Symmetry-Orchestrated Spin Relaxation in Bilayer CrI ₃ : A Time-Domain ab initio Study

The magnetic symmetry of van der Waals (vdW) magnets guides their fundamental properties. Bilayer CrI₃ presents an ideal prototype for investigating symmetry-tailored spin dynamics. However, the influence of varying magnetic space group symmetries on spin dynamics remains elusive. Here, we employ ab initio nonadiabatic molecular dynamics to unravel the magnetic symmetry-orchestrated hole relaxation in bilayer ferromagnetic CrI₃. Our results indicate that magnetic symmetry modulates interlayer coupling and electron-phonon scattering, altering scattering channels and thereby coupling the hole relaxation process to different phonon modes. We unravel that the relative rates of energy relaxation are governed by the degree of interlayer electronic state asymmetry rather than by the hierarchy of magnetic symmetry, while spin relaxation accelerates with reduced symmetry. This work demonstrates the critical role of magnetic symmetry manipulation in vdW magnets for tailoring spin dynamics and advancing next-generation spintronic devices.