Two-Dimensional Intrinsic Half-Metals With Large Spin Gaps

TLDR

FeCl₂, FeBr₂, and FeI₂ are stable layered 2D materials whose Fe²⁺ ions are high‑spin d⁶, giving a 4 μB magnetic moment. Using hybrid‑functional density‑functional calculations, we systematically screened layered bulk compounds and predicted three magnetic 2D materials with half‑metallic band structures. The predicted FeCl₂, FeBr₂, and FeI₂ exhibit easy‑plane anisotropy with Berezinskii‑Kosterlitz‑Thouless transition temperatures between 122 K and 210 K, unusually large spin gaps from 4.0 eV to 6.4 eV, and purely spin‑polarized currents with dispersive interlayer interactions, making them promising for 2D spin‑valve applications.

Abstract

Through a systematic search of all layered bulk compounds combined with density functional calculations employing hybrid exchange-correlation functionals, we predict a family of three magnetic two-dimensional (2D) materials with half-metallic band structures. The 2D materials, FeCl2, FeBr2, and FeI2, are all sufficiently stable to be exfoliated from bulk layered compounds. The Fe2+ ions in these materials are in a high-spin octahedral d6 configuration leading to a large magnetic moment of 4 μB. Calculations of the magnetic anisotropy show an easy-plane for the magnetic moment. A classical XY model with nearest neighbor coupling estimates critical temperatures, Tc, for the Berezinskii-Kosterlitz-Thouless transition ranging from 122 K for FeI2 to 210 K for FeBr2. The quantum confinement of these 2D materials results in unusually large spin gaps, ranging from 4.0 eV for FeI2 to 6.4 eV for FeCl2, which should defend against spin current leakage even at small device length scales. Their purely spin-polarized currents and dispersive interlayer interactions should make these materials useful for 2D spin valves and other spintronic applications.