Three-phonon coupled excitations in an antiferromagnet

Results of an experimental observation of the generation of three-phonon coupled excitations in an α-Fe₂O₃ high-temperature antiferromagnet in a transverse electromagnetic pumping field are presented. The underthreshold and superthreshold generation regimes are studied depending on the phase shift of pumping with respect to the phase of the three-phonon acoustic field correlator. The results agree well with the theory of the resonant nonlinear interaction of quasi-phonons with an electromagnetic field.