Effect of Blocking and Superconducting Layer Doping on the Superconductivity and Magnetic Properties of Polycrystalline Sr₂CaCu₂O₆

The possible difference in the properties upon doping the Sr₂CaCu₂O₆ superconducting or blocking layers with Fe and Eu respectively was investigated in this work. The homogeneous Sr_2−yEu_yCaCu₂O_6+δ and Sr₂CaCu_2−xFe_xO_6+δ (y = 0, 0.1, 0.5, x = 0, 0.05) compounds were produced by a high-pressure synthesis route. Judging by the magnetic susceptibility measurements, all samples exhibit a superconductivity transition and the Eu/Fe concentration dependencies on the diamagnetic moment and average T_c have been constructed using the experimental data. As a result, an unusual behavior of the T_c value was observed for the samples with doped Eu: a fivefold reduction in the europium concentration in the sample does not give a noticeable effect on the transition temperature value while the diamagnetic signal becomes more stronger. Complex superconducting dome was found for Eu-doped material: 0.1 ≤ y ≤ 0.5 region T_c vs. concentration data were approximated by inverted parabola-like curve with a maximum at y = 0.3. Difference in properties of the Eu and Fe-doped samples was also found in the behavior of the hysteresis loops showed the opposite orientations.