Raman Evidence of Phase Transitions for FePS₃ and FePSe₃ under High Pressure

Two-dimensional (2D) magnetic materials are of great interest in fundamental condensed-matter physics research, as well as for potential applications in spintronics and device physics. In particular, FePX3 (X = S and Se) are antiferromagnetic materials with the Ising model. Here, we perform a low-frequency Raman study on FePX3 at room temperature to investigate the lattice, electronic, and magnetic behaviors under pressure, which gives clear evidence for the structural phase transitions and magnetic collapse. The Raman measurements resolve two critical pressures at 6.9 and 15.8 GPa for FePS3 and one critical pressure at 9.7 GPa for FePSe3, which are characterized by the changes of Raman continuum and phonon modes. In addition, all Raman modes almost disappear above 16 GPa, indicating that the system turns into the metallic phase. Our Raman results are crucial for understanding high-pressure behavior in these materials and demonstrate a clear competition among the lattice vibration, spin-phonon coupling, magnetism, and electronic structure in 2D magnetic materials.