Relation between the critical current and the n value of ReBCO thin films: A scaling law for flux pinning of ReBCO thin films

Abstract

Detailed field and angle dependencies of the critical current and the n value for a SmBCO coated conductor have been measured. It was found that the field dependence of the n value can be fitted by an empirical power law with three parameters including the irreversibility field. We also found that there is a correlation between the critical current and the n value which can be described by the Kramer model including thermal activation. The model fits the field dependence of the empirical critical current data at various angles and temperatures with three fitting parameters, the pinning force maximum, the g factor, and the upper critical field. The upper critical field found from fitting was higher than the irreversibility field, and the angular dependence of the upper critical field is in agreement with the Tinkham model. The pinning force maxima do not show a correlation with the upper critical or the irreversibility fields, which is attributed to the difference in the pinning mechanism with a variation of the angle. It was further shown that the angular dependence of the critical current can be calculated by the Kramer model including thermal activation with empirical angular dependence expressions for each parameter. The critical current data reported by Yamada et al. [Supercond. Sci. Technol. 17, S25 (2004)] for YBCO thin films on various substrates deposited by pulsed laser deposition method can also be described by the Kramer model including thermal activation and the angular dependencies of each parameter were compared with the SmBCO coated conductor fitting results.

Comparison of ${J_{{C}}}$ in GdBCO Tape Using Dc Magnetization and Harmonic Ac Susceptibility Measurements

“…These are consistent with expected values at 80 [7]. It is important to note that one can only expect measurements made by Ac and Dc methods to agree when the electric fields induced in the two measurements are similar.…”

Lorentz-force dependence of the critical current for SmBCO coated conductor

“…7 It should be noted that even for the VLF configuration, the field dependences of the critical current and the n-value are in agreement with the same pinning model, the Kramer model including thermal activation, as for the case of CLF measurements. 4 and 5, where the field dependence of the critical current is presented in the form of Kramer plots, the field dependence of I c 1/2 ϫ B 1/4 .…”

“…1 On the other hand, for high T c cuprate superconductors, the relation between the Lorentz force and the pinning force is a bit dubious. 7 The model reasonably fits the data for a variety of ReBCO ͑Re, rare earth, Sm, or Y͒ thin films even if there is another maximum in the angular dependence of the critical current when the field is aligned along the c-axis. 2 The critical current measurements under various applied field configurations did not give conclusive results either.…”

Intrinsic and extrinsic pinning in NdFeAs(O,F): vortex trapping and lock-in by the layered structure

“…S3). In general, in case of random isotropic pinning, n scales with J c , as experimentally shown in many compounds (YBCO3839, MgB 2 40, Nb 3 Sn414243, Nb-Ti43), independently of temperature, field or angle. A relation of the type n  ∼  J c α was suggested and means that an increase of J c leads to an increase in the n -value.…”