Chiral spin-wave edge modes in dipolar magnetic thin films

TL;DR

This paper demonstrates that dipolar interactions in a 2D ferromagnetic particle array create chiral spin-wave edge modes with unidirectional propagation, whose properties depend on magnetic field strength and topology.

Contribution

It introduces a theoretical framework showing how magnetic dipolar interactions induce topologically non-trivial spin-wave edge modes in ferromagnetic arrays.

Findings

Chiral edge modes propagate unidirectionally along system boundaries.

Edge mode chirality depends on magnetic field direction and strength.

Magnetic dipolar interactions give rise to non-zero Chern numbers in spin-wave bands.

Abstract

Based on a linearized Landau-Lifshitz equation, we show that two-dimensional periodic allay of ferromagnetic particles coupled with magnetic dipole-dipole interactions supports chiral spin-wave edge modes, when subjected under the magnetic field applied perpendicular to the plane. The mode propagates along a one-dimensional boundary of the system in a unidirectional way and it always has a chiral dispersion within a band gap for spin-wave volume modes. Contrary to the well-known Damon-Eshbach surface mode, the sense of the rotation depends not only on the direction of the field but also on the strength of the field; its chiral direction is generally determined by the sum of the so-called Chern integers defined for spin-wave volume modes below the band gap. Using simple tight-binding descriptions, we explain how the magnetic dipolar interaction endows spin-wave volume modes with non-zero Chern integers and how their values will be changed by the field.