Pressure Induced Static Magnetic Order in Superconducting FeSe1-x

We report on a detailed investigation of the electronic phase diagram of FeSe1-x under pressures up to 1.4 GPa by means of ac magnetization and muon-spin rotation. At a pressure similar or equal to 0.8 GPa the nonmagnetic and superconducting FeSe1-x enters a region where static magnetic order is realized above T-c and bulk superconductivity coexists and competes on short length scales with the magnetic order below T-c. For even higher pressures an enhancement of both the magnetic and the superconducting transition temperatures as well as of the corresponding order parameters is observed. These exceptional properties make FeSe1-x to be one of the most interesting superconducting systems investigated extensively at present.