Halogen functionalization-induced modulation of ferromagnetism and electronic phases in CrXY monolayers

Abstract

Developing two-dimensional (2D) magnetic materials with tunable electronic and spintronic properties is essential for advancing next-generation quantum devices and low-power spintronic applications. Here, we systematically explore how halogen surface functionalization dramatically modulates the structural, electronic, and magnetic behaviors of Janus CrXY monolayers (X, Y = S, Se, and Te; X ≠ Y) using first-principles calculations. The functionalized CrXYT₂ (X, Y = S, Se, and Te; X ≠ Y; T = F, Cl, Br, and I) monolayers significantly enhance their magnetic performance and markedly increase the Curie temperatures (T_C) values compared to corresponding pristine CrXY monolayers. Most of the CrXY and CrXYT₂ monolayers possess strong perpendicular magnetic anisotropy, except for CrSSe, CrSTeCl₂, and CrSSeCl₂, which exhibit in-plane easy magnetization axes. While the pristine CrXY monolayers are half-metallic ferromagnets, functionalization induces magnetic phase transitions in several systems. Specifically, the CrSTeCl₂, CrSTeBr₂, CrSSeBr₂, and CrSSeI₂ monolayers transform into bipolar magnetic semiconductors, whereas the CrSeTeF₂ monolayer becomes a ferromagnetic metal. Additionally, spin-channel inversion is observed in CrSeTeI₂ and CrSTeI₂. The remaining CrXYT₂ monolayers retain their half-metallic ferromagnetic character, along with significantly enhanced T_C. The results show that surface functionalization is an effective strategy to regulate the CrXY monolayers. These findings broaden the application potential of two-dimensional Cr-based monolayers in spintronic devices and provide valuable theoretical guidance for future experimental synthesis.