Realization of Half-metallic Intrinsic Ferromagnetism with High Curie Temperatures by 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 (TC) of these Cr-based ferromagnets are lower than room temperature. The low oxidation states of transition metal atoms allow more d valence electrons, which can regulate the orbitals involved in hybridization, thus affecting the exchange coupling and raising the TC of 2D ferromagnets. In this study, a series of divalent cation-based monolayers, M₂YX₂ (M = Ti, V, Cr, Mn, Fe, Co, Ni; Y = S, Se, Te; X = Cl, Br, 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 TC well above room temperature, reaching 904 K and 578 K, respectively. In particular, the Cr2TeI2 monolayer demonstrates perpendicular magnetic anisotropy and non-vanishing anomalous Hall conductivity. The divalent Cr ions in Cr2TeBr2 and Cr2TeI2 monolayers fall into a high spin state, providing a large local magnetic moment. Furthermore, the highest occupied states (Cr-dxz/dyz) coupled with the p orbitals of Te atoms via a 180°d-p-d superexchange interaction well improve the magnetic critical temperature. 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 TC FM materials.