FORCE-DISPLACEMENT CHARACTERISTIC OF FLUXOIDS ALONG THE C-AXIS IN SUPERCONDUCTING BI-2212 SINGLE-CRYSTAL NEAR THE PEAK FIELD

Force-displacement characteristic of fluxoids in a superconducting Bi- 2212 single crystal was measured by using the Campbell method at low t emperatures and low magnetic fields where the peak effect of critical current density was observed. It is found that the interaction distanc e, d(i), has a peak around the peak field while the Labusch parameter, alpha(L), increases monotonously with increasing magnetic field. The peak of d(i) means an increment of flexibility of fluxoids to randomly distributed pins and this is considered to be brought about by some d eformation of fluxoid cores along the length. Although this may be ass ociated with the cross-over from three-dimensional flux lines to two-d imensional pancakes, the characteristic length of deformation is consi dered to be much longer than the distance between the CuO2 planes. (C) 1998 Elsevier Science B.V.