The electronic and magnetic properties of two-dimensional $\mathrm{Ni}{\mathrm{Br}}_2$ bilayer are systematically investigated using first-principles calculations. We find that the metastable antialigned stacking $\mathrm{Ni}{\mathrm{Br}}_2$ bilayer exhibits sliding ferroelectricity, where reversible out-of-plane polarization is enabled by interlayer sliding. In contrast, the ground-state aligned AB-stacked bilayer is an $A$-type antiferromagnetic (AFM) semiconductor. Upon applying a vertical electric field, this AFM semiconductor can be converted into a half-metal with 100% spin polarization. This transition is driven by the field-induced potential gradient, which triggers opposite energy shifts in the spin-resolved bands of the two layers. Furthermore, the conducting spin channel can be effectively switched by reversing the electric field direction. To achieve nonvolatile control, we propose a van der Waals heterostructure by integrating the $\mathrm{Ni}{\mathrm{Br}}_2$ bilayer with a ferroelectric ${\mathrm{Ga}}_2{\mathrm{S}}_3$ bilayer. Our results demonstrate that half-metallicity with 100% spin-down polarization is realized when the ${\mathrm{Ga}}_2{\mathrm{S}}_3$ polarization is upward ($\mathrm{P}\uparrow$), while the system reverts to a semiconducting state upon polarization reversal ($\mathrm{P}\downarrow$). Based on this polarization-dependent phase transition, a nonvolatile ferroelectric memory device is proposed, offering a promising platform for next-generation AFM spintronics.

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• Electric polarization
• Electronic structure
• Spintronics
• Heterostructures
• Density functional theory
• First-principles calculations