Magnetic Field Cooling of High-Tc Oxide Superconductor

We have observed asymmetries in the major loop and the dc bias field (Hb) dependence of the third harmonic component (V3f) of the minor loop of a field-cooled sintered Y-Ba-Cu-O superconductor disk sample. These asymmetries were investigated, focusing on the minima in the V3f-Hb loop which are shifted by field cooling. We found that: (1) the minima in the V3f-Hb loop appear at the points that satisfy the zero-field condition in the sample; (2) the inverse field for Hb caused by the vortex plays an important role in generating the zero-field condition in the sample; and (3) the asymmetries originate from the vortex induced by the field cooling process.