Possible transformation between half-metallic and metallic states of multiferroic MnGaSSe₂ monolayers

Multiferroic (MF) materials, exhibiting magnetic-electronic coupling properties, hold transformative potential for application in low-power spintronic devices. In this work, we investigate the structural, electronic and magnetic properties of a multiferroic MnGaSSe₂ monolayer using first-principles calculations. Our results show that the <i>O</i>-phase MnGaSSe₂ (<i>O</i>-MnGaSSe₂) monolayer exhibits a ferromagnetic (FM) semimetallic character with long-range magnetic order, while the <i>T</i>-phase MnGaSSe₂ (<i>T</i>-MnGaSSe₂) monolayer adopts an FM metallic ground state. The super-exchange interactions mediated by the Se-Mn-S atomic chains give rise to strong intralayer FM coupling, resulting in Curie temperatures (<i>T</i>_Cs) of 159 K and 75 K for <i>O</i>-MnGaSSe₂ and <i>T</i>-MnGaSSe₂, respectively. Moreover, the FM half-metallic (HM) properties of <i>O</i>-MnGaSSe₂ are robust under biaxial strain engineering, while <i>T</i>-MnGaSSe₂ undergoes a reversible phase transition from a FM metal to an antiferromagnetic (AFM) metal under 4% compressive strain. These findings establish a design strategy for intrinsic MF materials with coupled FM and ferroelectric (FE) properties.