Force-Displacement Characteristics of Fluxoid Lattice and Pinning Potential in Y-Ba-Cu-O Bulk Superconductor

Measurements of the pinning force density and the displacement of fluxoids in ac magnetic field were carried out for a melt -processed Y-Ba-Cu-O bulk superconductor using the Campbell method. The Labusch parameter, αL, and the interaction distance, di, were estimated from the obtained force-displacement profile. It was found that αL depended greatly on temperature and magnetic field, especially in the field parallel to the c-axcis, and di decreased gradually with increasing temperature. These variationss were deduced to be caused by flux creep. The depth of pinning potential, U0, for the trapped flux bundle was estimated using the values of αL and di. This was compared with the apparent pinning potential which is commonly observed from magnetic relaxation measurements.