Low-frequency magnetic shielding studies on high-Tc superconductor Y-Ba-Cu-O

Low frequency (10-Hz to 100-MHz) magnetic-shielding studies were performed on high-T_c superconductors Y-Ba-Cu-O to investigate the material´s shielding behavior. The critical field H_c1 in the superconductor was observed to be ⩽17.8 G. The superconductor shielded down to the background noise level independent of the frequency when the applied field strength was⩽ H_c1. In the vortex state, just above H_c1, the superconductor-type transformer behaved nonlinearly. A semiempirical model for the skin depth was used to fit the nonlinear data. In the high applied field limit, this shielding data was shown to have a square-root frequency dependence similar to ordinary shielding materials. At lower fields above H_C1, data tended toward frequency independence. Noise-limited experimental low-frequency results indicated that the superconductor shielded at least as well as common state-of-the-art materials