The Raman-active phonons (3A1g + 8Eg + 14T2g) in eight different aluminum, gallium, and iron garnet crystals have been investigated. The energies and symmetries of phonons in YbAIG, YbGaG, LuAIG, and LuGaG, as well as DyIG, ErIg, YbIG, and YIG, have been determined. The aluminum and gallium garnets were measured in transmission, by use of an argon laser (5145 and 4880 Å). The iron garnets were measured both in reflection, using an argon laser, and in transmission, using a Nd:YAG laser (1.064 µm). Owing to the linear magnetic birefringence of the iron garnets, the identification of phonon symmetries through polarization selection rules was not possible for our transmission data. An external magnetic field sufficient to align the magnetic domains of the iron garnets in the (110) plane at 80 K was applied both for the reflection and transmission measurements.
Jin-Joo Song, P. B. Klein, R. L. Wadsack, M. Selders, S. Mroczkowski, and R. K. Chang, "Raman-active phonons in aluminum, gallium, and iron garnets," J. Opt. Soc. Am. 63, 1135-1140 (1973)