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 flux oids in ac magnetic field were carried out for a melt-processed Y-Ba-C u-O bulk superconductor using the Campbell method. The Labusch paramet er, alpha(L), and the interaction distance, d(i), were estimated from the obtained force-diplacement profile. It was found that alpha(L) dep ended greatly on temperature and magnetic field, especially in the fie ld parallel to the c-axis, and d(i) decreased gradually with increasin g temperature. These variations were deduced to be caused by flux cree p. The depth of pinning potential, U0, for the trapped flux bundle was estimated using the values of alpha(L) and d(i). This was compared wi th the apparent pinning potential which is commonly observed from magn etic relaxation measurements.