The effect of isoelectronic substitution on the magneto-resistance of Sr2−xBaxFeMoO6

We report results from structural, transport and magnetic measurements on polycrystalline Sr_2−xBa_xFeMoO₆ (x=0, 1 and 2) half-metallic double perovskites. We find a large low field magneto-resistance (MR) of −25% at 0.8 T and 77 K for samples that have high resistivities. We show that the low field tunneling MR can be modeled by assuming that there is a disordered region near the insulating grain boundaries as proposed by Serrate et al. It is the magnetization from this region rather than the bulk magnetization that determines the MR in polycrystalline samples.     

Correlation among electronic polarizability, optical basicity and interaction parameter of Bi2O3–B2O3 glasses

For optical basicity and electronic polarizability, the previous studies basically concentrate on the wavelength range of the visible light region. However, heavy metal oxides glasses have a reputation of being good materials for infrared region. In this study, new data of the average electronic polarizability of the oxide ion _O^2-, optical basicity Λ and Yamashita–Kurosawa's interaction parameter A of Bi₂O₃–B₂O₃ glasses have been calculated in a wavelength range from 404.66 to 1083.03 nm. The present investigation suggests that both _O^2- and Λ increase gradually with increasing wave number, and A decreases with increasing wave number. Furthermore, close correlations are studied among _O^2-, Λ, A and refractive index n in this paper. Particularly, it has been found that a quantitative relationship between electronic polarizability and optical basicity is observed in a wavelength range from 404.66 to 1083.03 nm. Our present study extends over a wide range of _O^2-, Λ and A values.     

Influence of structure on coercivity in nanocrystalline (Fe1−xCox)86Hf7B6Cu1 alloys

The relationship between coercivity and structure in nanocrystalline (Fe_1−xCo_x)₈₆Hf₇B₆Cu₁ (x=0–1) alloys was surveyed. It was found that the increase of Co content in the alloys studied was accompanied by the increase of coercivity. However, we suggest that the factors influencing the coercivity change with the concentration of cobalt in these nanocrystalline alloys. In the iron-rich alloys, the average grain size and magnetostriction play predominant roles in the coercivity. On the other hand, in the case of cobalt-rich alloys, the coercivity mostly originates from the FCC-Co phase with large magnetocrystalline anisotropy and the weak exchange coupling between BCC-Fe(Co) and FCC-Co(Fe).     

The third-order optical nonlinearity of The pyrochlore phase 0.7Pb(Mg1/3Nb2/3)O3–0.3PbTiO3 thin film on quartz

The xPb(Mg_1/3Nb_2/3)O₃–(1−x)PbTiO₃ (PMNT) (with x=0.7) thin film is prepared on quartz substrates prepared using a sol–gel process. The PMNT thin film has a well-crystallized pyrochlore phase structure. The sign and magnitude of both real and imaginary parts of third-order nonlinear susceptibility χ⁽³⁾ of the thin film have been determined by the Z-scan technique performed at 800 nm with a femtosecond laser. The nonlinear refraction index coefficient γ, the nonlinear absorption coefficient β of the thin film are 1.37×10⁻¹² cm²/W and −6.73×10⁻⁸ m/W, respectively. The real and imaginary part of the third-order nonlinear susceptibility of the film are 1.06×10⁻¹⁷ and −1.65×10⁻¹⁹ m²/V², respectively. The results suggested that the nonlinearity is dominated by the refractive for the film.     

Jahn–Teller coupled charge density wave in a double exchange system

In a two orbital model, we formulate Jahn–Teller coupled charge density wave in one electron per lattice site limit. Softening of Jahn–Teller phonons corresponding to distortion modes Q₂ or Q₃ associated with perfect nesting of Fermi surface leads to this instability at low temperature. The gap equation for charge density wave state and its dependences on electron–lattice coupling are calculated explicitly when any one of the Jahn–Teller modes is excited cooperatively. We find that the Q₂ distortion mode yields lowest free energy. Effect of electron–lattice interaction on collective mode, such as amplitude mode, is more pronounced when the excited mode is Q₂.     

Density of states and phase diagram of the antiferromagnetic spin chain with Dzyaloshinsky–Moriya interaction and spin-phonon coupling

The effects of DM interaction on the density-of-states, the dimerization and the phase diagram in the antiferromagnetic Heisenberg chain coupled with quantum phonons have been studied by a nonadiabatic analytical approach. The results show that the effect of the DM interaction is to increase the staggered antisymmetric spin exchange interaction order but to decrease the spin dimerization and their competitions result in the lattice dimerization ordering parameter to increase for large staggered DM interaction parameter β and decrease for small β. A crossover of β exists in which the dimerization ordering parameter changes non-monotonously. As the DM interaction parameter D increases, depending on the appropriate values of spin-phonon coupling, phonon frequency and β, the system undergoes phase transition from spin gapless state to gapped state or reversely and can even reenter between the two states. The relation between the phonon-staggered ordering parameter, the spin-dimer order parameter and the staggered DM interaction order parameter gives clearly their contributing weights to the lattice dimerization.     

