Magnetic fluctuations under pressure on S-doped FeSe studied via 77Se NMR

FeSe1-xSx has attracted much attention among iron-based superconductors because the pure sample undergoes nematic and superconducting (SC) phase transitions without magnetism. A pressure-induced antiferromagnetic (AFM) phase emerges upon applying pressure. In the pressure (P)-temperature (T) phase diagram for the 12%-S doped sample, the AFM phase is separated from the nematic phase at around 3.0 GPa, and SC transition temperature (Tc) takes a maximum (∼30 K). We measured T1 of 77Se for the 12%-S doped FeSe at 3.0 GPa. We found from 1/T1T that low-energy AFM fluctuations are not so much enhanced under pressure compared with those at ambient pressure. The result suggests changes of topology and nesting of Fermi surfaces during pressurizing process