Optically Tunable Chiral Magnetic States and Exchange Engineering via Charge‐Transfer Excitation in a van der Waals Antiferromagnet CrPS 4

ABSTRACT 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 (). Its ligand‐to‐metal charge transfer gap serves as an intrinsic switching threshold: excitation below this gap drives – 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 (). 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.