{"id":35516,"date":"2025-04-20T11:56:15","date_gmt":"2025-04-20T11:56:15","guid":{"rendered":"https:\/\/www.europesays.com\/uk\/35516\/"},"modified":"2025-04-20T11:56:15","modified_gmt":"2025-04-20T11:56:15","slug":"spin-valley-coupling-enhanced-high-tc-ferromagnetism-in-a-non-van-der-waals-monolayer-cr2se3-on-graphene","status":"publish","type":"post","link":"https:\/\/www.europesays.com\/uk\/35516\/","title":{"rendered":"Spin-valley coupling enhanced high-TC ferromagnetism in a non-van der Waals monolayer Cr2Se3 on graphene"},"content":{"rendered":"<p>Fabrication and characterization of ML Cr2Se3<\/p>\n<p>First, we present fabrication and characterization of a ML Cr2Se3 film. Since Cr chalcogenides are stabilized with a few different chemical compositions such as CrSe2 (12 phase)<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" aria-label=\"Reference 38\" title=\"Freitas, D. C. et al. Antiferromagnetism and ferromagnetism in layered 1T-CrSe2 with V and Ti replacements. Phys. Rev. B 87, 014420 (2013).\" href=\"http:\/\/www.nature.com\/articles\/s41467-025-58643-3#ref-CR38\" id=\"ref-link-section-d325929573e1328\" target=\"_blank\" rel=\"noopener\">38<\/a>,<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" aria-label=\"Reference 39\" title=\"Li, B. et al. Van der Waals epitaxial growth of air-stable CrSe2 nanosheets with thickness-tunable magnetic order. Nat. Mater. 20, 818&#x2013;825 (2021).\" href=\"http:\/\/www.nature.com\/articles\/s41467-025-58643-3#ref-CR39\" id=\"ref-link-section-d325929573e1331\" target=\"_blank\" rel=\"noopener\">39<\/a> and Cr2Se3 (23 phase)<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" aria-label=\"Reference 26\" title=\"Adachi, Y. et al. Magnetic structure of rhombohedral Cr2Se3. J. Phys. Soc. Jpn. 63, 1548&#x2013;1559 (1994).\" href=\"http:\/\/www.nature.com\/articles\/s41467-025-58643-3#ref-CR26\" id=\"ref-link-section-d325929573e1340\" target=\"_blank\" rel=\"noopener\">26<\/a>, it is important to identify the 23-phase nature of our film. The reflection high-energy electron diffraction (RHEED) pattern of the fabricated film shows clear streaks associated with the 1\u2009\u00d7\u20091 structure of Cr2Se3, besides the 1\u2009\u00d7\u20091 pattern from 2\u2009ML graphene (Fig.\u00a0<a data-track=\"click\" data-track-label=\"link\" data-track-action=\"figure anchor\" href=\"http:\/\/www.nature.com\/articles\/s41467-025-58643-3#Fig1\" target=\"_blank\" rel=\"noopener\">1b<\/a>). The estimated in-plane lattice constant (3.6\u2009\u00c5) is close to the value (3.62\u2009\u00c5) from the first-principles calculations<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" aria-label=\"Reference 31\" title=\"He, Z. et al. Two-dimensional valleytronic semiconductor with spontaneous spin and valley polarization in single-layer Cr2Se3. Phys. Rev. B. 104, 075105 (2021).\" href=\"http:\/\/www.nature.com\/articles\/s41467-025-58643-3#ref-CR31\" id=\"ref-link-section-d325929573e1351\" target=\"_blank\" rel=\"noopener\">31<\/a> and supports the formation of the 23 phase, as directly confirmed by the transmission electron microscopy (TEM) measurements (for details, see Figs. S<a data-track=\"click\" data-track-label=\"link\" data-track-action=\"supplementary material anchor\" href=\"http:\/\/www.nature.com\/articles\/s41467-025-58643-3#MOESM1\" target=\"_blank\" rel=\"noopener\">1<\/a>\u2013S<a data-track=\"click\" data-track-label=\"link\" data-track-action=\"supplementary material anchor\" href=\"http:\/\/www.nature.com\/articles\/s41467-025-58643-3#MOESM1\" target=\"_blank\" rel=\"noopener\">3<\/a> in Supplementary Note\u00a0<a data-track=\"click\" data-track-label=\"link\" data-track-action=\"supplementary material anchor\" href=\"http:\/\/www.nature.com\/articles\/s41467-025-58643-3#MOESM1\" target=\"_blank\" rel=\"noopener\">1<\/a>). Low-energy electron diffraction (LEED) pattern shows sharp six-fold 1\u2009\u00d7\u20091 spots originating from the Cr2Se3 film besides the 1\u2009\u00d7\u20091 spots of graphene (Fig.\u00a0<a data-track=\"click\" data-track-label=\"link\" data-track-action=\"figure anchor\" href=\"http:\/\/www.nature.com\/articles\/s41467-025-58643-3#Fig1\" target=\"_blank\" rel=\"noopener\">1c<\/a>), indicative of its high single crystallinity. The clear observation of graphene spots in RHEED and LEED patterns is a signature of ML formation, as reported in TMDs<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" title=\"Nakata, Y. et al. Anisotropic band splitting in monolayer NbSe2: implications for superconductivity and charge density wave. Npj 2D Mater. Appl. 2, 12 (2018).\" href=\"#ref-CR40\" id=\"ref-link-section-d325929573e1373\">40<\/a>,<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" title=\"Nakamura, H. et al. Spin splitting and strain in epitaxial monolayer WSe2 on graphene. Phys. Rev. B 101, 165103 (2020).\" href=\"#ref-CR41\" id=\"ref-link-section-d325929573e1373_1\">41<\/a>,<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" aria-label=\"Reference 42\" title=\"Feng, J. et al. Electronic structure and enhanced charge-density wave order of monolayer VSe2. Nano Lett. 18, 4493&#x2013;4499 (2018).\" href=\"http:\/\/www.nature.com\/articles\/s41467-025-58643-3#ref-CR42\" id=\"ref-link-section-d325929573e1376\" target=\"_blank\" rel=\"noopener\">42<\/a>. Soft X-ray (SX) photoemission spectroscopy shows Cr3+ features and supports the formation of the 23 phase (for details, see Fig. S<a data-track=\"click\" data-track-label=\"link\" data-track-action=\"supplementary material anchor\" href=\"http:\/\/www.nature.com\/articles\/s41467-025-58643-3#MOESM1\" target=\"_blank\" rel=\"noopener\">4<\/a> of Supplementary Note\u00a0<a data-track=\"click\" data-track-label=\"link\" data-track-action=\"supplementary material anchor\" href=\"http:\/\/www.nature.com\/articles\/s41467-025-58643-3#MOESM1\" target=\"_blank\" rel=\"noopener\">2<\/a>). To clarify possible ferromagnetism, we carried out x-ray absorption spectroscopy (XAS) and magnetic circular dichroism (XMCD) at the Cr L edge (2p-3d transition). The XAS spectrum at T\u2009=\u200970\u2009K for both positive and negative out-of-plane magnetic field (\\(\\pm \\,\\)1.0\u2009T) shown in Fig.\u00a0<a data-track=\"click\" data-track-label=\"link\" data-track-action=\"figure anchor\" href=\"http:\/\/www.nature.com\/articles\/s41467-025-58643-3#Fig1\" target=\"_blank\" rel=\"noopener\">1d<\/a> is characterized by the Cr L3 and L2 main peaks at h\u03bd\u2009~\u2009577\u2009eV and 585\u2009eV, respectively. The XAS spectra show a small but finite difference between the +1.0\u2009T and \u22121.0\u2009T, signifying a finite XMCD signal indicative of ferromagnetism. This is better visualized by the difference spectrum plotted on an expanded y-scale (green\u00a0area) in which the overall XMCD spectral shape is consistent with that of ML Cr2Se3 and Cr2Te3<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" aria-label=\"Reference 30\" title=\"Liu, M. et al. Diverse structures and magnetic properties in nonlayered monolayer chromium selenide. J. Phys. Chem. Lett. 12, 7752&#x2013;7760 (2021).\" href=\"http:\/\/www.nature.com\/articles\/s41467-025-58643-3#ref-CR30\" id=\"ref-link-section-d325929573e1434\" target=\"_blank\" rel=\"noopener\">30<\/a>,<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" aria-label=\"Reference 43\" title=\"Burn, D. M. et al. Cr2Te3 thin films for integration in magnetic topological insulator heterostructures. Sci. Rep. 9, 10793 (2019).