Vortex dynamics in pure and SiC-doped MgB2

Hysteresis loop and magnetization relaxation measurements have been performed on a pure and a SiC-doped MgB2 samples. The normalized volume pinning forces determined from the hysteresis loop are observed to scale as a function of the reduced magnetic field (h=H/Hirr) with peaks at hmax∼0.2. This result implies that the dominating pinning mechanism in both materials is the pinning by normal surface defects. From magnetization relaxation measurements, the current dependence of the activation energy is found to be logarithmic