Strain-induced Valley Polarization and Quantum Anomalous Valley Hall Effect in Single Septuple Layer FeO2Si2N2

Two-dimensional (2D) valleytronics materials have garnered significant attention due to great potential for information encoding and processing. Here, we investigate the strain effect on the valley and topological properties of a novel septuple-layer FeO2Si2N2 monolayer by employing the first-principles calculations. The monolayer is affirmed to be a stable ferrovalley semiconductor with in-plane magnetization and high Curie transition temperature (156 K). Further, by applying the compressive strain from −3.24 to −3.4%, the magnetization of the monolayer can be tuned from in-plane to out-of-plane direction, and consequently, the monolayer exhibits topological nontrivial valley state with valley polarization due to the breaking of inversion and time-reversal symmetry, and higher Curie temperature (213 K) due to the enhanced superexchange interaction between Fe and O atoms. Thus, the long-sought valley-polarized quantum anomalous Hall (VQAH) effect can be realized in higher Curie temperature in FeO2Si2N2 monolayer by applying the appropriate compressive strain.