Extended Magnetic Dome Induced by Low Pressures in Superconducting FeSe\(_\mathrm{1\text{-}x}\)S\(_\mathrm{x}\)

We report muon spin rotation (\(\mu\)SR) and magnetization measurements under pressure on Fe\(_{1+\delta}\)Se\(_\mathrm{1\text{-}x}\)S\(_\mathrm{x}\) with x \(\approx 0.11\).Above \(p\approx0.6\) GPa we find 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 \(T_\mathrm{c}(p)\). The maximum of \(T_\mathrm{c}\) corresponds to the onset of magnetism while the minimum coincides with the pressure of strongest competition. A shift of the maximum of \(T_\mathrm{c}(p)\) 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 \(\geq0.2\).