\" href=\"http:\/\/www.nature.com\/articles\/s41467-025-58643-3#ref-CR43\" id=\"ref-link-section-d325929573e1437\" target=\"_blank\" rel=\"noopener\">43<\/a>,<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" aria-label=\"Reference 44\" title=\"Lee, I. H. et al. Modulating curie temperature and magnetic anisotropy in nanoscale-layered Cr2Te3 films: implications for room-temperature spintronics. ACS Appl. Nano Mater. 4, 4810&#x2013;4819 (2021).\" href=\"http:\/\/www.nature.com\/articles\/s41467-025-58643-3#ref-CR44\" id=\"ref-link-section-d325929573e1440\" target=\"_blank\" rel=\"noopener\">44<\/a>. Cluster model calculations are consistent with experiments (Fig.\u00a0<a data-track=\"click\" data-track-label=\"link\" data-track-action=\"figure anchor\" href=\"http:\/\/www.nature.com\/articles\/s41467-025-58643-3#Fig1\" target=\"_blank\" rel=\"noopener\">1d<\/a>) and indicate that ML Cr2Se3 is a negative-charge transfer material with Cr3+ t2g3\u2191 configuration and a magnetic moment of 3.4 \u03bcB\/Cr-atom (for details, see Supplementary Note\u00a0<a data-track=\"click\" data-track-label=\"link\" data-track-action=\"supplementary material anchor\" href=\"http:\/\/www.nature.com\/articles\/s41467-025-58643-3#MOESM1\" target=\"_blank\" rel=\"noopener\">3<\/a>). These results suggest that the 2D magnetism is realized in a non-van der Waals material. Since non-van der Waals 2D materials in the ultrathin limit cannot be easily obtained by a simple mechanical exfoliation of bulk crystal, the present result indicates the importance of molecular-beam epitaxy (MBE) for realizing properties unique to non-van der Waals 2D epitaxial films. One also expects a stronger interfacial effect with other materials due to the absence of a van der Waals gap, which would be useful for modulating or enhancing the magnetic properties.<\/p>\n<p>To clarify the electronic states relevant to the occurrence of ferromagnetism, we investigated the band structure in the FM phase. Energy distribution curves (EDCs) measured along the \u0393K cut of the hexagonal Brillouin zone (inset) in Fig.\u00a0<a data-track=\"click\" data-track-label=\"link\" data-track-action=\"figure anchor\" href=\"http:\/\/www.nature.com\/articles\/s41467-025-58643-3#Fig1\" target=\"_blank\" rel=\"noopener\">1e<\/a> signify highly dispersive valence bands located at the binding energy (EB) of 1\u20133\u2009eV, whereas the intensity within the EB range of 0\u20131\u2009eV is suppressed due to the band-gap opening. A careful look in close vicinity of EF around the K point reveals the existence of a Fermi-edge cut-off indicative of the metallic nature. This is due to the appearance of an electron pocket as seen in the magnified EDCs and corresponding intensity plots (insets of Fig.\u00a0<a data-track=\"click\" data-track-label=\"link\" data-track-action=\"figure anchor\" href=\"http:\/\/www.nature.com\/articles\/s41467-025-58643-3#Fig1\" target=\"_blank\" rel=\"noopener\">1e, f<\/a>). The overall valence-band structure is better visualized by the ARPES-intensity plot as a function of ky and EB in Fig.\u00a0<a data-track=\"click\" data-track-label=\"link\" data-track-action=\"figure anchor\" href=\"http:\/\/www.nature.com\/articles\/s41467-025-58643-3#Fig1\" target=\"_blank\" rel=\"noopener\">1f<\/a> which displays the complex band structure characterized by several holelike bands centered at the \u0393 point and an M-shaped band around EB\u2009~\u20092\u20132.5\u2009eV. From the energy separation between the top of valence bands at the \u0393 point and the bottom of conduction bands at the K point, it is suggested that ML Cr2Se3 is a semiconductor in non-doped regime with an indirect band gap of ~0.8\u2009eV. As shown by a side-by-side comparison of Fig.\u00a0<a data-track=\"click\" data-track-label=\"link\" data-track-action=\"figure anchor\" href=\"http:\/\/www.nature.com\/articles\/s41467-025-58643-3#Fig1\" target=\"_blank\" rel=\"noopener\">1f, g<\/a>, the overall band structure determined by ARPES shows a qualitative agreement with the calculated band structure for free-standing ML Cr2Se3 obtained from first-principles calculations for the FM phase assuming out-of-plane magnetic moments and an on-site Coulomb energy of U\u2009=\u20093.5 eV<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" aria-label=\"Reference 31\" title=\"He, Z. et al. Two-dimensional valleytronic semiconductor with spontaneous spin and valley polarization in single-layer Cr2Se3. Phys. Rev. B. 104, 075105 (2021).\" href=\"http:\/\/www.nature.com\/articles\/s41467-025-58643-3#ref-CR31\" id=\"ref-link-section-d325929573e1523\" target=\"_blank\" rel=\"noopener\">31<\/a>. For example, the experimental holelike band topped at the \u0393 point shows a good correspondence to the top of calculated up-spin bands (red curves), and the M-shaped down-spin bands (blue curves) are commonly recognized at ~1\u2009eV below the valence-band top, in both the experiment and calculation. The momentum location (the K point) of the bottom of the conduction band which is assigned to the up-spin Cr 3d\u00a0eg\u2191 band is also well reproduced by the calculation although the calculation underestimates the band-gap magnitude by ~30%. The appearance of the eg\u2191 electron pocket suggests that ML Cr2Se3 grown on 2\u2009ML graphene is a doped semiconductor with half-metallic nature. To identify the orbital character of observed bands, we carried out resonant ARPES measurements using SX photons around the Cr L3 absorption edge (for details, see Fig. S<a data-track=\"click\" data-track-label=\"link\" data-track-action=\"supplementary material anchor\" href=\"http:\/\/www.nature.com\/articles\/s41467-025-58643-3#MOESM1\" target=\"_blank\" rel=\"noopener\">5<\/a> of Supplementary Note\u00a0<a data-track=\"click\" data-track-label=\"link\" data-track-action=\"supplementary material anchor\" href=\"http:\/\/www.nature.com\/articles\/s41467-025-58643-3#MOESM1\" target=\"_blank\" rel=\"noopener\">4<\/a>). The results show a strong resonance enhancement of ARPES intensities at EB\u2009~\u20091.5\u20132.5\u2009eV associated with the Cr 3d-t2g\u2191 bands hybridized with the Se 4p states (for details of the orbital assignments, see Supplementary Note\u00a0<a data-track=\"click\" data-track-label=\"link\" data-track-action=\"supplementary material anchor\" href=\"http:\/\/www.nature.com\/articles\/s41467-025-58643-3#MOESM1\" target=\"_blank\" rel=\"noopener\">5<\/a>).<\/p>\n<p>Temperature dependence of the band structure across T<br \/>\n                           C<\/p>\n<p>Now that the overall band structure in the FM phase is established, next we show temperature evolution of the band structure in Fig.\u00a0<a data-track=\"click\" data-track-label=\"link\" data-track-action=\"figure anchor\" href=\"http:\/\/www.nature.com\/articles\/s41467-025-58643-3#Fig2\" target=\"_blank\" rel=\"noopener\">2a\u2013c<\/a> (detailed T-dependence is shown in Fig. S<a data-track=\"click\" data-track-label=\"link\" data-track-action=\"supplementary material anchor\" href=\"http:\/\/www.nature.com\/articles\/s41467-025-58643-3#MOESM1\" target=\"_blank\" rel=\"noopener\">13<\/a>). Key characteristics of the complex band structure seen at T\u2009=\u200940\u2009K in Figs.\u00a0<a data-track=\"click\" data-track-label=\"link\" data-track-action=\"figure anchor\" href=\"http:\/\/www.nature.com\/articles\/s41467-025-58643-3#Fig1\" target=\"_blank\" rel=\"noopener\">1<\/a>f, <a data-track=\"click\" data-track-label=\"link\" data-track-action=\"figure anchor\" href=\"http:\/\/www.nature.com\/articles\/s41467-025-58643-3#Fig2\" target=\"_blank\" rel=\"noopener\">2a<\/a>, such as the M-shaped band around EB\u2009~\u20092\u20132.5\u2009eV and a sharp valence-band top at the \u0393 point, still persist at T\u2009=\u2009150\u2009K (Fig.