摘要
Muon spin rotation measurements of (formula presented) (for (formula presented) reveal two distinct muon sites: one located in a SrO layer (which is superconducting at low temperatures) and the other in a (formula presented) layer (which is magnetically ordered at low temperatures). A precursor spin-glass state due to the Ru moments is detected in high fields (≈3.3 kOe) in (formula presented) layers, with a spin-glass temperature of (formula presented) The (formula presented) layers order ferromagnetically in the a-b planes at the Néel temperature, (formula presented) This in-plane ferromagnetism alternates direction between adjacent (formula presented) planes, resulting in a net antiferromagnetic structure. Although the onset of superconductivity is observed both by electron spin resonance and by dc susceptibility to occur for temperatures up to about (formula presented) this superconductivity is adversely affected by the Ru moments that fluctuate for (formula presented) producing magnetic fields that break pairs in the SrO layers. The muons, as well as other probes, sense the more-robust static superconductivity for (formula presented) In fact, resistance measurements only show zero resistance below (formula presented) at which temperatures the Ru moments that fluctuated for (formula presented) are frozen in-plane. Hence strictly speaking, the superconducting transition temperature is the same as (formula presented) which is far below (formula presented) Below (formula presented) there are no pair breaking fluctuating magnetic fields in the SrO layers where the hole condensate resides. © 2003 The American Physical Society.