Specific features of magnetoacoustic waves in Fe₃BO₆

The specific features of magnetoacoustic waves propagating in an orthorhombic antiferromagnet with weak ferromagnetism, namely, the Fe ₃BO₆ orthoborate, are investigated experimentally in the vicinity of the spontaneous, first-order orientational phase transition. It is revealed that, at the phase transition point, the amplitude of active acoustic waves interacting with spin waves increases significantly. A phenomenological theory of magnetoelastic waves in orthoferrites is proposed. This theory allows for an intermediate domain structure existing in the range of a first-order orientational phase transition and offers a satisfactory explanation of the experimentally observed anomaly in the amplitude of active acoustic waves.