Intrinsic ferrovalley non-Janus FeXI X I (X X = Cl, Br) with large valley polarization and nonvolatile reversible control of the anomalous valley Hall effect in multiferroic heterojunctions

Ferrovalley (FV) materials are promising for practical applications in valley electronics due to their spontaneous valley polarization, and the control of the anomalous valley Hall effect (AVHE) by external means is crucial for the development of valley electronic devices. This work presents a novel two-dimensional FV non-Janus FeXI (X = Cl, Br). Compared to the half-metallicity of Janus FeXI, non-Janus FeXI exhibits intrinsic FV semiconducting properties with a large valley splitting of 134 meV for FeClI and 129 meV for FeBrI due to the strong spin-orbit coupling. The AVHE can be realized by selective excitation of carriers at the valleys. However, most of the reported methods for controlling AVHE are either volatile or irreversible. To achieve nonvolatile reversible AVHE, we propose two models of multiferroic van der Waals heterojunctions (vdWHs) by introducing a ferroelectric (FE) substrate: FV/FE and FV/FE/FV. Based on the principle of band alignment, In2S3 and In2Se3 are selected as the FE substrates for FeClI and FeBrI, respectively. By modulating the direction of FE polarization, reversible switching of AVHE is achieved in FV/FE vdWHs, and layer-dependent Hall voltage is further obtained in FV/FE/FV vdWHs. Our findings validate the feasibility and effectiveness of FE modulation of AVHE and provide new insights into the design of valley electronics.