The magnetic structure of FeSe superconductor under pressure

Magnetism is in general a key ingredient for high-Tc superconductors because the corresponding spin fluctuations could mediate electronic Cooper pairing. FeSe with a nematic order of 90 K exhibits Neel and stripe spin fluctuations with no magnetic phase transition at ambient pressure. The Tc of FeSe can be dramatically enhanced by hydrostatic pressure, accompanied by the development of a magnetic order above ~ 1.2 GPa. Determining the pressure-induced magnetic structure is thus of particular interest, while neutron diffraction measurements are still lacking due to techinal difficulties. Recent muSR study revealed the static magnetism in Fe(Se,S) at lower pressure of 0.6 GPa, we therefore propose a neutron powder diffraction experiment in the helium pressure cell. Our results will be crucial for elucidating the magnetism and its interplay with nematicity and superconductivity in FeSe.