Ferroelectrically switchable magnetic multistates in MnBi2Te4(Bi2Te3)n and

Ferroelectric control of two-dimensional magnetism is promising in fabricating electronic devices with high speed and low-energy consumption. The newly discovered layered ${\mathrm{MnBi}}_{2}{\mathrm{Te}}_{4}{({\mathrm{Bi}}_{2}{\mathrm{Te}}_{3})}_{n}$ and their Sb counterparts exhibit $A$-type antiferromagnetism with intriguing topological properties. Here we propose to obtain tunable magnetic multistates in their thin films by ferroelectrically manipulating the interlayer magnetic couplings based on the Heisenberg model and first-principles calculations. Our strategy relies on the fact that interfacing the thin films with appropriate ferroelectric materials can switch on/off an interlayer hopping channel between Mn-${e}_{g}$ orbitals as the polarizations reversed, thus resulting in a switchable interlayer antiferromagnetism-to-ferromagnetism transition. On the other hand, the interface effect leads to asymmetric energy barrier heights for the two polarization states. These properties allow us to build ferroelectrically switchable triple and quadruple magnetic states with multiple Chern numbers in thin films. Our study reveals that ferroelectrically switchable magnetic and topological multistates in the ${\mathrm{MnBi}}_{2}{\mathrm{Te}}_{4}$ family can be obtained by rational design for multifunctional electronic devices, which can also be applied to other two-dimensional magnetic materials.