DISORDER-INDUCED TRANSITION TO ENTANGLED VORTEX SOLID IN ND-CE-CU-O CRYSTAL

Local magnetic measurements in a highly anisotropic Nd-Ce-Cu-O crystal reveal a sharp onset of an anomalous magnetization peak at a temperat ure-dependent field B-on. The same field marks a change in the field p rofiles across the sample, from profiles dominated by geometrical barr iers below B-on to Bean-like profiles above it. The temperature depend ence of B-on and the flux distribution above and below B-on imply a di sorder-induced transition at B-on from a relatively ordered vortex lat tice to a highly disordered, entangled vortex solid. Local magnetic re laxation measurements above B-on show evidence for plastic vortex cree p associated with the morion of dislocations in the entangled vortex s tructure.