Local fields in YBa 2Cu 3O 7− δ measured on [formula omitted] Mössbauer probes. : II. Vortex alignment in the field-cooled and zero field-cooled configurations

Abstract

We examine the directional properties of the vortex lattice in grain-oriented YBa 2Cu 3O 7 as a function of the direction of the applied field relative to the c-axis. The measurements are made by following the direction of the field produced by the vortex lattice on non-perturbing paramagnetic 170 Yb 3+ Mössbauer probes. In the field-cooled (FC) configuration, where the vortex density is uniform, the average vortex direction remains parallel to the applied field whatever the temperature and the direction of the applied field relative to the c-axis may be. We relate this behaviour to the competing influence of the effective mass anisotropy and the pinning to the twin planes. In the zero field-cooled (ZFC) configuration, where the vortex density is non-uniform, the average vortex direction may no longer be parallel to the applied field and its direction depends on the size and direction of the field and on the temperature. The critical currents now also play a role.