Magnetic ion doped Cu_(1-x)Tl_xBa_2Ca_(2-y)MgyCu_(1.5)Ni_(1.5)O_(10-δ) (y = 0, 0.5, 1.0, 1.5) superconductors and their improved inter-plane coupling

摘要

We have synthesized Cu0.5Tl0.5Ba2Ca2Cu3-yNiyO10-δ (y = 0, 0.5, 1.0, 1.5) superconductors at normal pressure and studied the enhanced correlation among CuO2/NiO2 planes of Cu0.5Tl0.5Ba2Ca2-yMgyCu1.5Ni1.5O10-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 Cu0.5Tl0.5Ba2Ca2Cu3-yNiyO10-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 Cu0.5Tl0.5Ba2Ca2-yMgyCu1.5Ni1.5O10-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 [Tc(R = 0)] and the magnitude of diamagnetism are increased with higher Mg doping in Cu0.5Tl0.5Ba2Ca2-yMgyCu1.5Ni1.5O10-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 Ni2+ sites and results in enhanced superconducting properties.