Tunable characteristics of one dimensional magnetic photonic crystal composed with single-negative materials

In this paper, we present the study of dispersion and transmittance characteristics of one dimensional magnetic photonic crystal composed by single negative indexed materials. For this structure, we have considered magnetic negative (MNG) with ? = 1 and μ < 0 and electric negative (ENG) with ? < 0 and μ = 4. We used simple transfer matrix method and Bloch's theorem for its analytical explanations. Analyzing transmittance characteristics of the proposed structure, we obtain the tunneling of certain frequency range where as the dispersion characteristic shows total forbidden for the same range for TM mode. The tunable property is found inside the band structure due to zero-?, zero-μ and magnetic behavior of the material. To identify zero-? and zero-μ of the structure, we have calculated the dispersion and the transmittance of the magnetic structure of MNG–ENG on different angles of incidence and thickness of layers.     

The effect of chemical pressure in rutheno-cuprates

We have studied the effect of negative chemical pressure in the RuGd_1.5(Ce_0.5?xPr_x)Sr₂Cu₂O_10?δ with Pr content of 0.0 ? x ? 0.2. This is also investigated using the bond length results obtained from the Rietveld refinement analysis. The c parameter and cell volume increase with x for 0.0 ? x ? 0.15. The width of the resistivity transition also increases with Pr concentration, indicating higher inhomogeneity and oxygen deficiency. The difference in the ionic valences of Pr^3+,4+ and Ce⁴⁺ causing different hole doping, the difference in the ionic radii, and oxygen stoichiometry affect the superconducting transition. The magnetoresistance shows a cusp around 135 K which lies between the antiferromagnetic and ferromagnetic transition temperatures, which is probably due to the presence of a spin glass region. There exist two magnetic transition temperatures for 0.0 ? x ? 0.2 which respectively change from T_M = 155 K to 144 K and from T_irr = 115 K to 70 K. The magnetization versus applied magnetic field isotherms at 77 K and 300 K show that the remanent magnetization and coercivity are lower for samples with higher Pr content.     

Hall anomaly in CNT-doped Y-123 high temperature superconductor

In order to study the Hall effect in pure and CNT-doped Y-123 polycrystalline samples, we have measured the longitudinal and transverse voltages at different magnetic field (0 ? 9 T) in the normal and vortex states. In the normal state, the Hall coefficient is positive and decreases with increasing temperature, and can be approximately fitted to R_H = a + bT^?1. We have found a sign reversal in the pure sample for the magnetic field of about 3 T, and double sign reversal of the Hall coefficient in the 0.7 wt% CNT-doped sample at about 3 and 5 T. The Hall resistivity in our samples depends on the pinning.     

Numerical exact diagonalization study on a phonon-assisted hole paring in the high-Tc cuprates

The numerical diagonalization study on an extended t ? J Holstein model, including the renormalization of the hole hopping t due to the phonon effect indicates that the breathing vibration of the in-plane oxygen can enhance the hole pairing for some parameters.     

An unconditionally stable time-domain discretization on cartesian meshes for the simulation of nonuniform magnetized cold plasma

In this paper an unconditionally stable, spatially and temporally implicit time-domain discretization for nonuniform magnetized cold plasma is developed. The discrete dispersion relation is free of spurious solutions and approximates the continuous dispersion relation for well-resolved wavelengths and frequencies (kΔ ? π, ωΔ_t ? π). For a specific choice of parameters, the discrete dispersion relation approximates the continuous dispersion relation for all wavelengths and frequencies up to the Nyquist limit. A few examples, amongst them one involving mode conversion, illustrate the new method.     

Modeling of supersonic plasma flow in the scrape-off layer

The substantial drop of the plasma temperature along magnetic field lines with increasing plasma density is one of the main features in tokamak divertors. As a result the temperature gradient at the divertor plates becomes very steep and the boundary condition normally applied for the parallel Mach number M at the target, M_t = 1, cannot be satisfied. In this case the value of M_t based on the general form of the Bohm criterion, M_t ⩾ 1, has to be determined from the continuity of plasma parameters.In the present paper a new approach to resolve the Mach number at the target for such a situation is proposed. This method avoids the singularity problem that arises by treating the particle balance and parallel motion equations in a differential form. Instead, the integral representation of the equations is formulated for an arbitrary form of particle and momentum sources. The approach can also take into account transport perpendicular to the magnetic field lines.The proposed method is demonstrated on the example of a one-dimensional stationary model for the scrape-off layer (SOL) plasma and includes the continuity-, parallel momentum- and heat transfer equations. The recycled neutrals are described in the diffusion approximation. In the case of low density the normal condition M_t = 1 is satisfied and the results are in agreement with the two-point model. At high enough plasma density solutions with the supersonic flow at the divertor plates, M_t > 1, are found. These states correspond to a partially detached plasma with a temperature of a few eV.     

