Magnon Lifetime and Its Effect on Magnon Sideband in MnO

Lifetime of magnon arising from magnon-magnon interaction is studied for the general helical spin system by spin wave approach using diagrammatic techniques. The antiferromagnetic MnO, whose spin structure can simply be described as a helix with a wave vector Q =[111]π/ a , is taken up, and the energies and lifetimes of magnons with wave vectors along [100], [111] and [110] are calculated as functions of temperature. The temperature-dependent line shape of the magnon sideband in MnO corresponding to the transition 6 A 1 g - 4 T 1 g of the Mn 2+ ions is studied with the inclusion of magnon lifetime. The calculated results are compared with the observation.