  In this work, we studied the flux creep phenomenon over a long period [viz.
about 1.5 10E7 s (i.e. for 6 months)] at liquid nitrogen temperature. For this
purpose, four high-Tc ring-shaped samples were field-cooled (one sample) or
ferromagnetic field-cooled (three samples) in order to induce a persistent
current. The resulting current decay was measured using a Hall probe system and
the results obtained revealed low relaxation rates in the ferromagnetic
field-cooled samples. Also, the experimental data were found to depart from the
prediction of the classical models after a long enough time. The slope of the
logarithmic current decay plot exhibited an oscillatory phenomenon at ca. 2
10E5 s (about 55 hours). Oscillations vanished at ca. 4-5 10E6 s (46-55 days),
after which the induced current remained stable throughout the remainder of the
experiencing period.
