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

Abstract

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.

Electromagnetic Waves in Canted Magnets

“…an effective field whose magnitude depends on the polarization P. The polarization is affected by static electric fields, temperature, and provides the magneto-electric coupling for time varying electric fields [34]. The canting, is assumed to be given by [35,36]…”

“…The approximations by Holmes [43] gives the exchange field, H E = 50 T, and from the relation H E = λM s we obtain the exchange constant as λ = 163.72 erg cm −3 Oe −2 . Further parameters for this material have also been provided by Gunawan and Stamps [35,36]. A plot of both bulk and surface modes is shown in Fig.…”