The effect of anisotropic field on magnon dispersion of antiferromagnetic metal fluoride materials

Abstract

This article investigates the dynamics of spin waves in two sublattice antiferromagnetic (AFM) system spins’ interaction and magnon dispersion relation. The analysis is done starting with a standard model that includes a uniaxial magnetic anisotropy field. Quantum field theory is employed in formulating the problem, and double-time temperature-dependent Green function technique is used to obtain magnon dispersion, whereby random phase approximation is considered to decouple and diagonalize the higher order terms. At low temperatures and long wavelength approximation, dispersion of uniaxial symmetric AFM crystal lattice of metallic fluoride materials, such as MnF2, FeF2, and RbMnF3, is analyzed for illustration. Our findings indicate that as the anisotropic field increases, the magnon dispersion vs wave vector k gradually varies, attempts linearity from being curved, and attains a sinusoidal structure when extended further in the first Brillouin zone. Perhaps, these results are useful to understand the feature of magnon dispersion of stable similar AFM materials for practical application.