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  • 1
    Electronic Resource
    Electronic Resource
    Test of unified picture of spin-dependent transport in perpendicular (CPP) giant magnetoresistance and bulk alloys (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 85 (1999), S. 4542-4544 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Measurements of current perpendicular (CPP) magnetoresistance (MR) on hybrid and exchange-biased spin valves allow determination of the layer anisotropy parameter β for ferromagnetic alloys, thus allowing testing of whether this CPP β is similar to values obtained from direct measurements on, and theoretical estimates for, dilute bulk ferromagnetic alloys. Of special interest are alloys where β is expected to be negative. In this article, we derive a value of β for a Ni97Cr3 alloy using such spin valves based upon permalloy. We confirm prior CPP-MR results that this β is negative, but our inferred value, β=−0.35±0.1, is closer to bulk and theoretical estimates. Our data thus provide new support for a unified picture of β in the CPP-MR and bulk alloys. We also derive a short spin-diffusion length in NiCr, lsf=3±1 nm. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.370402
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  • 2
    Electronic Resource
    Electronic Resource
    Plasma simulation studies using multilevel physics models : The 40th annual meeting of the division of plasma physics of the american physical society (1999)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 6 (1999), S. 1796-1803 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The question of how to proceed toward ever more realistic plasma simulation studies using ever increasing computing power is addressed. The answer presented here is the M3D (Multilevel 3D) project, which has developed a code package with a hierarchy of physics levels that resolve increasingly complete subsets of phase-spaces and are thus increasingly more realistic. The rationale for the multilevel physics models is given. Each physics level is described and examples of its application are given. The existing physics levels are fluid models (3D configuration space), namely magnetohydrodynamic (MHD) and two-fluids; and hybrid models, namely gyrokinetic-energetic-particle/MHD (5D energetic particle phase-space), gyrokinetic-particle-ion/fluid-electron (5D ion phase-space), and full-kinetic-particle-ion/fluid-electron level (6D ion phase-space). Resolving electron phase-space (5D or 6D) remains a future project. Phase-space-fluid models are not used in favor of δf particle models. A practical and accurate nonlinear fluid closure for noncollisional plasmas seems not likely in the near future. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.873437
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  • 3
    Electronic Resource
    Electronic Resource
    Tomography of full sawtooth crashes on the Tokamak Fusion Test Reactor (1996)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 3 (1996), S. 1647-1655 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Full sawtooth crashes in high temperature plasmas have been investigated on the Tokamak Fusion Test Reactor (TFTR) [Plasma Phys. Controlled Fusion 33, 1509 (1991)]. A strong asymmetry in the direction of major radius, a feature of the ballooning mode, and a remaining m=1 region after the crash have been observed with electron cyclotron emission image reconstructions. The TFTR data is not consistent with two-dimensional (2-D) models; it rather suggests a three-dimensional (3-D) localized reconnection arising on the bad curvature side. This process explains the phenomenon of fast heat transfer which keeps the condition q0〈1.©1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872025
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  • 4
    Electronic Resource
    Electronic Resource
    Effect of annealing on the grain growth and luminescent properties of SrS:Cu blue phosphors (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 85 (1999), S. 3999-4002 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Systematic studies of the postgrowth annealing of molecular beam epitaxial deposited SrS:Cu films are reported. In the as-grown SrS:Cu films, the grain size was small and the luminescence very weak. A step-annealing procedure in a H2S atmosphere was developed and found to be a very efficient way to improve the crystallinity and luminescent properties without damage to the low temperature glass substrate and insulator layer of the device. A model is presented in terms of the free energy of formation and the reaction kinetics of Cu with H2S. It was proposed that the weak luminescence in the as-grown films was attributed to Cu atoms segregated at the grain boundaries in the SrS film. The oxidation of atomic Cu by H2S and the diffusion of Cu+ into the SrS lattice during annealing were responsible for the grain growth and the improved luminescent properties. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.370303
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  • 5
    Electronic Resource
    Electronic Resource
    Thermomagnetic analysis of NdFeB melt-spun alloys with low Nd content (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 77 (1995), S. 4133-4135 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The phase transformation of NdFeB melt-spun alloys with low Nd content of 4–8 at. % was investigated by thermomagnetic analysis and x-ray diffractometry. Experimental results have shown that the metastable Nd2Fe23B3 compound formed in the alloys is considered to be transformed to Nd2Fe23B3+α-Fe+Fe3B in the temperature range of 550–690 °C, α-Fe+Fe3B+Nd1+eFe4B4 in the temperature range of 690–730 °C and finally α-Fe+Nd1+eFe4B4 above 840 °C. From the results, it has been concluded that Nd2Fe14B is not formed from metastable Nd2Fe23B3. On the other hand, the melt-spun alloy of Nd2Fe23B3 (∼Nd7.1Fe82.1B10.7) annealed under optimum conditions has been found to be composed of α-Fe, Fe3B, and Nd2Fe14B phases. The alloy has a coercivity comparable to Fe3B-based Nd4Fe77B19 and relatively high-energy product of about 71.6 kJ/m3 (∼9 MG Oe). © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.359501
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  • 6
    Electronic Resource
    Electronic Resource
