Magnetic behavior of Y-Ba-Cu-O superconductors prepared under different oxygen anneals

In our study of three YBa2 Cu3 oxides prepared with different oxygen anneals, we observed that the temperature derivative of the magnetization or susceptibility chi(T) of these high-T/sub c/ superconductors has a maximum at approximately the transition temperature, T/sub c/ . This temperature as estimated by the peak value of (partialchi/partialT)/sub H/ , ranged between 55 and 65 K. The most oxygen-poor sample showed the lowest T/sub c/ and the most oxygen-rich sample showed the highest T/sub c/ . In the subcritical region, a novel irreversibility is observed in the field-cooled warm-up and cool-down behaviors