Anomalous thickness dependence of Curie temperature in air-stable two-dimensional ferromagnetic 1T-CrTe2 grown by chemical vapor deposition

Abstract

The discovery of ferromagnetic two-dimensional van der Waals materials has opened up opportunities to explore intriguing physics and to develop innovative spintronic devices. However, controllable synthesis of these 2D ferromagnets and enhancing their stability under ambient conditions remain challenging. Here, we report chemical vapor deposition growth of air-stable 2D metallic 1T-CrTe2 ultrathin crystals with controlled thickness. Their long-range ferromagnetic ordering is confirmed by a robust anomalous Hall effect, which has seldom been observed in other layered 2D materials grown by chemical vapor deposition. With reducing the thickness of 1T-CrTe2 from tens of nanometers to several nanometers, the easy axis changes from in-plane to out-of-plane. Monotonic increase of Curie temperature with the thickness decreasing from ~130.0 to ~7.6 nm is observed. Theoretical calculations indicate that the weakening of the Coulomb screening in the two-dimensional limit plays a crucial role in the change of magnetic properties.

Two‐dimensional magnetic transition metal chalcogenides

“…Significant progress has also been made in the synthesis of 2D layered chromium dichacolgenides (CrX 2 ) by CVD, for example, magnetic CrSe 2 64 and CrTe 2 , 65 which demonstrate outstanding air stability. Duan's group reported the synthesis of 2D CrSe 2 nanosheets with tunable thickness down to the ML limit on dangling‐bond‐free 2D WSe 2 64 .…”

“…A Curie temperature T c of 65 K is estimated for the ML CrSe 2 , which gradually increases to 110 K at the thickness of 16 or more layers. In the other study, Meng et al grew 1T‐CrTe 2 on SiO 2 /Si surface with thicknesses ranging from a few to tens of nanometers 65 . They observed that the magnetic easy axis in the 2D CrTe 2 crystals changes from in‐plane to out‐of‐plane with the decreasing thickness at a critical thickness of ~10 nm.…”

Salt-assisted chemical vapor deposition of two-dimensional transition metal dichalcogenides

“…On the other hand, the SA-CVD, which uses alkali-metal-free metal halides/oxyhalides (e.g., MoCl 5 , CrCl 3 , FeCl 2 , MoOCl 4 , WO 2 Cl 2 , etc. ), has proven promising to eliminate the detrimental effects of alkali metals ( Chu et al., 2019 ; Hu et al., 2021 ; Meng et al., 2021 ; Okada et al., 2014 ; Wang et al., 2021 ; Zhang et al., 2019 ). Replacing the metal organic precursors with the TM halides/oxyhalides in the MOCVD system could be a good alternative to realize high quality growth of 2D TMDC monolayers.…”

Multiwavelength magnetic coding of helical luminescence in ferromagnetic 2D layered CrI3

“…FM Cr 2 Ge 2 Te 6 few-layer have demonstrated a p-type semiconducting behavior and gate-controllable magnetism ( Jiang et al., 2018a ; Verzhbitskiy et al., 2020 ); few-layer Fe 3 GeTe 2 FM metal have shown high Curie temperature ( Tc ) above room temperature through ionic/protonic gating, patterning, and interfacial exchange coupling ( Deng et al., 2018 ; Li et al., 2018 ; May et al., 2019 ; Wang et al., 2020a ); magnetic topological insulator MnBi 2 Te 4 has recently been reported to present layer-dependent magnetic phase and spin-flop behaviors ( Deng et al., 2020 ; Yang et al., 2021 ). Alternatively, air-stable metallic 2D vdW CrTe 2 and CrSe 2 with thickness-dependent magnetic orders have been directly synthesized by chemical vapor deposition (CVD) methods ( Li et al., 2021 ; Meng et al., 2021 ). However, thus far, few 2D vdW magnets have been revealed luminescence and exciton behaviors, and none examining magnetic coding of photoluminescence (PL), despite the discovery of luminescence in FM CrI 3 and AFM NiPS 3 ( Hwangbo et al., 2021 ; Kang et al., 2020 ; Seyler et al., 2017 ; Wang et al., 2021 ).…”