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

We report muon spin rotation ($\mu$SR) and magnetization measurements under pressure on Fe${}_{1+\delta }$Se${}_{1\text{-}\mathrm{x}}$S${}_{\mathrm{x}}$ with x $\approx 0.11$.Above $p\approx 0.6$ 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 $\ge 0.2$.