AC susceptibility measurements for superconducting Y-Ba-Cu-O powder

The effect of reversible motion. of fluxoids was investigated by measuring fundamental and third harmonic AC susceptibilities in Y-based superconducting powder in which the intergrain current is eliminated. The peak values of AC susceptibilities decrease monotonically with increasing DC magnetic field and/or temperature, suggesting that the reversible fluxoid motion becomes significant. The AC magnetic field dependence of the AC susceptibilities of cylindrical superconductors were numerically calculated for simplicity based on the Campbell model which describes the reversible fluxoid motion. The critical current density and the AC penetration depth were estimated from the AC susceptibilities and compared with the results from DC magnetization. These results agree fairly well, and small differences between the two measurements may be attributed to the distribution of the particle size. It is concluded that the observed AC susceptibilities are well explained by the Campbell model.