Valenzuela, S. O., H. Ferrari, V. Bekeris, M. C. Marconi, J. Guimpel, and F. de la Cruz. "Nonconventional short-time dc magnetometer for superconducting films." REVIEW OF SCIENTIFIC INSTRUMENTS 69, no. 1 (1998): 251–254.
Abstract: A nonconventional technique for the measurement of magnetic relaxation in superconducting films at short times (similar to 10(-5) s) is described. This technique combines the application of a pulsed magnetic field and a synchronized high-energy pulsed laser. Remanent magnetic relaxation in (Y;Gd)Ba2Cu3O7-delta thin films is reported over five decades time at reduced temperatures above 0.8. (C) 1998 American Institute of Physics.
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Tutzauer, H., P. Esquinazi, M. E. de la Cruz, and F. de la Cruz. "Production of ribbon quenched samples using an arc furnace." Review of Scientific Instruments 51, no. 6 (1980): 855–856.
Abstract: We describe a new device to produce ribbons of disordered metals by ultrarapid quenching combining an arc furnace with a rotating cylinder. The characterization of samples of disordered La70 Cu30 and La76Au24 prepared using this method shows good agreement with those obtained by other authors for the same alloys.
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Safar, H., E. Rodriguez, F. de la Cruz, P. L. Gammel, L. F. Schneemeyer, and D. J. Bishop. "Observation of two-dimensional vortices in Bi2Sr2CaCu2Ox." Physical Review B 46, no. 21 (1992): 14238–14241.
Abstract: We report transport measurements in the mixed state of single crystals of Bi2Sr2CaCu2Ox using a modified version of the dc flux transformer geometry pioneered by Giaever in low-Tc materials. We find that over a wide range of the phase diagram the vortices are effectively two dimensional in character. Our results suggest that vortex cutting is an efficient process and that it is unlikely that the vortices are strongly entangled in this region of the phase diagram.
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Safar, H., D. Lopez, P. L. Gammel, D. A. Huse, S. N. Majumdar, L. F. Schneemeyer, D. J. Bishop, G. Nieva, and F. de la Cruz. "Experimental evidence of a non-local resistivity in a vortex line liquid." Physica C: Superconductivity 235-240, no. 4 (1994): 2581–2582.
Abstract: We present transport measurements on YBCO single crystals in the vortex liquid regime using the DC flux transformer geometry. We show that the data are inconsistent with the material being an anisotropic, local conductor. The results provided evidence for non-local transport which indicate that there can be correlated vortex motion over macroscopic distances in this system. We have shown that this correlated vortex motion can be destroyed by either thermal fluctuations or the applications of large driving forces.
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Safar, H., P. L. Gammel, D. A. Huse, S. N. Majumdar, L. F. Schneemeyer, D. J. Bishop, D. Lopez, G. L. Nieva, and F. de la Cruz. "Observation of a nonlocal conductivity in the mixed state of YBa2Cu3O7-d: Experimental evidence for a vortex line liquid." Physical Review Letters 72, no. 8 (1994): 1272.
Abstract: We report on transport measurements in the mixed state of YBa2Cu3O7 single crystals using the dc flux transformer geometry. In the vortex fluid regime we have observed the onset of a nonlocal conductivity. At lower temperatures, close to but above the phase transition temperature the vortices become effectively three dimensional in character. This is in sharp contrast to recent flux transformer experiments on Bi2Sr2CaCu2O which have failed to see a nonlocal conductivity, confirming the two-dimensional character at high temperatures of the vortices in that system. These observations suggest that in a finite temperature interval, the vortex state in YBa2Cu3O7 is a line liquid.
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Safar, H., C. Durán, J. Guimpel, L. Civale, J. Luzuriaga, E. Rodríguez, F. de la Cruz, C. Fainstein, L. F. Schneemeyer, and J. V. Waszczak. "Logarithmic to nonlogarithmic flux creep transition and magnetic flux hardening in BiSrCaCuO superconducting ceramics." Physica C: Superconductivity 162-164, Part 1 (1989): 665–666.
Abstract: A sharp temperature and field dependent transition from a logarithmic to a non-logarithmic flux creep behavior has been found in BiSrCaCuO superconductors. The transition is not followed by any noticeable change in the magnetization. However, vibrating reed measurements show that it coincides with a strong hardening of the magnetic structure. The transition occurs at fields and temperatures well below the reversibility line. The possible relation to the recently proposed flux lattice melting is discussed.
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Safar, H., C. Durán, J. Guimpel, L. Civale, J. Luzuriaga, E. Rodriguez, F. de la Cruz, C. Fainstein, L. F. Schneemeyer, and J. V. Waszczak. "Logarithmic-to-nonlogarithmic flux-creep transition and magnetic-flux hardening in Bi-Sr-Ca-Cu-O superconducting ceramics." Physical Review B 40, no. 10 (1989): 7380.
Abstract: A sharp temperature- and field-dependent transition from a logarithmic to a nonlogarithmic flux-creep behavior has been found in Bi-Sr-Ca-Cu-O superconductors. The transition is not followed by any noticeable change in the magnetization. However, vibrating-reed measurements show that it coincides with a strong hardening of the magnetic structure. The transition occurs at fields and temperatures well below the reversibility line. The possible relation to the recently proposed flux lattice melting is discussed.
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Rodríguez, E., C. Duran, J. Luzuriaga, F. de la Cruz, and C. Fainstein. "Anomalous behaviour of the vortex structure in Bi4Ca2Sr4Cu4O16+y measured with a vibrating reed at low magnetic fields." Physica C: Superconductivity 165, no. 3-4 (1990): 315–320.
Abstract: The response of the vortex structure in ceramic samples of Bi4Ca2Sr4Cu4O16+y has been measured by means of a vibrating reed technique in magnetic fields below 0.2 T. An anomally in the response of the reed is seen at temperatures of around 30 to 40 K, well below the critical temperature, indicating a transition similar to that attributed to a melting of the Flux Line Lattice. There is a shift in the temperature at which the anomaly is detected when one increases the driving force on the reed, while the dissipation shows a maximum associated to the transition which scales with the square of the applied magnetic field. Comparison with magnetization measurements shows that there is non-zero critical current at the same temperature where the anomalous behaviour is detected with our technique.
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Righi, E. F., S. A. Grigera, G. Nieva, and F. de la Cruz. "Vortex phase coherence along the c axis in YBa2Cu3O7-d." Superconduvtivity Reviews 2 (1998): 205.
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Ridner, A., E. N. Martínez, and F. de la Cruz. "Surface-Temperature Determination in the Kapitza Problem." Physical Review Letters 35, no. 13 (1975): 855–858.
Abstract: It is shown that surface superconductivity can be used as a localized thermometer. Its application to the study of the thermal boundary resistance at a Pb-4He interface provides the first experimental evidence for the existence of a rapid temperature variation within microscopic distances from the surface.
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