Magnetic ion doped Cu 1− xTl xBa 2Ca 2− yMg yCu 1.5Ni 1.5O 10− δ ( y = 0, 0.5, 1.0, 1.5) superconductors and their improved inter-plane coupling

Abstract

We have synthesized Cu 0.5Tl 0.5Ba 2Ca 2Cu 3− y Ni y O 10− δ ( y = 0, 0.5, 1.0, 1.5) superconductors at normal pressure and studied the enhanced correlation among CuO 2/NiO 2 planes of Cu 0.5Tl 0.5Ba 2Ca 2− y Mg y Cu 1.5Ni 1.5O 10− δ ( y = 0.5, 1.0, 1.5) superconductors by doping Mg at the Ca sites. Surprisingly, we have not observed any substantial depression of critical temperature with Ni doping in Cu 0.5Tl 0.5Ba 2Ca 2Cu 3− y Ni y O 10− δ ( y = 0, 0.5, 1.0, 1.5) superconductors. The main objective of Mg substitution is to enhance the inter-plane coupling which may increase the interactions of the spins of Ni atoms in different planes. The increased inter-plane coupling may enhance interactions of the atomic spins with the free carriers and might be a key to understanding the effects of spin scattering and their role in the mechanism of high temperature superconductivity. We have observed a decrease of c-axis length with increased Mg concentration in Cu 0.5Tl 0.5Ba 2Ca 2− y Mg y Cu 1.5Ni 1.5O 10− δ ( y = 0.5, 1.0, 1.5) superconductors, showing an enhanced inter-plane coupling. The room temperature resistivity of the samples is decreased and the zero resistivity critical temperature [ T c( R = 0)] and the magnitude of diamagnetism are increased with higher Mg doping in Cu 0.5Tl 0.5Ba 2Ca 2− y Mg y Cu 1.5Ni 1.5O 10− δ superconductors. A maximum diamagnetism is observed in the samples when Mg atoms replace 75% of the Ca atoms, which shows that a higher Mg doping concentration enhances the inter-plane coupling which possibly promotes the de-localization of the carriers to the Ni 2+ sites and results in enhanced superconducting properties.