Ferroelectricity driven interlayer magnetic phase transitions in van der Waals homobilayers.

Exploring magnetoelectric coupling in bilayers represents a particularly intriguing topic in multiferroic physics, with current efforts predominantly focused on heterobilayer architectures. Herein, we present an unconventional approach to achieve electrically controlled interlayer magnetic phase switching in homobilayer systems. Our mechanism mediates reversible ferroelectrically driven transitions between antiferromagnetic (AFM) and ferromagnetic (FM) orders via polarization-dependent band engineering. The underlying mechanism stems from symmetry-broken interlayer charge transfer: antiparallel ferroelectric polarization enforces a parallel band configuration that stabilizes AFM interlayer coupling through local superexchange interactions, while parallel polarization creates type-III band alignment that satisfies the Stoner criterion and thus promotes FM interlayer ordering. Using first-principles, we demonstrate this paradigm in a Tl₂NO₂ homobilayer. Notably, the AFM phase hosts coexisting layer-polarized valley and spin Hall currents, whereas these novel features become mutually exclusive in the FM phase, enabling nonvolatile ferroelectric switching of both valley and spin degrees of freedom. This work establishes a fundamental design principle for creating electrically addressable two-dimensional multiferroics.