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

C.-W. Chuang (), T. Kawakami, K. Sugawara, K. Nakayama, S. Souma, M. Kitamura, K. Amemiya, K. Horiba, H. Kumigashira, G. Kremer, Y. Fagot-Revurat, D. Malterre, C. Bigi, F. Bertran, F. H. Chang, H. J. Lin, C. T. Chen, T. Takahashi, A. Chainani () and T. Sato ()
Additional contact information
C.-W. Chuang: Tohoku University
T. Kawakami: Tohoku University
K. Sugawara: Tohoku University
K. Nakayama: Tohoku University
S. Souma: Tohoku University
M. Kitamura: High Energy Accelerator Research Organization (KEK)
K. Amemiya: High Energy Accelerator Research Organization (KEK)
K. Horiba: National Institutes for Quantum Science and Technology (QST)
H. Kumigashira: Tohoku University
G. Kremer: Université de Lorraine
Y. Fagot-Revurat: Université de Lorraine
D. Malterre: Université de Lorraine
C. Bigi: L’Orme des Merisiers
F. Bertran: L’Orme des Merisiers
F. H. Chang: National Synchrotron Radiation Research Center
H. J. Lin: National Synchrotron Radiation Research Center
C. T. Chen: National Synchrotron Radiation Research Center
T. Takahashi: Tohoku University
A. Chainani: National Synchrotron Radiation Research Center
T. Sato: Tohoku University

Nature Communications, 2025, vol. 16, issue 1, 1-8

Abstract: 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 (TC ~ 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↑-t2g bands, accompanied by occupancy of the itinerant Cr 3d-eg valleys. The t2g-eg 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 TC and provides a guiding principle to realize 2D ferromagnetism at higher temperatures in non-van der Waals materials.

Date: 2025
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DOI: 10.1038/s41467-025-58643-3

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