Vortex state in a Nd1.85Ce0.15CuO4-delta single crystal

Magnetization data of a Nd1.85Ce0.15CuO4-delta Single crystal prepared by t he traveling solvent Boating zone method reveal a feature showing a sharply defined temperature range for the occurrence of the second-peak effect. A vortex phase diagram derived from these data on the basis of some of the ex isting models displays a number of perceptible changes in the temperature d ependencies bi the penetration field H-p, the irrevesibility line H-irr, an d the symmetry of the hysteresis loop, in conjunction with the observation of the peak effect. It is shown that effective penetration of the external magnetic-field in the three-dimensional vortex regime is a prerequisite to the transition from its quasilattice to disordered-glass vortex state assoc iated with occurence of the,peak effect. Comparison with previous results o n a similar sample further indicates certain sample-dependent nature of the data. [S0163-1829(99)02345-0].