Optically Tunable Chiral Magnetic States and Exchange Engineering via Charge-Transfer Excitation in a van der Waals Antiferromagnet CrPS4.

Controlling magnetism with light in two-dimensional van der Waals magnets could enable ultrafast, energy-efficient spintronics. However, selectively writing distinct magnetic phases, such as chiral magnetic states (e.g., spin spirals and skyrmions) for memory and collinear states for logic, within a single material remains an outstanding challenge. Here, we demonstrate deterministic, photon-energy-selective writing of magnetic order in the air-stable antiferromagnet chromium thiophosphate ( CrPS 4 ). Its ligand-to-metal charge transfer gap serves as an intrinsic switching threshold: excitation below this gap drives d - d transitions to stabilize chiral magnetic states due to a spin-spiral phase, while excitation above activates a photo-doping mechanism that renormalizes magnetic exchange and induces a collinear phase. These optically defined states are distinguished through polarization-resolved magneto-optical spectroscopy and probed via a proximal monolayer tungsten diselenide ( WSe 2 ). By establishing optical selectivity in a single material, our work provides a reconfigurable platform for opto-spintronic circuits where memory and logic functions can be dynamically toggled with light.