Realization of half-metallic intrinsic ferromagnetism with high Curie temperatures by the low oxidation state of chromium in Cr2TeX2 (X = Br, I) monolayers

Abstract

Cr-based compounds have gained significant attention in the search for ideal two-dimensional (2D) ferromagnetic (FM) materials. However, most Cr-based 2D ferromagnets, such as Cr₂Ge₂Te₆ and CrI₃, are based on Cr ions with high oxidation states, and the Curie temperatures (T_C) of these Cr-based ferromagnets are lower than room temperature. The low oxidation states of transition metal atoms allow more d valence electrons, which may regulate the orbitals involved in hybridization, thus affecting the exchange coupling and modulating the T_C of 2D ferromagnets. In this study, a series of divalent cation-based monolayers, M₂YX₂ (M = Ti, V, Cr, Mn, Fe, Co, and Ni; Y = S, Se, and Te; X = Cl, Br, and I), with an X–M–Y–M–X atomic layer stacking pattern were investigated. Notably, the monolayers of Cr₂TeBr₂ and Cr₂TeI₂ exhibit intrinsic FM half-metallicity with T_C well above room temperature, reaching 904 K and 578 K, respectively. In particular, the divalent Cr ions in Cr₂TeBr₂ and Cr₂TeI₂ monolayers fall into a high spin state, providing a large local magnetic moment. And the highest occupied states (Cr-d_xz/d_yz) coupled with the p orbitals of Te atoms via a 180° d–p–d superexchange interaction well improve the magnetic critical temperature. Furthermore, the Cr₂TeI₂ monolayer demonstrates perpendicular magnetic anisotropy and non-vanishing anomalous Hall conductivity. Our work not only presents two promising FM half-metals with excellent potential for spintronic applications, but also offers a viable pathway for the design of high T_C FM materials.