International Journal of Modern Physics B

In this paper, we carried out first-principles calculations based on density functional theory and nonequilibrium Green’s function to investigate the tunneling magnetoresistance effect in CoFe/Cu/MgO/CoFe magnetic tunnel junctions. Insertion of a nonmagnetic Cu layer between the tunnel barrier and the electrode is shown to result in the inverse and oscillation of the tunneling magnetoresistance as a function of the Cu layer at different bias voltage. The inverse phenomenon is discussed in terms of the conductance and the tunneling probability of electron at zero bias voltage. We suggest that the oscillation of tunneling magnetoresistance results from quantum well state formed in nonmagnetic Cu layer which can bring about the multiple scattering of tunneling electrons due to influence of the bias voltage on the oscillation period of the tunneling magnetoresistance.

In this study, we investigated stable structures for a transition metal atom–boron (CrB) wheel-like clusters and compared them with their corresponding 3D counterparts by means of density functional theory (DFT). In addition, hydrogen storage capability of the wheel-like system was investigated. All simulations were performed at the B3LYP/TZVP level of theory. We set out a complete route to the formation of CrB wheel-like clusters. Our results showed that, some of the clusters, investigated in this work (CrB_n; n = 4, 6, 7, 8), either prefer to be in a 3D geometry rather than 2D quasi-planar or planar geometry. However, hydrogen doping has an interesting effect on both 2D quasi-planar and 3D geometries of this system. Simply it transforms the 3D structure, first, into a 2D quasi-planar, then a planar geometry. Furthermore, our results show that H–cluster interaction is too high for reversible hydrogen storage for these clusters.

Based on the concept of generalized phononic crystals (GPCs), a type of 1D cylindrical shell of generalized phononic crystals (CS-GPCs) where two kinds of homogeneous materials are arranged periodically along radial direction was proposed in this paper. On the basis of radial, torsional shear and axial shear vibrational equations of cylindrical shell, the total transfer matrix of mechanical state vector were set up respectively, and the bandgap phenomena of these three type waves were disclosed by using the method of transfer matrix eigenvalue of mechanical state vector instead of the previous localized factor analyses and Bloch theorem. The characteristics and forming mechanism of these bandgaps of CS-GPCs, together with the influences of several important structure and material parameters on them were investigated and discussed in detail. Our results showed that, similar to the plane wave bandgaps, 1D CS-GPCs can also possess radial, torsional shear and axial shear wave bandgaps within high frequency region that conforms to the Bragg scattering effect; moreover, the radial vibration of CS-GPCs can generate low frequency bandgap (the start frequency near 0 Hz), as a result of the double effects of wavefront expansion and Bragg scattering effect, wherein the wavefront effect can be the main factor and directly determine the existence of the low frequency bandgaps, while the Bragg scattering effect has obvious enhancement effect to the attenuation. Additionally, the geometrical and material parameters of units have significant influences on the wave bandgaps of CS-GPCs.

In this paper, the $q$-deformed bosonic Tamm–Dancoff oscillator algebra is considered. First, the quantum algebraic and representative properties of these deformed bosons are analyzed in detail. The representations of the $q$-fermion algebra of Tamm–Dancoff type are also studied. Second, the high-temperature thermostatistical properties of a gas of Tamm–Dancoff type $q$-fermions are investigated. The fermionic distribution function and the other important thermodynamic functions such as the entropy and the specific heat are derived in terms of the real deformation parameter $q$. Finally, the time evaluation of a two-level atom in a Tamm–Dancoff oscillator trap interacting with a single-mode traveling light field is concisely discussed.

In this paper, the effect of minor element addition on the initial structural evolution during crystallization in a simple binary Cu–Zr bulk metallic glass (BMG) forming liquid has been investigated by using differential scanning calorimetry (DSC) and X-ray diffraction (XRD). Despite no changes in the completely crystallized products, the remarkable opposite impacts on the supercooled liquid region (SLR) and crystallization reaction rate constant $K_{\mathrm{\text{cr}}}$ are observed as a result of minor selective additions of an affine element, i.e., Sn and an immiscible element, i.e., Nb into the Cu–Zr BMG alloy, respectively. Furthermore, it is demonstrated that the primary devitrification pathway and crystalline phases are simultaneously modified, which leads to significant changes in kinetics of atomic rearrangement and thus thermal stability of this material. Such a finding offers a promising way to control the type of primary crystalline phases of BMG-forming metallic supercooled liquids to synthesize novel BMGs or BMG matrix composites for structural or functional applications.

