Low-Field Magnetization Curves of YBa sub 2 Cu sub 3 O sub 7--x and BiSrCaCu sub 2 O sub 5.5 : Effects of Josephson Medium

• Published in: Journal of low temperature physics Vol. 74; no. 5-6; pp. 503 - 517
• Main Authors: Kohl, M, Odehnal, M, Plintovic, M, Safrata, S
• Format: Journal Article
• Language: English
• Published: 01-03-1989
• ISSN: 0022-2291

The measurement is presented of dc magnetization curve of three samples of high-T sub c superconductors in relatively low magnetic field of plus/minus 5 mT and at temperatures of T = 4.2 and 77K by a SQUID susceptometer. The samples were polycrystalline YBa sub 2 Cu sub 3 O sub 7--x , a single crystal of YBa sub 2 Cu sub 3 O sub 7--x , and polycrystalline BiCaSrCu sub 2 O sub 5.5 . The influence of the Josephson medium inside the samples on their low-field magnetization is studied. Closed hysteretic loops in the field plus/minus 4 mT with "virgin" and "granular" slopes are found in the sample of polycrystalline YBaCuO and clear flux jumps corresponding to the penetration of low-field (Josephson) vortices. The pinning of these vortices in this case is rather low. In polycrystalline sample of BiCaSrCuO, only reversible magnetization curves, corresponding to very low pinning and/or to relatively low number of weak links, are found. 38 ref.--AA