Magnetoelastic gap and phase transitions

We have studied the long wavelength spectrum of coupled magnetoelastic vibrations. We obtain the dependence of the frequency on the magnitude of the wave vector for the general case without application of any model assumptions as to the form of the system energy. It is shown that in the typical case the magnetoelastic gap (the energy of activation for the quasimagnon part of the spectrum) is nonzero for all values of the external parameters, including the phase transition points. Conditions are found under which the gap may go to zero.

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