57Fe Mössbauer studies of BiPbSr2FeO6

57 Fe Mossbauer and magnetic measurements of BiPbSr 2 FeO 6 calcinated in air (sample I) or in N 2 gas (sample II) were made. Sample I is a weak-ferromagnet with T N =240 K. The temperature dependence of the magnetization shows an anomaly at 90 K. A large effect of the magnetic field cooling is observed. Fe ions are in trivalent state and 57 Fe nuclei feel a hyperfine magnetic field of 50 T at low temperature. Sample II is a weak ferromagnet with T N =300 K, but neither the anomaly at 90 K nor the field-cooling effect is detected for this sample.