Magnetoacoustic effects in rare-earth iron garnets

Abstract

We have used the techniques of linear magnetoacoustic birefringence and transverse ferroacoustic resonance to measure the real and imaginary parts of the index of refraction of soundwaves in the rare-earth iron garnets. The sound waves act as a probe to study the magnetoelastic coupling and the large rare-earth ion relaxation effects in concentrated samples. We investigated YbIG, DyIG and TbIG in the temperature range from 77°to 300°K. The transverse ferroacoustic resonance geometry, RπM, (R=acoustic shearwave polarization vector, M=magnetization) was used to study the linewidth broadening. In YbIG, even at 77°K, the linewidth is only slightly broader than in YIG and GdIG; in DyIG the broadening is pronounced, especially towards lower temperatures; and in TbIG it is so big that no ultrasonic echoes are observable below the magnetization compensation point. The linear birefringence geometry, R and M at 45°, was used to measure the difference in phase velocity between coupled and uncoupled shearwave components. We have attempted to calculate linewidths and effective magnetoelastic coupling constants, by applying the so-called "slow relaxation theory" to the phonon-coupled spin system. A comparison of this theory with our experimental results will be given. © 1967 The American Institute of Physics.