Even-odd layer-dependent multiferroic in freestanding rare-earth orthorhombic perovskite

Abstract

Freestanding oxide perovskites possess strong interlayer coupling between adjacent atomic layers, thus exerting a determinative effect on the magnetism and ferroelectricity of these atomic-scale materials. Here, we propose an effective strategy to manipulate magnetism and ferroelectricity in freestanding rare-earth orthorhombic perovskite via modulation of layer thickness. By performing first-principles calculations, an even-odd oscillation is demonstrated in few-layer GdAlO₃ perovskite (GAP). Specifically, odd-layer systems with charged atomic layers are ferromagnetic polar metals, while even-layer systems are antiferromagnetic ferroelectric semiconductors. This thickness-dependent magnetic phase transition originates from carrier doping, as rationalized by the Stoner criterion. Furthermore, we demonstrate the promotion of in-plane ferroelectricity via the concurrent application of two distinct antiferrodistortive displacements, each driven by formation and breaking of bonds. Analogous multiferroic phases may emerge in other transition metal oxide perovskites supporting multiple valence states, e.g., few-layer GdMO₃ (M = V, Cr, Mn, and Ni). This work puts forward a strategy for layer thickness engineering of magnetism and ferroelectricity in 2D oxide perovskite multiferroic materials.