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  • 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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  • 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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  • 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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  • 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
    Ferromagnetic behavior of phenanthrolineiron(II) dichloride and related compounds (1973)
    s.l. : American Chemical Society
    Journal of the American Chemical Society 95 (1973), S. 260-262 
    Details
    ISSN: 1520-5126
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ja00782a057
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  • 6
    Electronic Resource
    Electronic Resource
    High field irreversibility in NiFe2O4 nanoparticles (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. 5071-5071 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Several anomalous magnetic properties of organic coated NiFe2O4 nanoparticles have been reported previously by Berkowitz et al. These properties included low magnetization with a large differential susceptibility at high fields, shifted hysteresis loops after field cooling below 50 K, and Mössbauer spectra indicating a fraction of the material being magnetically ordered but not responsive to applied fields. It was suggested that a "strongly anisotropic phase'' was present on the particles surface, and that the organic coating was responsible for producing high local anisotropy fields on the surface atoms. The present study extends the original work in several ways. We find that the lack of saturation in high fields is accompanied by irreversibility up to 20 T, in some cases. We have confirmed the previously reported behavior, in addition to observing similar behavior in samples prepared without the organic surfactant. This implies that we are observing a finite size effect. We have recently reported time dependence of the remanent magnetization which persists down to 0.4 K and does not appear to follow a thermally activated law. Instead, the viscosity becomes temperature independent below 2 K. The model we propose for the high field irreversibility as well as the previously reported behaviors, is that there is a layer of spins at the surface which are spin glass-like, and that these spins can be reoriented irreversibly by a field or by thermal activation. The effect of surface spin interactions on magnetization relaxation will be discussed. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.361577
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  • 7
    Electronic Resource
    Electronic Resource
    The vibrating sample magnetometer: Experiences of a volunteer (invited) : The 40th annual conference on magnetism and magnetic materials (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 4740-4745 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: On its 40th anniversary, I describe how the vibrating sample magnetometer (VSM) was developed and, later, how the very low frequency VSM, a flux-integration device, was developed. The important features of the moving sample technique, detection coil symmetry, calibration, sensitivity, and image effects are discussed briefly. Some VSM adaptations discussed include operation at 3He and dilution refrigerator temperatures, at high hydrostatic pressures, in superconducting, high-power water-cooled and hybrid magnets, for very low frequency ac susceptibility, and with SQUID detectors. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.361657
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  • 8
    Electronic Resource
    Electronic Resource
    Critical current enhancement in NbN/AlN multilayers (1988)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 52 (1988), S. 504-506 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Measurements are presented of the critical current density, Jc, and parallel upper critical field, Hc2(parallel), for the refractory superconductor/insulator multilayer system NbN/AlN. A dramatic increase in Jc, together with an increase of Hc2(parallel), is observed with decreasing NbN layer thickness. The Jc enhancement arises from flux pinning in the AlN or at the NbN-AlN interface, not at defects in the NbN structure. The results indicate that the development of superconductor/insulator composites is a viable strategy to increase the critical current. Thermal stabilization which does not degrade the very high Jc values was also accomplished in a novel structure by addition of copper layers within the superlattice.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.99399
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  • 9
    Electronic Resource
    Electronic Resource
    Temperature anomalies observed in liquid 4He columns in magnetic fields with field–field-gradient products 〉21 T2/cm (1988)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 59 (1988), S. 2474-2476 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Previously reported temperature increases above 4.2 K in an immersion geometry in liquid 4He at fields 〉19 T have been verified and examined. Magnetic forces (B dB/dx) above a threshold level of ∼21 T2/cm were found to trap 4He bubbles near the center of the field. Significant heat input to the region (from conduction, radiation, etc.) can then raise the temperature by as much as several kelvins. Thus, measurements at very high B dB/dx should not depend on vapor pressure thermometry. To assure temperature accuracy and stability, the temperature should be measured directly at the sample position.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1139931
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  • 10
    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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