Spin-lattice relaxation effects in critical sound propagation

Authors:

• Andrzej Pawlak

Abstract

The nonasymptotic critical properties of sound propagation are studied in compressible Ising system above T_C. In the present paper we analyse a model where in addition to the coupling to two order-parameter fluctuations the sound mode couples linearly to the fluctuations of spin-energy and lattice-energy densities. Both subsystems exchange energy with the rate determined by the bare spin-lattice relaxation time. The total energy may be conserved or not. The crossover between insulator-like behaviour ∼t^-2α and metal-like behaviour ∼^t-(zv+α) in ultrasonic attenuation is investigated according to the value of ultrasonic frequency, the reduced temperature t, bare relaxation times and various coupling constants.