Effects of Fe doping on ac susceptibility of Pr0.75Na0.25MnO3

Ac susceptibility at low temperatures of Pr_0.75Na_0.25Mn_1-xFe_xO₃ (0 ≤ x ≤ 0.30) is investigated. The peak value of the real component of ac susceptibility χ' at the freezing temperature T_f is suppressed with the increasing frequency. The peak value of χ' shows a linear relation between T_f and the logarithm of the frequency ω. The normalized slope P = ΔT_f/T_fΔlgω, which is much lower than canonical insulating spin glass systems in which 0.06 ≤ P ≤ 0.08. The peak value of the imaginary component of the ac susceptibility χ' at T_f for the x = 0, 0.02, 0.30 samples increases with increasing frequency, suggesting a cluster glass ground state with a coexistence of charge-ordered phase and correlated ferromagnetic clusters in spin glass matrix. The peak value of χ' at T_f for the x = 0.10 sample decreases with increasing frequency, suggesting a phase separation ground state. The peak value of χ' at T_f for the x = 0.05 sample decreases with increasing frequency for ω ≤ 52 Hz and increases subsequently till 701 Hz, and then decreases with further increasing frequency for ω ≥ 1501 Hz. This complex behaviour is ascribed to the competition between the effects of large and little ferromagnetic clusters in the sample. The ground state of x = 0.05 sample is a transition state from cluster glass to phase separation.     

Effect of surface plasmon oscillations on Auger electron emission

The integrated areas of the Al L₂₃VV and O KL₂₃L₂₃ Auger peaks and the Al surface plasmon energy ?ω_S are reported for the Al(001) surface as a function of exposure to O in the exposure range 0–114 L(1 L=1langmuir=10^?6Torr sec). It is shown that for exposures below a critical value of 15 L, ?ω_S is constant within experimental error while the O Auger peak area increases linearly. For exposures above 15 L, ?ω_S decreases linearly from 10.5 eV to 8.5 eV and the O Auger peak area undergoes relatively slow linear increases correspondingly. The Al Auger peak area decreases by 30% per 1 eV decrease of ?ω_S. The results are discussed with reference to theory relating Auger transition intensities to the spectral density function.     

On the Generation and Detection of High-Frequency Gravitational Waves Optically Excited in Dielectric Media

The possibility of generating and detecting high-frequency gravitational waves based on nonlinear-optical processes in dielectric media at their excitation by intense laser radiation of visible or ultraviolet ranges is analyzed. The theory predicts the feasibility of the Hertz gravitational laboratory experiment in which the parametric conversion of intense laser radiation with frequency ω₀ = 2πf₀ (f₀ = 10¹⁴ ? 10¹⁵ Hz) to a gravitational wave with frequency ω _g = 2ω₀ and the reverse process of gravitational radiation reconversion to optical radiation are implemented in the condensed dielectric medium.     

Radiative decays of scalar mesons σ(600), f 0(980) and a 0(980) in the local Nambu-Jona-Lasinio model

The two-photon decay widths of scalar mesons σ(600), f ₀(980) and a ₀(980) as well a ₀ → ju(ω)γ and f ₀ → ju(ω)γ are calculated in the framework of the local Nambu-Jona-Lasinio model. The contributions of the quark loops (Hartree-Fock approximation) and the meson loops (next 1/N _c -approximation where N _c is the number of colors) are taken into account. The values of these contributions, as we show, are of the same order of magnitude. For the f ₀ decay the K-loop contribution plays the dominant role. The results for two-gamma decays are in satisfactory agreement with modern experimental data. The predictions for a ₀ → ju(ω)γ and f ₀ → ju(ω)γ widths are given.     

