Time-varying ferrimagnetic media: Magnetization dynamics, wave propagation, and spectral shaping
Phys. Rev. B 114, 094429 – Published 21 August, 2026
DOI: https://doi.org/10.1103/m9yv-k886
Abstract
We investigate magnetization dynamics in time-varying ferrimagnetic (or ferromagnetic) media (TVFMs) arising from temporal modulation of the bias magnetic field. Within the Landau-Lifshitz-Gilbert framework, we derive the full time-domain magnetic susceptibility without invoking the commonly used instantaneous-response or adiabatic approximations. The resulting susceptibility inherently includes memory and dispersion effects. The theory is further developed for sinusoidally modulated bias, showing how the magnetization harmonics follow Bessel-function weighting, thus enabling precise spectral shaping. We demonstrate that hundreds of harmonics can be generated with controlled energy concentration in selected orders. The propagation characteristics and band structure of Bloch waves in a bulk TVFM (with longitudinal modulation) are found, revealing a modulation-induced momentum band gap. We finally demonstrate scattering from a TVFM slab and show that the spectrum of the scattered field directly mirrors the harmonic spectrum predicted by the magnetization dynamics, with exact harmonic-amplitude correspondence in thin slabs.
