Ultrasonic studies of the critical dynamics of magnetically ordered crystals

The current state of ultrasonic research of dynamic critical phenomena in magnetically ordered crystals is reviewed. Based on relevant theoretical concepts, the conclusion is drawn that the experimental data on ferro-, ferri-, and antiferromagnetic materials in both the hydrodynamic and critical regions can be described in terms of the dynamic scaling concept and the theory of interacting modes. The influence of a magnetic field on the dynamics of critical fluctuations of magnetization and spin-energy density is discussed. (reviews of topical problems)