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  • 1990-1994  (9)
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Year
  • 1
    Electronic Resource
    Electronic Resource
    Thin film reaction kinetics of niobium/aluminum multilayers (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 72 (1992), S. 1341-1349 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Phase formation kinetics in Nb/Al multilayered thin films having overall compositions of 25, 33, 50, and 75 at. % Al have been investigated using scanning calorimetry, x-ray diffraction, and cross-sectional transmission electron microscopy. The first phase to form upon annealing the Nb/Al layered structure of all samples is the NbAl3 intermetallic. Calorimetry clearly identifies the NbAl3 formation to be a two-stage process. The first stage is the formation of a planar layer by nucleation and growth to coalescence while the second stage is the thickening of the planar layer. The large amount of heat released (and hence large volume fraction of NbAl3 formed) during the first reaction stage is consistent with heterogeneous nucleation at well-isolated sites in the Nb/Al interface. This is surprising in light of the large thermodynamic driving force expected for nucleation and suggests that the local nonequilibrium nature of the Nb/Al interface greatly reduces the driving force for nucleation. The next phase observed in samples of 25 and 33 at. % Al is the A15 superconducting phase, Nb3Al. The Nb3Al growth completes a first reaction stage similar to the NbAl3, but the subsequent thickening reaction stage is not observed without simultaneous Nb2Al growth. The high interface velocities derived from the calorimetry for formation of both NbAl3 and the A15 Nb3Al indicate that atomic transport must be by grain boundary diffusion.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.351744
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Pressure and magnetic field dependence of the antiferromagnetism of PrFe4P12 (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 4818-4820 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The compound PrFe4P12, which has the cubic LaFe4P12 modified CoAs3 -type structure, orders antiferromagnetically, with TN=6.2 K and with several field-induced magnetic transitions for T〈TN, up to 5 T for T(very-much-less-than)TN. Heat capacity measurements show the transition is a bulk effect, with magnetic entropy consistent with a magnetic doublet or triplet crystal-field ground state. dc magnetization measurements, M(H), at T=4.2 K up to 23 T reveal no further field-induced transitions, and M(H) attains only 54% of the Pr3+ free-ion moment at highest fields. Pulsed field measurements of dM/dH at 4.2 K up to 45 T fail to resolve further transitions. The transition to the antiferromagnetic state is accompanied by a very sharp Suezaki–Mori-type electrical resistivity transition due to critical scattering of electrons by spin fluctuations. Hydrostatic pressure decreases TN, (dTN/dP=−0.11 K/kbar), in sharp contrast to the behavior for the isomorphic semiconducting ferromagnet, UFe4P12 (TC=3.15 K; dTC/dP=+0.26 K/kbar). The field-induced magnetic transitions are also sharply reduced with pressure. The pressure dependence of the electrical resistivity showed a decrease in TN, with a concomitant decrease in the size of the Suezaki–Mori anomaly. The results are discussed in terms of crystal-field splittings of the Pr ion and possible hybridization effects.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.344773
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Magnetic properties of some tetravalent rare-earth perovskites : 35 th annual conference on magnetism and magnetic materials (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 69 (1991), S. 4874-4876 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The temperature dependence of the magnetic susceptibility for 1.5〈T〈300 K, the field dependence of the magnetization M(H), for 0〈H〈23 T and 1.5〈T〈15 K, and the temperature dependence of the heat capacity C(T), for 5〈T〈95 K are reported for the insulating distorted-perovskite systems PrBaO3, TbBaO3, TbSrO3, and CeBaO3, and the pseudoternary system (Pr,Ce)BaO3. X-ray analysis at room temperature indicates single-phase structures for all materials. PrBaO3 shows magnetic ordering below TN=11.7 K, possibly due to a canted antiferromagnetic structure. TN is nearly independent of applied field up to about 12 T. High-field M(H) isotherms show a well-defined upward sloping kink at 12.7 T, which is independent of temperature for T〈9.5 K. This is indicative of a spin-reorientation transition. The pressure dependence of TN is negligible: dTN/dP〈0.1 K/kbar. TbBaO3 and TbSrO3 both show antiferromagnetic ordering, but with low- field hysteresis effects below 34 K. Clear C(T) anomalies at TN=11.7 and 34 K are seen for PrBaO3 and TbBaO3, respectively. CeBaO3 is paramagnetic, but shows no magnetic order down to 1.8 K, although M(H) is field dependent at 4.2 K. The results in the Pr-based system are compared with previous work in high-Tc-related Pr-based systems.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.348209
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    Paper (German National Licenses)
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  • 4
