Anisotropy of flux penetration into BiSrCaCuO crystals

The onset of flux penetration in crystals of two-layer BiSrCaCuO is determined from measurements of the zero-field-cooled dc magnetization. For magnetic fields applied in the a-b plane, a flux penetration anomaly shifts linearly to lower temperature with increasing field, indicating low-temperature Hc1 values of 80-140 Oe, within a factor of two of the values for YBaCuO crystals. The much larger anisotropy reported earlier is suggested to arise from extrinsic intergrowths. © 1989.