Non-resonance spin-lattice absorption of ultrasound in Ising magnetic materials

The non-equilibrium statistical operator method is used to construct the theory of non-resonance acoustic absorption in Ising magnetic materials. It is assumed that the coupling between the spins and the sound occurs through the modulation of the Ising exchange integral-and the non-resonance absorption is caused by the interaction of the spin system with the thermal lattice vibrations. A determination is made of the frequency dependence of the absorption chi "(omega); this differs analytically from the well known Debye function. An analysis is made of the temperature dependence of chi "(omega) which is made up of: 1) the averages of the vibration variables and 2) the temperature dependence of the spin correlation functions of the linear Ising model. It is shown that the interrelation of the two subsystems (Ising and Zeeman) leads to the appearance of a second absorption peak in the low frequency region together with a maximum characteristic of the Debye curve.