Anomalous peak at low fields in the magnetization versus temperature curve in bulk ceramic high-temperature superconductors

When a bulk ceramic high-temperature superconductor is cooled in a small field and the magnetic moment of the sample is measured as the sample is warmed, an anomalous peak in the magnetic moment is observed. This peak can be as high as 50% of the low-temperature moment for fields less than 1 Oe, but it rapidly decreases as the magnetic field increases. We show that this anomaly is due to the interrelationship between flux trapping by intergranular weak links and the irreversible flux trapping properties of the superconducting grains as recently described by Hao and Clem.