Inducing Spin Splitting and Anomalous Valley Hall Effect in A-Type AFM Fe$_2$C(OH)$_2$ through Electric Field and Janus Engineering

Abstract: The antiferromagnetic (AFM) materials are distinguished by zero net magnetic moment, high resistance to external magnetic disturbances, and ultrafast dynamic responses. For advancing AFM materials in spintronic and valleytronic applications, achieving spontaneous valley polarization and the anomalous valley Hall effect (AVHE) is pivotal. We predict an A-type AFM monolayer Fe$_2$C(OH)$_2$, which shows a significant spontaneous valley polarization of 157 meV. In Fe$_2$C(OH)$_2$, spatial inversion symmetry (P) and time-reversal symmetry (T) are individually broken, yet the combined PT symmetry is preserved. This symmetry conservation leads to spin degeneracy, resulting in zero Berry curvature in the momentum space and absence of AVHE. However, a layer-locked hidden Berry curvature is produced, leading to the observation of the valley layer-spin Hall effect. Further, an external out-of-plane electric field can induce spin splitting by introducing layer-dependent electrostatic potential, enabling the layer-locked AVHE. Additionally, the introduction of a built-in electric field caused by the Janus structure also induces spin splitting in monolayer Fe$_2$C(OH)F due to the electric-potential-difference-AFM mechanism. The high out-of-plane magnetic anisotropy and realization of AVHE, offer promising opportunities for next-generation spintronic technologies.