Thermodynamics and kinetics of CO and benzene adsorption on Pt(111) studied with pulsed molecular beams and microcalorimetry

The adsorption and desorption of the system CO/Pt(111) and C₆H₆/Pt(111) at 300 K has been investigated with a pulsed molecular beam method in combination with a microcalorimeter. For benzene the sticking probability has been measured in dependence of the coverage θ. For coverages θ > 0.8 transient adsorption is observed. From an analysis of the time-dependence of the molecular beam pulses the rate constant for desorption is determined to be 5.6 s^? 1. With a precursor-mediated kinetic adsorption model this allows to obtain also the hopping rate constant of 95.5 s^? 1. The measured adsorption enthalpies could be best described by (199 ? 77θ ? 51θ²) kJ/mol, in good agreement with the literature values. For CO on Pt(111) also transient adsorption has been observed for θ > 0.95 at 300 K. The kinetic analysis yields rate constants for desorption and hopping of 20 s^?1 and 51 s^?1, respectively. The heats of adsorption show a linear dependence on coverage (131 ? 38θ) kJ/mol between 0 ≤ θ ≤ 0.3, which is consistent with the desorption data from the literature. For higher coverage (up to θ = 0.9ML) a slope of ?63 kJ/mol describes the decrease of the differential heat of adsorption best. This result is only compatible with desorption experiments, if the pre-exponential factor decreases strongly at higher coverage. We found good agreement with recent quantum chemical calculations made for (θ = 0.5ML).     

Analysis of current loss from a series-parallel combination of dye-sensitized solar cells using electrochemical impedance spectroscopy

Dye-sensitized solar cells (DSCs) have been proposed as a substitute for silicon crystalline solar cells which have a high manufacturing cost but it is still difficult to fabricate highly efficient DSC module assemblies. Therefore, in this work, an externally connected module assembly was investigated for industrial applications of DSCs. The equivalent circuit of a DSC was determined using typical electrical components and the cause of a current loss in the parallel connection was analyzed using electrochemical impedance spectroscopy. Also, an externally connected module has been constructed using 50 DSCs, where each cell has an active area of 8 cm² (4.62 cm × 1.73 cm) and a conversion efficiency of 4.21% under 1 sun illumination (P_in of 100 mW/cm²). As a result, the externally connected DSC module assembly has an output of 7.4 V and 200 mA, and shows stable performance, with an energy conversion efficiency of 4.44% under 0.45 sun illuminations.     

High-spatial-resolution monitoring of strong magnetic field using Rb vapor nanometric-thin cell

We have implemented the so-called λ-Zeeman technique (LZT) to investigate individual hyperfine transitions between Zeeman sublevels of the Rb atoms in a strong external magnetic field B in the range of 2500 ? 5000 G (recently it was established that LZT is very convenient for the range of 10 ? 2500 G). Atoms are confined in a nanometric thin cell (NTC) with the thickness L = λ, where λ is the resonant wavelength 794 nm for Rb D₁ line. Narrow velocity selective optical pumping (VSOP) resonances in the transmission spectrum of the NTC are split into several components in a magnetic field with the frequency positions and transition probabilities depending on the B-field. Possible applications are described, such as magnetometers with nanometric local spatial resolution and tunable atomic frequency references.     

Superconductivity of the platinum doped 122 iron arsenide SrFe2−xPtxAs2

Pt doped 122 iron arsenide SrFe_1?xPt_xAs₂ (0 ? x ? 0.4) was successfully synthesized. The tetragonal unit-cell volume and the lattice constant a increase with increasing the Pt content, while c decreases, suggesting that the Fe ions are indeed replaced by Pt ions. By the Pt doping, the magnetic order of the parent phase is suppressed, and superconductivity emerges at approximately x = 0.15. T_c reaches the maximum of 16 K at x = 0.2. The compounds series can be a suitable subject to investigate role of the doped 5d state in the superconducting 3d Fe–As layer.     

