Abstract
Some quantum effects of the magnon-photon interaction are investigated. A magnon life-time, arising from a radiative relaxation through the absorption and emission of one photon, is found. Multiple scattering of magnons and photons is indicated. The creation of a photon at one spin site and the resonant absorption of the same photon at a later time at a different site is found to lead to a spin-spin real radiation exchange interaction. The predicted effects are large enough to be experimentally observed.