Flux penetration into an artificially granular high-T-c superconductor

A YBa2Cu3O7-delta thin film is patterned into a hexagonal close-packed latt ice of disks. (2r=50 mu m) which are touching each other at the circumferen ces in order to enable the flow of an intergranular current. Such a sample was suggested by Koblischka et al. [Appl. Phys. Lett. 70, 514 (1997)] as a model for a layered granular structure like in a (Pb,Bi)(2)Sr2Ca2Cu3O10+del ta (Bi-2223) tape. The magnetization measurements reveal an anomalous posit ion of the low-field peak (central peak) similar to Bi-2223 tapes. Magneto- optic imaging is employed to visualize the local-field distributions. At lo w magnification,the flux patterns in the intergranular area between the dis ks are observed. The observations at high magnification reveal the flux pen etration and pinning within the disks. It is shown that such samples may se rve as model samples for granular high-T-c superconductors. [S0163-1829(99) 05617-9].