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  • 1
    Electronic Resource
    Electronic Resource
    Empirical potentials for rovibrational energy transfer of hydrogen fluoride in collisions with argon (2001)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 115 (2001), S. 4573-4585 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Rovibrational energy transfer of hydrogen fluoride in collisions with argon was investigated by using the coupled-states approximation to the quantum scattering problem. Empirically determined 3-D ab initio potential energy surfaces (PES) for the interaction between hydrogen fluoride and argon are presented. Second-order Møller-Plesset perturbation theory (MP2) was used to provide an initial approximate PES for the complex. The MP2 PES was subsequently modified to compensate for the underestimated dispersion interaction and adjusted until the desired agreement between calculated and observed spectroscopic quantities was achieved. Calculated rotational cross sections are in good agreement with experimental results as well as those obtained with a highly accurate vibrationally averaged empirical PES [J. M. Hutson, J. Chem. Phys. 96, 6752 (1992)]. The rate constants for the collision induced relaxation of the first vibrational state of hydrogen fluoride are presented as functions of temperature. The rate constants show structure at low temperature corresponding to cross-section resonances. The calculated rate constants are in good agreement with available high temperature experimental results. The calculations provide lower temperature rate constants and a wealth of detailed state-to-state information that are not available from experiment. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1388547
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  • 2
    Electronic Resource
    Electronic Resource
    Precise determination of the critical percolation threshold for the three-dimensional "Swiss cheese" model using a growth algorithm (2001)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 114 (2001), S. 3659-3661 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Precise values for the critical threshold for the three-dimensional "Swiss cheese" continuum percolation model have been calculated using extensive Monte Carlo simulations. These simulations used a growth algorithm and memory blocking scheme similar to what we used previously in three-dimensional lattice percolation. The simulations yield a value for the critical number density nc=0.652 960±0.000 005, which confirms recent work but extends the precision by two significant figures. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1338506
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  • 3
    Electronic Resource
    Electronic Resource
    Temperature programmed desorption studies of OD coadsorbed with H2 on Pt(111) (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 112 (2000), S. 7209-7218 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A molecular beam source of pure hydroxyl radicals has been developed and used to explore the water reaction catalyzed over Pt(111). An electrostatic hexapole selectively focused OD radicals from a supersonic corona discharge source onto a Pt target at a surface temperature of TS=143 K. Subsequent D2O temperature programmed desorption (TPD) spectra revealed two major features, one near TS∼170 K from desorption of molecular water overlayer and a second near TS∼210 K from the decomposition of an adsorbed OD intermediate. The latter feature was isolated and analysis of TPD spectra revealed that the D2O production reaction was approximately half-order in total oxygen coverage with a pre-exponential factor ranging from vd=4±1×1016 to 5±2×1018 molecules1/2 cm−1 s−1 and activation energy Ea=9.7±0.1 to 11.5±0.1 kcal mol−1 for initial coverage ranging from θ0=0.04 to 0.25 ML. Coadsorption studies of OD and H2 revealed that H atoms drive reactions with adsorbed OD at TS∼180 K to form all three water isotopes: D2O, HDO, and H2O. Oxygen (O2) TPD spectra contained three desorption features (TS=700 K, 735 K, and 790 K). The relative abundance of O2 from these three features was virtually the same in all low temperature (TS=143 K) TPD experiments. At elevated dosing temperatures (TS=223 K) the two features at TS=700 K and 790 K could be selectively titrated from the surface by hydrogen. The presence of hydrogen prior to OD exposure at this elevated temperature prevented the accumulation of oxygen on the surface. The implications of these observations on our mechanistic understanding of the low temperature (TS〈210 K) water reaction are discussed. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.481327
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  • 4
    Electronic Resource
    Electronic Resource
    An inertial range crossover in structure functions (2001)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 13 (2001), S. 1985-1994 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Experimental and numerical data within the traditional inertial subrange defined by the third-order structure function is used to study higher-order scaling exponents for the longitudinal and transverse structure functions. For 262〈Rλ〈3200, these exponents converge only over larger scales, r〉rS, where rS is between η and λ and has an Rλ dependence. Below these scales, scaling exponents cannot be determined for any of the structure functions without resorting to procedures such as extended self-similarity (ESS). With ESS, different longitudinal and transverse higher-order exponents are obtained that are consistent with earlier results. The relationship of these statistics to derivative and pressure statistics, to turbulent structures and to length scales is discussed. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1373683
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  • 5
    Electronic Resource
    Electronic Resource
    High speed characteristics of thin film write heads at deep submicron track width (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 87 (2000), S. 5416-5418 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: This article presents a micromagnetic study of the dynamic magnetic switching process in the pole tip region of stitched-pole thin film write heads. The impacts of track width reduction and pole material saturation moment on the high frequency performance of the heads have been investigated. It is found that the magnetic switching process of the pole tip region at low recording frequencies can be characterized by three stages: the nucleation of a vortex (or vortices), followed by the motion of the vortex (or vortices), and finally the annihilation of the vortex (or vortices). At high frequencies, however, a residual vortex (or vortices) will always remain in the pole tips, resulting in lower head field amplitude. Frequency roll-off characteristics of the head field response have been calculated. The roll off is the result of residual vortex (or vortices), and the vortex moving speed limits the operational frequency range of the head. Reducing the track width lowers the head field 3 dB roll-off frequency. The simulation also finds that the use of 45/55 NiFe, which has significantly higher moment than permalloy, results in higher roll-off frequency as compared to permalloy. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.373361