\u00a0<a data-track=\"click\" data-track-label=\"link\" data-track-action=\"figure anchor\" href=\"http:\/\/www.nature.com\/articles\/s41467-025-58643-3#Fig2\" target=\"_blank\" rel=\"noopener\">2b<\/a>). In contrast, at T\u2009=\u2009300\u2009K (Fig.\u00a0<a data-track=\"click\" data-track-label=\"link\" data-track-action=\"figure anchor\" href=\"http:\/\/www.nature.com\/articles\/s41467-025-58643-3#Fig2\" target=\"_blank\" rel=\"noopener\">2c<\/a>), the spectral feature becomes simpler and the M-shaped band is converted to a V-shaped band located around EB\u2009~\u20091.3\u20132.1\u2009eV. As shown later, the detailed analysis and temperature-dependent XMCD measurements suggest that TC lies between 225 and 250\u2009K, higher than the estimated TC value of ~200\u2009K in ML Cr2Se3 on HOPG<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" aria-label=\"Reference 30\" title=\"Liu, M. et al. Diverse structures and magnetic properties in nonlayered monolayer chromium selenide. J. Phys. Chem. Lett. 12, 7752&#x2013;7760 (2021).\" href=\"http:\/\/www.nature.com\/articles\/s41467-025-58643-3#ref-CR30\" id=\"ref-link-section-d325929573e1640\" target=\"_blank\" rel=\"noopener\">30<\/a>.<\/p>\n<p><b id=\"Fig2\" class=\"c-article-section__figure-caption\" data-test=\"figure-caption-text\">Fig. 2: Temperature evolution of band structure and evidence for spin-valley polarization.<\/b><a class=\"c-article-section__figure-link\" data-test=\"img-link\" data-track=\"click\" data-track-label=\"image\" data-track-action=\"view figure\" href=\"https:\/\/www.nature.com\/articles\/s41467-025-58643-3\/figures\/2\" rel=\"nofollow noopener\" target=\"_blank\"><img decoding=\"async\" aria-describedby=\"Fig2\" src=\"https:\/\/www.europesays.com\/uk\/wp-content\/uploads\/2025\/04\/41467_2025_58643_Fig2_HTML.png\" alt=\"figure 2\" loading=\"lazy\" width=\"685\" height=\"862\"\/><\/a><\/p>\n<p><b>a<\/b>\u2013<b>c<\/b> ARPES-intensity plots along the \u0393K cut measured at T\u2009=\u200940\u2009K, 150\u2009K, and 300\u2009K, respectively, measured with circularly polarized photons of h\u03bd\u2009=\u200975\u2009eV. Peaks p1 and p2 are also indicated. <b>d<\/b>, <b>e<\/b> Temperature-dependence of EDCs at selected k cuts at ky\u2009=\u20090.0\u00a0(\u0393), \u22121.1\u2009\u00c5\u22121\u00a0(K\u2019), respectively. <b>f<\/b> Temperature dependence of the peak position for valence-band peaks at EB\u2009~\u20092\u20132.5\u2009eV at the \u0393 point (ky\u2009=\u20090\u2009\u00c5\u22121) estimated by numerical fittings to the EDCs assuming Voigt peaks and linear background with error bars \u00b1 20\u2009meV. <b>g<\/b>, <b>h<\/b> Second-derivative intensity plots of Fig.\u00a02d, e, respectively. <b>i<\/b> EDCs for ML Cr2Se3, obtained at the K and K\u2019 points with C+ and C- polarized lights using h\u03bd\u2009=\u200975\u2009eV. Yellow and purple curves represent subtracted EDCs obtained with C+ and C- photons expanded vertically by 5 times. Inset shows the expansion near EF. One can recognize a clear circular dichroism (CD) associated with spin-valley polarization which reverses its sign between the K and K\u2019 points.<\/p>\n<p>Besides a drastic change in the band structure, a systematic T-dependent energy shift is observed in the EDCs and corresponding second-derivative intensity plots at the \u0393 point (ky\u2009=\u20090.0\u2009\u00c5\u22121) in Fig.\u00a0<a data-track=\"click\" data-track-label=\"link\" data-track-action=\"figure anchor\" href=\"http:\/\/www.nature.com\/articles\/s41467-025-58643-3#Fig2\" target=\"_blank\" rel=\"noopener\">2d, g<\/a>. All the bands, including the topmost valence band and corresponding spin-orbit split Se 4p states separated by ~0.2 eV<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" aria-label=\"Reference 45\" title=\"Pacil&#xE9;, D. et al. Photoemission and optical studies of ZrSe3, HfSe3, ZrS3. Phys. Rev. B 76, 155406 (2007).\" href=\"http:\/\/www.nature.com\/articles\/s41467-025-58643-3#ref-CR45\" id=\"ref-link-section-d325929573e1757\" target=\"_blank\" rel=\"noopener\">45<\/a>, systematically move toward EF on increasing temperature upto TC, with a gradual increase in the peak width associated with thermal broadening. This is also the case for the spectra at the K\u2019 point (ky\u2009=\u2009\u2212 1.1\u2009\u00c5-1; Fig.\u00a0<a data-track=\"click\" data-track-label=\"link\" data-track-action=\"figure anchor\" href=\"http:\/\/www.nature.com\/articles\/s41467-025-58643-3#Fig2\" target=\"_blank\" rel=\"noopener\">2e, h<\/a>). Besides the systematic band shift, some bands show additional energy splitting at low temperatures. For example, at the \u0393 point (Fig.\u00a0<a data-track=\"click\" data-track-label=\"link\" data-track-action=\"figure anchor\" href=\"http:\/\/www.nature.com\/articles\/s41467-025-58643-3#Fig2\" target=\"_blank\" rel=\"noopener\">2d<\/a>), a main peak at EB\u2009=\u20092.16\u2009eV with a shoulder feature at 2.36\u2009eV at T\u2009=\u200940\u2009K, signify the existence of a double peak (marked as p1 and p2 in Fig.\u00a0<a data-track=\"click\" data-track-label=\"link\" data-track-action=\"figure anchor\" href=\"http:\/\/www.nature.com\/articles\/s41467-025-58643-3#Fig2\" target=\"_blank\" rel=\"noopener\">2d<\/a>). This double peak consisting of Cr-Se hybridized states constituting the M-shaped band get merged into a single peak on increasing temperature, around T\u2009=\u2009225\u2013250\u2009K. We quantified the T-dependence of band energies from numerical fits to the EDCs and the peak positions are shown in Fig.\u00a0<a data-track=\"click\" data-track-label=\"link\" data-track-action=\"figure anchor\" href=\"http:\/\/www.nature.com\/articles\/s41467-025-58643-3#Fig2\" target=\"_blank\" rel=\"noopener\">2f<\/a>. The band splitting vanishes between T\u2009=\u2009225\u2013250\u2009K, corresponding to TC of ML Cr2Se3. The same trend is also recognized for the peaks at ~1.97\u2009eV and ~2.13\u2009eV at T\u2009=\u200940\u2009K for the K\u2019 point (Fig.\u00a0<a data-track=\"click\" data-track-label=\"link\" data-track-action=\"figure anchor\" href=\"http:\/\/www.nature.com\/articles\/s41467-025-58643-3#Fig2\" target=\"_blank\" rel=\"noopener\">2e, h<\/a>) and corresponding plots of the t2g band energies in Fig. S<a data-track=\"click\" data-track-label=\"link\" data-track-action=\"supplementary material anchor\" href=\"http:\/\/www.nature.com\/articles\/s41467-025-58643-3#MOESM1\" target=\"_blank\" rel=\"noopener\">7c<\/a> (for details, see Supplementary Note\u00a0<a data-track=\"click\" data-track-label=\"link\" data-track-action=\"supplementary material anchor\" href=\"http:\/\/www.nature.com\/articles\/s41467-025-58643-3#MOESM1\" target=\"_blank\" rel=\"noopener\">6<\/a>). We attribute the above observation to the band splitting associated with the FM transition, since the splitting sets in around TC, as is also confirmed by the T-dependent XMCD signal shown in Fig. S<a data-track=\"click\" data-track-label=\"link\" data-track-action=\"supplementary material anchor\" href=\"http:\/\/www.nature.com\/articles\/s41467-025-58643-3#MOESM1\" target=\"_blank\" rel=\"noopener\">18<\/a>. Such a clear T-dependent band splitting below TC has been rarely reported in 2D ferromagnets<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" aria-label=\"Reference 24\" title=\"Zhong, Y. et al. From Stoner to local moment magnetism in atomically thin Cr2Te3. Nat Commun 14, 5340 (2023).