Flux motion in new superconductor MgB2

Flux motion and its influence on the properties of the new discovered superconductor MgB 2 was studied by electric transport resistance as well as by ac susceptibility measurements. Different bias current I was applied perpendicular and parallel to applied dc field B d up to 7 T. The upper critical field B c2 and irreversibility field B irr were determined as functions of temperature T and bias current I . It is found that the larger the bias current I the smaller the B irr , and B c2 is observed to be affected by flux motion. The B irr ( T ) and B c2 ( T ) data determined by ac susceptibility measurement confirm the transport result. These results suggest that the influence of flux motion should be taken into account if resistively determined parameters for MgB 2 are considered. The present study also implies that the flux dynamics of MgB 2 is more like as that of high temperature superconductors rather than of low temperature superconductors.