Formation of the magnetization loops of high-T_c superconductors

摘要

We have investigated the irreversibility magnetic field and the critical current density of the high temperature superconductor Yba_2Cu_3O_(7-δ) single crystal. Vibrating sample magnetometer (V.S.M.) method was used for these measurements. Magnetization hysteresis loops scale and shape are strongly dependent on the temperature values and the angle θ between the direction of the applied magnetic field and c-axis. For the large single crystals at very low temperature the loops present several flux jumps "saw-tooth" and we observe the second peak "fish-tail" for high temperature values but not with applied magnetic field perpendicular to the ab-planes. Beyond θ= 30°, the irreversibility field H_(irr) increases deviates from different temperature values. The variation of the critical current density J_c with applied magnetic field parallel to c-axis for different temperatures was studied. Here, J_c is an effective critical current density deduced from the measured magnetization by the Bean formula.