Electric‐Field‐ and Stacking‐Tuned Antiferromagnetic FeClF Bilayer: The Coexistence of Bipolar Magnetic Semiconductor and Anomalous Valley Hall Effect

Abstract Valley polarization from broken inversion symmetry provides a new degree of freedom for carriers, bipolar magnetic semiconductor (BMS) generates a purely spin‐polarized current under a gate voltage, but few systems possess the coexistence of valley polarization and BMS. Based on the recent experimental FeCl₂ flakes, reversible electric‐field effect on the valley‐ and spin‐polarized Janus FeClF bilayer with different stackings are investigated herein. Janus FeClF bilayers in all three stacks possess interlayer antiferromagnetic (AFM) and intralayer ferromagnetic (FM) couplings. The most stable A (Cl‐Fe‐F‐Cl‐Fe‐F) stack possesses concurrent and spontaneous BMS nature and valley polarization with perpendicular magnetic anisotropy (PMA), while B (Cl‐Fe‐F‐F‐Fe‐Cl) and C (F‐Fe‐Cl‐Cl‐Fe‐F) stacks exhibit AFM semiconductor characters without valley polarization. Electric‐field achieves a transition of BMS and AFM semiconductor. Large ferrovalley (≈108 meV) exists and is mainly contributed by Fe‐d_xy and orbitals. With the out‐of‐plane to in‐plane to out‐of‐plane transition of the easy axis, anomalous valley Hall effect (AVHE) can be manipulated to presence and disappearance by perpendicular electric‐field, indicating the valley switch effect (VSE). The coexisting BMS feature, PMA, AVHE and VSE make Janus FeClF bilayer a promising candidate for multifunctional valleytronic and spintronic applications, favoring broad explorations for the low‐dimensional Janus family.