Optically Enhanced Magnetization by Exciton Recombination in an Atomically Thin Antiferromagnet

Two-dimensional (2D) semiconductors offer a unique platform for investigating the interplay between light and magnetization. Excitons are usually responsive probes of magnetic order, yet whether magnetic order responds to the presence of excitons is less frequently examined. In this work, we synchronize optical pumping of a 2D magnet to an ac sensing protocol on nitrogen-vacancy (NV) centers in diamond. Using this spatiotemporal-resolved magnetometry, we discover an enhancement of the magnetic moments in a few-layer van der waals antiferromagnet. Together with time-resolved photoluminescence measurements and density functional theory calculations, we infer that this enhancement arises from a defect-assisted Auger recombination, which involves localized excitons and drives electron hopping into the spin-polarized band. This study offers insights into defect engineering in 2D magnets and encourages the development of spintronic devices modulated by light.