Interaction Between Thermal Magnons and Phonons in a CoFeB/Au Multilayer

The dispersion relations of thermal magnons and phonons, which exist in a multilayered CoFeB/Au sample deposited on a silicon substrate, were determined by using Brillouin light scattering spectrometry in the oblique geometry, for the 45° angle between the in-plane-oriented static magnetization and the wave vector. Due to the low effective saturation magnetization of the multilayer, we were able to measure the crossing between the dispersion branches for spin waves and surface acoustic waves with the signature of the magnetoelastic interactions in the form of a coalescence of dispersion branches. The oblique geometry was chosen to enhance the interaction between both kinds of waves.