Brillouin light scattering study of magnon branch crossover in thin iron films

Brillouin light scattering has been used to measure frequency versus wave number for the surface and exchange branches of the magnon dispersion manifold in thin iron films. For the thickest film studied (750 {}), multiple-exchange branches and the surface mode could be distinguished. For a thinner 348-{} film, the branch crossing and repulsion between the single-exchange branch and the surface branch were particularly well resolved. The measured dispersion branches and branch repulsion are in good agreement with the theory. For the thinnest film studied, 232 {}, the surface magnons associated with both sides of the film were observed, and the intensity ratio for the two peaks was measured versus wave number. The results are consistent with simple penetration depth considerations.