Low field AC susceptibility of YBCO: the frequency and field dependence of intra- and intergrain coupling losses in the absence of vortices

Abstract

The AC susceptibility (χ + iχ ) of YBCO with and without intergrain coupling was measured in AC fields within 0.13 and 3.72 mT and frequencies from 20 Hz to 12.8 kHz. Intergrain coupling was eliminated by dispersing the powder in insulating varnish. For the coupled and uncoupled grains, the χ (T ) transition near T C is field independent, indicating that the fields used do not drive the sample into the mixed state. Thus, the χ and χ curves cannot be associated with vortex motion. In χ (T ), a peak near T C due to the intragrain response increases with applied AC field for both coupled and uncoupled grains. For the sample with sufficient grain coupling, a peak below T C shifts to low temperatures with increase in field. We attribute χ (T ) to eddy currents and explain its behaviour by taking into account the effect of the temperature dependence of the penetration depth and the electrical resistance on the eddy currents.

Effect of Graphene Nanoparticles Addition on Superconductivity of YBa2Cu3O7~δ Synthesized via the Thermal Treatment Method

“…The graphene nanoparticles can be a powerful material to act as an as effective pinning center. These findings were supported from the previous studies that had also reported that graphene/carbon base nanomaterials addition could be beneficial, especially in the Y123 superconductor performance [24,36,49,50]. However, further improvements of the Y123 superconducting performance are possible in order to obtain more higher of J cm values.…”

“…However, T p is broadened and shifted to the lower temperature with the increase of graphene nanoparticles in Y123 samples due to the weakening of intergranular coupling between grains, as shown in Figure 4 [48]. This decrement may be due to some defects at the grain boundaries such as grain disorientation, twin boundaries and vacancies that can act as weak links, therefore disturbing the T p and pinning forces [49]. The broad width of χ" might also be caused by the second superconducting transition of the secondary phase.…”

The Superconducting Transition and Mixed State of YBa$_2$Cu$_3$O$_{6.95}$: An Undergraduate Experiment

“…Figures6 and 7show the measured temperature dependencies of χ and χ for the polycrystalline and single crystal samples, respectively.The field strength at the sample site was calibrated using the same Texas Instruments DRV5055A2 Hall effect sensor described in section 2.4. As shown in figure4, the field strength is set by both the amplitude of the signal generator output and the value of the series resistance R.The polycrystalline measurements of figure6are qualitatively consistent with the results reported by Nikolo and others using more sophisticated apparatuses[9,15,16]. The temperature dependence of χ exhibits an inflection point at a temperature T * just below the superconducting transition temperature.…”

Structural and Superconducting Properties of Thermal Treatment-Synthesised Bulk YBa2Cu3O7−δ Superconductor: Effect of Addition of SnO2 Nanoparticles

“…However, the transition starts to broaden at x = 0.8 and x = 1.0, suggesting that x = 0.4 is the optimum weight percentage for SnO 2 addition. This broadened curve is caused by the magnetic flux penetrating the sample surface when there is a decrease in the screening current required to exclude the flux [30]. From T c-onset and the phase-lock in the temperature, T cj , tabulated in Table 3, maximum Josephson current, I 0 , can be estimated using the Ambegaokar-Baratoff theory in the following equation [31], I0=(1.57 ×10−8 A/K) Tc-onset2Tc-onset − Tcj…”