AC SUSCEPTIBILITY MEASUREMENTS FOR SUPERCONDUCTING Y-BA-CU-O POWDER

The effect of reversible motion. of fluxoids was investigated by measu ring fundamental and third harmonic AC susceptibilities in Y-based sup erconducting powder in which the intergrain current is eliminated. The peak values of AC susceptibilities decrease monotonically with increa sing DC magnetic field and/or temperature, suggesting that the reversi ble fluxoid motion becomes significant. The AC magnetic field dependen ce of the AC susceptibilities of cylindrical superconductors were nume rically calculated for simplicity based on the Campbell model which de scribes the reversible fluxoid motion. The critical current density an d the AC penetration depth were estimated from the AC susceptibilities and compared with the results from DC magnetization. These results ag ree fairly well, and small differences between the two measurements ma y be attributed to the distribution of the particle size. It is conclu ded that the observed AC susceptibilities are well explained by the Ca mpbell model.