Ferromagnetic resonance studies of (Ag/Fe)n multilayers (abstract)

Abstract

We report a detailed ferromagnetic resonance (FMR) study, at X band, of magnetic films constituted of (Ag‖Fe multilayer‖Ag) sandwiches deposited by sputtering on heated mica substrates, where the base and the top Ag layers are 550 Å thick. For this (Ag/Fe) system the corresponding series of single Fe layers is reported in Ref. 1 (structural characteristics, FMR study). The resonance spectrum is studied as a function of the orientation [angle θH = (N̂,Ĥ) with respect to the film normal N̂] of the applied dc field H in a plane perpendicular to the film. We will present results relative to a series of Fe multilayers (Ag‖Fe)n=9, with spacer tAg=70 Å, corresponding to a set of individual Fe layer thicknesses (tFe=24, 36, and 48 Å). In summary, at room temperature, all the features (line shape, signal phase, position, linewidth) which characterize the resonance spectrum of a Fe multilayer are found different from the ones relative to the single resonance line observed for the corresponding single Fe layer (same tFe). More precisely, the angular variation of the resonance spectrum of the (tFe=24 Å) multilayer shows the presence of a unique line in the range (90°<θH ≲ 30) and then the splitting in two lines for θH ∈ (0°,30°), with Hres(θH) of the higher-field line following closely the single Fe layer Hres whereas the second line remains in low field (∼3.2 kOe). These observations provide evidence for the presence of a dynamical coupling between the precessing magnetizations of adjacent Fe layers. We suggest that the mechanism responsible for the Fe layers coupling is to be associated with the diffusion (or transport) of the microwave-induced magnetization of the conduction electrons of the whole metallic structure.