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  • Articles  (149)
  • Articles: DFG German National Licenses  (149)
  • American Institute of Physics (AIP)  (89)
  • Wiley-Blackwell  (60)
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  • Articles  (149)
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  • 1
    Electronic Resource
    Electronic Resource
    Concentration dependence of the random field crossover scaling in FexZn1−xF2 : 35th annual conference on magentism and magnetic materials San Diego, California (USA) 29 Oct − 1 Nov 1990 (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 69 (1991), S. 5246-5248 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The proportionality between the field-induced shift ΔTc(H) of the transition temperature Tc(H) and the root-mean-square (rms) random-field hRF was studied over a wide range of concentration (0.31≤x≤0.84) in the nearly ideal random-field Ising model (RFIM) system FexZn1−xF2. Tc(H) was determined experimentally from the optical birefringence Δn, for which d(Δn)/dT exhibits a peak proportional to the magnetic specific heat. For all x studied, Tc(H) was found to shift from the H=0 transition at TN as ΔTc(H)ΔTc(H)= cTN h2/φRF as predicted, with φ=1.42±0.03 the universal random exchange to RFIM crossover exponent, after a mean-field correction bH2. The nonuniversal quantity c was found to be of order unity as expected, but slightly x dependent.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.348093
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  • 2
    Electronic Resource
    Electronic Resource
    Eddy-current analysis of isolated permanent-magnet drives using two- and three-dimensional finite-element methods (abstract) (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 4741-4741 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Present drive systems which rely on mechanical devices for torque transmission have some negative features: the driven component cannot be isolated from the drive motor, rotating seals have inherent leakage and friction problems, and mechanical failures often occur due to torque overloads. Magnetic couplings are especially well suited for use in isolated-drive systems. This is often the case in military and aerospace applications where pumps and compressors are vital parts of the thermal and fuel operating systems. The application of permanent-magnet couplings in isolated drives requires accurate calculation of the eddy-current losses induced on the hermetic vessel. This is because the losses along with the required output torque dictate the size and efficiency of the permanent-magnet coupling. The vessel isolates the drive member from the driven member of the turbocompressor. The paper will show the formulation of the computational method based on the Poynting-vector theorem and the concept of motional electric field intensity. The eddy-current losses are calculated using two- and three-dimensional magnetostatic finite-element (FE) analysis. A comparison of the results obtained by two- and three-dimensional FE analysis is made. The results of the analysis will be compared to test data for verification. The test-facility setup and procedure will also be described. This state-of-the-art technique for computation of eddy-current losses has several advantages over conventional analysis methods: the nonlinearities of the magnetic circuit are taken into account, magnetic field fringing and end-leakage effects are not neglected, and the method does not rely on the use of empirical factors. The significant benefits of this approach are that trial-and-error experimental design approaches are eliminated and test data provide validation of analytical results.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.344796
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  • 3
    Electronic Resource
    Electronic Resource
    Annealing kinetics of a-Si:H deposited by concentric-electrode rf glow discharge at room temperature (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 1826-1831 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The irreversible isothermal annealing of the as-deposited defects of hydrogenated amorphous silicon, a-Si:H, deposited at room temperature by concentric-electrode radio-frequency glow discharge is studied using dark and photoconductivity, space-charge limited current, and time-of-flight. The photoconductivity increases as a power law of the annealing time with exponent 0.8. The density of states at the Fermi level, measured by space-charge limited current, is inversely proportional to the annealing time. These results are compatible with bimolecular annealing kinetics. The dark conductivity obeys a Meyer–Nelder rule during the isothermal anneal.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.353167
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  • 4
    Electronic Resource
    Electronic Resource
    Incorporating susceptibility changes in a general thermally-stimulated polarization process (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 72 (1992), S. 290-290 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Generalization of a previously given expression dealing with processes in which temperature and electric field are simultaneously varied is proposed in order to include also susceptibility changes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.352134
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  • 5
    Electronic Resource
    Electronic Resource
    Self-consistent modeling of surface wave produced discharges at low pressures (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 70 (1991), S. 4147-4158 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A self-consistent theory of a low-pressure gas discharge sustained by a surface wave (SW) is presented which provides a complete description of the plasma density (ne) and SW-field distribution both in the radial (r) and the axial (z) directions. The theory is based on a complete set of equations including Maxwell's equations and the boundary conditions for the SW-field, the electron Boltzmann equation which yields local collisional and transport data versus the SW-electric field E, and the continuity and momentum transfer equations for the electrons and the ions. For given operating frequency, gas density, setup dimensions and total incident power Pi(0), the theory enables the determination of: (i) the SW-dispersion relation; (ii) ne(r,z) and E(r,z); (iii) Pi(z); and (iv) θ(z), the radially averaged mean absorbed power per electron. It is shown that E¯(z), the radially averaged field in the plasma, and θ(z) are practically constant along z, in spite of the fact that Pi(z) steadily decreases. Comparison with experiment is made for SW discharges in Ar operated at the frequencies of 433 MHz and 2.45 GHz.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.349137
