Sound Absorption in Magnetics

  • V. G. Kamensky


One of the important aspects of the dynamics of magnets is the sound propagation near the critical point. A number of theories have been developed for the case of ultrasonic attenuation at magnetic phase transitions (see for instance the paper by B. Luthi, T.J. Moran and R.J. Pollina [1] and references quoted there). The spin-phonon interaction, responsible for the critical effects, arises in most cases via the strain modulation of the exchange interaction (volume magnetostrictive coupling). As a result, the attenuation is proportional to the space-time Fourier Laplace transform of a four spin correlation function. This result is the starting point of all further calculations. Most of the present theories, however, consider temperatures above T c, and therefore come down to the calculation of the characteristic decay time, t e, of the spin fluctuations. Using the various expressions for t e, one gets the temperature dependence for the attenuation. As a result one finds for the attenuation coefficient γ ∿ ω2 τ (τ = (T - T c)/Tc). The critical changes in sound wave attenuation follow a quadratic frequency dependence, whilst the temperature dependence varies widely for different substances. The variation of the critical exponent can be characterized by the following parameters: spin structure (ferro- or antiferromagnets), degree of magnetic anisotropy of the spin interaction, and range of the exchange interaction.


Spin Wave Magnetic Phase Transition Sound Absorption Average Spin Phonon Line 
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Copyright information

© Plenum Press, New York 1976

Authors and Affiliations

  • V. G. Kamensky
    • 1
  1. 1.Landau Institute for Theoretical PhysicsAcademy of Sciences of the USSRMoscowUSSR

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