Effect of Fe on the superconductivity of the Ba-Y-Cu oxide system

We have substituted copper with iron in high-$T_c$ ${\mathrm{Ba}}_2\mathrm{Y}{\mathrm{Cu}}_3{\mathrm{O}}_{7-\delta }$ and formed ${\mathrm{Ba}}_2\mathrm{Y}{\mathrm{Cu}}_{3(1-x)\mathrm{}}{\mathrm{Fe}}_{3x}{\mathrm{O}}_{7-\delta }$. It is found that $T_c$ decreases with an increase of the Fe concentration, and the superconductivity is destroyed at $x=0.15\mathrm{}$. X-ray diffraction analysis shows that the material has an orthorhombic perovskite structure with larger lattice parameters and smaller $\Delta \mathrm{}(a-b)\mathrm{}$ than ${\mathrm{Ba}}_2\mathrm{Y}{\mathrm{Cu}}_3{\mathrm{O}}_{7-\delta }$. Magnetic measurements show that the doped samples possess considerable paramagnetism. The effect of Fe on the superconductivity of ${\mathrm{Ba}}_2\mathrm{Y}{\mathrm{Cu}}_3{\mathrm{O}}_{7-\delta }$ is discussed in detail.