Antiferromagnetism and superconductivity in YBa2Cu3Ox studied by μSR

We have used the technique of muon spin relaxation to study the competition between antiferromagnetism (AFM) and superconductivity (SC) in oxygen deficient YBa 2 Cu 3 O x for 6.0 x = 6.0 down to 2.5K for x = 6.40. Samples with x near 6.4 were both SC and AFM. In the x = 6.1 sample, where there is a narrow distribution of TN's, we have observed the critical slowing down of the Cu spins at the average TN.