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  • 6
    Electronic Resource
    Electronic Resource
    Barium ferrite thin film media with perpendicular c-axis orientation and small grain size (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 87 (2000), S. 6370-6372 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Barium ferrite thin films with perpendicular c-axis orientation and small grain size (about 300 Å) were successfully fabricated with careful control of sputtering conditions. The c-axis orientation of barium ferrite thin films is most sensitive to the oxygen partial pressure during deposition. All samples with oxygen gas during deposition have a random c-axis texture, as indicated by existence of both weak (00l) peaks and (106) peaks. All the samples without oxygen gas during deposition show only strong (00l) peaks, which indicate excellent perpendicular c-axis orientation. Transmission electron microscopy results show that oxygen gas promotes the growth of in-plane and/or randomly oriented grains. The effect of the Pt interlayer on the barium-rich films was also studied. The Pt interlayer was found to be very effective in improving c-axis orientation of barium-rich films. A relative increase in perpendicular nucleation sites over in-plane and/or random nucleation sites contributes to the improvement in perpendicular c-axis orientation. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.372709
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  • 7
    Electronic Resource
    Electronic Resource
    Exchange coupling of NiFe/CrMnPtx bilayers prepared by a substrate bias sputtering method (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 87 (2000), S. 410-415 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have investigated the unidirectional exchange anisotropy between a ferromagnetic Ni81Fe19 film and a disordered antiferromagnetic CrMnPtx (x=3, 6, or 9) film prepared by substrate bias sputtering. A hysteresis loop with the shape predicted by the planar domain-wall model was found in the sample without substrate bias, suggesting that the interfacial exchange coupling energy between the Ni81Fe19 and CrMnPtx layers is comparable to the antiferromagnetic domain-wall energy. The substrate bias on the Ni81Fe19 underlayers improved the texture of the CrMnPtx layers but also increased the interface roughness. The substrate bias effect on the exchange bias can be understood in terms of the planar domain-wall model. The interface roughness reduces the interfacial exchange coupling by introducing defects and disordering the antiferromagnetic moments at the interface. This leads to a triangular hysteresis loop. The texture improvement increases the exchange bias by increasing the domain-wall energy of the antiferromagnet. The differences between these substrate bias effects and those observed in the Ni81Fe19/Fe50Mn50 bilayer system are also discussed. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.371876
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  • 8
    Electronic Resource
    Electronic Resource
    Exchange biasing in sputtered NiFe/PtMn bilayers (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 87 (2000), S. 4918-4920 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The exchange coupling between ferromagnetic Ni81Fe19 and antiferromagnetic (AF) PtxMn1−x films prepared by rf and dc magnetron sputtering has been investigated. The Pt content in the PtxMn1−x film is in the range of 0 at. %〈x〈20 at. %. The exchange field and coercivity were found to depend strongly on the deposition conditions and the AF film composition. X-ray diffraction measurements and transmission electron microscopy measurement showed a γ-PtMn phase with a disordered fcc structure when the PtxMn1−x was deposited on top of the Ni81Fe19 layer. The exchange bias was found to depend on the texture and film composition of the γ-PtMn layers. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.373202
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  • 9
    Electronic Resource
    Electronic Resource
    Measurement dependence of the exchange bias (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 87 (2000), S. 4960-4962 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Recently, in addition to the conventional hysteresis loop measurement, several different measurement techniques, such as ac susceptibility, ferromagnetic resonance (FMR), and Brillouin light scattering, have been used to study the unidirectional exchange coupling induced in a ferromagnetic film in proximity to an antiferromagnet. In this article, we theoretically investigate how interface exchange coupling manifests itself in different measurements. The magnetic degrees of freedom of the antiferromagnet are incorporated in this analysis. Anisotropies from hysteresis loop measurements, ac susceptibility measurements, and FMR measurements are obtained. These results show that the measured exchange anisotropies differ with measurement techniques. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.373215
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  • 10
    Electronic Resource
    Electronic Resource
    Ferromagnetic resonance studies of exchange biasing in Ni81Fe19/Pt10Mn90 bilayers (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 87 (2000), S. 4367-4374 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In-plane ferromagnetic resonance (FMR) has been used to study exchange anisotropy in Ni81Fe19/Pt10Mn90 bilayers at room temperature. A theoretical calculation for the FMR resonance field was carried out based on a simple model of the exchange bias in a polycrystalline bilayer that incorporates reversible as well as irreversible behavior of the antiferromagnetic layer. In addition to the expected cos cursive-phiH contribution to the resonance field, where cursive-phiH is the direction of the applied field, there is a negative shift of the resonance field. It is argued that the negative shift of the resonance related to the irreversible behavior of the antiferromagnetic moments is not isotropic. The linewidth broadening of in-plane resonance for the exchange biased bilayers is also discussed. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.373080
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