バルクでは磁石に付かない物質を原子層厚の薄膜で磁石に変換 ～次世代スピントロニクスへの応用に期待～

2025-04-21 東北大学

＜関連情報＞

• https://www.tohoku.ac.jp/japanese/2025/04/press20250421-01-bulk.html
• https://www.tohoku.ac.jp/japanese/newimg/pressimg/tohokuuniv-press20250421_01web_bulk.pdf
• https://www.nature.com/articles/s41467-025-58643-3

グラフェン上の非バンデルワールス単原子層Cr2Se3におけるスピンバレー結合による高TC強磁性の増強 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 & T. Sato
Nature Communications  Published:18 April 2025
DOI:https://doi.org/10.1038/s41467-025-58643-3

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_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.