Photoexcitation induced magnetic phase transition and spin dynamics in antiferromagnetic MnPS₃ monolayer

Antiferromagnetic spin dynamics is the key issue to develop spintronic devices. We adopt ab initio nonadiabatic molecular dynamics with spin-orbit-coupling (SOC) to investigate photoinduced spin dynamics in an antiferromagnetic semiconductor MnPS3 monolayer. Optical doping triggers MnPS3 from Néel antiferromagnetic to ferromagnetic phase at an experimentally achievable electron-hole pair density of 1.11 × 10^14 cm−2. This phase transition can be ascribed to the light-induced mid-gap states of S-p orbitals, which lower the electron excitation energy and strengthen the SOC effect between S-p and Mn-d orbitals. The excited S-p electrons first decay to the mid-gap states due to p-p electron-phonon-coupling and then relax to the spin-down Mn-d orbitals via SOC. Such a dramatic relaxation process prolongs the photogenerated carrier lifetime up to 648 fs, providing an explanation for the unusual optoelectronic performance of MnPS3. The reversible switching of magnetic order via optical means gives an important clue for information storage and highly efficient photocatalysts utilizing antiferromagnetic semiconductors.