Using neutron reflectometry to understand enhanced dynamic linewidth in a magnetic trilayer device

We have studied the magnetic damping of CoFe/Ag/CoFe multilayer films using Ferromagnetic Resonance (FMR) spectroscopy. There is an anomalous linewidth enhancement, which oscillates with a period of around 1 nm as the Ag thickness is increased. One interpretation is related to the interlayer coupling which may be ferromagnetic or antiferromagnetic due to the well-known Ruderman-Kittel-Kasuya-Yosida (RKKY) mechanism. Theoretical studies predict such a dynamic exchange coupling across a non-magnetic spacer to affect the resonance linewidth; it is feasible that the enhanced damping found in CoFe/Ag/CoFe relies on the RKKY coupling. The aim of this experiment is to determine the RKKY coupling strength from depth-resolved vector magnetometry using polarised neutron reflectometry with polarisation analysis, to clarify interpretation of the anomalous linewidth behaviour in CoFe/Ag/CoFe.