Structure, Magnetic Properties And Size Effect Of α″-Fe₁₆N₂ Thin Films

The Fe-N thin films with high saturation magnetization were prepared by RFmagnetron sputtering. The effects of preparation conditions on the structures andmagnetic properties of Fe-N films and the relation between the saturationmagnetization and film thickness were investigated in detail. It was found that the nitrogen partial pressure and substrate temperature are thetwo important factors affecting the formation of Fe-N phases and their magneticproperties. The microstructures and magnetic properties are quite diversified atdifferent nitrogen partial pressures and substrate temperatures during the deposition.In our case, nitrogen partial pressure of ~2×10-4 Torr and substrate temperatures of100-150 C are the typical conditions for the formation of α″-Fe16N2 phase with high osaturation magnetization. The room temperature saturation magnetization of theFe-N films deposited under these conditions is as high as 2179 emu/cc, which ismuch higher than that of pure iron, 1714 emu/cc. The saturation magnetization of the FeN films with high α″-Fe16N2 volumefraction initially increases with film thickness and keeps its maximum of about 2179emu/cc in the thickness range of 300-570 nm, and then decreases with furtherincrease in film thickness. Film thickness dependence of microstructure shows thatthe average grain size increases with the increase of film thickness.