Defect-Assisted Recombination Accelerates Spin Depolarization in Monolayer CrSBr

Defect-controlled carrier charge and spin dynamics are central to the functionality of two-dimensional magnetic semiconductors. Here, ferromagnetic monolayer CrSBr with bromine vacancies is used to reveal how intrinsic defects couple nonradiative recombination to spin depolarization. Time-dependent density functional theory combined with nonadiabatic molecular dynamics including noncollinear spin shows that bromine vacancy introduces a localized, spin-polarized in-gap hole-trap state that reconstructs the recombination pathway. Unlike direct interband recombination in pristine CrSBr, the defective system follows a two-step mechanism involving hole trapping and subsequent fast defect-assisted recombination, shortening the carrier lifetime from ∼1.38 ns to ∼0.20 ns. The characteristic time for the decay of the population-weighted spin-polarization is correspondingly shortened, showing that the loss of spin polarization is closely coupled to defect-mediated charge relaxation. These results establish a microscopic link among defect localization, carrier recombination, and spin-polarization decay in two-dimensional magnetic semiconductors.