Brillouin light scattering detection of ferromagnetic resonance in thin films

Ferromagnetic resonance (FMR) in thin films of permalloy and yttrium iron garnet (YIG) has been studied by Brillouin light scattering (BLS) techniques. The measurements were made at 9.4 GHz on 22.4 to 75‐nm‐thick permalloy films and on 2.1‐ to 12.8‐μm‐thick YIG films. Intensity profiles for magnon scattered light versus in‐plane applied field were obtained by analyzing the forward scattered light through the films with a high‐contrast Fabry–Perot interferometer. The BLS profiles show a signal‐to‐noise ratio of 10‐100 for the permalloy and 100‐1000 for the YIG films, depending on the film thickness and the microwave power level. The FMR BLS response was quantified in terms of global response function, counts/s mW versus magnon occupation number Nu. The Nu parameter relates the scattering to the uniform mode FMR response (linewidth, field, frequency, etc.), input microwave power, and active sample volume. The response for permalloy was approximately10^-8 counts/s mW magnon, which translates into a limiting sample volume of 10^-12 cm³.