Enhanced flux pinning properties of Bi(Pb)2212 single crystals

Improvement of flux pinning properties of heavily lead-doped Bi2212 single crystals was attempted by cobalt-doping with low concentrations. Tc's of grown crystals with nominal compositions of Bi1.6Pb0.6Sr1.8Ca(Cu1-xCox)2Oy (x=0, 0.002, 0.005, 0.02) dramatically decreased with an increase of the cobalt-doping level x, however, crystals with x=0.002 and 0.005 showed largely improved flux pinning properties below 50 K. This result suggests that effective point-defect-type pinning sites were successfully introduced by small amount of cobalt-doping. For these crystals, both anisotropic in-plane Jc properties and the 'temperature induced pinning' effect due to interfaces of the lamella structure were observed, however these characteristic behaviours were suppressed in the crystal with x=0.02