Extended Magnetic Dome Induced By Low Pressures In Superconducting Fese1-Xsx

We report muon spin rotation and magnetization measurements under pressure on Fe1+delta Se1-xSx with x approximate to 0.11. Above p approximate to 0.6 GPa we find a microscopic coexistence of superconductivity with an extended dome of long range magnetic order that spans a pressure range between previously reported separated magnetic phases. The magnetism initially competes on an atomic scale with the coexisting superconductivity leading to a local maximum and minimum of the superconducting T-c(p). The maximum of T-c corresponds to the onset of magnetism while the minimum coincides with the pressure of strongest competition. A shift of the maximum of T-c(p) for a series of single crystals with x up to 0.14 roughly extrapolates to a putative magnetic and superconducting state at ambient pressure for x >= 0.2.