Phase separation at the magnetic–superconducting transition in La0.7Y0.3FeAsO1−xFx

Abstract

AbstractIn this paper we report a detailed µ+SR and 19F NMR study of the La0.7Y0.3FeAsO1−xFx class of materials. Here, the diamagnetic La1−yYy substitution increases chemical pressure and, accordingly, sizeably enhances the optimal superconducting transition temperature. We investigate the magnetic–superconducting phase transition by keeping the Y content constant (y = 0.3) and by varying the F content in the range $0.025\leq x\leq 0.15$. Our results show how magnetism and superconductivity coexist for x = 0.065. Such coexistence is due to segregation of the two phases in macroscopic regions, resembling what was observed in LaFeAsO1−xFx materials under applied hydrostatic pressure. This scenario is qualitatively different from the nanoscopic coexistence of the two order parameters observed when La is fully substituted by magnetic rare‐earth ions like Sm or Ce.