We present a comprehensive study of polar and magnetic excitations in BiFeO3 ceramics and a thin film epitaxially grown on an orthorhombic (110) TbScO3 substrate. Infrared reflectivity spectroscopy was performed at temperatures from 5 to 900 K for the ceramics and below room temperature for the thin film. All 13 polar phonons allowed by the factor-group analysis were observed in the ceramic samples. The thin-film spectra revealed 12 phonon modes only and an additional weak excitation, probably of spin origin. On heating towards the ferroelectric phase transition near 1100 K, some phonons soften, leading to an increase in the static permittivity. In the ceramics, terahertz transmission spectra show five low-energy magnetic excitations including two which were not previously known to be infrared active; at 5 K, their frequencies are 53 and 56 cm −1 . Heating induces softening of all magnetic modes. At a temperature of 5 K, applying an external magnetic field of up to 7 T irreversibly alters the intensities of some of these modes. The frequencies of the observed spin excitations provide support for the recently developed complex model of magnetic interactions in BiFeO3 (R.S. Fishman, Phys. Rev. B 87, 224419 (2013)). The simultaneous infrared and Raman activity of the spin excitations is consistent with their assignment to electromagnons.

The spin-order-induced ferroelectric anti-ferromagnet Ni 3 TeO 6 transcends the magnetoelectric performance of all other single-phase multiferroics, because it exhibits non-hysteretic colossal magnetoelectric coupling [Oh et al., Nat. Commun., 5, 3201 (2014)]. We investigated spin and lattice excitations in Ni 3 TeO 6 by a combination of infrared, Raman and THz spectroscopies. Two spin excitations (near 13 and 35 cm -1 ) were observed simultaneously in Raman and time-domain THz spectra below the Néel temperature T N =53 K. We propose to assign them to electromagnons, which are activated by the dynamic magnetoelectric coupling. A third magnon is seen only in the Raman spectra near 206 cm -1 .

We present a structural and spectroscopic study of a new compound Ni 2 MnTeO 6 , closely related to the polar antiferromagnet Ni 3 TeO 6 known to show a colossal magnetoelectric effect and pronounced elementary magnetoelectric excitations. For the first time, we prepared single crystals and polycrystalline samples of Ni 2 MnTeO 6 showing the same polar structure as Ni 3 TeO 6 from room temperature down to 4 K with the R3 space group symmetry. Magnetic and dielectric measurements have indicated an antiferromagnetic phase transition at T N ≈70 K, almost 20 K higher than that of Ni 3 TeO 6. Extensive infrared, Raman and THz spectroscopy experiments were employed for investigating lattice and spin excitations, revealing all phonons predicted by the factor group analysis. THz spectra below T N reveal one new excitation, which is strongly influenced by external magnetic field, thus assigned to a magnon.