Superconductivity and magnetic order in TbSr2Cu2.69Mo0.31O7

AC magnetic susceptibility, measured with weak probing fields, has been car ried out to study the intrinsic magnetic properties of polycrystalline TbSr 2Cu2.69Mo0.31O7. Superconductivity occurring below 38 K and antiferromagnet ic order of the Tb spins with T-N = 5.4 K were clearly evident in both the temperature dependence of the in-phase and the out-of-phase components of t he AC susceptibility. The diamagnetic responses that signify the occurrence of superconductivity were found to be extremely sensitive to the strength of the probing field used. Almost perfect diamagnetic responses were observ ed under a probing field of rms strength H-AC = 0.05 Oe, Increasing H-AC to 1 Oe suppresses 50% of the diamagnetic responses. Below 5.4 K, as the Tb s pins order, superconductivity and antiferromagnetism coexist. (C) 2000 Else vier Science B.V. All rights reserved.