Abstract
Irreversible magnetic properties of single crystals were studied by using several techniques including transport, magnetization, and magneto-optics. The mixed-state response was found to be very similar to high- cuprates, such as Y-Ba-Cu-O and Nd-Ce-Cu-O. In particular, we find a nonmonotonic “fishtail” shape of the magnetization loops and a corresponding feature in scans, as well as a very large magnetic relaxation rate. The supercurrent density, , in the critical state was evaluated from magnetization and from direct transport measurements close to . At 5 K we estimate a moderate . Analysis of the temperature and field dependencies of the magnetic relaxation is consistent with the collective pinning and creep (weak pinning and fast creep) model and suggests a crossover from the collective to the plastic creep regime in fields exceeding the field at which the fishtail magnetization is maximum. While the zero-field anisotropy of the magnetic properties in the superconducting state of is small, the vortex behavior changes for different orientations of magnetic field with respect to the crystal axes, implying field-dependent anisotropy of pinning properties.
7 More- Received 7 October 2008
DOI:https://doi.org/10.1103/PhysRevB.78.224506
©2008 American Physical Society