Electromagnon in ferrimagnetic eps-Fe2O3 nanograin ceramics

TL;DR

This paper reports the discovery of electromagnons in eps-Fe2O3 ceramics below 110 K, linking magnetic structure modulation to electromagnon activation, and demonstrates a combined spectroscopic approach for their detection.

Contribution

It introduces the first observation of electromagnons in eps-Fe2O3 ceramics and shows how combined spectroscopic techniques can detect them without crystal orientation analysis.

Findings

Electromagnons appear below 110 K in eps-Fe2O3.

Electromagnon energy matches a magnon from the Brillouin zone boundary.

No ferroelectricity detected down to 10 K in eps-Fe2O3.

Abstract

Electromagnons are known from multiferroics as spin waves excited by the electric component of electromagnetic radiation. We report the discovery of an excitation in the far-infrared spectra of eps-Fe2O3 which we attribute to an electromagnon appearing below 110 K, where the ferrimagnetic structure becomes incommensurately modulated. Inelastic neutron scattering shows that the electromagnon energy corresponds to that of a magnon from the Brillouin zone boundary. Dielectric measurements did not reveal any sign of ferroelectricity in eps-Fe2O3 down to 10 K, despite its acentric crystal structure. This shows that the activation of an electromagnon requires, in addition to the polar ferrimagnetic structure, a modulation of the magnetic structure. We demonstrate that a combination of inelastic neutron scattering with infrared and / or terahertz spectroscopies allows detecting electromagnons in ceramics, where no crystal-orientation analysis of THz and infrared spectra is possible.