NEW ASPECTS OF CRITICAL SOUND-ATTENUATION IN MAGNETIC SYSTEMS WITH SPIN-LATTICE RELAXATION

A general theory of critical sound propagation, including phonon-spin- energy coupling', is studied in anisotropic magnets above their transi tion temperature. The Kaurasaki weak singularity in the ultrasonic att enuation is found as a nonasymptotic effect. A new nonasymptotic regim e similar to the one in the binary mixture is also determined. The rol e of coupling constants and the bare relaxation times in establishing the dominance region of particular terms, is discussed.