Mössbauer study of chromium-substituted nickel ferrites

The structural and magnetic properties of the Cr substituted NiCr_xFe_1−xO₄ (0x1.4) spinel ferrites have been investigated by means of X-ray diffraction and Mössbauer spectroscopy techniques. Their crystal structures are found to be pure cubic phases. The Mössbauer spectra at 295 and 78 K of all samples showed two well-resolved magnetic patterns corresponding to the tetrahedral A-sites and octahedral B-sites. The cation distributions driven from the area under resonance curve of each site revealed that the compounds are gradually transferred from perfect inverse spinel to partially normal spinel structure. The behavior of the magnetic properties as a function of Cr³⁺ concentration has been explained on the basis of the driven cation distribution and it showed that the chrome-rich compositions can be explained in terms of the non-collinear spin model.     

Electronic and optical properties of BaTe, BaSe and BaS from first principles

Electronic and optical properties of barium chalcogenide compounds BaX (X=S, Se and Te) in NaCl crystal structure are calculated using the band structure results obtained through the full potential linearized augmented plane wave (FP-LAPW) method. The exchange correlation potential is treated by the generalized gradient approximation. The real and imaginary parts of the dielectric function ε(ω), the optical absorption coefficient I(ω), the reflectivity R(ω) and the energy loss function are calculated. The calculated results show good agreement with the available experimental results, particularly in the low-energy region of the spectra. Furthermore the interband transitions responsible for the structures seen in the spectra are specified. It is shown that the chalcogen p states and Ba 5d states play a major role in optical transitions as initial and final states, respectively. The effect of the spin–orbit coupling on the optical properties is also investigated and found to be significant, especially in high-energy regions.     

Energy of formation for and liquid binary alloys

We have investigated the free energy of formation for Ag_xIn_1-x and Ag_xSn_1-x liquid binary alloys at temperatures 1173 and 1250 K, respectively. A microscopic theory based on the first order perturbation has been applied. The interionic interaction and a reference liquid are the fundamental components of the theory. The interionic interaction is described by a local pseudopotential. A liquid of hard spheres (HS) of two different effective diametres and charges is used to describe the reference system. The results of the calculations for energy of formation agree very well with the available experimental data. Our calculations also reveal that a simple perturbative approach along with appropriate effective pair potentials can produce nearly quantitative results for the concerned alloys.     

Study of the decay

Using data from the FOCUS (E831) experiment at Fermilab, we present a new measurement for the Cabibbo-suppressed decay mode D⁰→K⁺K⁻π⁺π⁻. We measure: Γ(D⁰→K⁺K⁻π⁺π⁻)/Γ(D⁰→K⁻π⁻π⁺π⁺)=0.0295±0.0011±0.0008. An amplitude analysis has been performed in order to determine the resonant substructure of this decay mode. The dominant components are the decays D⁰→K₁(1270)⁺K⁻, D⁰→K₁(1400)⁺K⁻ and D⁰→ρ(770)⁰(1020).     

Discrete symmetry and CP phase of the quark mixing matrix

A simple specific pattern of the two 3×3 quark mass matrices is proposed, resulting in a prediction of the CP phase of the charged-current mixing matrix V_CKM, i.e., sin2₁(β)=0.733, which is in remarkable agreement with data, i.e., sin2₁=0.728±0.056±0.023 from Belle and sin2β=0.722±0.040±0.023 from BaBar. This pattern can be maintained by a discrete family symmetry, an example of which is D₇, the symmetry group of the heptagon.     

Measurements of decays into and

Based on a sample of 5.8×10⁷ J/ψ events taken with the BESII detector, the branching fractions of J/ψ→2(π⁺π⁻)η and J/ψ→3(π⁺π⁻)η are measured for the first time to be (2.26±0.08±0.27)×10⁻³ and (7.24±0.96±1.11)×10⁻⁴, respectively.     

Hybridization gap-open in CeIn3

Reflectivity spectra of CeIn₃ are measured at 7, 30, 50, 100, 150, 200 and 300 K in wild energy regions from 6 meV to 30 eV. Optical conductivity spectra are obtained from a Kramers–Kronig’ relation. A hump in the optical conductivity σ₁ is observed at about 500 cm⁻¹ below 100 K, resulting from strong hybridization between conduction electrons and Ce 4f electronic states. The low frequency plasmon indicating the existence of heavy particles is also observed below coherence temperature T^*  100 K.     

