Helicons and magnons in magnetically ordered conductors

The character of magnons and helicons in magnetically ordered conductors is considered. Conductors become transparent to circularly polarized electromagnetic waves, helicons, when ωcτ1, where ωc is the cyclotron frequency and τ is the relaxation time of the conduction electrons. It is shown that, in general, there exists a strong coupling between helicons and magnons, so strong that a perturbative approach is not adequate. The effect of this strong coupling is calculated and is shown to produce large effects on the magnon and helicon spectra at long wavelengths. The coupling between magnons and helicons can be varied by changing the external magnetic field. These effects should be experimentally observable.