Production of 62Zn radioactive nuclear beam and on-line PAC investigation of quadrupole interaction in nano-magnetic material Fe73.5Cu1Nb3Si13.5B9

An Isotope Separator On-Line (ISOL), dedicated to on-line perturbed angular correlation (PAC) and positron annihilation spectroscopy (PAS), has been constructed at CIAE based on the HI-13 tandem accelerator, and a 30 keV radioactive beam of ⁶²Zn with intensity of 2 ×10⁷/s produced by it. Using the ⁶²Zn radioactive beam the investigation of the nano-crystalline soft magnetic Fe_73.5Cu₁Nb₃Si_13.5B₉ materials has been fulfiled for the first time by the on-line time differential PAC technique. Two quadrupole interaction frequencies ω ₀₁ (?=?440 Mrad/s) and ω ₀₂ (?=?90 Mrad/s) were gained, indicating there are two implantation sites of ⁶²Zn. The frequency ω ₀₂ shows a fluctuation of the crystal lattice constants and proves the characteristic distribution model of nano-crystalline grain boundary. The frequency ω ₀₁ demonstrates that the implanted ⁶²Zn occupies the site of the ordered grain core. The fractions of ω ₀₁ and ω ₀₂ are f₀₁?=?38 % and f₀₂?=?62 %, respectively.     

Feldgleichungen der TREDERschen Gravitationstheorie,die aus einem Variationsprinzip ableitbar sind. I

In the frame work of TREDER 's gravitational theory we consider two classes of field equations which are derivable from two classes of LAGRANGE ian densities Ω⁽¹⁾(ω₁, ω₂), Ω⁽²⁾(s?₁, s?₂). ω₁, ω₂; s?₁, s?₂ are parameters. Ω⁽²⁾(ω₁, ω₂) gives us field equations which are up to the post-NEWTON ian approximation in the sense of NORDTVEDT , THORNE and WILL equivalent to the field equations given by BRANS and DICKE . For ω₂ = ?1 ?2ω₁ field equations follow from Ω⁽¹⁾(ω₁, ?1 ?2ω₁) which are in the above mentioned sense of post-NEWTON ian approximation equivalent to EINSTEIN 's equations. The field equations following from Ω⁽¹⁾(ω₁, ω₂) have a cosmological model with the well known cosmological singularities for T → ± ∞ in case that ω₁/(1 +3ω₁ +ω₂) ? γ > 0. For ω₁/(1 +3ω₁ +ω₂) ≤ 0 cosmological models with no cosmological singularities exist. From Ω⁽²⁾(s?₁, s?₂) we obtain field equations which at the best give us perihelion rotation 7% above EINSTEIN 's value and light deflection 7% below the corresponding EINSTEIN 's value. But in that case we are able to show the existence of a cosmological model without any cosmological singularity.     

Mode competition and frequency locking

A theoretical study is presented of frequency locking to be observed in lasers with broad homogeneous emission lines, when the cavity losses are reduced, at a certain frequency ω₀, by placing inside the cavity a suitable element (e.g., a selectively reflecting “mirror”). Two kinds of locking effects are analyzed: i) When tuning the center frequency of the laser output ω_f towards ω₀, by means of a filter or a grating, the laser frequency becomes locked to ω₀, when |ω_f ? ω₀| reaches a critical value. ii) In the absence of frequency-selective elements, the laser oscillates only in a narrow spectral range centered at ω₀. Special emphasis is given to the role played by mode competition in these locking phenomena.     

Electroluminescence spectra of structures based on the InGaN solid solution

The electroluminescence spectra of structures based on the InGaN solid solution (λ_max = 426 nm) have been investigated in the voltage range 3.2–3.6 V. The decrease in the growth rate of luminescence intensity with increasing current through a sample, which is observed in the current-intensity characteristics, is explained. The band gap of the material under study is determined. The change in this parameter with increasing voltage across the structure may be related to a change in the solid solution composition. Specific features of the dependences ?J/??ω = f(?ω) and ?β/?U = f(U) were used to determine the energy of the levels that can be involved in recombination.     

矢量介子φ的动力学模型及耦合常数fφKK2,fωKK2与fρKK2的值

假设矢量介子φ(Ι=0,ι=1,m_φ=7.30m_π)是K散射交换ρ,ω以及φ介子本身而形成的共振。应用双色散关系中的N/D方法,并设ρ,ω以及交换的φ介子的质量为已知,近似求出KK的分波散射振幅。当要求该振幅能重新给出正确的共振位置(φ的质量)和宽度时,即可得出偶合常数f_φKK²、f_ωKK²与f_ρKK²所必需满足的关系,从而给出它们可能取的数值。     

Plasmons in semiconductors and insulators: A simple formula

Based on the dielectric function of an excitonic system, a simple model dielectric function is constructed. The high energy zero of this function yields the plasma frequency, and is given by: (hω_x)² = (hω_f)² + E_x² where ω_f is the free electron plasma frequency and E_x the lowest exciton energy. It is argued that this formula is valid for both, Frenkel and Wannier excitons, and comparison is made with experiments on a variety of crystals, ranging from InSb to Ar. In all cases, surprisingly good agreement is found.     

