Because the bulk-type YBCO superconductor prepared by the MPMG process has high critical current density J_c. It is expected to be applied to various fields such as magnetic bearing, magnetic levitation, magnetic shielding, and etc. In such applications it is important to develop measurement methods of magnetic property to high-T_c superconductor. It is necessary to value not only DC magnetic property but also AC magnetic property. So we measured magnetic pmperty of the high-T_c superconductor under the AC magnetic field (5-500Hz).
From the experimental results we can understand that there are two different kinds of elements in AC magnetic property: the one is the first order lag element by the flux flow, and the other is the applied magnetic flux that go around the ring specimen into that inside. The magnetic property in low frequency is ruled by the flux flow.