Preparation and Magnetic Properties of Fe-N Thin Films by the Plasma Evaporation Method

The saturation magnetization Ms of films evaporated in an N2 atmosphere and in N2 plasma was carefully investigated. Films deposited by evaporation in an N2 atmosphere using an alumina crucible as the evaporation source had nearly the same Ms value (approximately 210 emu/g) as that of pure Fe, and were found by X-ray diffraction to contain no iron nitrides. The N, N2⁺ and N2* were produced various methods - discharge for plasma evaporation, an electron beam from an E-gun, and catalysis on a tungsten filament - were used to produce active species or ions of nitrogen. The N, N2⁺ or N2* is necessary to obtain Fe-N films. Ms of these films, which were deposited in a weak plasma (Vg = 50 V, Ig = 0.1 A) and at a low deposition rate (R = 1.0 Ã…/s), increased with decreasing film thickness. The high-moment phase Fe16N2 could be produced under the following conditions: (1) Low density N, N2⁺ or N2* exist in the reactive gas atmosphere; (2) the film thickness is smaller than about 500 Ã….