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  • 6
    Electronic Resource
    Electronic Resource
    Surface resistance studies of laser-deposited superconducting Tl2Ba2CaCu2O8 films (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 70 (1991), S. 496-498 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have measured the surface resistance Rs of laser-deposited Tl2Ba2CaCu2O8 thin films on LaAlO3 substrates. After correcting for leakage of radiation through the films, we find that the normalized surface resistance Rs/RN (with RN the normal-state surface resistance at T ≥ Tc) is comparable to YBa2Cu3O7 (123) films. The higher transition temperature of the Tl films leads to superior microwave performance in particular at temperatures around T=77 K and above.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.350257
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  • 7
    Electronic Resource
    Electronic Resource
    Concentration scaling of the specific heat in the d=3 random exchange Ising model system FexZn1−xF2 : 35th annual conference on magnetism and magnetic materials San Diego, California (USA) 29 Oct − 1 Nov 1990 (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 69 (1991), S. 5075-5077 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Linear magnetic birefringence Δnm was used to study the concentration dependence of both the total magnetic specific heat Cm and critical amplitudes in the random exchange Ising model (REIM) system FexZn1−xF2. We find the proportionality between Δnm and the magnetic energy Um is x independent for 0.24≤x≤1.0, since Δnm scales with x2 as does Um. However, the critical part of Cm is found to decrease with dilution very much faster than x2. To explain this, a scaling form is derived which describes the x-dependent crossover from pure Ising to REIM with a crossover exponent φ=α, the pure Ising specific heat exponent. The critical amplitudes A± of Cm = A±||t − tn||−α˜ are shown to scale as A±(x)A±(x)∼ (1 − x)(α˜−α)/(φ)∼ (1 − x)−1.9(3), using the experimental REIM value of α˜=−0.09(3), and theoretical value of α=0.105(7). Good agreement between theory and experiment is found.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.348127
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  • 8
    Electronic Resource
    Electronic Resource
    Antiferromagnetic coupling and magnetoresistance enhancement in Co-Re metallic superlattices (abstract) : The 5th Joint MMM−Intermag Conference (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 70 (1991), S. 5878-5878 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Co-Re metallic superlattices were prepared that show antiferromagnetic exchange coupling and enhanced saturation magnetoresistance for particular values of the Re spacer thickness. We report studies on films with the structure glass /150 A(ring) Re/[13 A(ring)Co/tRe]16/50 A(ring) Re, with tRe ranging from 3 to 40 A(ring). These structures were grown by magnetron sputtering in a system with a base pressure of 1×10−7 Torr with deposition rates of 0.3 and 0.4 A(ring)/s for Co and Re, respectively. x-ray diffractograms indicate the structure to be highly textured with the c axis perpendicular to the sample plane. The superlattice structure was obtained from high-angle θ-2θ scans. First-, second-, and third-order satellites are observed on both sides of the central [002] peak. Periodicity and bilayer composition are obtained from comparison of the data with a theoretical calculation of the x-ray diffractogram. Thickness calibration was confirmed by Rutherford backscattering and profilometer data. In-plane magnetization and magnetoresistance data (Δρ/ρ) indicate that stronger antiferromagnetic coupling and highest Δρ/ρ occur for tRe≈6 A(ring). The saturation field (Hs) needed to align contiguous antiferromagnetically coupled Co layers is about 1 T. This corresponds to an exchange coupling between the Co layer J≈−1 erg/cm2. (Δρ/ρ) reaches 2% in samples deposited at 170 °C. This data confirms results obtained by Parkin et al.1 in Co-Ru and Co-Cr superlattices.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.350116
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  • 9
    Electronic Resource
    Electronic Resource
    Comments on the dielectric theory: Non-Debye models and the superposition principle (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 68 (1990), S. 2526-2528 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Nonexponential relaxations may be decomposed into a distribution of elementary exponential relaxations. Although of mathematical interest, these distributions may not have a physical sense if the elementary process of dipolar orientation itself is nonexponential, that is, non-Debye. We analyze non-Debye models using the superposition principle and assume that they admit a rate equation. In this case the rate itself results to be time dependent. Using the superposition principle as a guide, it then is possible to find the polarization for nonisothermal processes and even for time-varying electric fields. We finally comment on defect diffusion models devised to explain the dynamics of the polarization and depolarization unit, which seem not to be in accord with the superposition principle.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.346473
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  • 10
    Electronic Resource
    Electronic Resource
    The hard ellipse liquid: An integral equation study (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 95 (1991), S. 7591-7602 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We investigate the structural and thermodynamic properties of the isotropic phase of the hard ellipse liquid for several length-to-breadth ratios (2,4,6), using the hypernetted chain (HNC) and Percus–Yevick (PY) integral equation theories. A comparison with the recent simulations of Cuesta and Frenkel [Phys. Rev. A 42, 2126 (1990)] is made. Satisfactory agreement is found with PY theory for small aspect ratios, while for larger ones, HNC results become superior. In addition, HNC (but not PY) predicts the orientational instability of the isotropic phase at a finite density for systems of aspect ratios 4 and 6, in good agreement with computer simulation results. In order to investigate the order of the orientational phase transition, density functional theories (DFT) calculations are carried out using as input the direct correlation functions of the isotropic liquid obtained in this work. No first-order transition is found within the version of DFT used herein.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.461385
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