Magnetism and candidate muon-probe sites in RBa2Cu3Oy

Key results of zero-field (ZF) and transverse-field (TF) muon-spin-relaxation (μSR) experiments on superconducting and insulating RBa2Cu3Oy (R123y, with R = Eu, Gd, Pr and Pr/Y; y = 6, 7) are examined. The chemical behavior of the positive muon probe is addressed, and muon-oxygen bonding is shown to occur in all these cuprates. To explain magnetic fields at muon-probe sites in PrxY1-xBa2Cu3Oy (0 < = x < 0.5, y = 7 and x = 0, y = 6) samples, improvements on the reported magnetic structures from neutron diffraction are necessary. Cu magnetism in Pr123y (y = 6, 7) is observed below TN1, which is near RT. The magnetism seen below TN2 can be interpreted assuming an additional ordering in the Cu-O chain layers. Alternatively, Pr ordering is also considered as the cause of the second phase transition. Considering the specific muon-probe location, a more detailed interpretation can be provided for the μSR parameters, measured in the normal and mixed states of these unconventional superconductors. (orig.)