Hamiltonian of the carrier-magnon interaction in a ferromagnetic semiconductor

The Hamiltonian of the electron-magnon Interaction in a ferromagnetic semiconductor of cubic symmetry is obtained. It is shown that many-magnon processes for T ? T_c make a small contribution to the transition probabilities. An expression is obtained for the s-d (s-f) exchange integral.     

Dynamical spin-spin correlation function of an isotropic ferromagnet at Tc in 6-ϵ dimensions

The dynamical spin-spin correlation function of an isotropic ferromagnet is calculated at T_c in 6-? dimensions. The asymptotic scaling part is determined to O(?). The shape function has a peak at ω = 0 with a narrowing width as ? increases. It is qualitative agreement with the mode coupling result in 3 dimensions.     

Femtosecond spectroscopy of relaxation processes in metals and high-T c superconductors

Spectral dependences of charge carrier relaxation rates, γ _e-e (?ω) and γ _e-ph (?ω), were observed in Au and Cu films and YBa₂Cu₃O_7-δ high-T _c superconductor films. The relaxation rates decreased substantially in the spectral region corresponding to interband transitions to the Fermi level region (?ω_Au = 2.45 eV, ?ω_Cu = 2.15 eV, and ? ω₁ = 1.89 eV and ?ω₂ = 2.08 eV for YBa₂Cu₃O_7-δ). This relaxation deceleration opens up possibilities for developing a new method, based on the spectral dependences of relaxation rates, for the determination of the Fermi level position and the parameters of electron-electron and electron-phonon interactions on the one hand and for studying deviations from the Fermi-liquid behavior in strongly correlated electronic systems. The linear γ _e-e (?ω) ∝ |?ω? E _F| spectral dependence was observed for a YBa₂Cu₃O_7-δ film near ?ω₂ = 2.08 eV, which may be evidence of a non-Fermi-liquid behavior of the electronic subsystem.     

High frequency cut-offs in superconductivity theory

The meaning of a high frequency cut-off for the Coulomb interaction at ±iω_max with ω_max ≈ E_f is investigated. It is not difficult to justify such a cut-off for nearly-free-electron metals. The real frequency Coulomb pseudopotential corresponding to the usual imaginary axis (μ¹, iω_c) pseudopotential is rigorously derived. It is markedly different from any assumed in previous work.     

An improved technique for the measurement of the complex susceptibility of magnetic colloids in the microwave region

Measurements by means of the short-circuit (S/C) and open circuit (O/C) transmission line techniques are well established methods for investigating the magnetic and dielectric properties of magnetic colloids, respectively. In particular, the S/C technique has been used in the investigation of the resonant properties of ferrofluids; resonance being indicated by the transition of the real component of the magnetic complex susceptibility, χ(ω)=χ′(ω)−iχ″(ω), from a positive to a negative value at a frequency, f_res. However, under certain circumstances, the accuracy of the S/C technique is affected by the dielectric properties of the sample, hence incurring errors in the measurement of χ(ω) and indeed of f_res. Here we present a model which, by combining short-circuit and open circuit measurements, is developed in a manner in which the permeability, μ, and the permittivity, ε, contribute simultaneously to the calculation of χ(ω), thereby providing superior experimental results in comparison to those obtained by the S/C technique alone. For the two ferrofluid samples measured it is demonstrated that the dielectric properties affect the high frequency content of the susceptibility spectrum.     

