Magnon dispersion in bilayers of two-dimensional ferromagnets

TL;DR

This paper analyzes magnon spectra in bilayer 2D ferromagnets with various interlayer couplings, revealing how exchange interactions influence magnon gaps and magnetic ordering stability.

Contribution

It provides analytic expressions for magnon bands in bilayer ferromagnets with different interlayer couplings, highlighting the interplay between exchange interactions and magnetic order.

Findings

Both exchange interactions determine the magnon gap.

Intralayer ferromagnetism stabilizes interlayer antiferromagnetic order.

The exchange-anisotropy models studied have trivial topology.

Abstract

We determine magnon spectra of an atomic bilayer magnet with ferromagnetic intra- and both ferro- and anti- ferromagnetic interlayer coupling. Analytic expressions for the full magnon band of the latter case reveal that both exchange interactions govern the fundamental magnon gap. The inter and intralayer magnetic ordering are not independent: the intralayer ferromagnetism stabilizes antiferromagnetic inter-layer order. The topology of these exchange-anisotropy spin models without spin-orbit interaction turns out to be trivial.