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

TLDR

The study uses a two‑dimensional spin model solved with the Landau–Lifshitz–Gilbert equation to theoretically investigate spin‑wave modes and their intense microwave‑field excitations in the skyrmion‑crystal phase of insulating magnets. The simulations reveal two ~1 GHz spin‑wave resonances with opposite circulation of out‑of‑plane spin components, a breathing mode for out‑of‑plane ac fields, and show that intense microwave excitation can melt the skyrmion crystal with a red‑shifted resonance 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.