Engineering charge ordering into multiferroicity

Multiferroic materials have attracted great interest but are rare in nature. In many transition-metal oxides, charge ordering and magnetic ordering coexist, so that a method of engineering charge-ordered materials into ferroelectric materials would lead to a large class of multiferroic materials. We propose a strategy for designing new ferroelectric or even multiferroic materials by inserting a spacing layer into each two layers of charge-ordered materials and artificially making a superlattice. One example of the model demonstrated here is the perovskite ${({\mathrm{LaFeO}}₃)}₂/{\mathrm{LaTiO}}₃$ (111) superlattice, in which the ${\mathrm{LaTiO}}₃$ layer acts as the donor and the spacing layer, and the ${\mathrm{LaFeO}}₃$ layer is half doped and performs charge ordering. The collaboration of the charge ordering and the spacing layer breaks the space inversion symmetry, resulting in a large ferroelectric polarization. As the charge ordering also leads to a ferrimagnetic structure, ${({\mathrm{LaFeO}}₃)}₂/{\mathrm{LaTiO}}₃$ is multiferroic. It is expected that this work can encourage the designing and experimental implementation of a large class of multiferroic structures with novel properties.