Ultrafast Spin Dynamics in 2D Fully Compensated Ferrimagnets: A Time-Dependent Ab Initio Study

Fully compensated ferrimagnets (CFiMs) represent a novel class of magnetic materials that combine zero net magnetization with strong spin polarization, offering considerable potential for spintronic applications. Here, we employ real-time time-dependent density functional theory (rt-TDDFT) to investigate ultrafast laser-induced spin dynamics in a two-dimensional (2D) Janus NiICl bilayer. The broken inversion symmetry gives rise to an asymmetric interlayer demagnetization process, leading to a transient net magnetization in this system within 50 fs. This phenomenon is attributed to the asymmetric charge accumulation and interlayered optically induced spin transfer (OISTR) between the two Ni magnetic sublattices, facilitated by the intrinsic structural and electronic asymmetry of the Janus configurations. The asymmetric interlayer interaction effectively leads to a transient ferrimagnetic state. Our work reveals the microscopic mechanism of the ultrafast spin dynamics of 2D CFiMs induced by lasers in ultrafast spintronics.