Magnon–phonon interaction in the transition layer of an epitaxial YIG film

It is shown that the effects of collinear magnetoelastic interaction of exchange spin waves (ESW) and acoustic waves (AW) arise in the transition layer of an epitaxial YIG film. The interaction is the most intense at the phase matching frequencies of the ESW and AW. In this case, there are effects of hybridization and energy conversion of ESW $\to$ AW type. The phase matching condition is fulfilled due to the transformation of the ESW lengths within the thickness of the transition layer. Coupling is weakened away from phase matching points; waves propagate independently of each other. Moreover, the acoustic wave can freely penetrate deep into the nonmagnetic substrate of the yttrium iron garnet film. In the future, this can be useful for providing phonon coupling of spin-wave excitations in films located on opposite sides of a nonmagnetic substrate.