Interlayer-Sliding-Enabled Multiferroicity and Giant Switchable Anomalous Hall Conductivity in RuO₂Zn₂F₂ Bilayer

Recently, a septuple-atomic-layer RuO₂Zn₂F₂ semiconducting monolayer, which belongs to the novel 2D materials MA₂Z₄ family, has emerged as a suitable above-room-temperature ferromagnet. Based upon these findings, first-principles calculations are performed to study the RuO₂Zn₂F₂ bilayer. A competitive interplay between ferromagnetic (FM) and A-type antiferromagnetic (AFM) ground states is found, indicating strong tunability of the magnetic phase. Moreover, the electronic band structures are sensitive to their magnetic order and stacking configuration. Particularly, the aligned-stacking configuration induces an out-of-plane electric polarization of 1.35 pC/m, which can be efficiently switched via interlayer sliding with an ultra-low energy barrier of 19.3 meV/unit cell, realizing sliding ferroelectricity. Furthermore, the sign of valley polarization reverses with the switching of the electric polarization in the AFM configuration. Besides, a pronounced switchable anomalous Hall conductivity exceeding ±250 S/cm is obtained in the AFM state, while a giant anomalous Hall conductivity of -527 S/cm is achieved in the FM state. Meanwhile, RuO₂Zn₂F₂ bilayer exhibits colossal in-plane (d₁₁ = 8.13 pm/V) and significant out-of-plane (d₃₁ = 0.61 pm/V) piezoelectric response. Consequently, the results establish RuO₂Zn₂F₂ bilayer as a promising platform for slidetronic, valleytronic, and spintronic applications.