Multiferroic materials, which simultaneously exhibit ferroelectric and magnetic orders, offer tremendous potential for next-generation electronic and spintronic devices. Here, we propose a novel design strategy toward a new type of multiferroics: the interlayer self-doping multiferroics. We show that, due to the different band filling preferences of antiferromagnetic and ferromagnetic orderings, homobilayer systems with intermediate band filling exhibit an intrinsic instability toward interlayer self-doping. This results in an antiferromagnetic order in one layer and ferromagnetic order in the other, accompanied by out-of-plane ferroelectricity. Distinct from conventional type-I and type-II multiferroics, the ferroelectric and magnetic orders in interlayer self-doping multiferroics are intrinsically coupled yet not relying on spin-orbit coupling, enabling potential persistence at elevated temperatures. Using first-principles calculations, we validate this mechanism in two concrete systems: bilayer ${\mathrm{CrTe}}_2$ and bilayer FeTe. Notably, the multiferroicity in bilayer ${\mathrm{CrTe}}_2$ is predicted to operate robustly at room temperature. Our Letter unveils a new type of multiferroics, and it opens a new route for designing 2D ultrathin multiferroics with high transition temperature and robust magnetoelectric response.

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• Electric polarization
• Ferroelectricity
• Magnetism
• 2-dimensional systems
• Multiferroics
• First-principles calculations