Analytical solutions for the magnon frequencies at high-symmetry points of the Brillouin zone in anisotropic kagome antiferromagnets

Abstract

The knowledge of the magnon dispersion relations in antiferromagnetic materials with nontrivial spin textures has considerable interest to the understanding of magnonic and spintronic phenomena involving these materials. One particularly interesting nontrivial spin texture existing in several antiferromagnets has spins at an angle of 120 • with the in-plane neighbors and arranged in kagome lattices. Here we present a spin-wave calculation for antiferromagnets with kagome spin lattices considering exchange and single-ion anisotropy interactions between the spins. The theory yields exact analytical expressions for the frequencies of magnons at high-symmetry points of the Brillouin zone, that can be readily use to obtain the interaction parameters from experimental data with one-and two-magnon inelastic light scattering. The analytical expressions are used to obtain the field parameters for the kagome lattice antiferromagnet L1 2 -IrMn 3 from four experimentally measured frequencies. Both exchange field parameters are in reasonable agreement with the values obtained with ab initio calculations, while the anisotropy field is in very good agreement with the one calculated with atomistic spin models and Monte Carlo simulations.