Electric-dipole-active magnetic resonance in the conical-spin magnetBa2Mg2Fe12O22

Electric-field $\left(E\right)$ drive of magnetic resonance in a solid has been a big challenge in condensed-matter physics and emerging spintronics. We demonstrate the appearance of distinct magnetic excitations driven by the light $E$ component in a hexaferrite ${\text{Ba}}_2{\text{Mg}}_2{\text{Fe}}_{12}{\text{O}}_{22}$. In the conical-spin state even with no spontaneous electric polarization $\left(P_{\text{s}}\right)$, a sharp and intense resonance is observed around 2.8 meV for the light $E$ vector parallel to the magnetic propagation vector in accord with the inelastic neutron scattering spectrum at the magnetic zone center. As the generic characteristic of the conical state, a weak magnetic field $\left(\sim 2\text{kOe}\right)$ can modify the spin structure, leading to a remarkable change (terahertz magnetochromism) in spectral shape and intensity (by $\sim 200\%$) of the electric-dipole-active magnetic resonance. The present observation implies that potentially many magnets with noncollinearly ordered spins may host such an electric-dipole-active resonance, irrespective of the presence or absence of $P_{\text{s}}$.