Spin-Wave Modes and Their Intense Excitation Effects in Skyrmion Crystals

TL;DR

This paper theoretically investigates spin-wave modes in skyrmion crystals of insulating magnets, revealing their resonance behaviors, polarization dependence, and the ability to induce skyrmion crystal melting through intense microwave excitation.

Contribution

It introduces a detailed numerical analysis of spin-wave excitations and their effects in skyrmion crystals, including the dynamic control of skyrmion phases via microwave fields.

Findings

Two main spin-wave resonance modes at ~1 GHz with opposite circulation directions.

Resonance spectra depend strongly on microwave polarization.

Intensive excitation causes skyrmion crystal melting within nanoseconds.

Abstract

We theoretically study spin-wave modes and their intense excitations activated by microwave magnetic fields in the skyrmion-crystal phase of insulating magnets by numerically analyzing a two-dimensional spin model using the Landau-Lifshitz-Gilbert equation. Two peaks of spin-wave resonances with frequencies of ~1 GHz are found for in-plane a.c. magnetic field where distribution of the out-of-plane spin components circulates around each skyrmion core. Directions of the circulations are opposite between these two modes, and hence the spectra exhibit salient dependence on the circular polarization of irradiating microwave. A breathing-type mode is also found for out-of-plane a.c. magnetic field. By intensively exciting these collective modes, melting of the skyrmion crystal accompanied by a red shift of the resonant frequency is achieved within nano seconds.