Structural, magnetic and ferroelectric properties of VOBr₂monolayer: A first-principles study

Abstract

On the basis of first-principles calculations, the structure, magnetism and ferroelectricity of VOBr₂ monolayer are studied systematically in the present work. The calculation results indicate that a spontaneous ferroelectric distortion takes place at low temperature, causing the structure of VOBr₂ to transform from a centrosymmetric paraelectric phase to a ferroelectric one. In contrast with its sister compound VOI₂, the dimerization of V is unstable in VOBr₂ and may quench the local magnetic moment on V ions. Additionally, the easy magnetization axis of VOBr₂ monolayer is in-plane along the <i>a</i>-axis, and the magnetic coupling between adjacent local moments is antiferromagnetic both along the <i>a</i>-axis and along the <i>b</i>-axis. Moreover, the ferroelectric displacement of V ions occurs in the <i>a</i>-axis, along the V—O—V chains direction, resulting in a polarization of about 40 μC/cm². Comparing with the ferro-to-paraelectric reversal pathway, the energy barrier can be effectively reduced for ferroelectric switching on partial or individual V—O—V chains. It is reasonable to believe that the dipole moment flipping on specific chain can be achieved through a moderate external field, thereby providing new direction for designing the low-energy-consumption and high-density ferroelectric memory device.