PARAMAGNETIC MEISSNER EFFECT IN A NIOBIUM DISK

The diamagnetic shielding and flux expulsion in a Nb disk have been studied as a function of temperature and magnetic field. Both the zero-field-cooled (ZFCM) and the field-cooled (FCM) magnetizations show diamagnetic responses for fields parallel to the surface of the disk and indicate two different transition temperatures, 9.26 K and 9.06 K. Whereas for fields perpendicular to the surface, the ZFCM shows an additional diamagnetic transition at 9.17 K which is strongly field dependent while the FCM shows a positive magnetization for temperatures below 9.17 K. These features are qualitatively similar to the so-called paramagnetic Meissner effect observed in granular high-T-c superconductors.