Equilibrium states and spectrum of precession excitations of incommensurate antiferromagnetic structure

The equilibrium states of a modulated antiferromagnetic structure, for which there is no Lifshitz invariant, in a magnetic field with modulation axis and the orientation of the field lying in the plane of the spiral are studied. The phase diagram of the states in the magnetic-field–temperature plane is constructed and it is shown that a tetracritical point of second-order phase transitions exists. The spectrum of precession excitations, whose characteristic feature is the presence of frequency branches with anomalous dispersion of the phason type, is obtained.

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