Spin-valley coupling enhanced high-T<sub>C</sub> ferromagnetism in a non-van der Waals monolayer Cr<sub>2</sub>Se<sub>3</sub> on graphene.
basic_science · Level V
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- Record sourced from PubMed, PMID 40251150.
- Also identified by DOI 10.1038/s41467-025-58643-3 and PMC identifier 12008187.
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Abstract
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<sub>C</sub> ~ 225 K) metallic ferromagnetism with spontaneous spin-valley polarization in monolayer Cr<sub>2</sub>Se<sub>3</sub> on graphene. Angle-resolved photoemission spectroscopy (ARPES) reveals systematic temperature-dependent energy shifts and splitting of localized Cr 3 d<sup>↑</sup>-t<sub>2g</sub> bands, accompanied by occupancy of the itinerant Cr 3d-e<sub>g</sub> valleys. The t<sub>2g</sub>-e<sub>g</sub> 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 Cr<sub>2</sub>Se<sub>3</sub> reveals the crucial role of valley carrier density in enhancing T<sub>C</sub> and provides a guiding principle to realize 2D ferromagnetism at higher temperatures in non-van der Waals materials.