Effect of Cr substitution on the superconducting and magnetic properties of RuSr2Eu1.5Ce0.5Cu2O10−δ

In this paper we investigate the properties of polycrystalline series of Ru_1?xCr_xSr₂Eu_1.5Ce_0.5Cu₂O_10?δ (0.0 ? x ? 0.40) by resistivity, XRD and dc magnetization measurements. EuRu-1222 is a reported magneto superconductor with Ru spins magnetic ordering at temperatures near 100 K and superconductivity occurs in Cu–O₂ planes below T_c ? 40 K. The exact nature of Ru spins magnetic ordering is still being debated and no conclusion has been reached yet. In this work, we found the superconducting transition temperature T_c = 20 K from resistivity and dc magnetization measurements for pristine sample. DC magnetization measurements exhibited ferromagnetic like transition for all samples.     

Magnetic properties of marine tertiary tephra investigated over a wide temperature range

We report on a detailed investigation of the magnetic properties of tertiary tephra as a function of temperature and magnetic field, over a wide temperature. The tertiary tephra were chosen from two marine sites in the South Indian Ocean. The measurements were made using the electron spin resonance (ESR) technique in the temperature range 4–1100 K and a SQUID magnetometer at temperatures from 4 to 300 K.We show that the magnetic properties of the studied ashes are mainly due to two contributions, a ferrimagnetic one and a paramagnetic one. At moderate magnetic fields, B<1 T, in the large temperature interval, 20 K<T<1000 K, the magnetic response is dominated by the ferrimagnetic component present in the ashes. The experimental data concerning the hysteresis cycles and the Curie temperatures allow us to suggest that (titano-)magnetite and a haematite-like phase could be responsible for the observed ferrimagnetic behaviour. In addition, by electron microscopy investigations, two types of morphologies containing Fe ions have been detected: vitreous splinters, in which embedded crystallised nanoparticles (60–200 nm) are present, and smectite flakes which are crystallised and in which the Fe concentration is higher than in the splinters. We speculate that the ferrimagnetic contribution is due to the nanoparticles and the paramagnetic one results from lamellar flake-like particles.     

Antiferromagnetic phase transition in garnet-type AgCa2Mn2V3O12 and NaPb2Mn2V3O12

Ferrimagnetism has been extensively studied in garnets, whereas it is rare to find the antiferromagnet. Present work will demonstrate antiferromagnetism in the two Mn–V-garnets. Antiferromagnetic phase transition in AgCa₂Mn₂V₃O₁₂ and NaPb₂Mn₂V₃O₁₂ has been found, where the magnetic Mn²⁺ ions locate only on octahedral A site. The heat capacity shows sharp peak due to antiferromagnetic order with the Néel temperature T_N=23.8 K for AgCa₂Mn₂V₃O₁₂ and T_N=14.2 K for NaPb₂Mn₂V₃O₁₂. The magnetic entropy change over a temperature range 0–50 K is 13.9 J K^?1 mol-Mn²⁺-ions^?1 for AgCa₂Mn₂V₃O₁₂ and 13.6 J K^?1 mol-Mn²⁺-ions^?1 for NaPb₂Mn₂V₃O₁₂, which are in good agreement with calculated value of Mn²⁺ ion with spin S=5/2. The magnetic susceptibility shows the Curie–Weiss behavior over the range 29–350 K. The effective magnetic moment μ_eff and the Weiss constant θ are μ_eff=6.20 μ_B Mn²⁺-ion^?1 and θ=?34.1 K (antiferromagnetic sign) for AgCa₂Mn₂V₃O₁₂ and μ_eff=6.02 μ_B Mn²⁺-ion^?1 and θ=?20.8 K for NaPb₂Mn₂V₃O₁₂.     

