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  • 1
    ISSN: 1573-8515
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1063-7826
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract The influence of low-temperature annealing on the photoluminescence of GaAs/AlGaAs single-quantum-well structures treated in a low-energy CF4 plasma is investigated. It is established that annealing at 160–300 °C causes a decrease of the photoluminescence intensity of the quantum wells located in the near-surface region, while annealing at 350–450 °C leads to partial restoration of their photoluminescence. The activation energy for the diffusion of plasma-produced point defects and the activation energy for the annealing of these defects are determined. These energies are equal to 150 and 540 meV, respectively. It is discovered that the photoluminescence of the quantum wells near the substrate, which had a low intensity in the as-grown sample, increases after treatment in the plasma and decreases after subsequent annealing monotonically with increasing annealing temperature. Repeated treatment in a CF4 plasma leads to a repeated increase in the photoluminescence intensity of these quantum wells. It is theorized that the defects induced by the CF4 plasma form complexes with defects introduced during growth and that these complexes are not recombination centers. After low-temperature annealing, the complexes dissociate, and the nonradiative recombination centers are recreated.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1090-6509
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The real part R s and the imaginary part X s of the surface impedance Z s=R s+ iX s of Tl2Ba2CaCu2O8−δ and YBa2Cu3O6.95 single crystals have been measured with high precision at frequency ω/2π=9.4 GHz in the temperature range 0〈T〈140 K. In the Tl2Ba2CaCu2O8−δ crystal a linear temperature dependence R s(T) has been found for T⩽50 K, and the magnetic field penetration depth λ(4.2 K)=X s(4.2 K)/ω μ 0≈3760 Å has been measured. Along with well known features of the function Z s(T) in high-quality YBa2Cu3O6.95 single crystals, such as the linearity of λ(T) and R s(T) for T〈T c/3 and a maximum of R s(T) at T∼T c/2, the linearity range of λ(T) extends to T≃50 K, and this curve has a plateau in the range 60〈T〈85 K. The curve of R s(T) in both the superconducting and normal states of YBa2Cu3O6.95 is well described by a two-fluid model with the electron-phonon mechanism of quasiparticle relaxation. A formula describing the curve of λ 2(0)/λ 2(T) throughout the studied temperature range is also given.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1090-6509
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The magnetic properties of the intermetallic compounds Gd1−x YxMn2Ge2 (0≤x≤0.5) (tetragonal crystal structure of the type ThCr2Ge2) have been measured in fields up to 40 T in the temperature range 4.2–120 K on free powders (whose particles are free to rotate in a magnetic field), fixed powders, and polycrystalline bulk samples. The temperature dependence of the crystal structure parameters of some of these intermetallic compounds was determined from x-ray diffraction measurements. It was found that the temperatures of magnetic disordering of the gadolinium magnetic subsystem and the transition of the manganese subsystem from the ferromagnetic to the antiferromagnetic state decrease as the gadolinium content is decreased, so that in compositions with x〈0.3 this transition is a first-order phase transition, and with further decrease of the gadolinium content it becomes second-order. In intermetallic compounds of this system with x=0.3 and 0.4 another spontaneous first-order transition is observed at lower temperatures. In a magnetic field the magnetization of all the investigated intermetallic compounds except for the composition x=0.5 undergo a metamagnetic transition. The T-x, H-x, and H-T magnetic phase diagrams are constructed. The experimental data are interpreted with allowance for the fact that according to the results of previous studies, the Mn-Mn exchange interaction is antiferromagnetic, and thus the examined intermetallic compounds are two-sublattice ferrimagnets with negative exchange interaction in one of the sublattices. Calculations performed within the framework of this model in the Yafet-Kittel approximation, which assumes that the sublattice with negative exchange can be divided into two sub-sublattices, permit a quantitative description of the experimental results in most cases.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Physics of the solid state 40 (1998), S. 1169-1174 
    ISSN: 1063-7834
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The aim of this study is to find universal critical values of the effective dimensionless coupling constant g 6 and refined universal values g 4 for Heisenberg ferromagnets with n-component order parameters. These constants appear in the equation of state and determine the nonlinear susceptibilities χ 4 and χ 6 in the critical region. Calculations are made of the first three terms of the expansion of g 6 in powers of g 4 in the limits of O(n) symmetry three-dimensional λϕ 4 theory, the resultant series is resummed by the Padé-Borel method, and then by substituting the fixed point coordinates g 4 * in the resultant expression, numerical values of g 6 * are obtained for different n. These numbers g 4 * for n〉3 were determined from a six-loop expansion for the β-function resummed using the Padé-Borel-Leroy technique. An analysis of the accuracy of these g 6 * values showed that they may differ from the true values by no more than 1.6%. These values of g 6 * were compared with those obtained by the 1/n expansion method which allowed the level of accuracy of this method to be assessed.