\" href=\"http:\/\/www.nature.com\/articles\/s41467-025-58643-3#ref-CR24\" id=\"ref-link-section-d325929573e1851\" target=\"_blank\" rel=\"noopener\">24<\/a>,<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" aria-label=\"Reference 46\" title=\"Zhang, X. et al. Room-temperature intrinsic ferromagnetism in epitaxial CrTe2 ultrathin films. Nat. Commun. 12, 2492 (2021).\" href=\"http:\/\/www.nature.com\/articles\/s41467-025-58643-3#ref-CR46\" id=\"ref-link-section-d325929573e1854\" target=\"_blank\" rel=\"noopener\">46<\/a>.<\/p>\n<p>Spin-valley coupling<\/p>\n<p>We found a signature of circular dichroism (CD) for the t2g\u2191 bands at the K and K\u2019 points at T\u2009=\u200940\u2009K for ML Cr2Se3, as shown Fig.\u00a0<a data-track=\"click\" data-track-label=\"link\" data-track-action=\"figure anchor\" href=\"http:\/\/www.nature.com\/articles\/s41467-025-58643-3#Fig2\" target=\"_blank\" rel=\"noopener\">2i<\/a>. Using right and left circularly polarized light (C+ and C-), the obtained EDCs at the K point (red and pink curves) show a difference between their peak intensities, signifying a finite CD. This CD is also observed at the K\u2019 point (blue and light blue curves) but with a sign reversal compared to the K point, as shown by the subtracted EDCs expanded vertically (yellow and purple curves). We found a sign reversal of CD also for the eg\u2191 pocket between the K and K\u2019 points (see inset to Fig.\u00a0<a data-track=\"click\" data-track-label=\"link\" data-track-action=\"figure anchor\" href=\"http:\/\/www.nature.com\/articles\/s41467-025-58643-3#Fig2\" target=\"_blank\" rel=\"noopener\">2i<\/a>). Intriguingly, the sign is also reversed between the t2g\u2191 and eg\u2191 bands. These observations suggest that photoelectron excitations are asymmetric between the K and K\u2019 points, supporting the valley-selective CD (i.e., valley polarization) which is a necessary condition for realizing anomalous valley Hall effect<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" aria-label=\"Reference 31\" title=\"He, Z. et al. Two-dimensional valleytronic semiconductor with spontaneous spin and valley polarization in single-layer Cr2Se3. Phys. Rev. B. 104, 075105 (2021).\" href=\"http:\/\/www.nature.com\/articles\/s41467-025-58643-3#ref-CR31\" id=\"ref-link-section-d325929573e1905\" target=\"_blank\" rel=\"noopener\">31<\/a>. It is noted that the observed CD is not likely to originate from experimental artifacts such as incomplete CD polarization or sample degradation, but is an intrinsic property of our Cr2Se3 film (for details, see Supplementary Note\u00a0<a data-track=\"click\" data-track-label=\"link\" data-track-action=\"supplementary material anchor\" href=\"http:\/\/www.nature.com\/articles\/s41467-025-58643-3#MOESM1\" target=\"_blank\" rel=\"noopener\">7<\/a>). This is also corroborated by the observation of three-fold symmetric LEED pattern suggestive of the inequivalently mixed structure domains rotated by 60\u00b0 from each other (in this regard, it is different from ML 1\u2009T\u2019 TMDs with equivalently mixed 120\u00b0 rotated domains<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" title=\"Tang, S. et al. Quantum spin Hall state in monolayer 1&#x2009;T&#x2019;-WTe2. Nat. Phys. 13, 68&#x2013;687 (2017).\" href=\"#ref-CR47\" id=\"ref-link-section-d325929573e1917\">47<\/a>,<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" title=\"Tang, S. et al. Electronic structure of monolayer 1&#x2009;T&#x2032;-MoTe2 grown by molecular beam epitaxy. APL Mater 6, 026601 (2018).\" href=\"#ref-CR48\" id=\"ref-link-section-d325929573e1917_1\">48<\/a>,<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" title=\"Ugeda, M. M. et al. Observation of topologically protected states at crystalline phase boundaries in single-layer WSe2. Nat. Commun. 9, 3401 (2018).\" href=\"#ref-CR49\" id=\"ref-link-section-d325929573e1917_2\">49<\/a>,<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" aria-label=\"Reference 50\" title=\"Choi, B. K. Visualizing orbital content of electronic bands in anisotropic 2D semiconducting ReSe2. ACS Nano 14, 7880&#x2013;7891 (2020).\" href=\"http:\/\/www.nature.com\/articles\/s41467-025-58643-3#ref-CR50\" id=\"ref-link-section-d325929573e1920\" target=\"_blank\" rel=\"noopener\">50<\/a>), making our Cr2Se3 film a valid candidate to observe valley polarization (for details, see Fig. S<a data-track=\"click\" data-track-label=\"link\" data-track-action=\"supplementary material anchor\" href=\"http:\/\/www.nature.com\/articles\/s41467-025-58643-3#MOESM1\" target=\"_blank\" rel=\"noopener\">8<\/a> and Supplementary Note\u00a0<a data-track=\"click\" data-track-label=\"link\" data-track-action=\"supplementary material anchor\" href=\"http:\/\/www.nature.com\/articles\/s41467-025-58643-3#MOESM1\" target=\"_blank\" rel=\"noopener\">7<\/a>).<\/p>\n<p>We found that the overall magnitude of CD is reduced in the 2\u2009ML sample with lower TC (see Fig. S<a data-track=\"click\" data-track-label=\"link\" data-track-action=\"supplementary material anchor\" href=\"http:\/\/www.nature.com\/articles\/s41467-025-58643-3#MOESM1\" target=\"_blank\" rel=\"noopener\">9<\/a> in Supplementary Note\u00a0<a data-track=\"click\" data-track-label=\"link\" data-track-action=\"supplementary material anchor\" href=\"http:\/\/www.nature.com\/articles\/s41467-025-58643-3#MOESM1\" target=\"_blank\" rel=\"noopener\">7<\/a>), signifying that the valley-selective CD is coupled to the ferromagnetism. This coupling of localized t2g-spins and itinerant eg-valley states is supported by considering the magnitude of experimental energy splitting for the strongly hybridized t2g bands at the K\/K\u2019 point for ML (~160\u2009meV) which is much larger than the SOC energy (\u0394SOC) of Cr3+ states (~50\u2009meV) and inversion-symmetry breaking of the crystal (at most a few tens meV)<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" aria-label=\"Reference 31\" title=\"He, Z. et al. Two-dimensional valleytronic semiconductor with spontaneous spin and valley polarization in single-layer Cr2Se3. Phys. Rev. B. 104, 075105 (2021).\" href=\"http:\/\/www.nature.com\/articles\/s41467-025-58643-3#ref-CR31\" id=\"ref-link-section-d325929573e1967\" target=\"_blank\" rel=\"noopener\">31<\/a>. But the observed splitting is comparable to the known \u0394SOC of ~200\u2009meV in Se bands<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" aria-label=\"Reference 45\" title=\"Pacil&#xE9;, D. et al. Photoemission and optical studies of ZrSe3, HfSe3, ZrS3. Phys. Rev. B 76, 155406 (2007).\" href=\"http:\/\/www.nature.com\/articles\/s41467-025-58643-3#ref-CR45\" id=\"ref-link-section-d325929573e1974\" target=\"_blank\" rel=\"noopener\">45<\/a>, which is about half of the atomic SOC energy \u0394\u2019SOC\u2009=\u2009418\u2009meV for Se 4p states. In a recent study on V1\/3NbS2 crystals, a giant valley-Zeeman coupling in surface states of the NbS2-termination top layer was reported to originate from hybridized V d orbitals and planar NbS2 orbitals with an exchange splitting \u0394ex\u2009~\u200952\u2009meV and \u0394SOC\u2009~\u200959\u2009meV aiding each other at the K point and opposing each other at the K\u2019 point. Using known values of valley-Zeeman splitting of ~0.2 meVT\u22121 for TMDs<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" aria-label=\"Reference 51\" title=\"Srivastava, A. et al. Valley Zeeman effect in elementary optical excitations of monolayer WSe2. Nat. Phys. 11, 141 (2015).