Emergent Altermagnetic Multiferroicity via Ferroelectrically Driven Magnetic Phase Transition

Altermagnetic multiferroicity is rapidly emerging as a transformative paradigm for both condensed matter physics and advanced spintronics. However, existing magnetoelectric mechanisms are inherently restricted to structural inversions, which merely reverse the momentum‐space spin splitting. Here, guided by symmetry principles and microscopic modeling, we unveil an emergent class of altermagnetic multiferroicity in 2D heterobilayers. This mechanism utilizes out‐of‐plane ferroelectric polarization to govern the interlayer coupling, thereby tuning the competition between localized antiferromagnetic superexchange and itinerant ferromagnetic double‐exchange. Crucially, this interfacial modulation triggers a reversible magnetic phase transition between a trivial ferromagnetic state and an altermagnetic state, establishing a distinct magnetoelectric coupling mechanism. Using first‐principles calculations, we demonstrate this mechanism in MnPS 3 /Sc 2 CO 2 heterostructure, where we further predict the emergence of two distinct altermagnetic phases. Our findings transcend geometric restrictions, establishing a physical framework for nonvolatile and programmable altermagnetic spintronics.