Critical Acoustic Relaxation in EuO

Abstract

Acoustic damping and dispersion in EuO have been measured at low kilohertz frequencies near the ferromagnetic critical point. The experimental observations are discussed in terms of thermoelastic and critical dissipative processes. Bounds are established for the critical relaxation rate for sound, $2\times {10}^5<{{\tau }_c}^{-1\mathrm{}}<2\mathrm{}\times {10}^7$ ${\sec }^{-1\mathrm{}}$, in order-of-magnitude agreement with the EuO spin-lattice relaxation rate calculated by Huber.