Waveguide-based ferromagnetic resonance measurements of metallic ferromagnetic films in transmission and reflection

In this work, we have studied the ferromagnetic and standing spin wave resonance response of in-plane magnetized exchange-coupled bi-layer ferromagnetic metallic films placed in a section of a rectangular waveguide. The measurements have been performed in transmission and reflection of electromagnetic waves in the 8-12 GHz frequency range. The 30 to 70 nm-thick Co-permalloy films on silicon substrates tightly fitted the cross-section of the waveguide. It was found that the responses of the films in transmission and reflection were very different. In transmission, the response of the fundamental mode dominates, but in reflection, the first (anti-symmetric) standing spin wave mode demonstrates the largest variation in amplitude with respect to the off-resonance regime. The results we obtain are in agreement with recently developed theory which demonstrates the high relevance of strong microwave screening (or shielding) by eddy currents in the film for the formation of the observed response. © 2013 American Institute of Physics.