Magnetic ion Fe and Ni doping in the Cu-O chain and the CuO2 plane in YBa2Cu3O7-δ: a positron study

Fe and Ni substitutions in the Cu-O chain and the CuO₂ plane are studied by positron lifetime experiment. Change of lifetime parameters is given and local electron density is evaluated as a function of substitution content. The results show fantastic and opposite behaviors for Fe and Ni substitutions. A strengthen effect of the localized carriers in the CuO₂ planes for Ni substitution and electronic weak localization in the Cu-O chains for Fe substitution are found in YBa₂Cu₃O_7-δ superconducting systems. The positron distribution and the annihilation mechanism are also discussed.