In the present study, samarium doped ceria (SDC) and SDC-based composite with the addition of K₂CO₃ were prepared by co-precipitation route and effects of pH of the solution and calcination temperature on microstructure of SDC and SDC-K₂CO₃, respectively, were investigated. Furthermore, experimentation was performed to investigate into the ionic conductivity of pure SDC by co-doping with yttrium i.e., YSDC, XRD and SEM studies show that the crystallite size and particle size of SDC increases with the increase in pH. The SEM images of all the samples of SDC synthesized at different pH values showed the irregular shaped and dispersed particles. SDC-K₂CO₃ was calcined at 600${}^{\circ }$C, 700${}^{\circ }$C and 800${}^{\circ }$C for 4 h and XRD results showed that crystallite size increases while lattice strain, decreases with the increase in calcination temperature and no peaks were detected for K₂CO₃ as it is present in an amorphous form. The ionic conductivity of the electrolytes increases with the increase in temperature and SDC-K₂CO₃ shows the highest value of ionic conductivity as compared to SDC and YSDC. Chemical compatibility tests were performed between the co-doped electrolyte and lithiated NiO cathode at high temperature. It revealed that the couple could be used up to the temperature of 700${}^{\circ }$C.

In this paper, the superconductor with the competition of superconducting gap and pseudogap in the below crossover temperature region is calculated. The superconducting gap and pseudogap is assumed to arise from independent and competing correlation. The critical temperature, superconducting gap and the specific heat jump are derived in the analytic form and the approximation is used to simplify the equations obtained for the region that crossover temperature and energy of pseudogap are higher than critical temperature. We find that the critical temperature is decreased as the energy of pseudogap and crossover temperature as increased. The superconductor with pseudogap has small specific heat jump in comparison with the BCS value. Increasing the crossover temperature and critical temperature, the specific heat jump is decreased.

The latest global financial tsunami and its follow-up global economic recession has uncovered the crucial impact of housing markets on financial and economic systems. The Chinese stock market experienced a marked fall during the global financial tsunami and China’s economy has also slowed down by about 2%–3% when measured in GDP. Nevertheless, the housing markets in diverse Chinese cities seemed to continue the almost nonstop mania for more than 10 years. However, the structure and dynamics of the Chinese housing market are less studied. Here, we perform an extensive study of the Chinese housing market by analyzing 10 representative key cities based on both linear and nonlinear econophysical and econometric methods. We identify a common collective driving force which accounts for 96.5% of the house price growth, indicating very high systemic risk in the Chinese housing market. The 10 key cities can be categorized into clubs and the house prices of the cities in the same club exhibit an evident convergence. These findings from different methods are basically consistent with each other. The identified city clubs are also consistent with the conventional classification of city tiers. The house prices of the first-tier cities grow the fastest and those of the third- and fourth-tier cities rise the slowest, which illustrates the possible presence of a ripple effect in the diffusion of house prices among different cities.

A nanoferrite series of composition ${\mathrm{\text{Ni}}}_{0.5-x}{\mathrm{\text{Mn}}}_x{\mathrm{\text{Mg}}}_{0.5}{\mathrm{\text{Fe}}}_2{\mathrm{\text{O}}}_4$ with $x=0,0.1,0.2,0.3$ and 0.4 has been prepared by a hydrothermal method. X-ray diffraction (XRD) confirmed the formation of cubic spinel structure. The average crystallite size is found to be in the range of 28–48 nm. The lattice parameter is found to increase linearly with an increase in ${\mathrm{\text{Mn}}}^{2+}$ content. Field Emission Scanning Electron Microscopy micrographs indicate that the samples have almost uniform sized crystallites with uniform grain growth. Fourier Transform Infrared (FTIR) Spectroscopy studies showed two absorption bands close to 603 and $400{\mathrm{\text{cm}}}^{-1}$ for the tetrahedral and octahedral sites respectively. Saturation magnetization attained a maximum value of 34.15 emu/g at $x=0.3$ and then decreases for higher concentrations of ${\mathrm{\text{Mn}}}^{2+}$ ions. Activation energy for compositions ${\mathrm{\text{Ni}}}_{0.3}{\mathrm{\text{Mn}}}_{0.2}{\mathrm{\text{Mg}}}_{0.5}{\mathrm{\text{Fe}}}_2{\mathrm{\text{O}}}_4$ and ${\mathrm{\text{Ni}}}_{0.2}{\mathrm{\text{Mn}}}_{0.3}{\mathrm{\text{Mg}}}_{0.5}{\mathrm{\text{Fe}}}_2{\mathrm{\text{O}}}_4$ are found to be 0.371 eV and 0.471 eV, respectively. For composition ${\mathrm{\text{Ni}}}_{0.2}{\mathrm{\text{Mn}}}_{0.3}{\mathrm{\text{Mg}}}_{0.5}{\mathrm{\text{Fe}}}_2{\mathrm{\text{O}}}_4$, maximum value of observed density, minimum porosity, maximum value of saturation magnetization, maximum initial permeability and minimum value of coercivity is obtained. DC resistivity is found to be of the order of $10^8\Omega \mathrm{\text{cm}}$. The obtained results have been explained based on possible mechanisms, models and theories.