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  • 1
    Electronic Resource
    Electronic Resource
    First principles determination of magnetocrystalline anisotropy for surfaces and interfaces using a torque method (abstract) : The 40th annual conference on magnetism and magnetic materials (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 5827-5827 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Perpendicular magnetic alignment is vital for high density magneto-optical recording materials. Despite the tremendous theoretical/computional advances made during the last few decades, the determination of magnetocrystalline anistropy (MCA) from first principles still remains a great challenge for complex systems. We will describe our recently proposed torque method for the first principles determination of MCA. In the usual first principles methods, one calculates the band energies associated with two magnetization directions and substracts one from the other. Within this approach, one has the difficulty of getting rid of the random fluctuations arising from the two different Fermi surfaces due to different magnetization directions. We show that to accurately determine the spin-orbit induced uniaxial ansisotropy energy for surfaces/interfaces, calculation of the torque at a specific angle is sufficient and one avoids the complexities associated with two Fermi surfaces by employing the Feynman-Hellman theorem. In the k-space integrations, we used both linear and quadratic interpolation schemes and convergence is assured when these two schemes agree to the accuracy desired. Examples, including Fe and Co multilayer systems, will be presented to demonstrate the efficiency and precision of this method. Detailed comparisons with previously proposed state-tracing method by Wang et al. are also made and discussed. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.362200
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  • 2
    Electronic Resource
    Electronic Resource
    Anomalous strains in the cubic-phase GaN films grown on GaAs (001) by metalorganic chemical vapor deposition (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 88 (2000), S. 3762-3764 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Strains in cubic GaN films grown on GaAs (001) were measured by a triple-axis x-ray diffraction method. Residual strains in the as-grown epitaxial films were in compression, contrary to the predicted tensile strains caused by large lattice mismatch between epilayers and GaAs substrates (20%). It was also found that the relief of strains in the GaN films has a complicated dependence on the growth conditions. We interpreted this as the interaction between the lattice mismatch and thermal mismatch stresses. The fully relaxed lattice constants of cubic GaN are determined to be 4.5038±0.0009 Å, which is in excellent agreement with the theoretical prediction of 4.503 Å. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1288779
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  • 3
    Electronic Resource
    Electronic Resource
    Effects of rapid thermal annealing on the optical properties of GaNxAs1−x/GaAs single quantum well structure grown by molecular beam epitaxy (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 87 (2000), S. 245-248 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The effect of rapid thermal annealing (RTA) on the optical properties of GaNxAs1−x/GaAs strained single quantum well (SQW) was studied by low-temperature photoluminescence (PL). The GaNxAs1−x/GaAs SQW structures were prepared by dc active nitrogen plasma assisted molecular beam epitaxy. PL measurements on a series of samples with different well widths and nitrogen compositions were used to evaluate the effects of RTA. The annealing temperature and time were varied from 650 to 850 °C and 30 s to 15 min, respectively. Remarkable improvements of the optical properties of the samples were observed after RTA under optimum conditions. The interdiffusion constants have been calculated by taking into account error function diffusion and solving the Schrodinger equation. The estimated interdiffusion constants D are 10−17–10−16 cm2/s for the earlier annealing conditions. Activation energies of 6–7 eV are obtained by fitting the temperature dependence of the interdiffusion constants. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.371852
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  • 4
    Electronic Resource
    Electronic Resource
    Magnetostriction and magnetism of rare earth intermetallic compounds: First principle study (2001)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 89 (2001), S. 7320-7322 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Magnetism and magnetostriction of rare earth intermetallic compounds, GdCo2, GdFe2, NdCo2, SmCo2, and ErCo2, have been studied by using the first principles full-potential linearized augmented plane-wave method with the generalized gradient approximation. The calculated magnetostriction coefficients agree well with experiment. The itinerant electrons of transition metal elements are found to play a significant role in magnetoelastic coupling. The strong anisotropy of magnetostriction in GdCo2 is explained. Contributions due to spatial anisotropic charge distribution of the incomplete 4f shells are calculated and discussed. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1356038
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  • 5
    Electronic Resource
    Electronic Resource
    Room-temperature optical transitions in Mg-doped cubic GaN/GaAs(100) grown by metalorganic chemical vapor deposition (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 87 (2000), S. 2064-2066 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The mechanism of room-temperature optical transitions in a Mg-doped cubic GaN epilayer grown on GaAs(100) by metalorganic chemical vapor deposition has been investigated. By examining the dependence of photoluminescence on the excitation intensity (which varied over four orders) at room temperature, four different emissions with different origins were identified. A blue emission at ∼3.037 eV was associated with a shallow Mg acceptor, while three different lower-energy emissions at ∼2.895, ∼2.716, and ∼2.639 eV were associated with a deep Mg complex. In addition to a shallow acceptor at E≅0.213 eV, three Mg-related deep defect levels were also found at around 215, 374, and 570 meV (from the conduction band). © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.372139
