Mixed modes of surface polaritons in a PML-type magnetoelectric multiferroic with canted spins.

We present a theoretical discussion of surface polaritons on a ferroelectric-antiferromagnet with magnetoelectric coupling which allows the magnetic subsystem to be canted. Canting of the antiferromagnet results in weak ferromagnetism. The surface polaritons for a semi-infinite film are calculated for a propagation parallel to the uniaxial easy axis, leading to mixed modes. A superposition of two plane waves is needed to generate mixed surface modes. We find two branches, one near the magnon resonance frequency and the other near the phonon resonance frequency. We also find that the surface modes are non-reciprocal due to magnetoelectric interaction, such that ω(k) ≠ ω(-k), where ω is the frequency and k is the propagation vector.