The Magnetization Properties of High-Tc Superconductor YBa2Cu3O∼7 at Low Magnetic Fields

The magnetization of a high-Tc superconductor YBa2Cu3O∼7 was measured at low magnetic fields (<100 Oe ) under the condition of constant temperature of about 80K. For the specimens used in this work, the magnetization curves deviate from the Meissner state at about 5 Oe. Most of the weak couplings between the superconducting grains are greatly weakened or even destroyed in the field region of 14–22 Oe. Then the effective penetration depth is about 0.13mm. The hysteresis due to the granular superconductivity was also observed.