Interpretation of the anomalous field-cooled-magnetization behavior of high-temperature granular superconductors at low magnetic field

The field-cooled magnetization of high-[ital T][sub [ital c]] superconducting ceramics measured in low magnetic fields has exhibited an unusual phenomenon, i.e., the diamagnetic signal initially increases with a decrease in temperature but reaches a maximum at temperature [ital T][sub [ital d]] and subsequently decreases with a decrease in temperature. In some samples the signal could even transform inversely into a paramagnetic regime once the sample was cooled below a temperature [ital T][sub [ital p]], provided the applied field was sufficiently small. This phenomenon has been observed in various high-[ital T][sub [ital c]] cuprates and been explained with different viewpoints. An alternative theoretical model was proposed in this work to account for these phenomena. The anomalous magnetization behavior in the present model was demonstrated to be a superposition of the diamagnetic signal, which occurs as a result of the intragranular shielding currents, and the paramagnetic signal, due to the induction of the intergranular component induced by these currents. The intergranular effect was demonstrated by this model to exist in granular superconductors. This intergranular effect would therefore be considered in evaluating the volume fraction of superconductivity for the samples from the Meissner signal, in particular, at a low magnetic field.