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

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.

Electric manipulation of magnetism in bilayer van der Waals magnets.

The ferromagnetism of the two dimensional (2D) Cr2Ge2Te6 atomic layers with the perpendicular magnetic anisotropy and the Curie temperature 30-50 K has recently been experimentally confirmed. By performing the density-functional theory calculations, we demonstrate that the magnetic properties of bilayer Cr2Ge2Te6 can be flexibly tailored, due to the effective band structure tuning by the external electric field. The electric field induces the semiconductor-metal transition and redistributes charge and spin between the two layers. Furthermore, the magnetic anisotropy energy of the bilayer Cr2Ge2Te6 can be obviously enhanced by the electric field, which is helpful to stabilize the long-range ferromagnetic order. Our study about the electric manipulation of magnetism based on the band structure engineering generally exists in 2D magnetic systems and will be of great significance in low-dimensional all-electric spintronics.

First-principles investigation of the interface magnetic anisotropy of Fe/SrTiO3.

Interface effects in magnetic nanostructures play a critical role in the magnetic properties. By using first-principles density functional theory calculations, we investigate the electronic and magnetic properties of Fe/SrTiO3 interfaces, in which both the nonpolar surface SrTiO3(0 0 1) and the polar surface SrTiO3(1 1 0) are considered. A particular emphasis is placed on the magnetic anisotropy energy (MAE). Comparing MAE of the Fe/SrTiO3 interfaces and the corresponding Fe monolayers, we find the Fe/SrTiO3(0 0 1) interface decreases MAE, while the Fe/SrTiO3(1 1 0) interface increases MAE. The interface orbital hybridization and orbital magnetic moments are analyzed in detail to understand the different interface magnetic anisotropy. Our investigation indicates that interface engineering can be an effective way to modulate the magnetic properties.