Evidence of current stabilization after long-time decay in high-TC superconductors

In this work, we have studied flux creep phenomenon over a long time period viz. about 1.5 × 107 s (i.e. for six months) at liquid nitrogen temperature. For this purpose, a high current was induced in four high-TC superconducting rings by means of a field-cooling (one sample) or a ferromagnetic field-cooling procedure (three samples). The resulting current decay was measured using a Hall probe system and the results obtained revealed lower relaxation rates in the ferromagnetic field-cooled samples. Also, the experimental data were found to leave the prediction of the classical Anderson-Kim model after a time long enough. The slope of the logarithmic current decay plot exhibited an oscillatory phenomenon at approximately 2 × 105 s (about 55 h). Oscillations vanished at approximately 4-5 × 106 s (46-58 days), after which the induced current remained stable throughout the remainder of the experiencing period.