Micromagnetic Study of the Dipolar-Exchange Spin Waves in Antiferromagnetic Thin Films

TL;DR

This study explores how dipolar interactions influence spin-wave dispersion in antiferromagnetic thin films, revealing conditions under which these interactions cause branch splitting and polarization changes.

Contribution

It provides a detailed analysis of dipolar effects on antiferromagnetic spin waves, highlighting their role in dispersion and polarization, which was previously overlooked due to the dominance of exchange interactions.

Findings

Dipolar coupling affects certain spin-wave branches depending on the Néel vector orientation.

Hybridization of dispersion branches occurs when the Néel vector is perpendicular to the wave vector.

Dipolar interactions induce elliptical polarization in specific configurations.

Abstract

In antiferromagnets, dipolar coupling is often disregarded due to the cancellation of magnetic moments between the two sublattices, leaving spin-wave dispersion predominantly determined by exchange interactions. However, antiferromagnetic spin waves typically involve a slight misalignment of the magnetic moments on the sublattices, giving rise to a small net magnetization that enables long-range dipolar coupling. In this paper, we investigate the role of this dipolar coupling in spin-wave excitations and its influence on the spin-wave dispersion. Our findings show that: (i) when the N\'{e}el 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 N\'{e}el 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.