THz, infrared and inelastic neutron scattering spectra of Z-hexaferrite ceramics were measured in a broad range of temperatures. A sharp electromagnon is observed near 1 THz, vanishing with increasing magnetic field until a phase transition occurs at H approximate to 2 T.
Then, another strong peak whose resonance frequency is linearly proportional to the magnetic field turns up from the sub-THz range. We assign this peak to a ferrimagnetic resonance.