Examinando por Autor "Fink, H. J."

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  • Miniatura
    ÍtemAcceso Abierto
    Fluxoid quantum number at Hc3
    (American Chemical Society, 1979) López, A.; Fink, H. J.
    For a cylinder in an axial magnetic field the laigest field at which superconductivity nucleates is the same as the surface nucleation field of the semi-infinite half-space when the radius R of the cylinder is much laiger than the temperature-depen dent coherence length ε. From the solution of the multiply connected surface sheath one obtains the number of fluxoid quanta which are locked-in at the nucleation field as a function of R/ε.
  • Miniatura
    ÍtemAcceso Abierto
    Model relating superconductive penetration depth and metallurgical phase separation in amorphous La70 Cu30
    (Pergamon Press, 1982) Arce, R. O.; Cruz, Francisco de la; Fink, H. J.
    A model is proposed to account for the large increase in the measured penetration depth of superconducting, amorphous La7oCu3o when the specimens are annealed sufficiently long near, but below, the crystallization temperature. It is suggested that a metallurgical phase separation occurs with domain dimensions in the submicrometer range. Penetration depth measurements as a function of temperature in a weak magnetic field are a useful tool to detect changes in phase separation in high-K materials.
  • Miniatura
    ÍtemAcceso Abierto
    Temperature dependence of the superconducting giant vortex state. Theory and experiment.
    (American Chemical Society, 1979) de la Cruz, F.; Fink, H. J.; Luzuriaga, J.
    When a type-1 superconductor with a surface nucleation field Hc2 ( T) > HC( T ) (thermodynamic critical field) is thermally cycled in an axially applied magnetic field H0 between the temperatures T(Hc3) and about T ( H2), experiments show that the magnetization changes reversibly. The latter is diamagnetic near T (Hc3) but can be paramagnetic just above T ( H2). This behavior is explained by assuming that the fluxoid quantum number b is fixed at the transition from the normal to the superconducting state and retained at lower temperatures. The value of b is determined almost entirely by the flux at the transition which is enclosed by a contour located at a distance ξ /1.7 from the surface inside the cylinder (ξ is the coherence length).The temperature variation of the order parameter / at the surface of the cylinder, the magnetization m, and the temperature at which m = 0 for / ^ 0 are calculated for R » ξ Conservation of the fluxoid quantum number, while T is varied causes the two opposing surface currents to become imbalanced. This is the source of the observed para- and diamagnetism.