Two-Dimensional Intrinsic Half-Metals With Large Spin Gaps

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 μ_B. Calculations of the magnetic anisotropy show an easy-plane for the magnetic moment. A classical XY model with nearest neighbor coupling estimates critical temperatures, T_c, 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.