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 ($7.9\times {10}^{-5}$ to $3.7\times {10}^{-4}$) 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.

• Received 26 August 2020
• Revised 8 December 2020
• Accepted 27 January 2021

DOI:https://doi.org/10.1103/PhysRevB.103.054409