Since the discovery of monolayer ferromagnets, magneto-optics plays a compelling role in revealing new physics of magnetism in the extreme nanoscale limit. Here, I will first discuss our recent discovery of the ultra-sharp exciton emission in the van der Waals antiferromagnetic NiPS3 from bulk to atomically thin flakes. Magneto-optical measurements under in-plane field is used to reveal the strong coupling between the spin the electrical dipole oscillator, leading to the linear polarization of the exciton emission. We will further discuss the splitting of the spin-correlated emission in NiPS3 under in-plane magnetic field along various directions of the crystal, supporting the Zhang-Rice exciton origin of the emission. Benefiting from the spin-correlated emission in NiPS3, the Néel vector orientation can be optically detected as perpendicular to the exciton polarization, providing an easy, fast, nondestructive strategy to determine the Néel vector orientation. We further utilize the magneto-optic effect to reveal the three-state nematicity and domain evolution in NiPS3.
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