Scaling of pinning forces in NdBa2Cu3O7-delta superconductors

The scaling of the volume pinning forces, F-p = j(c) x B-a, is performed ve rsus the reduced fields b(f) = B-a /B-fp (where B-a is the applied field, a nd B-fp denotes the peak position of F-p,F-max) and h = H-a/H-irr (where H- irr denotes the irreversibility field) for two different NdBa2Cu3O7-delta s uperconductors, a single crystal and a melt-processed sample. In both cases , an excellent natural scaling is found to hold. Based on these good scalin g results, we extend the scaling analysis towards lower temperatures. There , the scaling parameters are no longer directly accessible within our exper imental field range, but can be deduced from the F-p(B-a) curves normalized using fitting values of B-fp and F-p,F-max so that these overlap with the high temperature curves. It is shown that such a procedure allows to obtain reasonably good estimates of F-p,F-max and H-irr, which leads in turn to a n estimation of the irreversibility line well down to 0 temperature. At low temperatures, deviations from the analytical dependencies appear which are due to interference with the central and intermediate peak in the magnetiz ation loops. The shape of the irreversibility line is discussed. (C) 1999 A merican Institute of Physics.