The magnetic properties of one-dimensional spin-1 ferromagnetic Heisenberg model in a magnetic field within Callen approximation

The effect of magnetic field h on the magnetic properties of the one-dimensional spin-1 ferromagnetic Heisenberg model is studied by the double-time Green’s function method. The magnetization and susceptibility are obtained within the Callen approximation. The zero-field susceptibility is as a decreasing function of the temperature T. The magnetization m increases in the whole field region, but the susceptibility maximum χ(T_m) decreases. The position T_m of the susceptibility maximum is both solved analytically and fits well to be a power law T_m∼h^γ at low fields and to be linear increasing at high fields. The height χ(T_m) decreases as a power law χ(T_m)∼h^−β with h increasing. The exponents (γ,β) obtained in our results agree with the other theoretical results. Our results are roughly in agreement with the results obtained in the experiment of Ni(OH)(NO₃)H₂O.     

Negative capacitance of ZnGa2Se4/Si nano-heterojunction diode

The negative capacitance (NC) behavior in p-ZnGa₂Se₄/n-Si nano-crystalline HJD was characterized by admittance-voltage method. The C–V, G–V and R _s –V for the studied diode were analysed in the frequency range of 1–5 MHz and in the temperature range of 303–423 K. The capacitance and conductance plots were interpreted in terms of interface states and series resistance. The C–V and G/ω–V plots exhibit a pounced peak due to the interface states and the series resistance effects. The negative capacitance behavior in the studied diode can be explained in terms of the transient currents.     

The hysteresis loop of two-phase particulate magnetic composite with non-linear hard magnetic components

The method of calculating the B - H curve of two-phase ferromagnetic composite materials whose components have B - H relations of the form B = mH + Br is extended to include materials whose components have non-linear B - H relations. The functional form of the non-linear B - H curve of the components materials is simulated by hyperbolic tangent functions with adjustable parameters. The result of theoretical calculations are compared to experimental data on Mn-Al-C and Fe-Cr-Co particulate composites. Good agreement are obtained.     

Coevolutionary extremal dynamics on gasket fractal

We considered a Bak-Sneppen model on a Sierpinski gasket fractal. We calculated the avalanche size distribution and the distribution of distances between subsequent minimal sites. To observe the temporal correlations of the avalanche, we estimated the return time distribution, the first-return time, and the all-return time distribution. The avalanche size distribution follows the power law, P(s)∼s−τ, with the exponent τ=1.004(7). The distribution of jumping sites also follows the power law, P(r)∼r−π, with the critical exponent π=4.12(4). We observe the periodic oscillation of the distribution of the jumping distances which originated from the jumps of the level when the minimal site crosses the stage of the fractal. The first-return time distribution shows the power law, Pf(t)∼t−τf, with the critical exponent τf=1.418(7). The all-return time distribution is also characterized by the power law, Pa(t)∼t−τa, with the exponent τa=0.522(4). The exponents of the return time satisfy the scaling relation τf+τa=2 for τf?2.     

Design and energetic characterization of ZnO clusters from first-principles calculations

The energetics, stable configurations and electronic structures of the n(ZnO) clusters for n ranging from 9 to 64 have been studied by using first-principles calculations. The formation energy of the bubble-like (b-)clusters decreases with the increase of cluster size n, and exhibits an approximately linear relationship to 1/n for n>16. The b-clusters are energetically more favorable than the wurzite-derived (w-)clusters for n<26, but become less stable than the w-clusters for n?26. The HOMO-LUMO gap of the w-clusters is narrower than that of the b-clusters.     

The influence of Debye plasma on the ground state energies of exotic systems

The effect of plasma environment on the ground state energies of exotic systems ppμ, ddμ and ttμ has been analyzed within a generalized three-body formalism using multi-term correlated basis sets. The Debye screening model of the plasma has been adopted for such a study. The binding energies of p with pμ, d with dμ and t with tμ have been estimated for a range of values of the Debye screening parameters. The systems tend toward instability for increased screening. The effect of particle correlation has been investigated in detail and is found to play an important role for the stability in these systems.     

Inversion and internal rotation in methyl-d-amine: Microwave spectrum

The microwave spectrum of CH₂DNH₂ has been observed in the 8–74 GHz region. The spectrum shows that this molecule takes essentially two distinguishable conformers, trans and gauche forms, although a small amount of coupling between them can be detected. For each line of the trans form a small inversion splitting has been found. It is 93.97 MHz at K = 0 and a periodic function of K. The mean frequencies of the inversion pairs of lines are well explained as the frequencies of a rigid rotor. The gauche spectrum is extremely complicated; each rotational line splits into four because of inversion and gauche-gauche tunneling interactions. The analysis was carried out based on the theory developed in the preceding paper. Tunneling energy parameters of internal-rotation, ?_gg and ?_tg, and inversion, δ_gg and δ_tg, were determined as ?_gg = 3476.6 MHz, ?_tg = 3233.1 MHz, δ_gg = 2790.6 MHz and δ_tg = 3052.7 MHz. Energy difference between trans and gauche conformers ΔE_tg was estimated to be 7.060 cm^?1 from these values of parameters and also on the basis of the observed anomaly in the Q branch series of trans form which is due to an accidental degeneracy between the K = 1 level of trans and K = 2 level of gauche. The effects on the internal-rotation of other internal motions have also been discussed.     

