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  • 1
    Electronic Resource
    Electronic Resource
    Pressure dependence of magnetic ordering temperature for decamethylferrocenium tetracyanoethanide : 37th Annual conference on magnetism and magnetic materials (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 6563-6565 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: It has been demonstrated that the linear-chain charge-transfer salt, decamethylferrocenium tetracyanoethanide (DMeFc)(TCNE), is a ferromagnet with a transition temperature of ∼4.8 K. This low-temperature 3D ordering has been attributed to a strong intrachain and a weak interchain interaction. To study these interactions, we have determined the Tc up to 20 kbar by measuring the ac susceptibility χ at low frequency. Our results show that the Tc increases with pressure at a rate of ∼0.22 K/kbar, while the χ peak indicative of the ferromagnetic transition continues to decrease rapidly. A small peak was also detected above the main transition at pressures above 3 kbar. This new peak persists even after the pressure is removed. The result from dc magnetization suggests that this corresponds to a metamagnetic state. For the first time, we have observed pressure-induced phase-transition in this material.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.352564
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  • 2
    Electronic Resource
    Electronic Resource
    Probe the vortex state of YBa2Cu3O7−δ under small magnetic field using short time magnetic moment relaxation method (abstract) : 37th Annual conference on magnetism and magnetic materials (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 5874-5874 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: At the present time, there is a large amount of convergent experimental evidence pointing toward the existence of a vortex-glass state in the high temperature superconductor YBa2Cu3O7−δ in the presence of a high magnetic field, as predicted by Fisher1 and Fisher et al.2 However, the situation at low magnetic field is not so clear. The nature of the vortex state separating the Meissener state at low field and the vortex-glass state at very high field remains unsolved both theoretically and experimentally. To shed some light to this problem, we have measured the remnant magnetic moment relaxation of melt-textured bulk YBa2Cu3O7−δ samples in various magnetic fields from ∼10−4 to ∼300 s. Even at zero field, the time dependence of the relaxation follows the vortex-glass model prediction m(t)∝1/[ln(t)]1/μ but with a μ=1.4±0.2, contradicting the vortex-glass model. As the field is increased, the μ value decreases until it reaches a value of ∼0.2–0.3 above 1 T. The larger than one value of μ seems to point to a collective pinning behavior at low magnetic field.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.353557
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  • 3
    Electronic Resource
    Electronic Resource
    Pressure effect on the superconducting transition temperature of Dy1−xPrxBa2Cu3O7−δ : 37th Annual conference on magnetism and magnetic materials (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 5871-5873 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The pressure effect on the superconducting transition temperature (dTc/dP) has been measured for Dy1−xPrxBa2Cu3O7−δ with x=0, 0.02, 0.05, 0.1, 0.15, 0.2, and 0.3. Although the Tc suppression by Pr is in a different fashion for Y1−xPrxBa2Cu3O7−δ and Dy1−xPrxBa2Cu3O7−δ, the dTc/dP is similar in these two systems, with respect to x. The measured dTc/dP is positive at small x but becomes negative for x≥0.2 which is associated with the pressure effect on the normal-state resistivity (1/R)(dR/dP). The positive (1/R)(dR/dP) at x≥0.2 indicates that the number of carriers is decreasing under pressure and it supports the picture of hole localization through the hybridization of Pr-4f and O-2p bands. The mechanical pressure has a negative effect on Tc for x≥0.2, but chemical pressure has a positive effect on Tc according to the results of chemical substitution. This suggests that the large R (=rare earth element) may possibly reduce the Pr-O distance, and increase the hybridization of Pr-4f and O-2p bands.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.353556
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  • 4
    Electronic Resource
    Electronic Resource
    Hydrostatic pressure on HgBa2CaCu2O6+δ and HgBa2Ca2Cu3O8+δ : The 6th joint magnetism and magnetic materials (MMM)-intermag conference (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 6941-6943 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The superconducting transition temperature Tc and its pressure dependence dTc/dP of HgBa2CaCu2O6+δ (Hg-1212) and HgBa2Ca2Cu3O8+δ (Hg-1223) were measured up to 17 kbar. Tc increases with pressure approximately linearly for both compounds before oxidation. However, the nonlinearity in the Tc-P correlation shows up after oxidation in both compounds. For Hg-1212, the average dTc/dP decreases as oxygen doping increases, while it increases in Hg-1223. These observations are in conflict with the modified pressure-induced charge-transfer model, but might be attributed to the possible existence of fine electronic structure. These observations suggest that a Tc much higher than 140 K might be achievable in Hg-1223 by means of higher physical or chemical pressure.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.358122
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  • 5
    Electronic Resource
    Electronic Resource
