Peak Effect in Bi-2212 Single Crystal at Low Magnetic Field

Force-displacement characteristic of flux lines in a superconducting Bi-2212 single crystal was measured using the Campbell method at low temperatures and low magnetic fields where the peak effect of the critical current density was observed. It was found that the interaction distance, d i, had a peak around the peak field, while the Labusch parameter, α L, increased monotonously with increasing magnetic field. The peak of d i means an increment of the reversible limit of motion of pinned flux lines. This seems to be caused by an introduction of some disorder in the flux line lattice at the so-called 3-dimensional to 2-dimensional transition field. However, the characteristic length of the deformation along the c-axis is considered to be much longer than the distance between the CuO2 planes.