Magnetostatic wave analog of integer quantum Hall state in patterned magnetic films

TL;DR

This paper proposes a magnetostatic spin wave analog of the integer quantum Hall state in patterned ferromagnetic films, demonstrating topologically protected chiral edge modes through theoretical models and simulations.

Contribution

It introduces a novel topological phase in magnetic thin films, showing how soft spin-wave bands can acquire nontrivial Chern numbers and support chiral edge modes.

Findings

Chiral magnetostatic edge modes exist in patterned ferromagnetic films.

Softened spin-wave bands near saturation exhibit nontrivial topology.

Micromagnetic simulations confirm the presence of edge modes.

Abstract

A magnetostatic spin wave analog of integer quantum Hall (IQH) state is proposed in realistic patterned ferromagnetic thin films. Due to magnetic shape anisotropy, magnetic moments in a thin film lie within the plane, while all spin-wave excitations are fully gapped. Under an out-of-plane magnetic field, the film acquires a finite magnetization, where some of the gapped magnons become significantly softened near a saturation field. It is shown that, owing to a spin-orbit locking nature of the magnetic dipolar interaction, these soft spin-wave volume-mode bands become chiral volume-mode bands with finite topological Chern integers. A bulk-edge correspondence in IQH physics suggests that such volume-mode bands are accompanied by a chiral magnetostatic spin-wave edge mode. The existence of the edge mode is justified both by micromagnetic simulations and by band calculations based on a linearized Landau-Lifshitz equation. Employing intuitive physical arguments, we introduce proper tight-binding models for these soft volume-mode bands. Based on the tight-binding models, we further discuss possible applications to other systems such as magnetic ultrathin films with perpendicular magnetic anisotropy (PMA).