When conduction electrons in a solid are completely spin polarized, the single-spin transport results in great promise in spintronic (i.e., spin electronic) applications. Realizing high-efficiency spintronic devices based on 2D van der Waals (vdW) materials would tremendously impact nanoscale spintronics and the current information technologies. However, a minority of vdW materials are magnetic, among which antiferromagnets do not have net spin polarization whereas ferromagnets usually have limited imbalance between oppositely polarized electrons. Here, we show that antiferromagnetic vdW bilayers can be made half metallic, in which electrons of singular spin are metallic but those of the opposite spin are insulating, leading to 100% spin-polarized conduction electrons. Based on this finding, an interesting type of spin field effect transistor is proposed.
Engineering the electronic band structure of material systems enables the unprecedented exploration of new physical properties that are absent in natural or as-synthetic materials. Half metallicity, an intriguing physical property arising from the metallic nature of electrons with singular spin polarization and insulating for oppositely polarized electrons, holds a great potential for a 100% spin-polarized current for high-efficiency spintronics. Conventionally synthesized thin films hardly sustain half metallicity inherited from their 3D counterparts. A fundamental challenge, in systems of reduced dimensions, is the almost inevitable spin-mixed edge or surface states in proximity to the Fermi level. Here, we predict electric field-induced half metallicity in bilayer A-type antiferromagnetic van der Waals crystals (i.e., intralayer ferromagnetism and interlayer antiferromagnetism), by employing density functional theory calculations on vanadium diselenide. Electric fields lift energy levels of the constituent layers in opposite directions, leading to the gradual closure of the gap of singular spin-polarized states and the opening of the gap of the others. We show that a vertical electrical field is a generic and effective way to achieve half metallicity in A-type antiferromagnetic bilayers and realize the spin field effect transistor. The electric field-induced half metallicity represents an appealing route to realize 2D half metals and opens opportunities for nanoscale highly efficient antiferromagnetic spintronics for information processing and storage.