Electrically induced 2D half-metallic antiferromagnets and spin field effect transistors

Abstract

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.

Prospects and Opportunities of 2D van der Waals Magnetic Systems

“…chose the bilayer VSe 2 to demonstrate their idea. [ 173 ] The electronic structure by their density functional theory calculation indeed showed half metallic behavior. This opens another door for us to attain half metallicity in low dimensions.…”

“…In 2017, Gong et al [ 173 ] proposed a 2D antiferromagnetic half metal can be engineered by applying a vertical electric field across the plane of a bilayer A‐type antiferromagnet, provided that the A‐type antiferromagnet is an insulator(or semiconductor). The idea utilizes the electronic structure of A‐type AFM materials.…”

“…In the other layer, this order is reversed since the magnetic moments of two individual layers have to compensate each other(see Figure 1 in ref. [173]). Applying an out of plane electric field will shift bands of two constituent layers in opposite directions.…”

“…Applying an out of plane electric field will shift bands of two constituent layers in opposite directions. [ 173 ] This opposite shifts will cause one spin component to close bandgap, while the other spin component become more insulating. Gong et al.…”

“…[ 176 ] The concept is similar to the electrically induced half metallicity in bilayer A‐type magnet we discussed in the last section. [ 173 ] Besides cutting 2D materials to create boundaries, it has been shown experimentally that large‐area graphene samples will contain nanoboundaries. [ 177‐179 ] These inherent nanoboundaries can be considered as extended line defects in graphene.…”