Exact Hamiltonian for an analytic correlated ground-state wave function for He-like ions

A correlated three-parameter variational ground-state Ψ(r₁,r₂,r₁₂) proposed by Chandrasekhar for helium-like ions gives a high percentage of the electron correlation energy resulting from the interaction energy e²/r₁₂ and also yields an analytic ground-state electron density ρ(r). Here, we extract via Schrödinger equation an exact Hamiltonian for which the Chandrasekhar wave function is the ground-state. Properties of the potential energy function in this Hamiltonian are quantified. Finally, kinetic energy densities are plotted and related to the Laplacian of ρ(r).     

Binding energy of impurity states in an inverse parabolic quantum well under magnetic field

 We have investigated the effects of the magnetic field which is directed perpendicular to the well on the binding energy of the hydrogenic impurities in an inverse parabolic quantum well (IPQW) with different widths as well as different Al concentrations at the well center. The Al concentration at the barriers was always x_max=0.3. The calculations were performed within the effective mass approximation, using a variational method. We observe that IPQW structure turns into parabolic quantum well with the inversion effect of the magnetic field and donor impurity binding energy in IPQW strongly depends on the magnetic field, Al concentration at the well center and well dimensions.     

The finite-size scaling study of the specific heat and the Binder parameter for the six-dimensional Ising model

The six-dimensional Ising model with nearest-neighbor pair interactions is simulated on the Creutz cellular automaton by using the finite-size lattices with the linear dimensions L=4,6,8,10. The temperature variations and the finite-size scaling plots of the specific heat and Binder parameter verify the theoretically predicted expression near the infinite lattice critical temperature. The approximate values for the critical temperature of the infinite lattice T_C=10.838(1), T_C=10.836(20) and T_C=10.835(1) are obtained from the intersection points of specific heat curves, Binder parameter curves and the straight line fit of specific heat maxima, respectively. These results are in agreement with the more precise value of T_C=10.835(5). The value obtained for the critical exponent of the specific heat, i.e., =0.012(2) is also in agreement with =0 predicted by the theory.     

Materials with a desired refraction coefficient can be made by embedding small particles

A method is proposed to create materials with a desired refraction coefficient, possibly negative one. The method consists of embedding into a given material small particles. Given n₀(x), the refraction coefficient of the original material in a bounded domain , and a desired refraction coefficient n(x), one calculates the number N(x) of small particles, to be embedded in D around a point xD per unit volume of D, in order that the resulting new material has refraction coefficient n(x).     

Intense red mechanoluminescence from (ZnS)1−x(MnTe)x

Intense mechanoluminescent (ZnS)_1−x(MnTe)_x powder samples with x=0.02,0.05,0.10,0.15,0.20 and 0.25 were prepared by simple Solid State Reaction method. All samples were polycrystalline with wurtzite structure. Mechanoluminescence (ML) and Photoluminescence (PL) were observed in all the samples in the red region peaking around 650 nm. The red emission is attributed to the presence of Te along with Mn. ML is attributed to the release of holes due to the stress on the phosphors which then recombine with metastable Mn²⁺ emitting light. The intensity of ML is found to be strongly dependent on both the impact pressure and composition. The maximum intensities in both ML and PL were observed in samples with x=0.05.     

Aspects of “low field” magnetotransport in epitaxial thin films of the ferromagnetic metallic oxide SrRuO3

Epitaxial thin films of the conductive ferromagnetic oxide SrRuO₃ were grown on an (0 0 1) SrTiO₃ (STO) substrate by using DC sputtering technique. The magnetic and magnetoresistive properties of the films were measured by applying the magnetic field both perpendicular (out-of-plane) and parallel (in-plane) to the film plane and ever maintaining the direction of the applied field perpendicular to that of the transport current. The films grown on an (0 0 1) STO substrate showed identical magnetization properties in two orthogonal crystallographic directions of the substrate, [1 0 0]_S and [0 0 1]_S (in-plane and out-of-plane geometry), which suggests the presence of a multi domain structure within the plane of the film. For such samples, no anisotropic field (hard axis) along de [0 0 1]s direction, i.e., perpendicular to the film-plane could be detected. Nevertheless, a distinguishable temperature dependent out-of-plane anisotropic magnetoresistance (MR) along with strong temperature dependent low field hysteretic MR(H) behavior was detected for the studied films. A negative MR ratio MR(T)=[ρ(μ₀H=9 T; T)−ρ( μ₀H=0 T; T)]/ρ( μ₀H=0 T; T) on the order of a few percent, with maximums of 6% and 4% (right at the Curie temperature, T_C 160 K) was calculated for an in-plane and out-of plane measuring geometry, respectively. In addition there is an equally strong MR effect at low temperatures, which might be related to the temperature dependence of the magnetocrystalline anisotropy together with a magnetization rotation. Both the MR(T) behavior and the achieved values (except for T<30 K) are similar to those obtained on SrRuO₃ films grown on 2° miscut (0 0 1) STO substrates with the current parallel to the field and parallel to the direction, which was identified as the easier axis for magnetization.