Dispersion of the sound velocity in iron borate under nuclear magnetoacoustic resonance

The frequency dependence of the velocity of coupled magnetoelastic waves in the weak ferromagnet FeBO3 is investigated experimentally and theoreticall y. An anomalous frequency dependence of the transverse sound velocity is ob served for a single-domain sample under conditions of nuclear magnetoacoust ic resonance, when the frequency of sound excited in the sample is close to the NMR frequency of Fe-57 nuclei. It is shown that the observed dependenc e is associated with a considerable effect of nonequilibrium states of the nuclear spin system on the renormalization of elastic constants due to effe ctive magnetoelastic coupling. (C) 2000 MAIK "Nauka/Interperiodica".