Diffusive Regime for Critical Sound Attenuation and Dispersion in Magnets

A. Pawlak and M. Błaszak Institute of Physics, A. Mickiewicz University, Umultowska 85, 61-614 Poznań, Poland

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We consider a new regime of sound propagation in magnetic systems above the critical point. On the basis of a general statistical model including a flow of energy between spin and lattice subsystems we found that there is a region of parameters where the sound attenuation and dispersion can be expressed in a similar way as for noncritical systems for which only the heat conduction matters. Contrary to the case of the classical heat diffusion in the critical magnetic system both the specific heat, entering the reduced frequency, as well as the effective amplitude are frequency and temperature dependent reflecting the critical singularities present in the system near its critical point.

DOI: 10.12693/APhysPolA.97.905 PACS numbers: 05.70.Jk, 62.65.+k