Résumé
Superconducting YBa2Cu3Oy samples were doped with hydrogen and investigated by the muon spin rotation technique. For a hydrogen concentration above a threshold x, which depends on the oxygen stoichiometry of the sample, we find a well defined precession signal in zero external field. This is a clear indication of magnetic ordering in these samples. The data are consistent with the assumption that hydrogen acts as an electron donor filling the hole states in YBa2Cu3Oy.