Simultaneously time-reversal and spatial-inversion symmetry breakings provide the non-reciprocal propagation of electromagnetic waves. The non-reciprocity means the difference of refractive indeces between oppositely propagating waves. This is called the non-reciprocal directional dichroism (NDD)[1]. The NDD has been observed in terahertz region by using the antiferromagnetic magnon excitation of multiferroics[2]. However the NDD owing to the antiferromagnetic magnon excitation has not been reported in microwave region, because almost antiferromagnets have large magnetic anisotropy and exchange interaction. Here, we show that the multiferroic Ba₂MnGe₂O₇[3] has the two antiferromagnetic magnon modes in microwave region and that the magnon modes provide the NDD in microwave region.
[1] G.L.J.A. Rikken & E. Raupach, Nature 390, 493-494(1997).
[2] Y. Takahashi et al., Nat. Phys. 8, 121-125(2011).
[3] H. Murakawa et al., Phys. Rev. B 85, 174106(2012).