Parallel Pumping of Magnetoelastic Waves

Abstract

A general analysis of the longitudinal pumping of magnetoelastic waves near the magnon—transverse‐phonon crossover region has been performed. Variation of the directions of propagation and the applied field within the crystal lattice are taken into account and the effects of magnetic, elastic, and magnetoelastic anisotropy are included. When the applied field H₀ is in a [100] direction, the theory gives a magnetoelastic dispersion relation in agreement with previous treatments. When H₀ is in a [111] direction, the usual assumption that the body displacement vector is polarized along H₀ is found to be incorrect and a new dispersion relation is obtained. This correction modifies the calculation of magnetoelastic constants from experimental data. Variation in the direction of propagation of the unstable magnetoelastic wave, not considered in previous treatments, is found to be important in determining the asymmetry and size of the phonon pip. High‐resolution spin‐wave instability measurements near the transverse phonon interaction region have been performed at a pump frequency of 34 Gc/sec on yttrium iron garnet. The lineshape is in agreement with the present theory. Calculations of the elastic mode Q factors, taking into account the variation in propagation direction, give values an order of magnitude lower than would otherwise be obtained. Data showing the variation of effective exchange constant with magnetization in YGaIG are included.