization depend on the crystallography structure of Zinc Oxide. Also, the magnetic moment and the exchange splitting energy demonstrated different values for each structure.

ZnO nanocrystalline thin films were synthesized using cathodic reduction of Zn foil in aqueous electrolyte containing ZnCl2 and H2O2, followed by annealing at 400 oC in the air. The X-ray diffraction pattern exhibited a set of well-defined diffraction peaks corresponding to the ZnO wurtzite phase. Scanning electron microscope and transmission electron microscope images clearly revealed formation of randomly oriented ZnO nanowires having length up to several microns and diameter of ~ 100 nm. The field an emission studies were carried out in a planar diode configuration at a base pressure ~ 1x10-8 mbar. The turn-on field value, required to draw emission current density of 0.1 mA/cm2 was found to be ~ 1.2 V/mm. The Folwer-Nordheim (F-N) plot showed non-linear behavior in the entire range of applied field indicating the semiconducting nature of the emitter. The simplicity of the synthesis route, coupled with the better emission properties, proposes the electrochemically synthesized ZnO nanowire emitter as a promising electron source for high current density applications.

In this study, a manganite sample with a nominal formula of La0.9Sr0.1MnO3 was prepared by the microwave assisted sol-gel method and annealing at various temperatures. The structural and magnetic properties of the samples were investigated by XRD, FESEM and AC susceptometer, respectively. XRD analysis showed that the samples are a nearly single phase. FESEM micrographs showed that by increasing the annealing temperature from 600 to 1200 oC the size of particles increased from about 50 nm to micrometer. It was also found that the width of paramagnetic-ferromagnetic transition temperature and the magnitude of the susceptibility of samples decrease and increase by increasing annealing temperature, respectively. Also, in the resistivity curves of the micrometer particle sized samples, intergarnular and intragranular phase transition peaks were observed, while the intragranular peak was not seen in the nanometer particle sized sample. These behaviors are related to the surface effects.

In this paper, we investigate the coexistence between superconductivity and ferromagnetism in a ferromagnetic superconductor (FS) where FS is in antiparallel cooper pairing state and parallel cooper pairing state. By using spin generalized Bogoliubov de Gennes (SBdG) equations, we derive the superconducting order parameter of FS as a function of temperature (T) and exchange field (h) of FS. We find that for some values of T and h the order parameter behaves as a multi-value function, so to determine the physical value of order parameter we calculate the difference in thermodynamic potential between superconducting and normal states, and we present a phase diagram of an FS in T-h plane which separates the superconducting region from the normal region. As a result, we deduce that the non-zero order parameter is not sufficient for having superconducting state and it is necessary to calculate the difference in thermodynamic potential of normal and superconducting states. In other word, in some points of T and h, although there are non-zero order parameters, since in these points the thermodynamic potential of the normal state is lower than the superconducting state, the system falls into the normal state.