Direct determination of the velocity of vortices in high-Tc superconductors by a non-equilibrium method

As is shown, thermally assisted vortex motion can come into being in high-T -c superconductors due to the applied temperature gradient. Its behavior st rongly depends on the local and global microstructure of the samples, moreo ver on the temperature and magnetic field. Investigation of the density, si ze and intensity of the pinning centers of specimens leads to the conclusio n that the higher homogeneity immediately weakens and the lower one strengh tens the pinning, thus the former promotes and the latter impedes the vorte x motion. The non-equilibrium experimental technique together with a.c. sus ceptibility measurements render possible the direct determination of the ve locity of vortices. Depending on the actual microstructural state of sample s it has the values between 6 x 10(-2) mm/s and 18 x 10(-2) mm/s in the cas e of Y-Ba-Cu-O specimens investigated.