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  • 6
    Electronic Resource
    Electronic Resource
    Magneto-optical properties of FeAu alloys and Fe/Au superlattices (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 85 (1999), S. 5112-5114 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Magneto-optical Kerr effect (MOKE) of the Fe/Au superlattices and the FeAu L10 alloy has been studied by using the first principles full-potential linearized augmented plane-wave method. The calculated MOKE spectra show pronounced structures in the region from 2 to 6 eV, in agreement with experiment. The line shape of the MOKE spectra of Fen/Aun superlattices strongly depends on their lattice period (n) and interfacial interdiffusion.© 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.369094
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  • 7
    Electronic Resource
    Electronic Resource
    A rheo-light-scattering instrument for the study of the phase behavior of polymer blends under simple-shear flow (1995)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 66 (1995), S. 2914-2921 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A rheo-light-scattering instrument for investigating the influence of shear on the phase behavior of polymer blends was constructed from a commercial parallel-plate rheometer. Laser light scattering from the sample plane formed by the flow and vorticity directions was projected on a screen, and a combination of a camera lens and a charge-coupled device detector was used to record the scattering pattern. The rheometer, which can generate angular velocities of up to 100 rad/s and measure torque and normal forces up to 9.8×103 N m and 9.8×105 N, respectively, is suitable for studying polymer melts at stresses up to 9.1 kPa. The maximum accessible q range was from 5.72×10−4 to 7.11×10−3 nm−1 (3°–42° scattering angle and a laser wavelength of λ=632.8 nm). The performance of the light-scattering instrumentation and the accuracy of the correction algorithms were tested with a Ronchi ruling diffraction grating and a colloid of monodisperse polystyrene spheres. Example rheo-light-scattering measurements were made with a 50/50 blend of polystyrene and polyisobutylene oligomers and a 40/60 blend of polybutadiene and polyisoprene. All components had narrow molecular weight distributions. The first blend exhibits an upper critical solution temperature while the second blend shows a lower critical solution temperature. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1145577
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  • 8
    Electronic Resource
    Electronic Resource
    Soluble conjugated polymers with degenerate ground state derivatives of poly(1,6-heptadiyne) (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 99 (1993), S. 590-596 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We report the results of initial measurements on two derivatives of poly(1,6-heptadiyne): a di-ketone (PHDK) and a di-ester (PHDE). Both polymers have the degenerate ground state of poly(1,6-heptadiyne); both are soluble in common organic solvents. Electron spin resonance (ESR) measurements on pristine samples place an upper limit of 10−4 spins per monomer for both polymers. At low doping levels, we observe a single doping-induced absorption band at an energy of approximately half the π−π* gap, Eg/2; the doping-induced spectral features were fully reversible. In situ ESR and absorption measurements during doping show that charge is stored predominantly in spinless charge carriers. Because of the inequivalent carbons on the conjugated backbone, the results are discussed in terms of the (A=B)n polymer. Both PHDK and PHDE are relatively stable in air; the strength of the π−π* absorption band is nearly constant over a period of a week in air, decreasing to 80% of the initial value.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.465785
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  • 9
    Electronic Resource
    Electronic Resource
    Magnetization of an epitaxial YBa2Cu3O7−δ film at the critical field sweep rate (1997)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 82 (1997), S. 6116-6121 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have measured the magnetic hysteresis loops of an epitaxial YBa2Cu3O7−δ thin film using our recently developed device which can provide the field magnitude in the range of 0–1000 Oe and the field sweep rate up to 107 Oe/s. The shape of the hysteresis loop measured changes with the field-sweep rate up to the critical sweep rate; and over the critical sweep rate the ac magnetization reaches its real critical state where magnetization does not change even with a further increase in the field-sweep rate. The critical sweep rate is about 106 Oe/s at 77 K. With the hysteresis loops and Bean model, we have calculated the magnetization critical current density (Jcac) which is consistent with that obtained by I–V measurements. We have also studied flux motion and activation energy under the high sweep rate magnetic field. At temperature 77 K, the velocity of the flux motion is of the order 10 m/s and the pinning energy U0/k is about 339 K which is much smaller than the magnetization decay measurement. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.366484
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  • 10
    Electronic Resource
    Electronic Resource
    Energy loss spectra of group III nitrides (2000)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 77 (2000), S. 3042-3044 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Electron energy loss spectra (EELS) of cubic and hexagonal BN, AlN, GaN, and InN have been calculated by using the first principles full potential linearized augmented plane wave method. Accurate calculations of linear optical functions are performed in a photon energy range up to 60 eV. The electron excitation energies related to the bulk plasmons are obtained for both reflection and transmission geometries. The predicted EELS data are discussed in comparison with available experimental results. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1323992
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