First-principles predictions of ferromagnetism in monolayers of the 2D materials Cr₂X₄Y (X = S, Se; Y = Ga, Ge, In, Sn)

Abstract Research on two-dimensional magnetic materials has gained significant attention in recent years owing to their unique thickness-dependent magnetism, tunable properties, and potential applications in spintronics, quantum computing, and next-generation data storage technologies. This study investigated the intrinsic ferromagnetic (FM) properties of Cr 2 X 4 Y (X = S, Se; Y = Ga, Ge, In, Sn) monolayers, with emphasis on their potential application in spintronic devices. Comprehensive stability analyses confirmed the feasibility of synthesizing these materials. Our results predict that all of these materials would exhibit robust ferromagnetism with magnetic moments of ∼4 µ B per Cr atom and high Curie temperatures ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msub> <mml:mi>T</mml:mi> <mml:mrow> <mml:mi mathvariant="normal">c</mml:mi> </mml:mrow> </mml:msub> </mml:mrow> </mml:math> ) ranging from 170 K to 691 K, with Cr 2 S 4 Ga achieving the highest <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msub> <mml:mi>T</mml:mi> <mml:mrow> <mml:mi mathvariant="normal">c</mml:mi> </mml:mrow> </mml:msub> </mml:mrow> </mml:math> . The FM behavior, attributed to superexchange interactions, remains stable under biaxial strain (−6% to 6%). Based on their electronic structures, half-metallicity is predicted for Cr 2 X 4 Y (Y = Ga, In), which enables 100% spin polarization, whereas Cr 2 X 4 Y (Y = Ge, Sn) are semiconductors with sizable band gaps. These findings indicate that the Cr 2 X 4 Y monolayers are promising candidates for room-temperature spintronic devices with tunable magnetic properties.