STRUCTURAL AND MAGNETIC-PROPERTIES OF FE-CO THIN-FILMS ELABORATED BY ION-BEAM SPUTTERING

Iron-cobalt thin films with thicknesses of 100-1000 nm were evaporated using an ion-beam sputtering device with either neutral (Ar+) ions or reactive (N+ or N2+) ions as projectiles. The structure is determined by X-ray diffraction, transmission electron microscopy (TEM) and X-ra y photoelectron spectrometry (XPS). The films deposited with Ar+ ions are bcc and their average grain size is small, about 10-15 nm. Cross-s ectional TEM analysis shows a fibrous structure throughout the film th ickness. As far as the films evaporated with N+ ions are concerned, Fe 2N and Fe3N nitrides are identified which correspond to the epsilon ph ase in addition to the Fe-Co bcc phase. XPS results clearly exhibit tw o types of Fe-N binding, in agreement with the already determined epsi lon and bcc structures. Mossbauer spectra were performed at room tempe rature using the conversion electron technique; both the orientation a nd the modulus of the Fe-57 nucleus hyperfine field were measured. In films deposited using Ar+ ions, the spins are randomly distributed and the average hyperfine field corresponds to the disordered bulk alloy one. From films obtained using N+ ions, only a central doublet is obse rved, thus indicating either a paramagnetic or a superparamagnetic com ponent. To isolate the role of cobalt in nitride formation, thin films were deposited using an iron target by N+ ion sputtering.