FMR studies of single Fe layers sandwiched by Ag (abstract)

Abstract

We report a systematic FMR study, at X band, of magnetic films constituted of (Ag‖single Fe layer‖Ag) sandwiches deposited by sputtering on heated mica substrates (base Ag layer 550 Å thick; top one 275 Å). The conditions of deposition used enable to get a polycrystalline Ag base layer with large lateral size (∼2000 Å) of the crystallites, as determined using scanning tunneling microscopy, and a preferred (111) orientation perpendicular to the film. The resonance spectrum is studied as a function of the orientation [θH=(N̂,Ĥ) with respect to the film normal N̂] of the applied dc field H in a plane perpendicular to the film: (i) for the ultrathin Fe layers (<100 Å) the angular variation Hres(θH) of the unique mode observed can be essentially accounted for in terms of (4πM−HA), i.e., the total component of perpendicular uniaxial anisotropy where HA=2K/M is a uniaxial anisotropy field (N̂ easy axis). From the observed proportionality of HA to 1/tFe it is deduced Ks≂1.45±0.1 erg/cm2 for the value of the effective interface-induced anisotropy of the (Ag/Fe) interface. (ii) Additional information on the interface pinning parameter is provided, in the ‘‘thick’’ Fe layers (≳400 Å), by the observation, besides the principal mode, of a higher field mode identified to a surface exchange mode. At low temperatures more complex phenomena are observed (shift of Hres and line broadening) which are interpreted, as already suggested,1 in terms of the dissipative part of the magnetic interfacial coupling at the Fe/Ag interface (to be associated to the diffusion of the microwave induced magnetization of the conduction electrons from one metal to the other).