Superconducting and magnetic properties of ${\mathrm{TlSr}}_2$${\mathrm{Ca}}_{1\mathrm{-}\mathit{x}}$${\mathit{R}}_{\mathit{x}}$${\mathrm{Cu}}_2$${\mathrm{O}}_7$ [R=Pr,Tb]

The magnetic and superconducting properties of the ${\mathrm{TISr}}_2$ ${\mathrm{Ca}}_{1\mathrm{-}\mathit{x}}$ ${\mathit{R}}_{\mathit{x}}$ ${\mathrm{Cu}}_2$ ${\mathrm{O}}_7$ [R=Pr (x=0.2–1.0); Tb (x=0.6 and 1.0)] system are reported. The observation of superconductivity in ${\mathrm{TISr}}_2$ ${\mathrm{Ca}}_{0.4}$ ${\mathrm{Pr}}_{0.6}$ ${\mathrm{Cu}}_2$ ${\mathrm{O}}_7$ (${\mathit{T}}_{\mathit{c}}$=74 K) suggests that the Pr ions are in the trivalent state. The value of the effective magnetic moment, ${\mathrm{\mu }}_{\mathrm{eff}}$=3.15${\mathrm{\mu }}_{\mathit{B}}$, for the ${\mathrm{TISr}}_2$ ${\mathrm{Ca}}_{0.4}$ ${\mathrm{Pr}}_{0.6}$ ${\mathrm{Cu}}_2$ ${\mathrm{O}}_7$ compound, lies between the free-ion values expected for ${\mathrm{Pr}}^{3+}$ (3.58 ${\mathrm{\mu }}_{\mathit{B}}$) and ${\mathrm{Pr}}^{4+}$ (2.54${\mathrm{\mu }}_{\mathit{B}}$). The reduced value of ${\mathrm{\mu }}_{\mathrm{eff}}$ for the ${\mathrm{Pr}}^{3+}$ ion is explained in terms of crystal-field effects. For ${\mathrm{TISr}}_2$ ${\mathrm{TbCu}}_2$ ${\mathrm{O}}_7$, the Tb magnetic moments order antiferromagnetically at 7.0 K, which is the highest magnetic ordering temperature among the known Tb-containing high-${\mathit{T}}_{\mathit{c}}$ related compounds. Superconductivity (${\mathit{T}}_{\mathit{c}}$=74 and 62 K) and antiferromagnetic ordering (