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 1090-6487
    Keywords: 75.10.−b ; 64.60.Ak ; 64.60.Cn ; 05.10.Ln
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We study the critical behavior of frustrated systems by means of the Padé-Borel resummed three-loop renormalization group expansions and numerical Monte Carlo simulations. Amazingly, for six-component spins, where the transition is second-order, both approaches disagree. This unusual situation is analyzed both from the point of view of the convergence of the resummed series and from the possible relevance of nonperturbative effects.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Physics of the solid state 40 (1998), S. 1467-1469 
    ISSN: 1063-7834
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract A study is made of the dynamics of self-consistent motion and growth of spherical new-phase nuclei from a eutectic melt. The growth rate of nuclei is shown to be proportional to supersaturation in both components. Motion of a single nucleus in a concentration-gradient field and of a pair of nuclei in a self-consistent concentration field is investigated. The velocity of motion of the nucleus as a whole has been established to depend on the key parameters of the problem, namely, supersaturation, radii of the nuclei, and their separation. The force of mutual attraction between nuclei is estimated, and it is shown to be inversely proportional to the fifth power of their separation.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Physics of the solid state 42 (2000), S. 2151-2158 
    ISSN: 1063-7834
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The paper is devoted to the calculation of renormalization-group (RG) functions in the O(n)-symmetry two-dimensional model of the λϕ 4 type in the five-loop approximation and to an analysis of the critical behavior of systems described by this model. Five-loop expansions for the β function and the critical indices are determined in bulk theory. They are summed up using the Padé-Borel and Padé-Borel-Le Roy methods, making it possible to optimize the summation procedure and to estimate the accuracy of the obtained numerical values. It is shown that in the Ising (n=1) case, as well as in other cases, the inclusion of the five-loop contribution to the β function displaces the coordinate of the Wilson fixed point only insignificantly, leaving it outside the interval formed by the results of computations on lattices; even “spreads” of the error in the renormalization group and lattice estimates do not overlap. This discrepancy is attributed to the effect of the nonanalytic com-ponent of the β function, which cannot be determined in perturbation theory. A computation of critical indices proves that, although the inclusion of the five-loop terms in the corresponding RG expansion slightly improves the concordance with the exact results, the nonanalytic contributions are apparently also significant in this case.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    JETP letters 71 (2000), S. 412-416 
    ISSN: 1090-6487
    Keywords: 75.10.Hk ; 75.40.Cx ; 05.50.+q ; 05.70.Jk
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The renormalization-group functions governing the critical behavior of the three-dimensional weakly-disordered Ising model are calculated in the five-loop approximation. The random fixed point location and critical exponents for impure Ising systems are estimated by means of the Padé-Borel-Leroy resummation of the renormalization-group expansions derived. The asymptotic critical exponents are found to be γ=1.325 ± 0.003, η=0.025 ± 0.01, ν= 0.671 ± 0.005, α=−0.0125 ± 0.008, β=0.344 ± 0.006, while for the correction-to-scaling exponent, a less accurate estimate ω=0.32 ± 0.06 is obtained.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    Journal of experimental and theoretical physics 84 (1997), S. 383-387 
    ISSN: 1090-6509
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The surface impedance Z s=R s+iX s of samples of Ba0.6K0.4BiO3 in the temperature range 4〈T〈50 K is measured at 9.42 GHz. The BCS theory completely describes the electrodynamic properties of Nb in the dirty limit, and its application to Ba0.6K0.4BiO3 allows determination of the London penetration depth λ L(0)=3100±100 Å.
    Type of Medium: Electronic Resource
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