MAGNETOACOUSTICS OF RARE-EARTH ORTHOFERRI TES

Experimental and theoretical work on the magnetoacoustics of rare-eart h orthoferrites near orientational phase transitions (OPT) is reviewed . The temperature and field dependences of magnetoresonant soft-mode f requencies and the sound velocity and attenuation near various OPTs, a s obtained by RF and ultrasonic spectroscopy, are given. A spin-wave a pproximation theoretical analysis of orthoferrite magnetoacoustics is presented, accounting as fully as possible for interactions between al l the subsystems involved, including the ordered ferrous, elastic, par amagnetic rare-earth, and dipole (electromagnetic) subsystems. The ori gin of energy gaps in the spin-wave spectrum is discussed in detail, a s are the ultrasound dispersion, propagation velocity, and attenuation changes at OPT points. The energy gaps measured and the sound velocit y behaviour observed are shown to result from the interaction of the o rthoferrite subsystems. In most cases experimental data agree well wit h theoretical predictions.