Magnetic properties of transition metal substituted MnP

The magnetic properties of polycrystalline samples of Mn_1?tT_tP (T = V, Cr, Fe and Co for 0.00 ≦ t ≦ 0.50) are studied by magnetic susceptibility, magnetization and neutron diffraction measurements. The magnetic phase diagrams of the Mn_1?tT_tP phases exhibit paramagnetic, ferromagnetic, helimagnetic and spin glass regions depending on temperature and substitution (T, t). The concentrated spin glass regions observed in Mn_1?tV_tP and Mn_1?tCo_tP (0.30 ≦ t ≦ 0.50) are believed to result from the disorder in the metal sublattice. The variation of the magnetic moment of the ordered Mn_1?tT_tP phases with the substitution (T, t) is discussed.     

Localization and transmission coefficient for two coupled metal chains with disorder

The equation for distribution of probabilities for the transmission coefficient T has been obtained for an electron passing through the finite section of the length L, consisting of two coupled disordered chains. The behavior of the mean 〈lnT〉 = - L/l_loc suggests localization of the electron on the length l, which depends on the coupling energy t between the chains. The ratio l_loc(t =)/l_loc(t?v_F/l) is found to be equal to 1 ? 1/π.     

Die Temperaturabhängigkeit der magnetischen Jordan-Nachwirkung von Nickel

The magnetic after effect of pure polycristalline nickel and of a single crystal was measured between ?196 and +340 °C by a Förster second harmonic magnetometer. The viscosity constantS _v is shown to be proportional toB(T)·H_c(T) with an increasing functionB(T) for specimens of different magnetic hardness. The temperature dependence S_v(T) atH _c is rather complex in comparison to the simpleT- or √T-behaviour of former theoretical models. The latter is observed only forT??100 °C, whileS _v is nearly independent ofT between ?100 and +300 °C, and drops abruptly to zero forT?300 °C.     

Near-threshold ω-and φ-meson production in pn → dM reactions and OZI-rule violation

The reactions pn → dω and pn → dφ are investigated near the corresponding thresholds. The S-wave amplitudes are calculated within the two-step model described by a triangle graph with π, ρ, and ω mesons in the intermediate state. The cross sections for the reactions pn → dω and pn → dφ are predicted to be significantly larger than the cross sections for the corresponding reactions pp → ppω and pp → ppφ at the same values of the c.m. excess energy Q. The phi-to-omega yield ratio is found to be (34±10)×10^?3.     

Correlations entre defauts ponctuels et proprietes de transport dans PbF2 dope

The investigation of the transport properties of the Pb_1−xM²⁺ⁿ_xF_2+nx(n = 1,2) solid solutions shows a maximum of the activation energy ΔE_max associated to a minimum of the conductivity for a very small value of x : x_min. (x_min. ≅ 0.01 for n = 1; x_,in ≅ 0.005 for n = 2). The value of ΔE_max. depends closely on the nature of the substituting cation. Correlations have been established between the transport properties and the nature of the point defects which are supposed to occur in the considered composition range (nn or innn pairs) by analogy with similar alkali-earth fluorides. The size difference Δr between host and substitutional cations seems to play an essential role. The evolution of ΔE_max. and the preferential stability of the nn or nnn pairs is discussed as a function of Δr.     

Phase transitions in N—n-propylpyridinium-TCNQ2 and N—n-butylpyridinium-TCNQn at high pressures

The electrical resistivity of N-n-propylpyridinium-TCNQ₂ (NPPy-TCNQ₂) and N-n-butylpyridinium-TCNQ_n (NBPy-TCNQ_n) has been measured as a function of temperature and pressure. Phase transitions in these salts have been studied at high pressures. The transition temperature (T_c) in NPPy-TCNQ₂ at atmospheric pressure increased with increasing pressure at the rate of dT_c/dP = + 12.0 degkbar^?1. The value of volume change calculated from the Clapeylon-Clausius relation was + 4.4 cm³ mol^?1. The electrical resistivity along the a- and c-axis increased with increasing pressure below 7 kbar. This anomalous electrical behaviour is closely related to the crystal structure of NPPy-TCNQ₂. The resistivity dropped sharply at about 11 kbar. This abrupt change may be due to a new pressure induced phase transition.The T_c of the NBPy-TCNQ_n increased remarkably with increasing pressure up to 0.7 kbar, above which the phase transition disappeared. The phase transitions of N-n-alkyl-substituted pyridinium TCNQ salts depend strongly on the nature of cations.     

