Magnetic and superconducting properties of ${\mathrm{TlSr}}_2$${\mathrm{Ca}}_{1\mathrm{-}\mathit{x}}$${\mathit{R}}_{\mathit{x}}$${\mathrm{Cu}}_2$${\mathrm{O}}_7$ [R=Gd (x=0.6,1.0); Ho,Yb (x=1.0)]: High ${\mathit{T}}_{\mathit{N}}$(=3.1 K) in a Gd system

Magnetic and superconducting properties of single-Tl-O-layered ${\mathrm{TlSr}}_2$ ${\mathrm{Ca}}_{1\mathrm{-}\mathit{x}}$ ${\mathit{R}}_{\mathit{x}}$ ${\mathrm{Cu}}_2$ ${\mathrm{O}}_7$ [R=Gd (x=0.6,1.0);Ho,Yb (x=1.0)] have been studied. The antiferromagnetic ordering temperature of Gd moments in nonsuperconducting ${\mathrm{TlSr}}_2$ ${\mathrm{GdCu}}_2$ ${\mathrm{O}}_7$ is 3.1 K, which is the highest among the corresponding nonsuperconducting parent cuprates. The materials based on Ho and Yb do not order magnetically down to 1.5 K. Superconductivity (${\mathit{T}}_{\mathit{c}}$=60 K) and antiferromagnetic ordering (${\mathit{T}}_{\mathit{N}}$=1.8 K) coexist in ${\mathrm{TlSr}}_2$ ${\mathrm{Ca}}_{0.4}$ ${\mathrm{Gd}}_{0.6}$ ${\mathrm{Cu}}_2$ ${\mathrm{O}}_7$. The low value of the effective magnetic moment (2.9${\mathrm{\mu }}_{\mathit{B}}$) of Yb along with the lattice constant anomaly suggest that Yb ions are in a mixed valence state in ${\mathrm{TlSr}}_2$ ${\mathrm{YbCu}}_2$ ${\mathrm{O}}_7$.