    Electronic Resource
    Electronic Resource
    Erratum: Detection coil, sensitivity function, and sample geometry effects for vibrating sample magnetometers [Rev. Sci. Instrum. 53, 1344 (1982)] (1991)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 62 (1991), S. 2293-2293 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1142509
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  • 5
    Electronic Resource
    Electronic Resource
    Grain size reduction in Nb3Sn wire using composite powder metallurgy filaments with Cu(Sn) artificial pinning centers (1994)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 65 (1994), S. 1042-1044 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Cu(Sn) artificial pinning centers (APCs) were introduced into multifilamentary Nb3Sn wire using powder metallurgy Nb+Cu rods. In the composite Nb+Cu filaments the Cu ribbons had a thickness of either 20 or 5 nm before reaction. During the 600 °C anneal the APCs enhanced the reaction rate and reduced the Nb3Sn grain size to 〈20 nm. The Cu concentration in the filaments decreased. In 20% Cu-20 nm APC wires the critical current density over the A15 area was 2250 A/mm2 at 12 T and 4.2 K. Flux pinning increased strongly with decreasing field.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.112146
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  • 6
    Electronic Resource
    Electronic Resource
    The effect of oxygen on phase formation in Al/Nb diffusion couples (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 3780-3784 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The effect of an aluminum oxide layer at the interface of Al/Nb on phase formation in thin-film binary diffusion couples was studied. Al/Nb bilayers with or without aluminum oxide at the interface were prepared by electron-beam evaporation. The samples were annealed at a constant heating rate of 50 °C/min to temperatures in the range 800–950 °C, and the progress of the reaction was monitored by x-ray diffraction and measurement of the superconducting transition temperature. The presence of an aluminum oxide layer at the interface was found to significantly retard the formation of the superconducting A15 Nb3Al phase.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.345023
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  • 7
    Electronic Resource
    Electronic Resource
    High magnetic-field facilities: Opportunities in research and technology (invited) (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 5687-5692 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Recently the NSF Division of Materials Research Panel on Large Magnetic Fields concluded that the opportunities for research and technology in high magnetic fields are compelling for support of a new national magnet laboratory with the following components as goals: (i) dc hybrid magnet facilities (water-cooled magnets surrounded by superconducting magnets) of at least 45 T; (ii) state-of-the-art superconducting magnets and NMR magnet facilities greater than 25 T; (iii) intense pulsed magnet facilities for ms to 75 T and above; (iv) short pulsed magnets for μs intervals to 200 T; (v) a variety of water-cooled magnets reaching 25 T; and (vi) quasistatic magnets for transient fields of 0.5 s or more up to 65 T. A 20-MW highly regulated solid-state power supply is central for the dc magnets and separate pulsed power sources are required for the pulsed facilities. This paper outlines the main conclusions of the panel report and discusses some of the opportunities for high-field research and technology. Active overseas high magnetic facilities also are outlined.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.345933
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  • 8
    Electronic Resource
    Electronic Resource
    Phase formation sequence for the reaction of multilayer thin films of Nb/Al (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 7313-7322 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have investigated the phase formation sequence for the reaction of Nb and Al in multilayer films using cross-sectional transmission electron microscopy and x-ray diffraction. NbAl3 is the first intermetallic phase to form. Contrary to previous reports, we find evidence from cross-sectional transmission electron microscopy that the sigma phase, Nb2Al, is not bypassed in the reaction sequence. Instead, its formation is concurrent with the formation of the superconducting A15 phase, Nb3Al. However, depending on the periodicity and the composition of the film, the Nb2Al phase can be consumed by the Nb3Al phase for long annealing times. The significance of this phase formation sequence to powder metallurgically processed magnet wire is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.344517
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  • 9
    Electronic Resource
    Electronic Resource
    High-strength high-conductivity Cu-Nb microcomposite wire by powder metallurgy (1990)
    Springer
    Journal of materials science 9 (1990), S. 1484-1487 
    Details
    ISSN: 1573-4811
    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
    URL: http://dx.doi.org/10.1007/BF00721624
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