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

AC magnetic susceptibility, measured with weak probing fields, has been carried out to study the intrinsic magnetic properties of polycrystalline TbSr2Cu2.69Mo0.31O7. Superconductivity occurring below 38 K and antiferromagnetic order of the Tb spins with TN=5.4 K were clearly evident in both the temperature dependence of the in-phase and the out-of-phase components of the 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 observed under a probing field of rms strength HAC=0.05 Oe. Increasing HAC to 1 Oe suppresses 50% of the diamagnetic responses. Below 5.4 K, as the Tb spins order, superconductivity and antiferromagnetism coexist