Abstract
Dc magnetization measurements were carried out on YBa2(Cu1-xMnx)3O7-δ samples with x taking values 0, 0.01, 0.015, 0.02, 0.025, 0.035 and 0.05, YBa2(Cu0.975Fe0.025)3O7-δ, YBa2(Cu0.975Ni0.025)3O7-δ and YBa2(Cu0.975Zn0.025)3O7-δ samples up to a maximum field of 5 T at temperatures 5, 50 and 77 K. The effect of Mn on the zero field critical current density, Jcg(0), estimated from the remnant magnetization, in general, is a monotonic suppression up to a concentration of 2.5% Mn and shows a saturation beyond that concentration. The field and temperature dependences of 2.5% Mn doped YBa2Cu3O7-δ samples were better than those of the Ni, Fe and Zn at the same doping level. Anomalous increases in Jcg(0), the indicative lower critical field, H*c1g, and the bulk flux pinning force, Fp, observed in the 2.0% Mn doped sample, at 50 and 77 K, have been attributed to the matching of the Abrikosov vortex density generated over these temperatures and the defect induced number of pinning sites due to the Mn doping.