The results of temperature and time (at T = 4.2 K ) dependent magnetization (M) measurements on polycrystalline high T c superconductor EuBa 2 Cu 3O7−δ are reported for different magnetic fields from 2.2 kOe to 35 kOe. The measurements were performed in the field-cooled regime (measuring the Meissner effect). A new phenomenon is found: the magnetization sign inversion from negative to positive during the time at which the external conditions (T, H) remains unchanged. The differential susceptibility in a new mixed state with M > 0 is diamagnetic. It is shown that origin of this state is not connected with a flux trapping, but rather caused by the unusual nature of the vortex themselves in FC mixed state of high T c superconductors.
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