Spin-valley coupling enhanced high-T_C ferromagnetism in a non-van der Waals monolayer Cr₂Se₃ on graphene

Spin-valley magnetic ordering is restricted to layered van der Waals type transition-metal dichalcogenides with ordering temperatures below 55 K. Recent theoretical studies on non-van der Waals structures have predicted spin-valley polarization induced semiconducting ferromagnetic ground states, but experimental validation is missing. We report high-Curie temperature (T_C ~ 225 K) metallic ferromagnetism with spontaneous spin-valley polarization in monolayer Cr₂Se₃ on graphene. Angle-resolved photoemission spectroscopy (ARPES) reveals systematic temperature-dependent energy shifts and splitting of localized Cr 3 d^↑-t_2g bands, accompanied by occupancy of the itinerant Cr 3d-e_g valleys. The t_2g-e_g spin-valley coupling at the K/K’ points of hexagonal Brillouin zone leads to ferromagnetic ordering. Circular dichroism in ARPES shows clear evidence of spin-valley polarized states. Comparison with bilayer and trilayer Cr₂Se₃ reveals the crucial role of valley carrier density in enhancing T_C and provides a guiding principle to realize 2D ferromagnetism at higher temperatures in non-van der Waals materials.