A 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 H_int=i[∑_σt⁺(b_σt⁺β_σ-h.c.)+ ∑_σt,λ#936;_σt,λ(b_σt⁺β_λαλ+σ-h.c.)], where ∓_σt+ and Ψ_σt,λ are appropriate coupling constants and b_σt+, β_λ and α_λ the phonon-creation and magnon-annihilation operators of the respective branches. These mechanisms lead to a temperature-dependent 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 play a significant role in the paramagnetic relaxation of some doped ionic crystals.