Flux dynamics and vortex phase diagram of the new superconductor MgB₂

الأصل · EN

Magnetic critical current density and relaxation rate have been measured on MgB₂ bulks from 1.6 K to Tc at magnetic fields up to 8 Tesla. A vortex phase diagram is depicted based on these measurement. Two phase boundaries Hirrbulk(T) and Hirrᵍ(T) characterizing different irreversible flux motions are found. The Hirrbulk(T) is characterized by the appearance of the linear resistivity and is attributed to quantum vortex melting induced by quantum fluctuation of vortices in the rather clean system. The second boundary Hirrᵍ(T) reflects the irreversible flux motion in some local regions due to either very strong pinning or the surface barrier on the tiny grains.