Luminescence of Eu2+–vc− dipoles and their associates in CsI:Eu crystals

Spectral-kinetics properties of photo-scintillation excited with single light pulses of a nitrogen laser (λ=337.1 nm, t_1/2=5 ns, Q=1 mJ) have been studied in CsI:Eu crystals at temperature within 80–300 K. It is found that the exponential decay of 463 nm emission band has a time constant which grows from 0.85 μs at 78 K to 1.6 μs at 380 K. Such an anomalous temperature behavior of 463 nm emission decay kinetics is discussed in terms of the crystal thermal expansion. It has been proposed that 463 nm emission is caused by a cluster center consisting of three dipoles Eu²⁺v_c^? bounded with each other in a hexagon. Owing to the exchange resonance in the cluster, the energy passes from an excited dipole to a non-excited one and the distance between them gets longer due to thermal expansion of the crystal.     

Structural and electrochemical properties of LiNi0.5Mn0.5 − xAlxO2 (x = 0, 0.02, 0.05, 0.08, and 0.1) cathode materials for lithium-ion batteries

Layered LiNi_0.5Mn_0.5 ? xAl_xO₂ (x = 0, 0.02, 0.05, 0.08, and 0.1) series cathode materials for lithium-ion batteries were synthesized by a combination technique of co-precipitation and solid-state reaction, and the structural, morphological, and electrochemical properties were examined by XRD, FT-IR, XPS, SEM, CV, EIS, and charge–discharge tests. It is proven that the aliovalent substitution of Al for Mn promoted the formation of LiNi_0.5Mn_0.5 ? xAl_xO₂ structures and induced an increase in the average oxidation number of Ni, thereby leading to the shrinkage of the lattice volume. Among the LiNi_0.5Mn_0.5 ? xAl_xO₂ materials, the material with x = 0.05 shows the best cyclability and rate ability, with discharge capacities of 219, 169, 155, and 129 mAh g^? 1 at 10, 100, 200, and 400 mA g^? 1 current density respectively. Cycled under 40 mA g^? 1 in 2.8–4.6 V, LiNi_{0. 5}Mn_0.45Al_0.05O₂ shows the highest discharge capacity of about 199 mAh g^? 1 for the first cycle, and 179 mAh g^? 1 after 40 cycles, with a capacity retention of 90%. EIS analyses of the electrode materials at pristine state and state after first charge to 4.6 V indicate that the observed higher current rate capability of LiNi_{0. 5}Mn_0.45Al_0.05O₂ can be understood due to the better charge transfer kinetics.     

Magnetic properties of GdCo12B6 compound under high pressures

The effects of hydrostatic pressure up to 10 kbar on Curie temperature T_C, compensation temperature T_COMP and spontaneous magnetization M_S of ferrimagnetic GdCo₁₂B₆ compound have been studied. Two antiferromagnetically coupled sublattices that are carrying magnetization of typically 0.42 μ_B/Co atom and 7 μ_B/Gd cancel out at compensation temperature at about 50 K and magnetic ordering temperature T_C=163±2 K. The volume dependence of intrinsic magnetic properties of the GdCo₁₂B₆ compound has been determined by studying it under hydrostatic pressure. The observed increase of M_S with pressure (dM_S/dp=+0.005 μ_B kbar^?1 at 5 K) is attributed predominantly to the pressure induced decrease of Co magnetic moments. The crucial role of Co in this behavior is confirmed by the change of sign of the pressure slope at temperatures above T_COMP and by the fact that the estimated decrease of m_Co is also quite comparable with pressure induced decrease of M_S in YCo₁₂B₆ (dM_S/dp=?0.007 μ_B kbar^?1). The decrease of m_Co is also responsible for the increase of T_COMP with pressure (dT_COMP/dp=+0.06 K kbar^?1). The decrease of T_C with pressure (dT_C/dp=?0.55 K kbar^?1) is comparable to the decrease observed on RCo₁₂B₆ compounds with non-magnetic R and can be attributed to the volume dependence of Co–Co exchange interactions. The remarkable role of the hybridization as a consequence of small distances between Co and B atoms could be a background of this rather unexpected volume stability of magnetic properties.     

