Micromagnetic study of the dipolar-exchange spin waves in antiferromagnetic thin films

In antiferromagnets, dipolar coupling is often disregarded due to the cancellation of magnetic moments between the two sublattices, so that the spin-wave dispersion is predominantly determined by exchange interactions. However, antiferromagnetic spin waves typically involve a slight misalignment of the magnetic moments on the sublattices, which gives rise to a small net magnetization enabling long-range dipolar coupling. In this paper, we investigate the role of dipolar coupling in spin-wave excitations and its influence on the resulting dispersion. Our findings show that: (i) when the Néel vector is perpendicular to the film plane or lies within the film plane and parallel to the wave vector, the dispersion branches can be divided into two groups: those unaffected by the dipolar field and those influenced by it. In these cases, the total magnetic moment remains linearly polarized, but the polarization directions differ between the two types of branches; (ii) when the Néel vector lies in the film plane and is perpendicular to the wave vector, the dipolar interactions affect both types of dispersion branches, leading to their hybridization. This hybridization alters the polarization of the magnetic moment, resulting in elliptical polarization.