Complex Susceptibilities of Co-Doped YBa₂Cu₃O_7-d Synthesized by the Polymerized Complex Method

We studied the ac-magnetic response of Co-doped YBa₂Cu₃O_7-d oxide superconductors, YBa₂Cu_3-xCo_xO_7-d (x = 0-0.5), in terms of complex susceptibility χ = χ′ - iχ″. The samples were synthesized by the polymerized complex method. We found the onset temperature decreased with increasing x, and for x ≥ 0.4, no superconducting transition was observed down to 5 K. The transition width ΔT(10-90%) for the sample of x = 0.05 is 1.9 K, which is much better than that of the specimens prepared by the ordinary treatment. The transition width was also found to increase as x increases. Details of the experiment are presented together with some discussion of the coupling phase involved.