Abstract
We have combined magnetic measurements and imaging of the vortex lattice at low fields in single crystals with different oxygen content. Those with high critical temperature >80 K have a reversible region while those with low <30 K have an irreversible magnetization in the whole range of temperatures, up to . The presence of the reversible region allows the formation of ordered vortex structures, while amorphous structures are obtained when no reversible region is present below . The results are discussed in terms of vortex nucleation processes in the individual pinning regime.
DOI:https://doi.org/10.1103/PhysRevB.55.14610
©1997 American Physical Society