Substrate Contribution to Ultrafast Spin Dynamics in 2D van der Waals Magnets

We propose a model that is able to reproduce the type-II ultrafast demagnetization dynamics observed in 2D magnets. The spin system is coupled to the electronic thermal bath and is treated with atomistic spin dynamics, while the electron and phonon heat baths are described phenomenologically by coupled equations via the two-temperature model. Our proposed two-temperature model takes into account the effect of the heated substrate, which for 2D systems results in a slow demagnetization regime. We applied the framework to a generic 2D system, CrI_{3}, and we are able to observe a type-II demagnetization process characterized by two steps, the first step being attributed to the free electrons generated when the system behaves as a quasimetal under optical excitation, and the second step, the slower demagnetization region, due to the heated substrate. Finally, after laser excitation, we are able to observe domain formation in CrI_{3}, similar to recent experimental observations. Our generalized two-temperature model enhances the modeling of ultrafast magnetization dynamics processes by effectively describing the quasimetallic behavior of certain magnetic materials and the influence of a heated adjacent layer.