Magnetic order and superconductivity inRBa2Cu3Oz

Mössbauer studies ${}_{}{}^{57}{}_{}{}^{}\mathrm{Fe}$ in $R{\mathrm{Ba}}_{2-y}{\mathrm{K}}_y{\left({\mathrm{Cu}}_{1-x}{\mathrm{Fe}}_x\right)}_3{\mathrm{O}}_z$, with $R=\mathrm{Y} \mathrm{and} \mathrm{Pr}$, $y=0\mathrm{} \mathrm{and} 0.5$, $x=0.01,0.05, \mathrm{and} 0.1$, and $z$ between 5.9 and 7.1, have been performed. A minority of the iron ions enter the Cu(2) site and reveal its magnetic order. For $R=\mathrm{Y}$, $y=0\mathrm{}$, and $x=0.1\mathrm{}$, $T_N$ equals 280 and 415 K for $z=6.5\mathrm{} \mathrm{and} 6.1$, respectively. The magnetic moments lie in the basal plane. In tetragonal, oxygen-rich Pr${\mathrm{Ba}}_2$ ${\left({\mathrm{Cu}}_{0.9}{\mathrm{Fe}}_{0.1}\right)}_3$ ${\mathrm{O}}_{6.9}$, $T_N=325\mathrm{}$ K; in superconducting Y${\mathrm{Ba}}_2$ ${\left({\mathrm{Cu}}_{0.9}{\mathrm{Fe}}_{0.1}\right)}_3$ ${\mathrm{O}}_{7.1}$ there is no magnetic order. In nonsuperconducting Y${\mathrm{Ba}}_{1.5}$ ${\mathrm{K}}_{0.5}$ ${\left({\mathrm{Cu}}_{0.95}{\mathrm{Fe}}_{0.05}\right)}_3$ ${\mathrm{O}}_{6.1}$ two distinctly inequivalent magnetic iron sites are observed, corresponding to iron in the Cu(2) site with different Ba-K neighbors. Moments of iron ions that have three Ba and one K as first-nearest neighbors have a different temperature dependence and $T_N$ ($T_N=450\mathrm{}$ K) from those with four Ba neighbors, where $T_N=415\mathrm{}$ K, showing that the antiferromagnetic exchange in the Cu(2) planes is strongly affected by the replacement of