The interaction of terahertz (THz) radiation with high-frequency spin resonances in complex magnetic materials is central for modern ultrafast magnonics. Here we demonstrate strong variations of the excitation efficiency of the sub-THz exchange magnon in a single crystal ferrimagnet (Gd,Bi)3Fe5O12. An enhancement of the exchange magnon amplitude is observed when its frequency matches an eigenmode of the cavity created by the sample interfaces. Moreover, this enhancement is accompanied by a 5-fold decrease in effective damping of the exchange mode. The THz-exchange magnon interaction in the cavity is analyzed within the developed Landau-Lifshitz-Gilbert formalism for three coupled magnetization sublattices and cavity-enhanced THz field. This work presents a novel approach for the THz excitation of spin dynamics in ferrimagnets and outlines promising pathways for the controlled optimization of light-spin coupling in single crystals.
@article{arxiv.2406.19849,
title = {THz Control of Exchange Mode in a Ferrimagnetic Cavity},
author = {Chris Reinhoffer and Ilya Razdolski and Philipp Stein and Semyon Germanskiy and Andrzej Stupakiewicz and Paul H. M. van Loosdrecht and Evgeny A. Mashkovich},
journal= {arXiv preprint arXiv:2406.19849},
year = {2024}
}