Ultrafast Core-Shell Spin Transfer and Spin-Selective Relaxation in an Endohedral Cage Cluster.

Ultrafast optical control of spin states offers a promising route to molecular-scale magnetic manipulation, yet the mechanisms of laser-driven spin dynamics in atomically precise clusters remain poorly understood. Here, we investigate the ultrafast spin dynamics of the endohedral Mn@Sn12 cluster using real-time time-dependent density functional theory simulations. Strong Mn 3d-Sn 5p orbital hybridization couples the localized Mn center to the Sn12 cage. Upon femtosecond laser excitation, the Mn@Sn12 cluster exhibits a pronounced transient magnetic response within several femtoseconds, accompanied by changes in the local magnetic moments of both subsystems. Time-dependent analyses of spin-resolved electronic occupations, spin density, and density of states provide evidence for early time intersite redistribution of spin-polarized electronic populations between the Mn center and Sn12 cage. Excited-state relaxation analysis further shows that spin-conserving relaxation is substantially faster than spin-flip relaxation, reflecting efficient electron-vibration coupling and limited spin-orbit-mediated mixing between opposite-spin states. These results elucidate the microscopic origin of ultrafast spin dynamics in molecular nanoclusters and highlight endohedral metal clusters as promising platforms for atomic-scale optical spin control.