\" href=\"http:\/\/www.nature.com\/articles\/s41467-025-58643-3#ref-CR51\" id=\"ref-link-section-d325929573e2002\" target=\"_blank\" rel=\"noopener\">51<\/a>, the authors estimated that a magnetic field exceeding 250\u2009T was operative in V1\/3NbS2 to give the observed splitting. However, the results showed that the surface states of V1\/3NbS2 exhibit the same magnetic ordering temperature as the bulk, with TN\u2009~\u200953 K<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" aria-label=\"Reference 37\" title=\"Edwards, B. et al. Giant valley-Zeeman coupling in the surface layer of an intercalated transition metal dichalcogenide. Nat. Mater. 22, 459&#x2013;465 (2023).\" href=\"http:\/\/www.nature.com\/articles\/s41467-025-58643-3#ref-CR37\" id=\"ref-link-section-d325929573e2019\" target=\"_blank\" rel=\"noopener\">37<\/a>. In the present case, we see ferromagnetism with a relatively high TC\u2009~\u2009225\u2009K for ML Cr2Se3 case compared to an antiferromagnetic TN\u2009~\u200945\u2009K for bulk Cr2Se3<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" aria-label=\"Reference 26\" title=\"Adachi, Y. et al. Magnetic structure of rhombohedral Cr2Se3. J. Phys. Soc. Jpn. 63, 1548&#x2013;1559 (1994).\" href=\"http:\/\/www.nature.com\/articles\/s41467-025-58643-3#ref-CR26\" id=\"ref-link-section-d325929573e2039\" target=\"_blank\" rel=\"noopener\">26<\/a>. However, we see an experimental energy splitting for the t2g bands at the K\/K\u2019 point for ML (~160\u2009meV) suggesting a spin-splitting-dominated spin-valley coupling since the valley splitting is calculated to be just 18 meV<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" aria-label=\"Reference 31\" title=\"He, Z. et al. Two-dimensional valleytronic semiconductor with spontaneous spin and valley polarization in single-layer Cr2Se3. Phys. Rev. B. 104, 075105 (2021).\" href=\"http:\/\/www.nature.com\/articles\/s41467-025-58643-3#ref-CR31\" id=\"ref-link-section-d325929573e2048\" target=\"_blank\" rel=\"noopener\">31<\/a>. Moreover, the gradual reduction of the splitting energy with a small reduction in TC by increasing number of layers (see Fig. S<a data-track=\"click\" data-track-label=\"link\" data-track-action=\"supplementary material anchor\" href=\"http:\/\/www.nature.com\/articles\/s41467-025-58643-3#MOESM1\" target=\"_blank\" rel=\"noopener\">7<\/a> in Supplementary Note\u00a0<a data-track=\"click\" data-track-label=\"link\" data-track-action=\"supplementary material anchor\" href=\"http:\/\/www.nature.com\/articles\/s41467-025-58643-3#MOESM1\" target=\"_blank\" rel=\"noopener\">6<\/a>) also supports the intimate coupling of spin and valley degrees of freedom for an enhanced TC in 2\u2009ML and 3\u2009ML films compared to bulk TN\u2009~\u200945\u2009K.<\/p>\n<p>Besides the spin-valley coupling, another intriguing characteristic of ML Cr2Se3 is the evolution of the eg\u2191 electron pocket at the K\/K\u2019 point. The EDCs in Fig.\u00a0<a data-track=\"click\" data-track-label=\"link\" data-track-action=\"figure anchor\" href=\"http:\/\/www.nature.com\/articles\/s41467-025-58643-3#Fig3\" target=\"_blank\" rel=\"noopener\">3a<\/a> signify a sharp peak associated with the eg\u2191 band at T\u2009=\u200940\u2009K for both the K and K\u2019 points. Upon increasing temperature, the spectral weight of eg\u2191-peak is monotonically reduced and the peak has almost vanished at T\u2009=\u2009300\u2009K. This suggests that ferromagnetism in ML Cr2Se3 is associated with spectral weight of the eg\u2191 pocket. Figure\u00a0<a data-track=\"click\" data-track-label=\"link\" data-track-action=\"figure anchor\" href=\"http:\/\/www.nature.com\/articles\/s41467-025-58643-3#Fig3\" target=\"_blank\" rel=\"noopener\">3a<\/a> shows that the total spectral weight at fixed temperature is higher at the K point than at the K\u2019 point (see purple or blue curves). This intensity asymmetry is attributed to the inequivalent valley states at the K and K\u2019 points predicted by the density-functional-theory (DFT) calculation<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" aria-label=\"Reference 31\" title=\"He, Z. et al. Two-dimensional valleytronic semiconductor with spontaneous spin and valley polarization in single-layer Cr2Se3. Phys. Rev. B. 104, 075105 (2021).\" href=\"http:\/\/www.nature.com\/articles\/s41467-025-58643-3#ref-CR31\" id=\"ref-link-section-d325929573e2116\" target=\"_blank\" rel=\"noopener\">31<\/a> and associated with the spin-valley coupling. We have carefully examined this inequivalent valley states between the K and K\u2019 points, and found that the asymmetric nature is reproducible for different samples. More intriguingly, the asymmetry gets enhanced after applying out-of-plane magnetic field, supporting the spin-valley coupling (for details, see Figs. S<a data-track=\"click\" data-track-label=\"link\" data-track-action=\"supplementary material anchor\" href=\"http:\/\/www.nature.com\/articles\/s41467-025-58643-3#MOESM1\" target=\"_blank\" rel=\"noopener\">10<\/a> and S<a data-track=\"click\" data-track-label=\"link\" data-track-action=\"supplementary material anchor\" href=\"http:\/\/www.nature.com\/articles\/s41467-025-58643-3#MOESM1\" target=\"_blank\" rel=\"noopener\">11<\/a> in Supplementary Note\u00a0<a data-track=\"click\" data-track-label=\"link\" data-track-action=\"supplementary material anchor\" href=\"http:\/\/www.nature.com\/articles\/s41467-025-58643-3#MOESM1\" target=\"_blank\" rel=\"noopener\">8<\/a>).<\/p>\n<p><b id=\"Fig3\" class=\"c-article-section__figure-caption\" data-test=\"figure-caption-text\">Fig. 3: Thickness dependence of electronic states.<\/b><a class=\"c-article-section__figure-link\" data-test=\"img-link\" data-track=\"click\" data-track-label=\"image\" data-track-action=\"view figure\" href=\"https:\/\/www.nature.com\/articles\/s41467-025-58643-3\/figures\/3\" rel=\"nofollow noopener\" target=\"_blank\"><img decoding=\"async\" aria-describedby=\"Fig3\" src=\"https:\/\/www.europesays.com\/uk\/wp-content\/uploads\/2025\/04\/41467_2025_58643_Fig3_HTML.png\" alt=\"figure 3\" loading=\"lazy\" width=\"685\" height=\"781\"\/><\/a><\/p>\n<p><b>a<\/b>\u2013<b>c<\/b> Temperature dependence of EDCs near EF at the K (ky\u00a0= 1.1 \u00c5\u22121; left panel) and K\u2019 (ky= \u22121.1 \u00c5\u22121\ufeff; right panel) points to the evolution of the eg\u2191 electron pocket for ML Cr2Se3. The spectral weight is normalized to the valence-band t2g peak. <b>d<\/b>\u2013<b>f<\/b> Temperature dependence of the peak position for valence-band peaks p1 and p2 at the \u0393 point estimated by numerical fittings to the EDCs for ML, 2\u2009ML, and 3\u2009ML Cr2Se3, respectively, suggesting the gradual reduction of TC upon increasing the number of layers n. <b>g<\/b>\u2013<b>i<\/b> ARPES-intensity plots as a function of ky and EB along the \u0393K cut measured with h\u03bd\u2009=\u200975\u2009eV photons at T\u2009=\u200940\u2009K for ML, 2\u2009ML, and 3\u2009ML Cr2Se3, respectively. Inset to (<b>h<\/b>) shows the ARPES intensity with enhanced color contrast around the K point. B. E. stands for binding energy.