Ferroelectricity coexisted with p-orbital ferromagnetism and metallicity in two-dimensional metal oxynitrides

Abstract

Two-dimensional (2D) multiferroics have attracted increasing interests in basic science and technological fields in recent years. However, most reported 2D magnetic ferroelectrics are based on the d-electron magnetism, which makes them rather rare due to the empirical d⁰ rule and limits their applications for low magnetic phase transition temperature. In this work, we demonstrate that the ferroelectricity can coexist with the p-electron-induced ferromagnetism without the limitation of d⁰ rule and metallicity in a family of stable 2D MXene-analogous oxynitrides, X₂NO₂ (X = In, Tl). Remarkably, the itinerant character of p electrons can lead to the strong ferromagnetic metallic states. Furthermore, a possible magnetoelectric effect is manifested in a Tl₂NO₂/WTe₂ heterostructure through the interface engineering. Our findings provide an alternative possible route toward 2D multiferroics and enrich the concept of ferroelectric metals.