    Annealing temperature and O2 partial pressure dependence of Tc in HgBa2CuO4+δ : The 6th joint magnetism and magnetic materials (MMM)-intermag conference (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 7127-7129 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Samples of HgBa2CuO4+δ (Hg-1201) were annealed under various conditions. After carefully controlling annealing time, annealing temperature (Ta), and O2 partial pressure (P0), we were able to find the reversible annealing conditions for Hg-1201. Under 1 atm O2 at 260 °C≤Ta≤400 °C, the obtained Tc is nearly the same (∼97 K). However, it decreases quickly with Ta(approximately-greater-than)300 °C in high vacuum (P0∼10−8 atm), and reaches zero at Ta=400 °C. On the other hand, Tc decreases with the decrease of Ta in high-pressure O2 (∼500 atm) and reaches ∼20 K at about 240 °C. In the entire annealing region, the oxygen surplus varies significantly from 0.03 to 0.4, and a wide range of Tc variation (0→97 K→20 K) was obtained with anion doping alone.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.358052
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  • 6
    Electronic Resource
    Electronic Resource
    Local chemical composition of HgBaCaCuO high-temperature superconductors (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 1100-1104 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The microchemical composition and the electronic structure of the two superconductors HgBa2Ca2Cu3O8+δ (Hg-1223) and HgBa2Ca1Cu2O6+δ (Hg-1212) were analyzed with the technique of photoemission with high spatial resolution. This enabled primary spectral peaks to be separated from their satellites due to local charging induced by the primary photon beam. Each sample contains superconducting and impurity phases with inhomogeneous spatial distributions. The oxygenation-induced increase in the critical temperature is related to a increase in the Cu-O plane carrier concentration.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.357829
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  • 7
    Electronic Resource
    Electronic Resource
    Comparison between the magnetic and transport critical current densities in high critical current density melt-textured yttrium barium copper-oxide (1991)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 58 (1991), S. 92-94 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Using our recently developed pulsed critical current density (Jc) measuring system, the Jc of the high Jc melt-textured YBa2Cu3O7−δ (Y123) bulk samples has been determined. I-V curves with a voltage resolution of 0.5 μV were obtained, and transport Jc's along the a-b plane (Jc(parallel) a-b) as high as 7.2×1 04 A/cm2 were extracted. These results are comparable to the values obtained magnetically. On the other hand, transport Jc along the c axis (Jc(parallel)c) were found to be two orders of magnitude smaller, even though the magnetic Jc(parallel)c is only about five times smaller than Jc(parallel)a-b. We suggest that for the high-temperature superconducting materials which are highly anisotropic, caution should be taken when using the nontransport magnetic methods to determine Jc.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.104401
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  • 8
    Electronic Resource
    Electronic Resource
    Unusually large shielding fields in single-grain YBa2Cu3O7−δ (1994)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 65 (1994), S. 907-909 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Magnetic field trapping and shielding by several unirradiated single-grain YBa2Cu3O7−δ disks have been investigated between 4.2 and 71 K up to 20 T. Flux avalanches due to thermal instabilities limited the trapping field to ∼5 T below 45 K and often caused microcracks in the disks. However, a shielding field greater than 19 T was detected at 4.2 K in the same sample assembly even after it was damaged by flux avalanches. This violates the expected symmetry between shielding and trapping fields. The shielding field of (approximately-greater-than)19 T exceeds the total quench field of 10 T predicted by the Swartz–Bean model. The observations suggest that thermomechanical properties play an important role in field shielding and trapping and mechanical stress may be effectively used to enhance the field trapped by disks of high temperature superconductors.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.112197
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  • 9
    Electronic Resource
    Electronic Resource
    High magnetic field trapping in monolithic single-grain YBa2Cu3O7−δbulk materials (1993)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 63 (1993), S. 260-262 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Results of our study on high magnetic field trapping in unirradiated, high quality monolithic single-grain YBa2Cu3O7−δ disks are reported. A record high 4 T trapped field at the surface of the unirradiated disks is observed. However, below 11 K, large flux avalanches caused by thermal instability severely limit the remnant trapped field. Therefore, flux avalanche, rather than Jc×d, dictates the maximum trapped field at low temperatures. To overcome this problem, a strong high temperature superconductor trapped field magnet is proposed. A novel application of the avalanche effect is also mentioned.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.110360
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  • 10
    Electronic Resource
    Electronic Resource
    Effects of material processing in high temperature superconducting magnetic bearings (1991)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 59 (1991), S. 2442-2444 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A study of the levitation forces related to superconducting bearing design was conducted on free-sintered and melt-textured Y1Ba2Cu3O7−δ(YBCO) materials. Comparisons were made between free sintered, variously oriented, and randomly oriented melt-textured materials. Magnetic force measurements were also conducted on oriented YBCO before and after neutron irradiation. A magnetic bearing of new design utilizing the phenomenon of flux pinning was then fabricated using melt-textured YBCO with permanent magnets and a speed of 135 000 rpm was achieved. Rotational dissipation and magnetic stiffness measurements were performed on the bearing prototype.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.105989
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