The current flow and the flux pinning properties on struts of superconducting YBa 2 Cu 3 O x foams are analyzed in detail in the temperature range 60 K ≤ T ≤ T c . For this purpose, magnetization loops were measured on foam struts taken from various positions of a 5 × 2 × 2 cm 3 large foam sample prepared at RWTH Aachen. From these data, the critical current densities, j c , and the flux pinning forces, F p = j c × B, were calculated and pinning force scaling diagrams F p /F p ,max versus h = H a /H irr were established. The scaling in the temperature range 60 K < T < 90 K was found to be well developed for all samples with peak positions, h 0 , above 0.4, which is an indication of δT c -pinning. The shape of the pinning functions is found to be completely different from all other high-T c materials and varies only slightly with position. This specific dome shape cannot be described by an addition of several pinning functions, and the parameters p and q do not fit to the description of Dew-Hughes. Therefore, we employ Kramer plots to obtainmore information on the flux pinning mechanism.
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Condensed Matter Physics
- Electrical and Electronic Engineering