Predicted new electrodynamic effect for thin films of layered cuprates—surface Hall currents induced by electric inductionD ⊥ film

A new electrodynamic effect in layered cuprates is predicted—surface Hall currentsj^{(2 D)} ∝ D_n × B_tinduced in thin (d_film ⪡ λ_London) superconducting films by normal-to-the-layer electric inductionD_nand homogeneous parallel-to-the-film magnetic fieldB_t. An experimental set-up is proposed for observation of the new electrodynamic effect. Within London’s electrodynamics, an elementary theory of the effect is presented, and details of a BCS derivation are briefly discussed. The analyzed numerical example shows that an experiment can easily be performed in every lab involved in the development of superconducting field effect transistors SU-FET. For the fundamental physics of high- T_csuperconductivity the experimental confirmation will give a unique method for the measurement of the effective mass m ^* of Cooper-pairs moving in a conducting CuO₂plane.     

Improved critical current density in Zn doped YBCO single crystals

Magnetic measurements were made using pure YBCO and Zn doped YBa₂(Cu_1?xZn_x)₃O_7?σ. Single crystals with Zn concentration of 0.5%, 1.5%, 3.0% and 4.3%. The magnetic hysteresis loops for these samples were measured in the temperature range 0.1 ? T/T_c ? 0.96 under magnetic fields of 5 T using SQUID. It was found that the critical current density J_c increased for low Zn content samples up to 3% Zn concentration compared to pure YBCO sample and decreased for the higher Zn content samples. These values varied consistently when compared at magnetic fields of 1 T and 3 T. Moreover Zn doped samples showed significant values of J_c in the temperature range of 0.7–0.9T_c, close to critical temperature compared to pure YBCO sample. The irreversibility field H_irr was also enhanced in this temperature range showing consistent decrease with increase of Zn concentration. The peak field H_p above H_c1 and irreversibility field H_irr, both show power law dependence of the form H = m₁(1 ? T/T_c)^m2 in the temperature range of 0.75–0.96T_c. The values of parameter m₂ increased from 1.44 to 1.95 for the samples up to 3% Zn content and decreased to 1.37 for higher Zn contents. The ratio H_irr/H_p was found to be 3–4 for the lower Zn content samples and was 7–8 for the sample with high Zn content indicating more disorder for higher Zn content samples. The region between peak field H_p and irreversibility field H_irr was broadened with the increase of Zn concentration. The strong effect of Zn substitution in modifying behavior of these samples even at elevated temperatures is possibly due to the changes in the anisotropy of our samples with the increase of Zn concentration and also due to the locally induced changes in magnetic moments by Zn substitution.     

Inelastic neutron scattering on iron-based superconductor BaFe2(As,P)2

Inelastic neutron scattering has been performed on powder sample of an iron-based superconductor BaFe₂(As_0.65P_0.35)₂ with superconducting transition temperature (T_c) = 30 K, whose superconducting (SC) order parameter is expected to have line node. In the normal state, constant-E scan of dynamical structure factor, S(Q, E), exhibits a peak structure centered at momentum transfer Q ～ 1.20 Å^?1, corresponding to antiferromagnetic wave vector. Below T_c, the redistribution of the magnetic spectral weight takes place, resulting in the formation of a peak at E ～ 12 meV and a gap below 6 meV. The enhanced magnetic peak structure is ascribed to the spin resonance mode, evidencing sign change in the SC order parameter similar to other iron-based high-T_c superconductors. It suggests that fully-gapped s_± symmetry dominates in this superconductor, which gives rise to high-T_c (=30 K) despite the nodal symmetry.     

Experimental investigation of flame spreading over pure methane hydrate in a laminar boundary layer

Flame spreading over pure methane hydrate in a laminar boundary layer is investigated experimentally. The free stream velocity (U_∞) was set constant at 0.4 m/s and the surface temperature of the hydrate at the ignition (T_s) was varied between ?10 and ?80 °C. Hydrate particle sizes were smaller than 0.5 mm. Two types of flame spreading were observed; “low speed flame spreading” and “high speed flame spreading”. The low speed flame spreading was observed at low temperature conditions (T_s = ?80 to ?60 °C) and temperatures in which anomalous self-preservation took place (T_s = ?30 to ?10 °C). In this case, the heat transfer from the leading flame edge to the hydrate surface plays a key role for flame spreading. The high speed flame spreading was observed when T_s = ?50 and ?40 °C. At these temperatures, the dissociation of hydrate took place and the methane gas was released from the hydrate to form a thin mixed layer of methane and air with a high concentration gradient over the hydrate. The leading flame edge spread in this premixed gas at a spread speed much higher than laminar burning velocity, mainly due to the effect of burnt gas expansion.