Intrinsic spin-dynamical properties of two-dimensional half-metallic FeX2 ( X = Cl, Br, I) ferromagnets: Insight from density functional theory calculations

Ultrathin two-dimensional (2D) ferromagnets with intrinsic half-metallicity are highly prospective in designing nanoscale spintronics devices. In this work, we systematically investigate the spin transport and dynamical properties of one such group of promising 2D ferromagnets---monolayer iron dihalides (${\mathrm{FeX}}_{2}$, X = Cl, Br, I)---using density functional theory (DFT). First, we explore the spin transport properties of these ${\mathrm{FeX}}_{2}$ monolayers by combining the nonequilibrium Green's function (NEGF) technique with DFT. This study shows an inherent half-metallicity with a large spin gap that offers $100%$ spin-polarization over a wide Fermi window (>1 eV). We then focus on understanding their magnetocrystalline anisotropy, Gilbert damping, and exchange interactions, in-depth, which are the key aspects in controlling the spin dynamics. We use force theorem to determine the magnetocrystalline anisotropy and Kambersky's torque-torque correlation model for Gilbert damping. Our calculations reveal a sizable perpendicular anisotropy (0.04 to 0.25 mJ/${\mathrm{m}}^{2}$) along with a relatively low Gilbert damping ($7.9\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5}$ to $3.7\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}$) in these materials. Using spin-polarized Green's function formalism, we finally explore the effective exchange interactions in these materials and determine their spin-wave stiffness, exchange stiffness constants, and Curie temperatures. All these calculations, collectively, provide significance of these 2D ${\mathrm{FeX}}_{2}$ ferromagnets for next-generation spintronics applications.