Photon-driven magnetization switching in Fe₃GeTe₂ enables programmable, multilevel magnetic memory

The rediscovery of van der Waals magnets has revitalized research into intrinsic two-dimensional magnetism and motivated unconventional strategies, such as electrostatic gating and strain, to switch magnetic states. Photon-driven magnetization switching, however, remains largely unexplored but holds promise for fast, high-density, and energy-efficient spintronic applications. Here, we show that the itinerant van der Waals ferromagnet Fe₃GeTe₂ exhibits tunable magnetism under optical pulsed excitation, with the response governed by photon energy, fluence, and polarization. This is evident from our magneto-optic measurements, which reveal that pulses with 2.3 eV photon energy effectively reduce the coercivity of Fe₃GeTe₂. When coercivity is sufficiently lowered by strong pulse fluence, the magnetic order becomes helicity-dependent, enabling reversible suppression and restoration of the out-of-plane magnetization. Further studies indicate that these phenomena originate from distinct semiconductor-like transitions in Fe₃GeTe₂, through which photons of opposite helicity induce distinct modifications in the electronic structure, thereby altering magnetic anisotropy and the ground state differently via optical doping effect. Building on this understanding, we further demonstrate the potential of Fe₃GeTe₂ for optically controlled nonvolatile memory, capable of multilevel information storage with reversible writing and erasing, as well as spatially defined spin states, offering promise for next-generation spintronics.