The Preparation And Study Of The Effect Of Cu Buffer Layer On The γ’-Fe₄n Films

Iron nitride thin films have attracted a great deal of attention formany years due to their high corrosion resistance, good wearresistance, oxidation resistance, and excellent magnetic properties.There are many iron nitride phases in the binary Fe-N phase diagram.Among them, the γ’-Fe4N is the most stable phase with stablethermal stability and chemical stability. Hence, most of the interesthas been paid to γ’-Fe4N among the ferromagnetic nitrides. In thiswork, the γ’-Fe4N films were fabricated by a dc magnetronsputtering method. The influence of annealing temperature,substrate temperature, the fraction of nitrogen and Cu buffer layeron the structure, morphology and magnetic properties of γ’-Fe4Nfilms has been investigated in details. The results are summarizedas follows:(1) The Fe-N magnetic films are synthesized by direct currentreactive magnetron sputtering with different nitrogen fraction. Theas-deposited films were annealed at different temperatures. The structure, magnetic and thermal stability of the as-deposited andpost-annealed iron nitride films were studied. The Fe is present inthe films at relative lower annealing temperatures. With theincrease of annealing temperature, the Fe4N phases can beobserved but it transforms into Fe3N phases at higher annealingtemperatures. The saturation magnetization and coercivity of thefilms are increased with the increase of annealing temperature. At acertain annealing temperature, the Fe3N phase increases with theincrease of N2flow rate, and results in the reduction of thesaturation magnetization of the films.(2) The single-phase γ’-Fe4N films were deposited on glasssubstrates using reactive magnetron sputtering. A systematic studyhas been done on the influence of substrate temperature, thenitrogen fraction and thickness on the structure, morphology andmagnetic properties of γ’-Fe4N films. The sing-phase γ’-Fe4N filmswith different thickness were obtained at the substratetemperature of700°C (the actual temperature is430°C) and theflow rate of nitrogen of3.5sccm. With the increasing thickness, theintensity of the diffraction peaks from Fe4N films increases and thefilms mainly exhibit (100) orientation. It was also found that thequasi-square grains appeared on the surface of the γ’-Fe4N films.The grain size of the films increases with the increase of film thickness. The magnetic measurements indicated that the filmthickness has an obvious effect on the saturation magnetization ofthe γ’-Fe4N films.(3) The Fe4N films with Cu underlayrers films were deposited onglass and Si substrates simultaneously by magnetron reactivesputtering. The effect of Cu underlayer on the structure,morphology and magnetic properties of the γ’-Fe4N films werestudied. It was found that the intensity of (200) peak from the Fe4Nfilms decreased and surface of the films became rough after addingthe Cu underlayer. The single phase γ’-Fe4N films with Cu underlayeron the glass substrates is obtained, while the mixture of Fe andγ’-Fe4N phase is observed on the Si substrate. The magneticmeasurements indicate that the films exhibit a good softferromagnetic behavior. The enhanced coercivity in the films withCu underlayer is observed due to the degeneration of thecrystallographic structure as well as the rougher surface.In summary, we obtained single-phase γ’-Fe4N using reactivemagnetron sputtering. We found that the substrate temperatureplays an important role in fabricating the single-phase γ’-Fe4N films.The coercive fields of films was increased after adding the Cuunderlayer. These results will provide more reference for the studyof γ’-Fe4N films in the future.