Effect of the external pressure at the crossover between magnetism and superconductivity in LnFeAsO1-x Fx (Ln = La0.7Y0.3, Ce) superconductors

The interplay between magnetism and superconductivity is tuned as a function of the external pressure in LnFeAsO1-xFx at x values close to the appearance of superconductivity for lanthanide ion Ln=La0.7Y0.3 and Ce. The results show that in these compounds, both superconductivity and magnetism are reinforced by pressure. Furthermore, muon spin rotation and relaxation measurements reveal qualitative remarkable differences among the samples: Ln=Ce displays nanoscopic coexistence of magnetism and superconductivity in the same volume fraction while Ln=La0.7Y0.3 shows macroscopic phase separation. The Ln-dependent results can be due to a complex combination of the external and chemical pressure, the latter being driven by the different average ionic Ln radius.