    Photoluminescence properties of ZnGa2O4:Mn powder phosphors (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 78 (1995), S. 5691-5695 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The results of a systematic photoluminescence study of ZnGa2O4:Mn powder phosphor are reported. At room temperature this phosphor exhibits bright green luminescence with a spectral peak at 2.46 eV and Commission International de l'Eclairage chromaticity coordinates of x=0.073 and y=0.696. At low temperatures the luminescence was found to consist of three components assigned to the 4T1–6A1 inner transition of the 3d electrons of Mn2+ ions located on three different sites of the host crystal. Selective excitation and lifetime measurements were used to investigate the assignment of these features. The photoluminescence lifetime showed a single exponential decay of about 4 ms and at T=1.6 K an optical-phonon-related fine structure [Ephonon=(8.2±0.2) meV] of the main photoluminescence line was observed. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.359627
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  • 7
    Electronic Resource
    Electronic Resource
    Photoluminescence properties of ZnS epilayers (1997)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 81 (1997), S. 2803-2809 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A comprehensive study is reported of the photoluminescence properties of ZnS thin films between 1.6 and 320 K grown by metalorganic molecular beam epitaxy and chemical beam epitaxy on GaAs substrates. Both heavy- and light-hole free excitons were observed at low temperatures with linewidths of 7.0 and 5.3 meV, respectively, as well as donor- and acceptor-bound excitons and free-to-bound recombination along with their longitudinal optical (LO) phonon replicas. The free exciton emission was observed up to 320 K, and enabled the room temperature band gap of ZnS to be unambiguously determined as 3.723 eV. The temperature dependence of the peak position, intensity, and linewidth was well described by the conventional empirical relations and by Toyozawa's exciton line shape theory. The bound exciton peak positions were found to follow the temperature dependence of the band gap whereas the free-to-bound recombination feature was displaced by (1/2)kT above the band gap energy. Thermal quenching of the donor-bound exciton was described by a one-step quenching process with an activation energy of 14.4 meV. The self-activation (SA) center was also observed at 2.846 eV with a linewidth of 410 meV. The temperature dependence of the SA emission was well described by the configuration coordinate model. From the thermal broadening of the SA emission, an average phonon energy of 47.5 meV was determined, in good agreement with the LO phonon energy. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.363937
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  • 8
    Electronic Resource
    Electronic Resource
    Charge compensation study of molecular beam epitaxy grown SrS:Ce (1997)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 71 (1997), S. 2268-2270 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A study is reported of the codoping of SrS:Ce by Ag and Cu in order to achieve charge compensation of the trivalent Ce atom. Both Ag and Cu codoping produced a blue shift in the photoluminescence spectra and much higher electroluminescent device performance. These improvements were attributed to the substitutional incorporation of Ag and Cu onto the Sr lattice site which minimized the vacancy formation and provided charge compensation. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.120047
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  • 9
    Electronic Resource
    Electronic Resource
    Luminescence decay kinetics in homogeneously and delta-doped ZnS:Mn (1998)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 84 (1998), S. 6852-6858 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The luminescence decay kinetics of homogeneously and delta-doped ZnS:Mn thin film phosphors was investigated. A quantitative model based on the hopping model of energy transfer theory was developed to described the concentration quenching phenomenon in ZnS:Mn. The model predicted the dependence of the energy transfer rate on material parameters such as the Mn and defect concentrations. The luminescence decay of homogeneously doped ZnS:Mn consisted of two exponential components at 10 K. The fast component of 120 μs was attributed to exchange-coupled pair emission and the slow component of 1.6 ms to isolated Mn ions. As the temperature was increased, the exchange-coupled pair emission disappeared and the decay became strongly nonexponential. The nonexponentiality was attributed to nonradiative energy transfer processes. The concentration dependence of the effective lifetime was also found to change with temperature. The investigation on the temperature dependence revealed two regimes of concentration which showed distinct temperature dependencies. From the temperature dependence, it was concluded that the energy transfer between Mn ions was active only when the Mn concentration was greater than 2 at. %. By comparing these results with the results of Dexter's theory, the energy transfer between Mn ions was found to be mediated by an electric dipole–dipole interaction. The delta-doped ZnS:Mn showed faster decay times due to the enhanced overlap between 3d and s-p host states caused by lattice strain. From the temperature dependence, a two-dimensional confinement of energy transfer was observed when the doping planes were far apart. However, when the doping planes were brought close together, the delta-doped samples behaved similarly to the homogeneously doped ZnS:Mn indicating that the energy transfer was no longer two-dimensionally confined. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.368980
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  • 10
    Electronic Resource
    Electronic Resource
    Low-energy electron point source microscope with position-sensitive electron energy analyzer (1999)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 70 (1999), S. 4304-4307 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A low-energy electron point source microscope equipped with a position-sensitive energy analyzer is constructed. A nanometer-sized feature can be zoomed in and its energy-loss spectrum can be measured with a retarding field-type energy analyzer mounted in front of the imaging screen. The geometric and the electronic structures of carbon nanotubes are measured with the present system. Interference between the scattered and the transmitted electron beams through the carbon nanotubes is observed using an atomically sharp field emitter. The electron energy-loss spectrum shows two prominent peaks at ∼7 and 16–17 eV, which are identified as the π plasmon and (π+σ) surface-plasmon peaks. This result is consistent with the measurements of high-energy electron energy-loss spectroscopy as well as the theoretical calculation. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1150070
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