Modelling of the magnetic behaviour of random granular superconductors by the single junction model

Abstract

The magnetic measurements of the Josephson critical field and intergranular critical currents are presented for the Bi2223 compound. The investigations prove that the Josephson critical field value is mainly dependent on the intergranular critical current density. The other factors like the grain dimensions and shapes, sample porosity and density are less important. The relation between the Josephson critical field and critical current H cJ (J c ) is well described within the single junction model, H cj ∝ J c λ J . The temperature dependence of H cJ can also be well fitted according to the single junction model with a critical current dependence, J c ∝ (1 − T /T cJ ) α . The critical current density versus temperature is almost linear indicating the presence of superconductor-insulator-superconductor (SIS) type junctions.

Josephson-coupled superconducting regions embedded at the interfaces of highly oriented pyrolytic graphite

“…As an example, we show the results at 100 K in figure 7. The observed changes of the hysteresis as a function of the maximum applied field, namely from a reversible (zero hysteresis) at low maximum applied fields (H 100 Oe) to a Bean-like behavior at fields of the order of 300 Oe, to the narrowing of the hysteresis at the largest fields, agrees with that expected for granular superconductors [44][45][46], as has recently been reported for water-treated graphite powders [11]. The change in the slope of the virgin first curve is also typical of a granular superconducting response.…”

Evidence for room temperature superconductivity at graphite interfaces

“…2(b) shows the hysteresis loops of water-treated graphite powder at 300 K and at different maximum applied fields, after subtraction of a linear diamagnetic background. The hysteresis loops at fields below and above h J c1 are qualitatively similar to the one obtained in granular superconductors, see Figure 2(a) and also [9,10]. Similar curves were obtained after treatment the graphite powder with alkanes.…”

“…The magnetization results of graphite powders, after a certain water or alkane [9]. b) Similar plot for a water-treated graphite powder at different maximum applied fields at 300 K, after subtraction of linear in field diamagnetic background, adapted from [7].…”

“…[9,10]. Due to the granularity and the Josephson coupling between grains, the strength of an applied magnetic field influences in a non simple way the field hysteresis.…”

Microstructure and properties of Cu–Nb and Cu–Ag nanofiber composites

“…7 and 12 above). Superconducting properties of this wire can be also strongly affected by the presence of Josephson junctions (Barone and Paterno, 1982) formed at interfaces between superconducting Nb particles because they usually exhibit suppressed critical temperature and low density of critical currents (Piekoszewski et al 2005 andAndrzejewski et al 2001). where R is the mean radius of the grains or Nb filaments.…”