Abstract
Measurements are reported of the static, instantaneous, and dynamic spin correlations in single crystals of . The as-grown crystals show antiferromagnetic long-range order. However, the Néel temperatures and spin-stiffness constants are greatly reduced from their respective values in . After reduction and annealing, the crystals superconduct with =23 K, but inclusions of the antiferromagnetic phase, albeit with reduced Néel temperatures, are always present. Based on these data, we suggest that the disorder due to excess oxygen in as-grown samples stabilizes the magnetic correlations. This leads to a speculative model for the effects of deoxygenation in which the removal of the excess oxygen causes the magnetic correlations to diminish and hence superconductivity to become possible.
- Received 18 December 1991
DOI:https://doi.org/10.1103/PhysRevB.45.12548
©1992 American Physical Society