مجله پژوهش فیزیک ایران
سال شانزدهم شماره 1 (بهار 1395)

High magneto- crystalline anisotropy AWT IMAGE of L10-FePt nanoparticles are an excellent candidate for ultra high-density magnetic recording. The 4 nm FePt nanocrystals were prepared by superhydride reduction of FeCl2·4H2O and Pt(acac)2 precursors in the phenyl ether by reduction of the 1, 2-hexadecanediol and LiBEt3H superhydride. The crystal and magnetic structures were studied by XRD and VSM analysis. By TEM and EDS analyses the size distribution and molar concentration of Fe/Pt of the nanoparticles were determined. The results showed that the particles are first superparamagnetic before heat treatment and then a phase transition accrue from disorder fcc to order fct structure after annealing. Finally, the phase transition leads the magnetic anisotropy of hard FePt nanoparticles to increase to 7 kOe.

We present a method to gauge second class systems consisted of two constraints in the chain structure. In this method we added a momentum counterpart of Wess Zumino coordinate to primary constraint and used the first class condition to find a new and gauged Hamiltonian. Primary constraints were assumed as identities in configuration and phase space and we tried to find general Hamiltonians.

A new model is presented herein to calculate optimal value for ultra-cold neutron (UCN) production rate of a UCN source. The cold neutron (CN) converter is the main component of UCN source. In this paper, we study the UCN source which contains the D2O neutron moderator, the sD2 converter, 590 Mev proton beam, and the spallation target (a mixture of Pb, D2O and Zr). In order to determine the quantities, the neutron transport equation, written in MATLAB, has been combined with the MCNPX simulation code. The neutron transport equation in cylindrical coordinate has been solved everywhere in sD2 by using simulated CN flux as boundary value. By loading a cylindrical shell with different materials, surrounding the converter, different values for UCN production rate and density were obtained. The results of the UCN production rate and density and their comparison with previous results show that the present method has a good capability for optimization of UCN source parameters.

In this paper, the effect of photocatalytic reduction on hydrophilicity of graphene oxide nanosheets is presented. The graphene oxide nanosheets were prepared by oxidation and exfoliation of natural graphite. The prepared samples were exposed to UV irradiation in presence of TiO2 nanoparticles. Raman spectroscopy and atomic force microscopy show that roughness of the surface is increased due to increasing irradiation. Also, the hydrophilicity of samples by measuring the contact angle of micro-liter droplets of deionized water, showed that by increasing exposure time up to 8 hours the contact angle of samples in crease from about 27 degrees to about 89 degrees.

To understand the mechanism of superconductivity in unconventional super onductors is one of the big challenges in the field of superconductivity. Based on the BCS theory, there is a direct relation between the pairing mechanism and the symmetry of the order parameter. Therefore, identification of the structure of the superconducting gap or the order parameter provides key information on the pairing mechanism. The s-wave conventional superconductors have full point symmetry of the crystal lattice, thus they have full gap symmetry around the Fermi surface. This leads to the exponential temperature dependence of many physical properties in the superconducting state at low temperature. However, the presence of nodes imposed by symmetry in the gap function of unconventional superconductors implies a different order parameter other than conventional s-wave, which may lead to a different pairing mechanism. Here, we show how thermal conductivity measurements in CeIrIn5 at very low temperatures detect the superconducting gap structure.

of 3d transition metals (Sc, Ti, Cr, Mn , Fe, Co, Ni) in both far and close situations were studied based on spin polarised density functional theory using the generalized gradient approximation (LDA) with SIESTA code. The electronic structures show that zigzag (0,9) GaAs nanotubes are non-magnetic semiconductors with direct band gap. It was revealed that doping of 11.11 % Fe and Mn concentrations substituted in Ga sites in ferromagnetic phase in far situation and Cr sites in ferromagnetic phase in near situation introduces half metallic behavior with %100 spin polarization. The unique structure of spin polarised energy levels is primarily attributed to strong hybridization of 3d transition metal and its nearest-neighbor As-4p orbitals. The results of this study can be useful for empirical studies on diluted magnetic semiconductors (DMSs) and systemic investigation in 3d transitional metals. We suggest that GaAs nanotubes doped by transition metals would have a potential application as a spin polarised electron source for spintronic devices in the future.

In this paper a novel optical pressure and acceleration sensor based on micro electro mechanical systems (MEOMS) has been designed. For this purpose an integrated Mach- Zander interferometer has been used in LiNbO3 diaphragm. In this sensor, the strain caused by applied pressure or acceleration leads to a change in refractive index of the wave guide in the diaphragm due to the photoelastic effect. The refractive index change leads to a phase change in the light wave that propagates in the waveguide. This phase change is converted to intensity change using the Mach- Zander interferometer. The software ANSYS 14.5 was used for calculation of the strain in the diaphragm. The pressure and acceleration sensitivity of the designed sensor have been obtained 2.33×10-4 (rad /Pa) and 2.16×10-5 (rad.s2/m), respectively.

