Magnetic shielding properties of YBa2Cu3O7−<i>x</i> superconductors

We have developed a highly sensitive ac magnetic method, using a modified two-coil technique, for measuring magnetic shielding effectiveness (S) of high-temperature superconductors in planar form. Incorporated in the measurement was a pair of iron E pieces, which significantly reduce flux leakage around the sample edge. Below a threshold field, the S values measured at 77 K for bulk superconducting YBa2Cu3O7−x compounds were typically 110 dB. This method is particularly useful for determining threshold field and observing trapped-flux behaviors in high-temperature superconductors.