Abstract
The fields for the first vortex entry and last vortex exit, and , and the lower critical field for a grain-aligned, sintered superconductor have been determined from saturated magnetic-hysteresis loops using an extended critical-state model. For fields oriented along the grain c axis, increases with decreasing temperature, showing an upturn below 50 K, whereas remains small and positive, in general agreement with the theory of Bean-Livingston surface barriers. has a Bardeen-Cooper-Schrieffer temperature dependence above 50 K, but it rises at low temperatures. For fields oriented in the ab plane, has a similar temperature dependence, but surface barriers are not evident in the magnetization.
- Received 5 February 1993
DOI:https://doi.org/10.1103/PhysRevB.48.6426
©1993 American Physical Society