A new mechanism of magnon-phonon relaxation process in ferrimagnetic insulators

Abstract

A new mechanism is proposed for relaxation processes in ferrimagnetic insulators (assumed to be ionic e.g. yttrium iron garnet, YIG), whereby magnons of the optical spin wave branch couple directly with the transverse optical modes of lattice vibrations which are, energetically, "on speaking terms". This direct interaction is brought about by the near-zone magnetic field associated with the transverse optical modes of vibrations in ionic lattices and was found to be important in spin-lattice relaxation studies, as reported in our earlier paper. This magnon-phonon interaction is shown to lead to a temperature dependent linewidth of ferrimagnetic resonance. An order of magnitude estimate of linewidth for a typical system (YIG, Y₃Fe₂Fe₃O₂) shows that the present mechanism is important in certain temperature regions. Moreover, the temperature dependence of resonance linewidth, obtained theoretically, exhibits a linewidth maximum which again is in agreement with experimental observations.