EQUILIBRIUM MAGNETIC-PROPERTIES AND MEISSNER EXPULSION OF MAGNETIC-FLUX IN BI2SR2CACU2OX SINGLE-CRYSTALS

The unusual spatial transformation of the magnetic-flux structure in B i2Sr2CaCu2Ox single crystals during magnetization of zero-field cooled samples and during field cooling (the Meissner flux expulsion) is dir ectly visualized by means of the magneto-optical technique. In both ca ses similar inhomogeneous flux distributions are observed at high temp eratures in a magnetic field applied perpendicularly to the basal plan e: The magnetic field in the crystal center is approximately equal to the applied field, but at the crystal perimeter a belt of lower field occurs. A model of such an equilibrium flux structure is developed tak ing into account the real shape of the crystals. The distribution of t he Meissner screening current in this geometry is directly measured fo r the first time.