Magnetic properties of (Bi, Pb) 2(Sr, La) 2(Ln, La) 2Cu 2O z (Ln=Sm, Eu, Gd, Dy)

SQUID and ESR measurements were performed for (Bi, Pb) ₂(Sr, La) ₂(Ln, La) ₂Cu ₂O _z (Ln=Sm, Eu, Gd, Dy) heat-treated under a high pressure of oxygen, and their magnetic properties were investigated. A weak diamagnetic magnetization due to superconductivity was observed in a temperature range below 44-46 K, and its magnetic susceptibility was determined as -(1.2∼2.0)×10 ^-4 at 5 K under the static magnetic field of 5 kOe. Further, a weak or short-range antiferromagnetic order was observed even at room temperature in paramagnetic (Bi, Pb) ₂(Sr, La) ₂(Gd, La) ₂Cu ₂O _z, and its temperature variation was investigated. The exchange field between Gd ³⁺ spins was concluded to be larger than 3 kOe at room temperature.