Evaluation of anisotropy of critical current density in stoichiometric Bi-2212 single crystals

The anisotropy of the critical current density was estimated for stoichiometric Bi 2 Sr 2 CaCu 2 O y (Bi-2212) and Bi 2.1 Sr 1.8 Ca 1.0 Cu 2.0 O y single crystals. For this purpose, the critical current density in the a–b plane J c ab and that along the c-axis J c c were discriminated from measurement of DC magnetic moments for specimens with different aspect ratio. The magnetic moment of specimen was measured by a SQUID magnetometer in a magnetic field parallel to the wide surface which is normal to the c-axis. Both of J c ab and J c c are larger in the stoichiometric specimen. In addition, the anisotropy, J c ab / J c c , is found to be significantly reduced in the stoichiometric specimen.