Study on the Irreversible Line of Bi-based High-T_c Phase Superconductors at Low Magnetic Field

The irreversible lines of Bi-based high-T phase superconductor samples in the form of bulk,powder and crystal slices are obtained by measuring a.c.susceptibility of the samples at the applied d.c.magnetic field.The irreversible lines of the bulk,powder and crystal slice samples at a low magnetic field and LN₂ temperature range are (1-T_P/T_c)∝H^0.68、(1-T_P/T_c)∝H^0.61 and (1-T_P/T_c)∝H^0.40 respectively.The significane of the irreversible line,and,the strength and characteristic of the flux pinning for the three kinds of samples are discussed.The retationship hips between these and the microscopic structure of the samples are also aralyzed.