Electric-Field-Induced Two-Dimensional Fully Compensated Ferrimagnetism and Emergent Transport Phenomena

The recent discovery of altermagnetism has demonstrated that spin-split electronic band structures can emerge in magnetic systems with zero net magnetization. In contrast, fully compensated ferrimagnetic (fFIM) systems remain far less explored, despite exhibiting similar characteristics such as vanishing magnetization and spin-split bands. Here, based on first-principles calculations combined with theoretical analysis, we demonstrate that monolayer CoS and CoSe can be driven into fFIM states by an external electric field. These materials possess collinear antiferromagnetic ground states with out-of-plane Néel vectors, and their electronic bands are spin degenerate due to $\mathrm{PT}$ symmetry. When an out-of-plane electric field is applied, $\mathrm{PT}$ symmetry is broken, inducing fFIM states with pronounced spin splitting. Moreover, we show that the resulting fFIM states host fully spin-polarized currents, anomalous Hall effects, and magneto-optical Kerr and Faraday effects. Our results establish monolayer CoS and CoSe as promising platforms for electric-field-controlled fFIM states and spintronic applications.