In this paper, a theoretical study of electromagnetic wave passing through inhomogeneous over-dense plasma was performed. It was supposed that the plasma layer is immersed in vacuum and the plasma density has aparabolic profileform. In this way, the electric permittivity profile decreases gradually, acquires negative values, and then again becomes positive on the other side of the slab. It has been shown that how this structure is suitable for the transmission of electromagnetic waves in a wide range of the incident angle.To this end, the normal mode and the oblique incident was considered. Then the amplitude of the electromagnetic waves and the reflection coefficient were analytically and exactly calculated and discussed. Dependence of the coefficient of the entire structure to the parameters influencing the problem was evaluated.

Bonner spheres system is one of the ways of measuring neutron energy distribution which is often applied in spectrometry and neutron dosimetry. This system includes a thermal neutron detector, being located in the center of several polyethylene spheres, and it is still workable due to the isotropic response of the system which in turn is derived from the spherical symmetry of moderators and the broad measurable range of the energy. In order to practically use this spectrometer, it is necessary to calibrate this system using standard neutron sources. This research aimed to determine the calibration factor of Bonner spheres spectrometry system and energy spectrum of two standard 241Am-Be and 252Cf sources in the atomic energy organization. Calibration and experimental measurement were done via the two standard sources. The response vector of each detector was derived by using MCNPX simulation code, based on the Monte Carlo method. The spectra unfolding of this system was performed through iterative method using the SPUNIT code done in software NSDUAZ6LiI and BUMS.

In this paper, we investigated the produced cusp in the 0p invariant mass spectrum from the Kd 0p reaction at K energies of 1.45 and 1.65 GeV. According to these calculations the peak of spectrum was around 2 Mp 2130 MeV / c and the width was 13MeV . To interpret this cusp we applied a coupled-channel treatment for the two decay processes pp and Np . The results of the inelastic channel (N p) showed more
consistency to the experimental data.

In this research, Ni50Mn34In16 ferromagnetic shape memory alloy has been prepared by mechanical alloying method. XRD patterns of the samples showed that after 10 hours of ball milling, the alloy structure was completely formed and continuing of the milling process led to more fine particle size. Also the role of annealing on improvement of the alloy properties was studied. It was found that the sample annealing at 900ºC followed by quenching improves the crystal structure and helps to reach L21 structure. Ac susceptibility measurements showed that for the occurrence of magnetic transition, annealing and quenching process on the ball milled powder is necessary.

Investigation of broken symmetry phases with long range order in strongly correlated electron systems is among subjects that have always been of interest to condensed matter scientists. In this paper we tried to study the existence of the 120 degrees magnetic spiral order, based on anisotropy in geometrically frustrated triangular lattices, using variational cluster approximation. We observed that by increasing the anisotropy in the system, the spiral order can be found for AWT IMAGE and for AWT IMAGE; however, it is limited by decreasing AWT IMAGE since antiferromagnetism is dominant for AWT IMAGE. Studying the Mott transition shows that a paramagnetic insulating phase, called quantum spin liquid, happens in the neighborhood of the spiral ordered phase.

Information obtained from nucleus as a bound system of nucleons and from nucleon-nucleon scattering experiments is a strong tool for studying various aspects of nuclear forces. Deuteron-deuteron scattering as a four-nucleon system can provide useful information. So, scattering experiment of a polarized beam of deuteron with kinetic energy of65 MeV/nucleon from a liquid-deuterium target was done at Kernfysisch Versneller Instituut (KVI) and the Big Instrument for Nuclear-polarization Analysis (BINA) was utilized. The obtained data from this experiment were analyzed and presented in this paper. Some results for vector and tensor analyzing powers for a part of the phase space of the Three-Body Break-up channel in d-d scattering are discussed herein. This dataset will be used to test the upcoming theoretical calculations for a four nucleon system, especially for studying the three-nucleon force effects.

The effect of increasing quantum bits and Unruh effect on quantum Prisoners’ dilemma has been investigated for both entangled and unentangled initial states. The Nash equilibrium, as an important result of quantum game theory, was obtained through the different payoffs resulted from choosing various strategies. It has been shown that the non-inertial frame disturbs the symmetry of the game. Actually, selection of the basic quantum strategy by players and calculating the payoff of the game via the density matrix of 4-qubit quantum states can represent a scale of influence of entanglement in a quantum mechanical system

Electronic transport has been investigated in four-quantum-dot combination coupled to metal electrodes using the non-equilibrium Green’s function method, and curves I-V and conductance (dI/dV) were analyzed for special combination. We have showed that the emergence of negative differential conductivity is due to asymmetric distribution of quantum dots in the central region, existence of non-coupled dots (side quantum dots), and the interference effect. We found that more side quantum dots lead to more negative differential conductance.