Optical Phonons in Iron Garnets

Raman spectra of different rare-earth iron garnets (REIG), i.e., GdIG, Gd2.34Tb0.66IG, TbIG, and YIG have been measured. The spectra were excited with the 5145-Å line of an argon-ion laser on the surface of a (111) plane. The observed lines are due to scattering on phonons and a group-theoretical assignment of the observed modes has been carried out. Resonance effects and the possible observation of magnons is discussed. The spectra are also compared with data obtained from gadolinium gallium garnet (GdGG) and some correlations are proposed.