Vortex arrangement and reversible magnetization of Bi2.1Sr1.9Ca1.0Cu2.0Ox single crystals for the in-plane magnetic field

The field dependence of magnetization of the Bi2.1Sr1.9Ca2.0Cu2.0Ox single crystals with dimensions of 5*3.6*0.4 mm(3) and 5.5*5*1.3 mm(3) was studied for the in-plane magnetic field with a 7 T SQUID magnetometer equipped with the sample rotation system. It was found that the absolute value of the negative magnetization increases with increasing magnetic field in a wide field range of H-c1<< H H-c2. The results are in a good agreement with the laminar structure approximation for the magnetization distribution inside a superconductor. The negative susceptibility in a high external field of 7 T does not vanish up to a temperature of 140 K which is significantly higher than the T-c=88K of the crystal. The data can be interpreted as an indication of remaining of the superconductivity above T-c, presumably in the areas of closely spaced CuO2 planes of Bi-2212.