No abstract

Local magnetic measurements in a highly anisotropic Nd-Ce-Cu-O crystal reveal a sharp onset of an anomalous magnetization peak at a temperature-dependent field B on . The same field marks a change in the field profiles across the sample, from profiles dominated by geometrical barriers below B on to Bean-like profiles above it. The temperature dependence of B on and the flux distribution above and below B on imply a disorder-induced transition at B on from a relatively ordered vortex lattice to a highly disordered, entangled vortex solid. Local magnetic relaxation measurements above B on show evidence for plastic vortex creep associated with the motion of dislocations in the entangled vortex structure.[S0031-9007 (97)04113-6]

No abstract

No abstract