Investigation of the 4f-electron-phonon-coupling in the ferromagnet LiTbF4 by inelastic scattering of light

Abstract

The polarized Raman spectra of LiTbF4 in an external magnetic field (B≦8 T) have been recorded in the wavenumber interval 0≦500 cm−1 and at temperatures of 1.8 K and 4.2 K. We have studied effects of the 4f electron-phonon (magnetoelastic) coupling manifesting itself in the splitting of a twofold degenerate phonon mode and in anticrossing effects between phonons and electronic transitions. In the spectra probing the scattering tensor elements (xz) and (zy) this anticrossing shows an asymmetry with respect to the frequencies and scattering intensities of the quasi-degenerate components. These effects are discussed in detail and can be interpreted by the theory of magnetoelastic interaction and by taking into consideration the finite widths of the electronic and phonon components (“critical coupling”). Brillouin scattering has been used to determine the sound velocities in thea-direction. No effect of the magneto-elastic interaction could be detected in this case.