PHASE-DIAGRAM OF THE VORTEX-SOLID PHASE IN Y-BA-CU-O CRYSTALS - A CROSSOVER FROM SINGLE-VORTEX (1D) TO COLLECTIVE (3D) PINNING REGIMES

We construct a "phase diagram" of the vortex-solid phase of Y-Ba-Cu-O crystals by making a first overall connection of the shape of the magnetic hysteresis M(H,T) with the single-vortex (1D) and collective (3D) pinning regimes. The crossovers between different regimes are visualized from contours of constant J(c) in the H-T plane. We identify the transition from 1D to 3D pinning, and from the nonlocal into a local behavior of vortex bundles in the collective pinning regime. A direct correlation between M(H) and the thermal relaxation rate is demonstrated. We also identify a signature of the thermal softening boundary at which thermal fluctuations on the scale of the coherence length xi are relevant.