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

الأصل · EN

In 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 ≤ x ≤ 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.