Rıza Erdem1 and Mustafa Keskin2

1Department of Physics, Gaziosmanpaşa University, 60110 Tokat, Turkey

2Department of Physics, Erciyes University, 38039 Kayseri, Turkey


          Critical behaviors of the sound attenuation in a spin-1 Ising system with bilinear and biquadratic interactions [1] are investigated within the framework of Onsager theory of irreversible thermodynamics [2]. The sound-wave is assumed to couple mainly to the order parameter fluctuations which decay via order parameter relaxation processes. Two relaxation times are obtained and an expression is found for the sound attenuation coefficient (a) in terms of these relaxation times. The temperature behavior of the sound attenuation is anayzed according to various values of Onsager or phenomenological rate coefficients (Lij). For all LS and LQ values it is observed that the sound attenuation peaks occur below the phase transition points and depend on both frequency (w) and off-diagonal Onsager coefficient (L). On the other hand, a convergence is found in attenuation just below the critical and the tricritical points as (Tc-T), while a jump-discontinuity is observed for the first-order behavior. Moreover, the frequency variation of the sound attenuation is also investigated and w2-attenuation dependence is observed in the hydrodynamic regime. These results are in a good agreement with ultrasonic investigations of some magnetic systems, such as MnF2, FeF2, and RbMnF3 [3].



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[2] L. Onsager, Phys. Rev. 37, 405 (1931); 38, 2265 (1931); S. R. de Groot, Thermodynamics of Irreversible Processes (North-Holland Publishing Company, Amsterdam, 1951); S.R. de Groot and P. Mazur, Non- equilibrium Thermodynamics (North-Holland, Amsterdam, 1961).
[3] T. J. Moran and B. Lüthi, Phys. Rev. B4, 122 (1971); A. Ikushima and R. Feigelson, J. Phys. Chem. Solids 32, 417 (1971); T. Jimbo and C. Elbaum, Phys. Rev. Lett. 28, 1393 (1972); A. Bachellerie, J. Joffrin and A. Levelut, Phys. Rev. Lett. 30, 617 (1973).