Two-Dimensional Multiferroics with Intrinsic Magnetoelectric Coupling in A -Site Ordered Perovskite Monolayers.

The magnetoelectric coupling effect in multiferroics provides a route to realize the control of magnetism by electric field. Here, we demonstrate the coexistence and coupling of ferroelectricity and ferromagnetism in designed -site ordered perovskite oxide monolayers by combining symmetry analysis and first-principles calculation. These monolayers all exhibit a layered ordering and tilt distortion, and some of them exhibit rotation or Jahn-Teller distortion simultaneously, leading to the emergence of in-plane ferroelectricity. The Mn-based monolayers exhibit robust ferromagnetism, while some monolayers tend to form -type spin order due to the splitting of the nearest-neighbor exchange interactions. Whether polarization reversal can lead to magnetization reversal depends on the mode of ferroelectric switching, that is, only the ferroelectric switching that reversing the tilt distortion can lead to magnetization reversal. This work demonstrates the feasibility of controlling the direction of magnetization by electric field in the monolayer limit of perovskites.