COMPARISON OF THE MAGNETIZATION BEHAVIOR OF NI-DOPED AND CO-DOPED YBA2CU3-XMXO7-DELTA (M=NI, CO) SINGLE-CRYSTALS

We prepared YBa(2)Cu(3-x)MxO(7-delta) (M = Ni, CO) single crystals usi ng the flux method and then measured the in proper thermodynamic param eters. The Hao-Clem model was used to analyze their magnetization in a n external magnetic field parallel to the c-axis. The superconducting properties (such as the superconducting transition temperature, the Gi nzburg-Landau parameter, and the penetration depth) changed more drast ically for Ni substitution than for Co substitution. This difference b etween the Ni and the Co substitutions is explained by the preferentia l substitution of for the two ions at two different Cu sites.