Wasaburo Ohta

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

The saturation magnetization M<inf>s</inf> of films evaporated in an N<inf>2</inf> atmosphere and in N<inf>2</inf> plasma was carefully investigated. Films deposited by evaporation in an N<inf>2</inf> atmosphere using an alumina crucible as the evaporation source had nearly the same M<inf>s</inf> value (approximately 210 emu/g) as that of pure Fe, and were found by X-ray diffraction to contain no iron nitrides. The N, N<inf>2</inf>⁺ and N<inf>2</inf>* 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, N<inf>2</inf>⁺ or N<inf>2</inf>* is necessary to obtain Fe-N films. M<inf>s</inf> of these films, which were deposited in a weak plasma (V<inf>g</inf> = 50 V, I<inf>g</inf> = 0.1 A) and at a low deposition rate (R = 1.0 Å/s), increased with decreasing film thickness. The high-moment phase Fe<inf>16</inf>N<inf>2</inf> could be produced under the following conditions: (1) Low density N, N<inf>2</inf>⁺ or N<inf>2</inf>* exist in the reactive gas atmosphere; (2) the film thickness is smaller than about 500 Å.