Dynamics of ferroelectricity in monolayer AgCr2S4 calculated with a machine learning potential

Ferroelectric materials hold significant potential for high-density nonvolatile memory applications. Understanding the dynamic mechanism of ferroelectricity is crucial for maximizing the utilization of these materials. In this study, we investigate the ferroelectric properties of monolayer ${\mathrm{AgCr}}_{2}{\mathrm{S}}_{4}$ by combining density functional theory (DFT) calculations with molecular dynamics (MD) simulations that utilize machine learning potentials. Our investigation reveals that the off-center displacement of Ag ions primarily drives the ferroelectricity in monolayer ${\mathrm{AgCr}}_{2}{\mathrm{S}}_{4}$. Remarkably, the system exhibits a high ferroelectric-paraelectric phase transition temperature of 600 K. Under low temperatures, a distinctive domain structure emerges, characterized by domain walls that induce silver vacancy defects and interstitial atoms. Moreover, ferroelectric hysteresis loops indicate that the out-of-plane and in-plane polarizations of the ${\mathrm{AgCr}}_{2}{\mathrm{S}}_{4}$ monolayer are switchable by applying an external electric field. Thus, our findings suggest that monolayer ${\mathrm{AgCr}}_{2}{\mathrm{S}}_{4}$ retains ferroelectricity at room temperature, highlighting its promising potential for applications in ferroelectric devices.