<\/p>\n<p>In particular, ARPES measurements on ML Cr2Se3 film with improved statistics were carried out to confirm the inequivalence of valley states at K and K\u2019 points. ARPES intensity maps around the K\u2019 and K points, obtained after normalizing the total spectral weight over the plotted EB range of EF to 2.7\u2009eV (Fig. S<a data-track=\"click\" data-track-label=\"link\" data-track-action=\"supplementary material anchor\" href=\"http:\/\/www.nature.com\/articles\/s41467-025-58643-3#MOESM1\" target=\"_blank\" rel=\"noopener\">10<\/a>a, <a data-track=\"click\" data-track-label=\"link\" data-track-action=\"supplementary material anchor\" href=\"http:\/\/www.nature.com\/articles\/s41467-025-58643-3#MOESM1\" target=\"_blank\" rel=\"noopener\">b<\/a>) indicate that the intensity of the electron pocket around the K point is higher than that around the K\u2019 point, confirming the inequivalent valley states around K and K\u2019. Overlapped EDCs at positive ky\u2019s and negative ky\u2019s (Fig. S<a data-track=\"click\" data-track-label=\"link\" data-track-action=\"supplementary material anchor\" href=\"http:\/\/www.nature.com\/articles\/s41467-025-58643-3#MOESM1\" target=\"_blank\" rel=\"noopener\">10c<\/a>) clearly indicate that the spectral weight of the eg -derived peak for positive ky\u2019s is higher than that for negative ky\u2019s.<\/p>\n<p>To clarify the possible coupling of inequivalent valley states to the spin degrees of freedom, we performed ARPES measurements after magnetizing the sample by applying an out-of-plane magnetic field with the strength of <b>B<\/b>\u2009=\u2009+ 0.1\u2009T (see EDCs in Fig. S<a data-track=\"click\" data-track-label=\"link\" data-track-action=\"supplementary material anchor\" href=\"http:\/\/www.nature.com\/articles\/s41467-025-58643-3#MOESM1\" target=\"_blank\" rel=\"noopener\">10d<\/a>). While the overall spectral intensity of the electron pocket is slightly reduced, the asymmetric intensity of the EDCs between the K and K\u2019 points indicate that the inequivalence is preserved even after applying <b>B<\/b>. To our surprise, we found that a broad shoulder feature appears at EB\u2009~\u20090.2\u2009eV more prominently for negative ky\u2019s, i.e., around the K\u2019 point, suggesting that the shape of the EDCs becomes more inequivalent after applying <b>B<\/b>. This change is highlighted by a direct comparison of EDCs at the K and K\u2019 points (Fig. S<a data-track=\"click\" data-track-label=\"link\" data-track-action=\"supplementary material anchor\" href=\"http:\/\/www.nature.com\/articles\/s41467-025-58643-3#MOESM1\" target=\"_blank\" rel=\"noopener\">11<\/a>a, <a data-track=\"click\" data-track-label=\"link\" data-track-action=\"supplementary material anchor\" href=\"http:\/\/www.nature.com\/articles\/s41467-025-58643-3#MOESM1\" target=\"_blank\" rel=\"noopener\">b<\/a>) indicating that the spectral weight of the shoulder feature is enhanced at the K\u2019 point after applying <b>B<\/b>, which is also confirmed by our numerical analysis of EDCs (Fig. S<a data-track=\"click\" data-track-label=\"link\" data-track-action=\"supplementary material anchor\" href=\"http:\/\/www.nature.com\/articles\/s41467-025-58643-3#MOESM1\" target=\"_blank\" rel=\"noopener\">12<\/a>). We found that the shoulder feature becomes much weaker and the EDC shows a simpler peak shape at the K\u2019 point upon reversing <b>B<\/b>, becoming similar to the spectrum at the K point obtained by applying positive <b>B<\/b> (Fig. S<a data-track=\"click\" data-track-label=\"link\" data-track-action=\"supplementary material anchor\" href=\"http:\/\/www.nature.com\/articles\/s41467-025-58643-3#MOESM1\" target=\"_blank\" rel=\"noopener\">11c<\/a>). In addition, we confirmed that this result is reproducible for different samples, by measuring another ML Cr2Se3 sample (Fig. S<a data-track=\"click\" data-track-label=\"link\" data-track-action=\"supplementary material anchor\" href=\"http:\/\/www.nature.com\/articles\/s41467-025-58643-3#MOESM1\" target=\"_blank\" rel=\"noopener\">11d<\/a>). This finding strengthens our argument on the observation of inequivalent valley states between the K and K\u2019 points and their coupling to the spontaneous ferromagnetism.<\/p>\n<p>Band structure of multilayer Cr2Se3<\/p>\n<p>Next, we fabricated 2\u2009ML and 3\u2009ML Cr2Se3 films to investigate thickness evolution of their band structure and relation with spin-valley states. We found that the energy bands of 2\u2009ML and 3\u2009ML films (Fig.\u00a0<a data-track=\"click\" data-track-label=\"link\" data-track-action=\"figure anchor\" href=\"http:\/\/www.nature.com\/articles\/s41467-025-58643-3#Fig3\" target=\"_blank\" rel=\"noopener\">3h, i<\/a>) are shifted upward by ~0.4 and ~0.5\u2009eV, respectively, compared to the ML film (Fig.\u00a0<a data-track=\"click\" data-track-label=\"link\" data-track-action=\"figure anchor\" href=\"http:\/\/www.nature.com\/articles\/s41467-025-58643-3#Fig3\" target=\"_blank\" rel=\"noopener\">3g<\/a>). Simultaneously, the Cr 3d t2g bands get significantly broadened, and also show larger band splitting at the \u0393 point. Detailed analysis at the \u0393 point (and the K point; see Fig. S<a data-track=\"click\" data-track-label=\"link\" data-track-action=\"supplementary material anchor\" href=\"http:\/\/www.nature.com\/articles\/s41467-025-58643-3#MOESM1\" target=\"_blank\" rel=\"noopener\">7<\/a> in Supplementary Note\u00a0<a data-track=\"click\" data-track-label=\"link\" data-track-action=\"supplementary material anchor\" href=\"http:\/\/www.nature.com\/articles\/s41467-025-58643-3#MOESM1\" target=\"_blank\" rel=\"noopener\">6<\/a>) shown in Fig.\u00a0<a data-track=\"click\" data-track-label=\"link\" data-track-action=\"figure anchor\" href=\"http:\/\/www.nature.com\/articles\/s41467-025-58643-3#Fig3\" target=\"_blank\" rel=\"noopener\">3d\u2013f<\/a> suggests that the TC gradually decreases on increasing the number of layers n; TC\u2009=\u2009225\u2013250\u2009K, 175\u2013200\u2009K, and 150\u2013175\u2009K, for ML, 2\u2009ML, and 3\u2009ML, respectively (for detailed T-dependent ARPES data and quantitative analyses of the band splitting, see Figs. S<a data-track=\"click\" data-track-label=\"link\" data-track-action=\"supplementary material anchor\" href=\"http:\/\/www.nature.com\/articles\/s41467-025-58643-3#MOESM1\" target=\"_blank\" rel=\"noopener\">13<\/a>\u2013<a data-track=\"click\" data-track-label=\"link\" data-track-action=\"supplementary material anchor\" href=\"http:\/\/www.nature.com\/articles\/s41467-025-58643-3#MOESM1\" target=\"_blank\" rel=\"noopener\">17<\/a> in Supplementary Note\u00a0<a data-track=\"click\" data-track-label=\"link\" data-track-action=\"supplementary material anchor\" href=\"http:\/\/www.nature.com\/articles\/s41467-025-58643-3#MOESM1\" target=\"_blank\" rel=\"noopener\">9<\/a>). We have confirmed that TC\u2019s estimated by ARPES and XMCD well coincide with each other, suggesting the validity of the TC estimation from the band splitting (for details, see Fig. S<a data-track=\"click\" data-track-label=\"link\" data-track-action=\"supplementary material anchor\" href=\"http:\/\/www.nature.com\/articles\/s41467-025-58643-3#MOESM1\" target=\"_blank\" rel=\"noopener\">18<\/a> in Supplementary Note\u00a0<a data-track=\"click\" data-track-label=\"link\" data-track-action=\"supplementary material anchor\" href=\"http:\/\/www.nature.com\/articles\/s41467-025-58643-3#MOESM1\" target=\"_blank\" rel=\"noopener\">10<\/a>). The TC reduction is correlated with the spectral weight at EF of metallic eg\u2191 pocket seen for ML (Fig.\u00a0<a data-track=\"click\" data-track-label=\"link\" data-track-action=\"figure anchor\" href=\"http:\/\/www.nature.com\/articles\/s41467-025-58643-3#Fig3\" target=\"_blank\" rel=\"noopener\">3a<\/a>), which gets reduced in 2\u2009ML (Fig.