Electric-dipole-active magnetic resonance in the conical-spin magnet Ba_2Mg_2Fe_(12)O_(22)

摘要

Electric-field (E) 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 Ba_2Mg_2Fe_(12)O_(22). In the conical-spin state even with no spontaneous electric polarization (P_s), 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 (～2 kOe) can modify the spin structure, leading to a remarkable change (terahertz magnetochrornism) in spectral shape and intensity (by ～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_s.