Multiferroics in Two-Dimensional Silica with Li Encapsulation

Two-dimensional (2D) multiferroics have attracted tremendous interest recently, yet their experimental realizations are quite rare. Here, we demonstrate strongly coupled polarization and magnetism in Li-encapsulated 2D silica (Li@SiO2) through first-principles calculations. In Li@SiO2, the antiferroelectric (AFE) phase is energetically more favorable than the ferroelectric (FE) phase, and both AFE and FE phases hold a zigzag-like antiferromagnetic (AFM) configuration. It is revealed that magnetism originates from polarization, suggesting strong magnetoelectric coupling. Intriguingly, by tuning of the electric field and working temperature, multiple distinct phases could be achieved, including a metallic paraelectric state, a semiconducting FE state with frustrated spins, and semiconducting FE and AFE states with AFM ordering. Effects of graphene and SiC substrates on multiferroics are also discussed for practical experiments. Our work not only provides a promising avenue for realizing 2D multiferroics in silicon-based systems but also sheds light on the feasibility of nonvolatile nanodevices integrated with the mature semiconductor technology.