Geometric frustration and strain-engineered magnetic phase transitions in the pentagonal FeS 2 monolayer

Two-dimensional pentagonal materials have recently emerged as a promising platform for exploring novel magnetic phenomena. Using first-principles calculations, we systematically investigate the strain-tunable optical and magnetic properties of $\mathrm{penta}\text{\ensuremath{-}}{\mathrm{FeS}}_{2}$ monolayer. Our results reveal that the system stabilizes into a distinct stripy-AFM ground state under ambient conditions. This ordering is driven by strong magnetic frustration originating from the dominant third-nearest-neighbor antiferromagnetic exchange interaction $(|{J}_{3}|\ensuremath{\gg}|{J}_{1}|)$. Furthermore, biaxial strain serves as a robust knob to tune these properties. Tensile strain induces a semiconductor-metal transition, where the emergence of itinerant electrons creates a screening effect that weakens the long-range exchange interaction, triggering a phase transition from stripy-AFM to N\'eel-AFM. In contrast, compressive strain preserves the semiconducting gap while enhancing the interorbital hybridization. Additionally, tensile strain promotes a spin reorientation transition from in-plane to out-of-plane. Our work demonstrates the microscopic interplay among lattice geometry, electronic screening, and magnetism in $\mathrm{penta}\text{\ensuremath{-}}{\mathrm{FeS}}_{2}$, positioning it as a versatile candidate for magneto-optoelectronic applications.