\u00a0<a data-track=\"click\" data-track-label=\"link\" data-track-action=\"figure anchor\" href=\"http:\/\/www.nature.com\/articles\/s41467-025-58643-3#Fig3\" target=\"_blank\" rel=\"noopener\">3b<\/a>) and almost vanishes in 3\u2009ML (Fig.\u00a0<a data-track=\"click\" data-track-label=\"link\" data-track-action=\"figure anchor\" href=\"http:\/\/www.nature.com\/articles\/s41467-025-58643-3#Fig3\" target=\"_blank\" rel=\"noopener\">3c<\/a>) (note that a tiny electron pocket still exists at low temperatures for 2\u2009ML, as seen in the image with enhanced color contrast in the inset to Fig.\u00a0<a data-track=\"click\" data-track-label=\"link\" data-track-action=\"figure anchor\" href=\"http:\/\/www.nature.com\/articles\/s41467-025-58643-3#Fig3\" target=\"_blank\" rel=\"noopener\">3h<\/a>). This is consistent with the observed valence-band shifts on increasing n and indicates that the highest doping of electron carriers occurs in the ML film at low-T. It is noted that the asymmetric intensity distribution of the eg\u2191 band between the K and K\u2019 points observed for ML gets reduced for 2\u2009ML and 3\u2009ML (Fig.\u00a0<a data-track=\"click\" data-track-label=\"link\" data-track-action=\"figure anchor\" href=\"http:\/\/www.nature.com\/articles\/s41467-025-58643-3#Fig3\" target=\"_blank\" rel=\"noopener\">3b, c<\/a>), confirming the coupling of valley anisotropy and ferromagnetism. Interestingly, a very recent study<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" aria-label=\"Reference 24\" title=\"Zhong, Y. et al. From Stoner to local moment magnetism in atomically thin Cr2Te3. Nat Commun 14, 5340 (2023).\" href=\"http:\/\/www.nature.com\/articles\/s41467-025-58643-3#ref-CR24\" id=\"ref-link-section-d325929573e2467\" target=\"_blank\" rel=\"noopener\">24<\/a> on Cr2Te3 showed that 3\u2009ML and 6\u2009ML films with TC\u2009=\u2009170\u2009K and T-dependent band shifts, exhibit a reduced TC\u2009=\u200990\u2009K in ML with no energy band shifts, indicating a Stoner to Heisenberg (itinerant to localized)-type FM order. In contrast, Cr2Se3 shows an enhancement of TC in the ML case with TC\u2009~\u2009225\u2009K compared to 2\u2009ML (TC\u2009~\u2009175\u2009K) and 3\u2009ML films (TC\u2009~\u2009150\u2009K), derived from spin-valley coupling of localized and itinerant states.<\/p>\n<p>The most reasonable explanation of the observed n-dependent band structure and FM TC\u2019s is the charge transfer from the graphene substrate<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" aria-label=\"Reference 39\" title=\"Li, B. et al. Van der Waals epitaxial growth of air-stable CrSe2 nanosheets with thickness-tunable magnetic order. Nat. Mater. 20, 818&#x2013;825 (2021).\" href=\"http:\/\/www.nature.com\/articles\/s41467-025-58643-3#ref-CR39\" id=\"ref-link-section-d325929573e2518\" target=\"_blank\" rel=\"noopener\">39<\/a>,<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" aria-label=\"Reference 52\" title=\"Chua, R. et al. Room temperature ferromagnetism of monolayer chromium telluride with perpenicular magnetic anisotropy. Adv. Mater. 33, 2103360 (2021).\" href=\"http:\/\/www.nature.com\/articles\/s41467-025-58643-3#ref-CR52\" id=\"ref-link-section-d325929573e2521\" target=\"_blank\" rel=\"noopener\">52<\/a>, which is also supported by directly comparing the binding energy of the Dirac point of graphene bands before and after the fabrication of ML Cr2Se3 (for details, see Fig. S<a data-track=\"click\" data-track-label=\"link\" data-track-action=\"supplementary material anchor\" href=\"http:\/\/www.nature.com\/articles\/s41467-025-58643-3#MOESM1\" target=\"_blank\" rel=\"noopener\">19<\/a> in Supplementary Note\u00a0<a data-track=\"click\" data-track-label=\"link\" data-track-action=\"supplementary material anchor\" href=\"http:\/\/www.nature.com\/articles\/s41467-025-58643-3#MOESM1\" target=\"_blank\" rel=\"noopener\">11<\/a>). Accordingly, the doped electron carrier density per unit Cr2Se3 layer is expected to be reduced for multilayer films since the total amount of transferred charge carriers across the interface is fixed; this behavior is realized in the present study. Since the Mermin-Wagner theorem<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" aria-label=\"Reference 12\" title=\"Mermin, N. D. &amp; Wagner, H. Absence of ferromagnetism or antiferromagnetism in one- or two-dimensional isotropic Heisenberg models. Phys. Rev. Lett. 17, 1133 (1966).\" href=\"http:\/\/www.nature.com\/articles\/s41467-025-58643-3#ref-CR12\" id=\"ref-link-section-d325929573e2540\" target=\"_blank\" rel=\"noopener\">12<\/a> suggests that FM order is suppressed upon reducing n, in contrast to present observations, the enhancement of TC up to 225\u2013250\u2009K in ML is likely due to the RKKY mechanism associated with maximum carrier density in eg\u2191 valley states. This argument also explains why the insulating ML Cr2Se3 films fabricated on Al2O3 or SiO2\/Si do not show FM but AF order, as in the bulk crystal<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" aria-label=\"Reference 26\" title=\"Adachi, Y. et al. Magnetic structure of rhombohedral Cr2Se3. J. Phys. Soc. Jpn. 63, 1548&#x2013;1559 (1994).\" href=\"http:\/\/www.nature.com\/articles\/s41467-025-58643-3#ref-CR26\" id=\"ref-link-section-d325929573e2568\" target=\"_blank\" rel=\"noopener\">26<\/a>,<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" aria-label=\"Reference 28\" title=\"Roy, A. et al. Structural and magnetic properties of molecular beam epitaxy grown chromium selenide thin films. Phys. Rev. Mater. 4, 025001 (2020).\" href=\"http:\/\/www.nature.com\/articles\/s41467-025-58643-3#ref-CR28\" id=\"ref-link-section-d325929573e2571\" target=\"_blank\" rel=\"noopener\">28<\/a>,<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" aria-label=\"Reference 29\" title=\"Zhu, X. et al. Spin glass state in chemical vapor-deposited crystalline Cr2Se3 nanosheets. Chem. Mater. 33, 3851&#x2013;3858 (2021).\" href=\"http:\/\/www.nature.com\/articles\/s41467-025-58643-3#ref-CR29\" id=\"ref-link-section-d325929573e2574\" target=\"_blank\" rel=\"noopener\">29<\/a>, because no charge transfer is expected from insulating Al2O3 or SiO2\/Si in contrast to the present study which uses a metallic 2\u2009ML graphene\/SiC substrate. It also explains the observation of high-TC ferromagnetism (TC\u2009~\u2009200\u2009K) for ML Cr2Se3 on HOPG<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" aria-label=\"Reference 30\" title=\"Liu, M. et al. Diverse structures and magnetic properties in nonlayered monolayer chromium selenide. J. Phys. Chem. Lett. 12, 7752&#x2013;7760 (2021).\" href=\"http:\/\/www.nature.com\/articles\/s41467-025-58643-3#ref-CR30\" id=\"ref-link-section-d325929573e2598\" target=\"_blank\" rel=\"noopener\">30<\/a>, comparable to the present work because charge-transfer characteristics of graphene and HOPG are expected to be similar with nearly equal work functions.<\/p>\n<p>Finally, we discuss important differences between Cr2Se3 and Cr-Te based van der Waals ferromagnets Cr2Ge2Te6 and CrTe2. A critical difference is that tellurium compounds commonly show ferromagnetism in the bulk whereas bulk Cr2Se3 is an antiferromagnetic (TN\u2009~\u200945\u2009K) semiconductor. Moreover, only Cr2Se3 transforms into a ferromagnetic metal with TC\u2009~\u2009225\u2009K for ML films grown on graphene (TC\u2009~\u2009200\u2009K for ML Cr2Se3\/HOPG; ref. <a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" aria-label=\"Reference 30\" title=\"Liu, M. et al. Diverse structures and magnetic properties in nonlayered monolayer chromium selenide. J. Phys. Chem. Lett. 12, 7752&#x2013;7760 (2021).