Ultrafast Demagnetization Dynamics in Room-Temperature vdW Ferromagnet Fe ₃ GaTe ₂

Femtosecond-laser-induced ultrafast demagnetization in two-dimensional van der Waals (vdW) ferromagnets offers an ideal testbed for probing spin relaxation proximate to the Curie temperature (TC). Here we report a systematic time-resolved magneto-optical Kerr effect study of ultrafast spin dynamics in exfoliated Fe3GaTe2, a robust room-temperature vdW ferromagnet. A two-step demagnetization process within ∼100 ps is observed and quantitatively reproduced by a microscopic three-temperature model coupling electronic, lattice, and spin subsystems. The spin-relaxation time τ increases monotonically with pump fluence but exhibits a nonmonotonic temperature dependence peaking near TC. Global fitting yields a demagnetization rate constant R = 0.118 ps–1. Our analysis links the observed Type-II behavior to a low spin-flip probability combined with proximity to TC. These findings provide quantitative benchmarks for Elliott-Yafet spin relaxation in two-dimensional metallic magnets.