Ultrasonic absorption with infrared divergence in cluster spin glass

The infrared divergence response theory is applied to reorientational relaxa tion process of magnetic cluster in cluster spin glass (CoF₂)_0.5(BaF₂)_0.2(NaPO₃)_0.3 to study the behaviour of low temperature ultrasonic absorption in this system.Our calculation showed that the reorientational process makes the main contribution to the magnetic part of the ultrasonic absorption for T<4.0K;as for T>4.0K,the intraprocess of the cluster can not be neglected.