\" href=\"http:\/\/www.nature.com\/articles\/s41467-025-58643-3#ref-CR30\" id=\"ref-link-section-d325929573e2644\" target=\"_blank\" rel=\"noopener\">30<\/a>). In contrast, the van der Waals ferromagnets, namely Cr2Ge2Te6 (ref. <a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" aria-label=\"Reference 13\" title=\"Gong, C. et al. Discovery of intrinsic ferromagnetism in two-dimensional van Der Waals crystals. Nature 546, 265&#x2013;269 (2017).\" href=\"http:\/\/www.nature.com\/articles\/s41467-025-58643-3#ref-CR13\" id=\"ref-link-section-d325929573e2654\" target=\"_blank\" rel=\"noopener\">13<\/a>) and CrTe2 show a reduction in TC on decreasing thickness (although there are conflicting reports for Cr2Te3 as discussed above<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" aria-label=\"Reference 23\" title=\"Wen, Y. et al. Tunable room-temperature ferromagnetism in two-dimensional Cr2Te3. Nano. Lett. 20, 3130&#x2013;3139 (2020).\" href=\"http:\/\/www.nature.com\/articles\/s41467-025-58643-3#ref-CR23\" id=\"ref-link-section-d325929573e2669\" target=\"_blank\" rel=\"noopener\">23<\/a>,<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" aria-label=\"Reference 24\" title=\"Zhong, Y. et al. From Stoner to local moment magnetism in atomically thin Cr2Te3. Nat Commun 14, 5340 (2023).\" href=\"http:\/\/www.nature.com\/articles\/s41467-025-58643-3#ref-CR24\" id=\"ref-link-section-d325929573e2672\" target=\"_blank\" rel=\"noopener\">24<\/a>). Reference <a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" aria-label=\"Reference 24\" title=\"Zhong, Y. et al. From Stoner to local moment magnetism in atomically thin Cr2Te3. Nat Commun 14, 5340 (2023).\" href=\"http:\/\/www.nature.com\/articles\/s41467-025-58643-3#ref-CR24\" id=\"ref-link-section-d325929573e2676\" target=\"_blank\" rel=\"noopener\">24<\/a> showed that the dominantly Te character orbitals cross EF in Cr2Te3 and form the Fermi surface, leading to an itinerant Stoner type ferromagnetism in thick Cr2Te3 films, but for ML Cr2Te3 film, the Stoner condition is not satisfied and a local moment Heisenberg exchange driven ferromagnetism is realized. In contrast, the Se bands in Cr2Se3 sink well below EF and the occupation of the valley electron pockets with Cr 3d eg character, which couple with localized t2g spins, promotes the ferromagnetism. These aspects suggest that the origin of ferromagnetism in Cr2Se3 films on graphene or HOPG can be expected to be qualitatively different from the van der Waals ferromagnets (it is noted here that, in the ML limit, Cr2Te3 suffers from a trigonal distortion<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" aria-label=\"Reference 24\" title=\"Zhong, Y. et al. From Stoner to local moment magnetism in atomically thin Cr2Te3. Nat Commun 14, 5340 (2023).\" href=\"http:\/\/www.nature.com\/articles\/s41467-025-58643-3#ref-CR24\" id=\"ref-link-section-d325929573e2724\" target=\"_blank\" rel=\"noopener\">24<\/a> with a 2\u2009\u00d7\u20092 superstructure whereas Cr2Se3 maintains its 1\u2009\u00d7\u20091 structure, which can lead to differences in their magnetic properties). Also, the double exchange mechanism is usually considered for the case of mixed valent materials, which is unlikely for Cr2Se3 films on graphene, distinct from the situation of Cr2Ge2Te6 (refs. <a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" aria-label=\"Reference 53\" title=\"Trzaska, L. et al. Charge doping into spin minority states mediates doubling of TC in ferromagnetic CrGeTe3. arXiv 2312, 00440 (2023).\" href=\"http:\/\/www.nature.com\/articles\/s41467-025-58643-3#ref-CR53\" id=\"ref-link-section-d325929573e2743\" target=\"_blank\" rel=\"noopener\">53<\/a>,<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" aria-label=\"Reference 54\" title=\"Wang, N. et al. Transition from ferromagnetic semiconductor to ferromagnetic metal with enhanced curie temperature in Cr2Ge2Te6 via organic ion intercalation. J. Am. Chem. Soc. 141, 17166&#x2013;17173 (2019).\" href=\"http:\/\/www.nature.com\/articles\/s41467-025-58643-3#ref-CR54\" id=\"ref-link-section-d325929573e2746\" target=\"_blank\" rel=\"noopener\">54<\/a>); for a detailed discussion, see Supplementary Note\u00a0<a data-track=\"click\" data-track-label=\"link\" data-track-action=\"supplementary material anchor\" href=\"http:\/\/www.nature.com\/articles\/s41467-025-58643-3#MOESM1\" target=\"_blank\" rel=\"noopener\">12<\/a>. Our results in Fig.\u00a0<a data-track=\"click\" data-track-label=\"link\" data-track-action=\"figure anchor\" href=\"http:\/\/www.nature.com\/articles\/s41467-025-58643-3#Fig3\" target=\"_blank\" rel=\"noopener\">3<\/a>, corroborated by temperature-dependent XMCD, suggest that the reduction of TC on increasing the number of layers is caused by a reduction in the electron carrier density transferred from the substrate across the interface. The results taken together indicate that the TC is proportional to the carrier density (this is supported by the plot of TC vs spectral density of states at EF in Fig. S<a data-track=\"click\" data-track-label=\"link\" data-track-action=\"supplementary material anchor\" href=\"http:\/\/www.nature.com\/articles\/s41467-025-58643-3#MOESM1\" target=\"_blank\" rel=\"noopener\">20<\/a>), and hence suggest that the ferromagnetism is likely due to the localized t2g spins coupled by the RKKY interaction active in the valley electron pockets of Cr2Se3 films grown on graphene.<\/p>\n","protected":false},"excerpt":{"rendered":"Fabrication and characterization of ML Cr2Se3 First, we present fabrication and characterization of a ML Cr2Se3 film. Since&hellip;\n","protected":false},"author":2,"featured_media":35517,"comment_status":"","ping_status":"","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[3845],"tags":[20546,17715,3965,17354,3966,74,70,17353,16,15],"class_list":{"0":"post-35516","1":"post","2":"type-post","3":"status-publish","4":"format-standard","5":"has-post-thumbnail","7":"category-physics","8":"tag-electronic-properties-and-materials","9":"tag-ferromagnetism","10":"tag-humanities-and-social-sciences","11":"tag-interfaces-and-thin-films","12":"tag-multidisciplinary","13":"tag-physics","14":"tag-science","15":"tag-surfaces","16":"tag-uk","17":"tag-united-kingdom"},"share_on_mastodon":{"url":"https:\/\/pubeurope.com\/@uk\/114370169199973438","error":""},"_links":{"self":[{"href":"https:\/\/www.europesays.com\/uk\/wp-json\/wp\/v2\/posts\/35516","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.europesays.com\/uk\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.europesays.com\/uk\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.europesays.com\/uk\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/www.europesays.com\/uk\/wp-json\/wp\/v2\/comments?post=35516"}],"version-history":[{"count":0,"href":"https:\/\/www.europesays.com\/uk\/wp-json\/wp\/v2\/posts\/35516\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.europesays.com\/uk\/wp-json\/wp\/v2\/media\/35517"}],"wp:attachment":[{"href":"https:\/\/www.europesays.com\/uk\/wp-json\/wp\/v2\/media?parent=35516"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.europesays.com\/uk\/wp-json\/wp\/v2\/categories?post=35516"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.europesays.com\/uk\/wp-json\/wp\/v2\/tags?post=35516"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}