Magnetic and superconducting properties of tlsr2ca1-xrxcu2o7 [r = gd (x=0.6,1.0) - ho, yb (x=1.0)] - high tn (=3.1-k) in a gd system

Abstract

Magnetic and superconducting properties of single-Tl-O-layered TlSr2Ca1-xRxCU2O7 [R = Gd (x = 0.6, 1.0); Ho, Yb(x = 1.0)] have been studied. The antiferromagnetic ordering temperature of Gd moments in nonsuperconducting TISr2GdCu2O7 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 (T(c) = 60 K) and antiferromagnetic ordering (T(N) = 1.8 K) coexist in TlSr2Ca0.4Gd0.6CU2O7. The low value of the effective magnetic moment (2.9 mu(B)) of Yb along with the lattice constant anomaly suggest that Yb ions are in a mixed valence state in TlSr2YbCu2O7.