Ferromagnetic resonance study of structure and relaxation of magnetization in NiFe/Ru superlattices

The structural properties and relaxation processes of magnetization in [Ni81Fe19(t(1))/Ru(t(2))](N) superlattices (N = number of bilayers) were analyzed by ferromagnetic resonance (FMR) with a fixed microwave frequency. One series of samples was deposited with constant NiFe layer thickness (t(1)) and variable Ru layer thickness (t(2)); the other series, with constant t(2) and variable t(1). A single FMR mode was observed for t(2) < 15 angstrom and t(1) > 75 angstrom and it has been attributed to the resonance of the exchange-coupled NiFe layers across the Ru interlayers. For the other values of t(1) and t(2), several FMR modes appeared and they were associated to non-coupled magnetic phases with different effective magnetization formed during the multilayer growth. The FMR linewidths were analyzed as a function of the magnetic layer thickness and a strong dependence on t(1)(-2) was observed It was attributed to the contribution of the two-magnon scattering mechanism for the linewidth. (C) 2013 Elsevier B.V. All rights reserved