Magnetization and magnetic levitation of ring samples made of melt textured YBa2Cu3Ox

We present measurements of the magnetization and the levitation force of va rious superconducting rings made of melt textured YBa2Cu3Ox. We compare the measurements on the rings to those when a slit is cut into them. The slit prevents shielding currents from forming complete loops around the perimete r of the rings. For most small rings used for the magnetization measurement s (5 mm diameter or less), the slit reduces the magnetization according to Bean's model. For some rings, however, this decrease was much smaller that the theoretical value. Consistently, however, magneto-optical images reveal ed the presence of weak, links cutting across those rings. The larger rings used for the levitation experiments (20 mm diameter) were not of the same quality, i.e., the ratio of the levitation force before and after the slit was cut was below the theoretical value for all rings investigated. Because of their large size, magneto-optical images of those rings could not be ta ken. It is very likely that these larger rings have weak links which preven t large-diameter circulating shielding currents. (C) 1998 Published by Else vier Science B.V. All rights reserved.