New mechanism of linewidth maxima in ferrimagnetic resonance

Abstract

A new mechanism for magnon-phonon relaxation process in ferrimagnetic insulators (e.g., YIG) is proposed which involves direct coupling of the magnons of various spin-wave modes with phonons of the transverse optical modes. This direct interaction emanates from the near-zone magnetic field associated with the transverse optical modes of vibrations in ionic lattices. The dominant part of the interaction term has the form . Hint= -i[ 2; <I>.,+(b.,+~.-h.c.) + 2; tf.'.A(b.'+~A~+a-h.c.)], tTt crt,X where <1>.,+ and tf,'.A are appropriate coupling constants and b •• +, ~A and "'A the phonon-creation and magnon"annihilation operators of the respective branches. These mechanisms lead to a temperaturedependent linewidth of ferrimagnetic resonance exhibiting maxima at certain values of temperature. An order of magnitude agreement with experimental results on YIG is obtained for a reasonable choice of parameters involved. Spin-phonon interaction processes due to transverse optical modes have been shown to playa significant role in the paramagnetic relaxation of some doped ionic crystals.