Exact results of a mixed spin-1/2 and spin-1 Ising chain with both longitude and transverse single-ion anisotropies

The mixed spin-1/2 and spin-1 Ising chain with both longitude and transverse single-ion anisotropies Dz and Dx is solved exactly by means of a mapping to the spin-1/2 Ising chain with the alternating transverse fields and the Jordan-Wigner transformation. The analytical expressions of the quasi-particles' spectra Λk, the minimal energy gap Δ₀ for exciting a fermion quasi-particle, the minimal energy gap Δh for exciting a hole, and the ground state energy are obtained. The phase diagram of the ground state is also given. The results show that when Dz?0 for any finite value of Dx, there is no quantum critical point and the ground state is always in a spin ordered phase disregard of the boundary condition in the present system.     

Microwave spectrum of 3-iodopropene

The microwave spectra of 3-iodopropene were measured in the frequency region 12–18 GHz. The a-type R-branch and the b-type Q-branch rotational transitions of one conformer, skew, have been assigned and the rotational constants of the ground state have been obtained: A = 17 644.34, B = 1588.12, and C = 1538.64 MHz. The second-order quadrupole effects give rise to anomalous hyperfine splittings and are analyzed by taking into account χ_ab of the quadrupole coupling tensor. The nuclear quadrupole coupling constants have been determined to be χ_aa = ?1337, χ_bb = 387, χ_cc = 950, and ∥χ_ab∥ = 1081 MHz.     

The mixed-spin ternary-alloy in the form of ABpC1−p on the Bethe lattice

The AB_pC_1−p type of mixed ferromagnetic-ferrimagnetic ternary-alloy with A (spin-3/2), B (spin-1) and C (spin-5/2) ions was studied on the Bethe lattice with the odd numbered shells containing only A ions, while the even numbered shells either containing B or C ions randomly. The phase diagrams were obtained on the (R=|J_AC|/J_AB,kT_c/J_AB) and (p, kT_c/J_AB) planes for given values of p and R, respectively, with the coordination numbers z=3, 4, 5 and 6. The explicit dependence of the phase diagrams on z and each shell of the Bethe lattice having only one type of ion lead to some differences when compared with the previous works. The model presents one or two compensation temperatures for appropriate values of the system parameters.     

A dynamical theory for the off-shell continuation of the πNt-matrix

A dynamical theory, based on analyticity and dispersion theory, for the half-off-shell continuation of the on-shell πNt-matrix is proposed and developed. The resulting half-shell t-matrix is covariant, unitary, crossing symmetric, and based on a field-theoretic foundation. The dynamical information required to continue half off shell is obtained from field theory and consists of the off-shell amplitudes corresponding to the exchanges of the nucleon in the s- and u-channels and the ? and σ mesons in the t-channel. A coupled system of integral equations is derived for the partial wave half-shell t-matrix, which is truncated at the S- and P-waves and solved numerically. The results are compared with those obtained from various separable models of the πNt-matrix. The half-shell t-matrix is examined for separability and is found to be approximately separable in the P₃₃ and P₃₁ states. The dynamical content of the half-shell t-matrix is further illustrated by modeling the dynamical equation.     

Thermal entanglement of Hubbard dimers in the nonextensive statistics

The thermal entanglement of the Hubbard dimer (two-site Hubbard model) has been studied with the nonextensive statistics. We have calculated the auto-correlation (O_q), pair correlation (L_q), concurrence (Γ_q) and conditional entropy (R_q) as functions of entropic index q and the temperature T. The thermal entanglement is shown to considerably depend on the entropic index. For q<1.0, the threshold temperature where Γ_q vanishes or R_q changes its sign is more increased and the entanglement may survive at higher temperatures than for q=1.0. Relations among L_q, Γ_q and R_q are investigated. The physical meaning of the entropic index q is discussed with the microcanonical and superstatistical approaches. The nonextensive statistics is applied also to Heisenberg dimers.     

Three-photon excited PL spectroscopy and photo-generated Frenkel defects in wide-bandgap layered CdI2 semiconductors

We performed a three-photon excitation nonlinear photoluminescence (PL) spectroscopy in single crystals of wide-bandgap semiconductors (WBSs). The crystal temperature (TL)-dependent PL emission intensity (IPL) excited with different excitation power density (P) was measured. The PL emissions showed characteristics IPL with their maxima at around 520 nm. The IPL might be due to the presence of the photo-generated Frenkel defects (FDs) in WBSs. A detailed analysis of the PL spectra showed a third-order power law dependence of the maximum IPL on P for all the crystal temperature TL. The IPL was found to increase with decreasing TL. The results demonstrated the existence of the self-trapped excitons resulting from the presence of the FDs in the crystals.     

Proximity effect in the finite and incommensurate ferromagnet/superconductor systems

The original theory of a proximity effect is proposed for the bi- and tri-layered system ferromagnetic metal/superconductor (F/S) in dirty limit. The F₁/S/F₂ trilayer is examined more closely. The distinctions in materials, in thicknesses of F layers (d_f1 and d_f2), in parameters interfaces, and in local environments of layers are considered among the causes of incommensurability of trilayer. The peculiar T_c(d_f1, d_f2) interference pattern is predicted for the F₁/S/F₂ systems. The reentrant superconductivity and possibility of the better observability of the spin-valve regime are discussed.