OBSERVATION OF PARAMAGNETIC MEISSNER EFFECT IN NIOBIUM DISKS

For several superconducting niobium disks, the de field-cooled magneti zation (FCM) shows a paramagnetic response below their superconducting transition temperature T-c approximate to 9.2 K when the applied magn etic filed is normal to the disk. At 8.6 K, the FCM reaches a maximum in fields of 5 to 10 Oe and becomes diamagnetic for fields larger than 20 Oe. This FCM behavior is qualitatively similar to the paramagnetic Meissner effect (PME) recently observed in high-T-c cuprate supercond uctors. Various surface treatments to the Nb disks result in changes i n both the zero-field-cooled magnetization and the FCM, including the disappearance of the PME.