Interactions of magnons with optical phonon in rare earth orthoferrites

We present the magnetoelastic invariants which describe the interaction of magnons with optical phonons of a definite type in rare-earth orthoferrites RFeO3. The frequencies of coupled oscillations of magnons and optical phonons which are excited by an alternating electric field are calculated. It is shown that these electroactive phonons interact only with oscillations the rare-earth sublattice of orthoferrites