Properties of (Bi1/9Na2/3)(Mn1/3Nb2/3)O3 analysed within dielectric permittivity,conductivity, electric modulus and derivative techniques approach

The (Bi_1/9Na_2/3)(Mn_1/3Nb_2/3)O₃ ceramics with perovskite structure were sintered. The XRD test proved that the samples are cubic (a?=?3.920?±?0.001?Å). Microstructure and atomic composition were determined with a SEM (JSM-5410) equipped with energy dispersion X-ray analyser (ISIS-300). The fluctuation in the chemical composition was found indicating on local disorder. Broadband dielectric spectroscopy in the range 10^?1–3?·?10⁷?Hz was applied within the range of 100–650?K. The real, ?′(f,?T), and imaginary, ?″(f,?T), parts of complex dielectric permitivity characteristics, both in the temperature and frequency domain, show relaxation processes partially covered by electric conductivity. At high temperatures the electric conductivity exhibits a thermally activated behaviour σ(f,?T)?∝?exp(?E _a/kT) but the variable range hopping (VRH) dependence σ?∝?exp[?(T ₀/T)^1/4] is manifested at low temperatures. The derivatives technique in the frequency (??log??/??log?ω) and temperature (??log??/?T) domain enabled various relaxation processes to be distinguished. The data converted to electric modulus representation, M*(f,?T)?=?1/?*, exhibited clearly resolved relaxation peaks. The relaxation times obtained from the peaks position show a slightly non-Arrhenius temperature behaviour with the activation energy varying in 0.4–0.6?eV range and characteristic time of the electric conductivity relaxation of the order of 10^?12?s. The relaxation times can be fitted at better accuracy with the VRH dependence where T ₀ are of the order of 10⁸?K. It is shown that the low frequency ac-conductivity converges to dc-conductivity and the relation σ(0)?～?ω_m?～?τ_m ^?1 typical for the disordered solids applies. The conduction current relaxation relationship behaves in accord with the VRH system: σ_dc?∝?(T/T ₀)^q (e ²/kT) ω_c, where ω_c?=?ν_ph exp[?(T ₀/T)^1/4] is valid for the locally disordered (Bi_1/9Na_2/3)(Mn_1/3Nb_2/3)O₃ compound.     

Photoemission of adsorbed CO and H2O on Pt: Valence band studies

In this paper, using monochromatic He and Ne discharge lines, we report the ultraviolet photoemission results for CO and H₂O adsorbed on a Pt crystal. For chemisorbed CO, we use the energy dependence of the photoionization cross section to deduce that the 5σ?1π splitting is approximately 1 eV and that the 5σ is located at about ?8.1 eV while the 1π is at ?9.1 eV. The distribution of metal electrons changes in two ways upon CO chemisorption: a d character peak is found at ?4 to ?5 eV and emission at E_f is strongly depleted. For the weakly adsorbed water molecule, we find preferential attenuation of Pt states near E_f that has heretofore been observed for strongly chemisorbed systems.     

The f-electron contribution to the elastic property of Ce3S4

The elastic constant, C’, of Ce₃S₄ has been measured as a function of temperature. It is shown that the curve is markedly different from that of La₃S₄. Since the only basic difference between the two compounds is the existence of a f-electron in Ce, we propose a theoretical scheme in which the f-electron plays a crucial role. It is shown that the existence of the f-electron in Ce₃S₄ prevents the band Jahn–Teller type structural transition when the temperature is lowered. The theory is consistent with the experiment and also with the theoretically predicted instability of cubic f-electronelements at zero temperature. Received: 5 October 1999 / Accepted: 11 October 1999 / Published online: 24 March 2000     

AtomicL-subshell yields from the electron capture decays of 65 157 Tb and 65 158 Tb

Sources of the mass and chemically separated terbium isotopes,A=157 and 158, have been used to study inner shell phenomena atZ=64. In coincidence experiments employing high resolution Ge and Si(Li) detectors photon spectra characteristic of 2s,2p _1/2, and 2p _3/2 vacancies have been measured. The following results were obtained:f ₁₂=0.20±0.03,f ₁₃=0.289±0.015,f ₂₃=0.14±0.02,v ₁=0.179±0.014,v ₂=0.21±0.02,ω ₃=0.183±0.015. From thisω ₁=0.084±0.016 andω ₂=0.185±0.020 were deduced. Generally good agreement with the calculations is found, while larger discrepancies pertain to an overall fit of previous experimental results. The electron capture decay energy of¹⁵⁷Tb was inferred from the measured 2s-fluorescence yield to be 62.2±0.6 keV.